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"Eeyore" wrote in message
...


EADGBE wrote:

(Scott Dorsey) wrote:

Does an ohmmeter show them as open or not?


SCOTT:

The fuse resistor that didn't blow reads exactly 1.04 ohms (that's an
in-circuit reading).

The fuse resistor that blew reads open circuit....and that is with the
resistor TAKEN OUT of circuit completely.

I figured I could replace the fuse resistor with a regular 1-ohm
resistor and get things working again, but I also realize that that is
NOT safe, and so the deck will not be powered up again until it has a
new 1-ohm fuse resistor in place...and I might even replace the other
1-ohm fuse resistor whilst I'm at it.


I wouldn't excessively fret over not fitting a genuine fusible resistor.
The
only difference between them and normal resistors is that they are (a)
designed
to fail open and (b) are flameproof. There's still another one in circuit
!

If one of those fusibles had failed (as it seems) that's why you have no
display.

Graham


I completely concur. Two fusible R's in a single winding to single filament
circuit such as this appears to be, is an overkill. At least as a temporary
measure, I would have no qualms about subbing a standard 1 ohm resistor at
all, and all the 'usual suspects' that know me on here, would readily
confirm that I *never* advocate *any* practice that is in *any way*
dangerous. By all means fit a genuine replacement in the end if that makes
you feel better, but to try it, just put your pliers across the failed one
.... Honestly, you can !!

Arfa


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First of all, I would like to extend a HUGE THANK YOU to everyone who
helped me figure out the problem with my CR-7A cassette deck.

I had made a couple of hasty assumptions, and you folks put me on the
right track.

Now if I could only find a couple of 1-ohm, 1/4-watt fusible
resistors....these things are BLOODY HARD to find!!!!!!!!!!!!

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Eeyore wrote:
The filament btw acts as a directly heated cathode in a VFD. The segments that
illuminate are the anodes and the remaining connections are control grids.

It's a big multipin triode.


Umpteenode?

--
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"You can't block traffic if you're not in the way."
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"EADGBE" wrote in message
ups.com...

First of all, I would like to extend a HUGE THANK YOU to everyone who
helped me figure out the problem with my CR-7A cassette deck.

I had made a couple of hasty assumptions, and you folks put me on the
right track.

Now if I could only find a couple of 1-ohm, 1/4-watt fusible
resistors....these things are BLOODY HARD to find!!!!!!!!!!!!


Where are you ? If it's really that hard in your locality, I'll bung a
couple in a Jiffy bag for you ! I have a drawer full of 'em ...

Arfa


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EADGBE wrote:

Now if I could only find a couple of 1-ohm, 1/4-watt fusible
resistors....these things are BLOODY HARD to find!!!!!!!!!!!!


As I said earlier, MCM electronics stocks them. Other places that cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may help
as well. Parts Express MIGHT have them, but they don't carry too many TV
set parts any more.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


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On Sep 29, 7:51 am, (Scott Dorsey) wrote:

As I said earlier, MCM electronics stocks them. Other places that cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may help
as well. Parts Express MIGHT have them, but they don't carry too many TV
set parts any more.


SCOTT:

Thanks, but I have already checked all of those sites, including MCM.
Nobody seems to stock a 1/4-watt, 1-ohm fusing resistor. I may have
overlooked the part in my search results, but I have tried all of
those sites (and others) multiple times.

I can't believe that this part would be this hard to find.

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On Sep 29, 7:32 am, "Arfa Daily" wrote:

Where are you ? If it's really that hard in your locality, I'll bung a
couple in a Jiffy bag for you ! I have a drawer full of 'em ...


ARFA:

I may have to get you to send some to me. They are rare as hen's
teeth around here.

Thanks!


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On Sat, 29 Sep 2007 06:46:28 -0700, EADGBE
wrote:

On Sep 29, 7:51 am, (Scott Dorsey) wrote:

As I said earlier, MCM electronics stocks them. Other places that cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may help
as well. Parts Express MIGHT have them, but they don't carry too many TV
set parts any more.


SCOTT:

Thanks, but I have already checked all of those sites, including MCM.
Nobody seems to stock a 1/4-watt, 1-ohm fusing resistor. I may have
overlooked the part in my search results, but I have tried all of
those sites (and others) multiple times.

I can't believe that this part would be this hard to find.


Radiospares have them. Part No 267-1569

d

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"EADGBE" wrote in message
oups.com...
On Sep 29, 7:32 am, "Arfa Daily" wrote:

Where are you ? If it's really that hard in your locality, I'll bung a
couple in a Jiffy bag for you ! I have a drawer full of 'em ...


ARFA:

I may have to get you to send some to me. They are rare as hen's
teeth around here.

Thanks!


Well, if you need me to, just contact me off-group using the same e-mail
address as I use to post. Even if you are the other side of the world to me,
it's only gonna set me back the cost of a coupla stamps to get you out of
trouble, and I guess that I can stand that without going bankrupt ...

Arfa


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Don Pearce wrote:

EADGBE wrote:
(Scott Dorsey) wrote:

As I said earlier, MCM electronics stocks them. Other places that cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may help
as well. Parts Express MIGHT have them, but they don't carry too many TV
set parts any more.


SCOTT:

Thanks, but I have already checked all of those sites, including MCM.
Nobody seems to stock a 1/4-watt, 1-ohm fusing resistor. I may have
overlooked the part in my search results, but I have tried all of
those sites (and others) multiple times.

I can't believe that this part would be this hard to find.


Radiospares have them. Part No 267-1569


They have an absurd minimum order charge.

Graham



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On Sat, 29 Sep 2007 21:10:22 +0100, Eeyore
wrote:



Don Pearce wrote:

EADGBE wrote:
(Scott Dorsey) wrote:

As I said earlier, MCM electronics stocks them. Other places that cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may help
as well. Parts Express MIGHT have them, but they don't carry too many TV
set parts any more.

SCOTT:

Thanks, but I have already checked all of those sites, including MCM.
Nobody seems to stock a 1/4-watt, 1-ohm fusing resistor. I may have
overlooked the part in my search results, but I have tried all of
those sites (and others) multiple times.

I can't believe that this part would be this hard to find.


Radiospares have them. Part No 267-1569


They have an absurd minimum order charge.

Graham


You can always top up with useful stuff - they have plenty.

d

--
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http://www.pearce.uk.com
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Don Pearce wrote:
On Sat, 29 Sep 2007 21:10:22 +0100, Eeyore
wrote:


Don Pearce wrote:

EADGBE wrote:
(Scott Dorsey) wrote:
As I said earlier, MCM electronics stocks them. Other places that cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may help
as well. Parts Express MIGHT have them, but they don't carry too many TV
set parts any more.
SCOTT:

Thanks, but I have already checked all of those sites, including MCM.
Nobody seems to stock a 1/4-watt, 1-ohm fusing resistor. I may have
overlooked the part in my search results, but I have tried all of
those sites (and others) multiple times.

I can't believe that this part would be this hard to find.
Radiospares have them. Part No 267-1569

They have an absurd minimum order charge.

Graham


You can always top up with useful stuff - they have plenty.

d


NAh if you do that, you`ll end up with all the crap you ordered to make
up the value, and the resistors will be out of stock!

Ron(UK)
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"Ron(UK)" wrote in message
...
Don Pearce wrote:
On Sat, 29 Sep 2007 21:10:22 +0100, Eeyore
wrote:


Don Pearce wrote:

EADGBE wrote:
(Scott Dorsey) wrote:
As I said earlier, MCM electronics stocks them. Other places that
cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may
help
as well. Parts Express MIGHT have them, but they don't carry too
many TV
set parts any more.
SCOTT:

Thanks, but I have already checked all of those sites, including MCM.
Nobody seems to stock a 1/4-watt, 1-ohm fusing resistor. I may have
overlooked the part in my search results, but I have tried all of
those sites (and others) multiple times.

I can't believe that this part would be this hard to find.
Radiospares have them. Part No 267-1569
They have an absurd minimum order charge.

Graham


You can always top up with useful stuff - they have plenty.

d


NAh if you do that, you`ll end up with all the crap you ordered to make up
the value, and the resistors will be out of stock!

Ron(UK)


Oh Ron, and haven't we all been *there* !! Last time for me just two weeks
ago ...

Arfa


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Don Pearce wrote:

Eeyore wrote:
Don Pearce wrote:
EADGBE wrote:
(Scott Dorsey) wrote:

As I said earlier, MCM electronics stocks them. Other places that cater
to the (rapidly dwindling) TV repair crowd like B+D Enterprises may help
as well. Parts Express MIGHT have them, but they don't carry too many TV
set parts any more.

SCOTT:

Thanks, but I have already checked all of those sites, including MCM.
Nobody seems to stock a 1/4-watt, 1-ohm fusing resistor. I may have
overlooked the part in my search results, but I have tried all of
those sites (and others) multiple times.

I can't believe that this part would be this hard to find.

Radiospares have them. Part No 267-1569


They have an absurd minimum order charge.



You can always top up with useful stuff - they have plenty.


What exactly would the OP want to 'top up' with ? He's not a repairman.

Graham

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In article .com,
EADGBE wrote:
On Sep 29, 7:32 am, "Arfa Daily" wrote:

Where are you ? If it's really that hard in your locality, I'll bung a
couple in a Jiffy bag for you ! I have a drawer full of 'em ...


ARFA:

I may have to get you to send some to me. They are rare as hen's
teeth around here.


Digi-Key part PPC1.0ATR-ND. That's a 1/3 watt and not a 1/4 watt but should
be fine.

MCM only has half-watt ones, part number 370-1.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


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Thanks for all the help, folks!

I finally found 1/4-watt, 1-ohm fusible resistors from a supplier in
Europe. They should be in my mailbox in about a week, hopefully.

It's weird that a part that I would have assumed to be fairly common
is so hard to find in the U.S.

Have fusible resistors "gone out of style" in place of something else?

I was pretty sure I could have used a regular flameproof 1-ohm
resistor for this particular circuit, but I was just paranoid enough
to want to be able to use exactly the right part. Why? Well, the
unit in question had undoubtedly been hit with some sort of voltage
surge, causing several other power supply components to fry.

Those other components have been replaced, and the deck's power supply
has been stable so far. However, this latest component failure, in a
very low-voltage circuit that is completely unrelated to the
previously-repaired circuits, shows me that there could be other
weakened components hiding just about anywhere--so I might as well re-
install ALL of the original protective elements and keep a watchful
eye until I am convinced the deck is completely rehabilitated.

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"EADGBE" wrote in message
oups.com...
Thanks for all the help, folks!

I finally found 1/4-watt, 1-ohm fusible resistors from a supplier in
Europe. They should be in my mailbox in about a week, hopefully.

It's weird that a part that I would have assumed to be fairly common
is so hard to find in the U.S.

Have fusible resistors "gone out of style" in place of something else?

I was pretty sure I could have used a regular flameproof 1-ohm
resistor for this particular circuit, but I was just paranoid enough
to want to be able to use exactly the right part. Why? Well, the
unit in question had undoubtedly been hit with some sort of voltage
surge, causing several other power supply components to fry.

Those other components have been replaced, and the deck's power supply
has been stable so far. However, this latest component failure, in a
very low-voltage circuit that is completely unrelated to the
previously-repaired circuits, shows me that there could be other
weakened components hiding just about anywhere--so I might as well re-
install ALL of the original protective elements and keep a watchful
eye until I am convinced the deck is completely rehabilitated.


Not a bad philosophy at the end of the day.

Arfa


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On Oct 2, 7:32 am, Meat Plow wrote:

I just realized your nickname is the standard tuning of a guitar.


Yep! That's it! :-)


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On Oct 2, 2:32 pm, Meat Plow wrote:

So i take it you play?


Oh, yes. My love of playing comes from the same spot as my love of
fine stereo/audio equipment, both analogue and digital.


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EADGBE wrote:

Meat Plow wrote:

So i take it you play?


Oh, yes. My love of playing comes from the same spot as my love of
fine stereo/audio equipment, both analogue and digital.


On the subject of the original post, have you tried powering the VFD display and
is it working now ?

Graham




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On Oct 2, 6:22 pm, Eeyore
wrote:

On the subject of the original post, have you tried powering the VFD display and
is it working now ?

Graham


GRAHAM:

No, I haven't powered it on yet. I'm still waiting for the
replacement fusible resistors to arrive from my parts source.

I didn't want to use just a regular flameproof resistor, partly
because of my own paranoia and partly because the fusible resistors
are marked as "critical components" in the Nakamichi service manual.



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EADGBE wrote:

Eeyore wrote:

On the subject of the original post, have you tried powering the VFD display and
is it working now ?



GRAHAM:

No, I haven't powered it on yet. I'm still waiting for the
replacement fusible resistors to arrive from my parts source.

I didn't want to use just a regular flameproof resistor, partly
because of my own paranoia and partly because the fusible resistors
are marked as "critical components" in the Nakamichi service manual.


They're simply 'covering themselves' when they say that but I won't argue with your
caution.

Graham


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Nice guitars! I like the Les Paul Studio flametop.

I could see the small versions of the photos but I couldn't supersize
them. Must be a glitch.

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Eeyore wrote:

EADGBE wrote:

Eeyore wrote:
On the subject of the original post, have you tried powering the VFD display and
is it working now ?


GRAHAM:

No, I haven't powered it on yet. I'm still waiting for the
replacement fusible resistors to arrive from my parts source.

I didn't want to use just a regular flameproof resistor, partly
because of my own paranoia and partly because the fusible resistors
are marked as "critical components" in the Nakamichi service manual.


They're simply 'covering themselves' when they say that but I won't argue with your
caution.

Graham


If you were to be supercautious, you should order the absolutely correct
part direct from Naki

Ron(UK)
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On Oct 3, 8:58 am, "Ron(UK)" wrote:

If you were to be supercautious, you should order the absolutely correct
part direct from Naki

Ron(UK)


I had always heard that Nak would not sell parts directly to consumers
(a common policy among manufacturers).

And since Nakamichi's decline, I would have been very surprised to
hear that anyone could order anything at all from them.

Do you have ordering information? I would really appreciate it.
Thanks!




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EADGBE wrote:
On Oct 3, 8:58 am, "Ron(UK)" wrote:
If you were to be supercautious, you should order the absolutely correct
part direct from Naki

Ron(UK)


I had always heard that Nak would not sell parts directly to consumers
(a common policy among manufacturers).

And since Nakamichi's decline, I would have been very surprised to
hear that anyone could order anything at all from them.

Do you have ordering information? I would really appreciate it.
Thanks!


Well it was meant to be a joke actually, if you read the manual it
generally says that only the manufacturers specified part number should
be used where a crucial safety component is marked.

I`m surprised you had trouble finding 1R fusibles, they are a pretty
common component in a great many items.

I find Rapid Electronics are pretty good for small orders in the UK


Ron(UK)

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On Oct 3, 10:02 am, "Ron(UK)" wrote:

I`m surprised you had trouble finding 1R fusibles, they are a pretty
common component in a great many items.

I find Rapid Electronics are pretty good for small orders in the UK

Ron(UK)


RON:

Whoops! I should have known it was a joke. Sorry about that.

Yes, I did indeed have lots of trouble finding 1R fusibles. But
perseverance paid off!

Thanks for the tip about Rapid Electronics. I'll try to remember
them!


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"Arfa Daily" wrote in message
...

"Eeyore" wrote in message
...


EADGBE wrote:

(Scott Dorsey) wrote:

Does an ohmmeter show them as open or not?

SCOTT:

The fuse resistor that didn't blow reads exactly 1.04 ohms (that's an
in-circuit reading).

The fuse resistor that blew reads open circuit....and that is with the
resistor TAKEN OUT of circuit completely.

I figured I could replace the fuse resistor with a regular 1-ohm
resistor and get things working again, but I also realize that that is
NOT safe, and so the deck will not be powered up again until it has a
new 1-ohm fuse resistor in place...and I might even replace the other
1-ohm fuse resistor whilst I'm at it.


I wouldn't excessively fret over not fitting a genuine fusible resistor.
The
only difference between them and normal resistors is that they are (a)
designed
to fail open and (b) are flameproof. There's still another one in circuit
!

If one of those fusibles had failed (as it seems) that's why you have no
display.

Graham


I completely concur. Two fusible R's in a single winding to single
filament circuit such as this appears to be, is an overkill. At least as a
temporary measure, I would have no qualms about subbing a standard 1 ohm
resistor at all, and all the 'usual suspects' that know me on here, would
readily confirm that I *never* advocate *any* practice that is in *any
way* dangerous. By all means fit a genuine replacement in the end if that
makes you feel better, but to try it, just put your pliers across the
failed one ... Honestly, you can !!

Arfa


I'll agree that Arfa never advocates anything that is dangerous. If he says
it is ok you can take his word. I also see no problem doing this either..
You still have one fuse in the line. In your house's wiring there is only
one fuse or circuit breaker in the supply. Using 2 is overkill.

Mike


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"Michael Kennedy" wrote in message
. ..

"Arfa Daily" wrote in message
...

"Eeyore" wrote in message
...


EADGBE wrote:

(Scott Dorsey) wrote:

Does an ohmmeter show them as open or not?

SCOTT:

The fuse resistor that didn't blow reads exactly 1.04 ohms (that's an
in-circuit reading).

The fuse resistor that blew reads open circuit....and that is with the
resistor TAKEN OUT of circuit completely.

I figured I could replace the fuse resistor with a regular 1-ohm
resistor and get things working again, but I also realize that that is
NOT safe, and so the deck will not be powered up again until it has a
new 1-ohm fuse resistor in place...and I might even replace the other
1-ohm fuse resistor whilst I'm at it.

I wouldn't excessively fret over not fitting a genuine fusible resistor.
The
only difference between them and normal resistors is that they are (a)
designed
to fail open and (b) are flameproof. There's still another one in
circuit !

If one of those fusibles had failed (as it seems) that's why you have no
display.

Graham


I completely concur. Two fusible R's in a single winding to single
filament circuit such as this appears to be, is an overkill. At least as
a temporary measure, I would have no qualms about subbing a standard 1
ohm resistor at all, and all the 'usual suspects' that know me on here,
would readily confirm that I *never* advocate *any* practice that is in
*any way* dangerous. By all means fit a genuine replacement in the end if
that makes you feel better, but to try it, just put your pliers across
the failed one ... Honestly, you can !!

Arfa


I'll agree that Arfa never advocates anything that is dangerous. If he
says it is ok you can take his word. I also see no problem doing this
either.. You still have one fuse in the line. In your house's wiring there
is only one fuse or circuit breaker in the supply. Using 2 is overkill.

Mike

Thanks Michael. Support appreciated, as always.

Arfa


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Default PROBLEM: Nakamichi CR-7A Power Transformer

On Friday, 28 September 2007 04:46:58 UTC+1, EADGBE wrote:
Thanks for the link - I have already downloaded the service manual.
That's how I know the voltages for the secondary outputs.

I should have made that more clear in my original post (sorry).


Hi, I came across this thread as I just had my display on my CR7 cut out, and some mild burning smell.

After investigation my 4r7 fusible resistors are both blown so I need to investigate further.

The service manual I DLed has no mention of transformer voltages and so I wondered if you could hint me the link that was deleted, or tell me the voltages expected on the red wires from the transformer.

cheers


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Scott Dorsey Scott Dorsey is offline
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Default PROBLEM: Nakamichi CR-7A Power Transformer

wrote:
On Friday, 28 September 2007 04:46:58 UTC+1, EADGBE wrote:
Thanks for the link - I have already downloaded the service manual.
That's how I know the voltages for the secondary outputs.

I should have made that more clear in my original post (sorry).


Hi, I came across this thread as I just had my display on my CR7 cut out, and some mild burning smell.

After investigation my 4r7 fusible resistors are both blown so I need to investigate further.


There are four of them. Which ones are blown?

The service manual I DLed has no mention of transformer voltages and so I wondered if you could hint me the link that was deleted, or tell me the voltages expected on the red wires from the transformer.


The paper one from the manufacturer lists them. T1 has 36VCT, 30VCT, then some
3.5V and 5V windings.

But replace the fuses, check the pass transistors, the filter caps, and the
bridge rectifiers, and then disconnect the logic board from the power supply
board and see if the unloaded voltages are good.

You may have an issue on the power supply board causing it to pull too much
current (such as a shorted filter cap), or you might have something on the
logic board causing it to pull too much current (such as bad decoupling caps
on the logic board).

cheers


I haven't worked one of of these things for more than twenty years and I
recall them being a real pain. I really hate consumer electronics.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Tim Sprout Tim Sprout is offline
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Default PROBLEM: Nakamichi CR-7A Power Transformer

On 1/29/2015 10:29 AM, Scott Dorsey wrote:
wrote:
On Friday, 28 September 2007 04:46:58 UTC+1, EADGBE wrote:
Thanks for the link - I have already downloaded the service manual.
That's how I know the voltages for the secondary outputs.

I should have made that more clear in my original post (sorry).


Hi, I came across this thread as I just had my display on my CR7 cut out, and some mild burning smell.

After investigation my 4r7 fusible resistors are both blown so I need to investigate further.


There are four of them. Which ones are blown?

The service manual I DLed has no mention of transformer voltages and so I wondered if you could hint me the link that was deleted, or tell me the voltages expected on the red wires from the transformer.


The paper one from the manufacturer lists them. T1 has 36VCT, 30VCT, then some
3.5V and 5V windings.

But replace the fuses, check the pass transistors, the filter caps, and the
bridge rectifiers, and then disconnect the logic board from the power supply
board and see if the unloaded voltages are good.

You may have an issue on the power supply board causing it to pull too much
current (such as a shorted filter cap), or you might have something on the
logic board causing it to pull too much current (such as bad decoupling caps
on the logic board).

cheers


I haven't worked one of of these things for more than twenty years and I
recall them being a real pain. I really hate consumer electronics.
--scott


Gotta love USENET, a followup question to a post posted in 2007 being
answered in 2015. Speaks to the long term integral use of this newsgroup.

Tim Sprout
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JackA JackA is offline
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Default PROBLEM: Nakamichi CR-7A Power Transformer

On Thursday, September 27, 2007 at 9:24:01 PM UTC-4, EADGBE wrote:
I have a Nakamichi CR-7A that works and sounds great, but it has
developed a problem, and I am wondering how difficult it will be to
repair.

The flourescent meter window has stopped working.

I know a little about electronics, so I opened up the deck and checked
the voltages coming off of the transformer.

As expected, there were various different outputs of AC voltage,
including an output of 3.5v AC.

This 3.5v AC output feeds the flourescent meter window AND NOTHING
ELSE.

But this output has stopped working. No smoke, no fire, everything
else on the deck works perfectly fine. There is just no more 3.5v AC
output from the transformer.

QUESTION 1: What happened? Did the transformer have a meltdown or is
it as simple as some kind of internal fuse? (I should point out that
this deck's power supply circuit had been damaged at some point,
possibly by a power surge, but it was professionally repaired by an
authorized Nak repair center).

QUESTION 2: Can this be fixed - and if so, how difficult is it?

QUESTION 3: Will it be possible to find a replacement transformer?
For the record, this transformer has the following PAIRS of outputs:

3.5v AC (two of them)
5v AC (two of them)
15v AC (two of them)
18v AC (two of them)

Any help would be much appreciated.


Strange that one winding would open. Check continuity of that winding. If open, tear off coil wrapper to see if a cold solder joint (lead wire to magnet wire) is the problem.

I think this has the schematic, too....

http://www.ant-audio.co.uk/Tape_Reco...AMICHI_CR7.pdf
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JackA JackA is offline
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Default PROBLEM: Nakamichi CR-7A Power Transformer

On Thursday, January 29, 2015 at 3:38:00 PM UTC-5, Tim Sprout wrote:
On 1/29/2015 10:29 AM, Scott Dorsey wrote:
wrote:
On Friday, 28 September 2007 04:46:58 UTC+1, EADGBE wrote:
Thanks for the link - I have already downloaded the service manual.
That's how I know the voltages for the secondary outputs.

I should have made that more clear in my original post (sorry).

Hi, I came across this thread as I just had my display on my CR7 cut out, and some mild burning smell.

After investigation my 4r7 fusible resistors are both blown so I need to investigate further.


There are four of them. Which ones are blown?

The service manual I DLed has no mention of transformer voltages and so I wondered if you could hint me the link that was deleted, or tell me the voltages expected on the red wires from the transformer.


The paper one from the manufacturer lists them. T1 has 36VCT, 30VCT, then some
3.5V and 5V windings.

But replace the fuses, check the pass transistors, the filter caps, and the
bridge rectifiers, and then disconnect the logic board from the power supply
board and see if the unloaded voltages are good.

You may have an issue on the power supply board causing it to pull too much
current (such as a shorted filter cap), or you might have something on the
logic board causing it to pull too much current (such as bad decoupling caps
on the logic board).

cheers


I haven't worked one of of these things for more than twenty years and I
recall them being a real pain. I really hate consumer electronics.
--scott


Gotta love USENET, a followup question to a post posted in 2007 being
answered in 2015. Speaks to the long term integral use of this newsgroup.

Tim Sprout


Did he ever get it fixed? :-)
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Default PROBLEM: Nakamichi CR-7A Power Transformer

On Thursday, 29 January 2015 19:29:17 UTC, Scott Dorsey wrote:
wrote:
On Friday, 28 September 2007 04:46:58 UTC+1, EADGBE wrote:
Thanks for the link - I have already downloaded the service manual.
That's how I know the voltages for the secondary outputs.

I should have made that more clear in my original post (sorry).


Hi, I came across this thread as I just had my display on my CR7 cut out, and some mild burning smell.

After investigation my 4r7 fusible resistors are both blown so I need to investigate further.


There are four of them. Which ones are blown?

The service manual I DLed has no mention of transformer voltages and so I wondered if you could hint me the link that was deleted, or tell me the voltages expected on the red wires from the transformer.


The paper one from the manufacturer lists them. T1 has 36VCT, 30VCT, then some
3.5V and 5V windings.

But replace the fuses, check the pass transistors, the filter caps, and the
bridge rectifiers, and then disconnect the logic board from the power supply
board and see if the unloaded voltages are good.

You may have an issue on the power supply board causing it to pull too much
current (such as a shorted filter cap), or you might have something on the
logic board causing it to pull too much current (such as bad decoupling caps
on the logic board).

cheers


I haven't worked one of of these things for more than twenty years and I
recall them being a real pain. I really hate consumer electronics.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


I already disconnected the logic board. Voltages seemed good from the other windings, and made sense after the bridge rectifiers, apart from the reds which were 40v in and 1v out. I expect the 1v was from a cap or some other backwards flow as the 4r7's were both blown. You say 4 of them, are you including the 1 ohm ones on the display circuit? These seem ok (haven't lifted a leg to double check but no reason to think they are an issue)

Voltages seem high but this is with no load so is probably fine (41v, 7.9v etc)

I'll just have to try the 4r7's and see if it all works ok. thanks for the info


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Scott Dorsey Scott Dorsey is offline
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Default PROBLEM: Nakamichi CR-7A Power Transformer

wrote:

I already disconnected the logic board. Voltages seemed good from the other=
windings, and made sense after the bridge rectifiers, apart from the reds =
which were 40v in and 1v out. I expect the 1v was from a cap or some other =
backwards flow as the 4r7's were both blown. You say 4 of them, are you inc=
luding the 1 ohm ones on the display circuit? These seem ok (haven't lifted=
a leg to double check but no reason to think they are an issue)


No. There are four of them for the two supplies that go to connectors six
and seven. R423, R424, R425, and R426. Which ones are blown?

Tack fusible resistors in parallel with the open ones. Apply AC power with
the connector to the logic board removed. Do they blow? Do the voltages
on the (CH-7 or CH-6) connector match the numbers in the manual?

What do you mean "the reds?" Do you mean D407, D404, D401, or one of the
other bridges?

If you see 40V going into a bridge rectifier and 1V coming out, the bridge
is bad. If the bridge were good and the output shorted, it would pull the
input down. (Make sure you're using the DC setting to measure the output
and the AC setting to measure the input of course.)

Voltages seem high but this is with no load so is probably fine (41v, 7.9v =
etc)


Except for the ones that are zero, presumably.

Also, the manual may be old enough that it expects voltages to be measured
with a low-Z meter.

Because Japanese line voltages are often lower than US voltages, you will
sometimes see higher than normal unregulated voltages in Japanese gear.
Don't worry about that unless it's a Dokorder (in which case throw it away).
Once you get past the regulator stage, though, they should match the ones
on the schematic.

I'll just have to try the 4r7's and see if it all works ok. thanks for the =
info


Fuses don't just blow for no reason, find out what is blowing them. Your
first job is to find out if it's on the logic board or the supply board.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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