Kenwood KR-A57R receiver: worth messing with?

[David Nebenzahl]

I was given this unit in non-working condition. Powers on, front panel
display works perfectly, appears to tune in stations correctly. Plus the
power supply appears to be working correctly: at least I measured
voltage at the output transistors. But nothing but silence from the
speaker outputs. The speaker relay clicks when the impedance-selection
switch is moved.

The boards are very dusty and covered with lint. Other than this,
everything appears to be as it should be.

Any advice for working on this receiver? Is it even worth messing with?
If not, next step is cannibalization.


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

[Chris Hornbeck]

On Thu, 01 Jan 2009 13:43:13 -0800, David Nebenzahl
> wrote:

>I was given this unit in non-working condition. Powers on, front panel
>display works perfectly, appears to tune in stations correctly. Plus the
>power supply appears to be working correctly: at least I measured
>voltage at the output transistors. But nothing but silence from the
>speaker outputs. The speaker relay clicks when the impedance-selection
>switch is moved.
>
>The boards are very dusty and covered with lint. Other than this,
>everything appears to be as it should be.
>
>Any advice for working on this receiver? Is it even worth messing with?
>If not, next step is cannibalization.

Pre-out/ main-in jumpers, etc. ?

Headphone out works?

You gotta give us some more to start with.

All good fortune,
Chris Hornbeck

[David Nebenzahl]

On 1/1/2009 7:05 PM Chris Hornbeck spake thus:

> On Thu, 01 Jan 2009 13:43:13 -0800, David Nebenzahl
> > wrote:
>
>>I was given this unit in non-working condition. Powers on, front panel
>>display works perfectly, appears to tune in stations correctly. Plus the
>>power supply appears to be working correctly: at least I measured
>>voltage at the output transistors. But nothing but silence from the
>>speaker outputs. The speaker relay clicks when the impedance-selection
>>switch is moved.
>>
>>The boards are very dusty and covered with lint. Other than this,
>>everything appears to be as it should be.
>>
>>Any advice for working on this receiver? Is it even worth messing with?
>>If not, next step is cannibalization.
>
> Pre-out/ main-in jumpers, etc. ?

I don't see any such jumpers, or am I missing something? Lots of
soldered-in jumpers on the boards. There's only the usual row of input
jacks on the back (plus speaker outputs, antennae connectors, etc.)

> Headphone out works?

Nope, silent.

Thanks for your reply. Any other ideas?


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

[Kevin McMurtrie[_2_]]

In article >,
David Nebenzahl > wrote:

> On 1/1/2009 7:05 PM Chris Hornbeck spake thus:
>
> > On Thu, 01 Jan 2009 13:43:13 -0800, David Nebenzahl
> > > wrote:
> >
> >>I was given this unit in non-working condition. Powers on, front panel
> >>display works perfectly, appears to tune in stations correctly. Plus the
> >>power supply appears to be working correctly: at least I measured
> >>voltage at the output transistors. But nothing but silence from the
> >>speaker outputs. The speaker relay clicks when the impedance-selection
> >>switch is moved.
> >>
> >>The boards are very dusty and covered with lint. Other than this,
> >>everything appears to be as it should be.
> >>
> >>Any advice for working on this receiver? Is it even worth messing with?
> >>If not, next step is cannibalization.
> >
> > Pre-out/ main-in jumpers, etc. ?
>
> I don't see any such jumpers, or am I missing something? Lots of
> soldered-in jumpers on the boards. There's only the usual row of input
> jacks on the back (plus speaker outputs, antennae connectors, etc.)

Some older decks have tape and EQ loop jacks. There'd be jumpers across
the jacks in case you had nothing to put there.

> > Headphone out works?
>
> Nope, silent.
>
> Thanks for your reply. Any other ideas?

I found an image of your deck and it has a pretty cool retro-tech look.
I'd save it. Pretty much everything I owned in the 80s died from having
solder evaporate off the leads of power components. Circuits back then
had new high temperature components but they didn't have copper sheets
in the PCB to improve dissipation. Resolder areas of the board that have
discolored from heat aging.

--
Google is a pro-spamming service. I will not see your reply if you use Google.

[David Nebenzahl]

On 1/1/2009 9:39 PM Kevin McMurtrie spake thus:

> In article >,
> David Nebenzahl > wrote:
>
>> On 1/1/2009 7:05 PM Chris Hornbeck spake thus:
>>
>> > On Thu, 01 Jan 2009 13:43:13 -0800, David Nebenzahl
>> > > wrote:
>> >
>> >>I was given this unit in non-working condition. Powers on, front panel
>> >>display works perfectly, appears to tune in stations correctly. Plus the
>> >>power supply appears to be working correctly: at least I measured
>> >>voltage at the output transistors. But nothing but silence from the
>> >>speaker outputs. The speaker relay clicks when the impedance-selection
>> >>switch is moved.
>> >>
>> >>The boards are very dusty and covered with lint. Other than this,
>> >>everything appears to be as it should be.
>> >>
>> >>Any advice for working on this receiver? Is it even worth messing with?
>> >>If not, next step is cannibalization.
>> >
>> > Pre-out/ main-in jumpers, etc. ?
>>
>> I don't see any such jumpers, or am I missing something? Lots of
>> soldered-in jumpers on the boards. There's only the usual row of input
>> jacks on the back (plus speaker outputs, antennae connectors, etc.)
>
> Some older decks have tape and EQ loop jacks. There'd be jumpers across
> the jacks in case you had nothing to put there.
>
>> > Headphone out works?
>>
>> Nope, silent.
>>
>> Thanks for your reply. Any other ideas?
>
> I found an image of your deck [...]

It's a receiver, not a deck.


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

[Chris Hornbeck]

On Thu, 01 Jan 2009 21:08:08 -0800, David Nebenzahl
> wrote:

>> Pre-out/ main-in jumpers, etc. ?
>
>I don't see any such jumpers, or am I missing something? Lots of
>soldered-in jumpers on the boards. There's only the usual row of input
>jacks on the back (plus speaker outputs, antennae connectors, etc.)
>
>> Headphone out works?
>
>Nope, silent.
>
>Thanks for your reply. Any other ideas?

Cool. The first line of defense in unknown new-to-you amplifiers
is to check for speaker-relay closing (check!), pre-out/main-in
jumpers (check!), speaker switches turned on (headphones don't work,
so, check!) no tape monitors engaged (?).

Do you have another audio system that you can connect to? (Please
don't answer foolishly - of course you do). Connect record outs
from your new box into record in's of your existing one.

(Does this new contraption have modern wierdnesses like "input
mode" or "digital/analog/auto" or "ext. input" or ....?)

The radio built into your receiver is sometimes a very
powerful diagnostic tool. No matter how modern (and stupid)
a receiver, it's almost certain to recognise its own tuner
and play it with minimal hassles. First make the radio play.


Do whatever it takes to get (the new box's radio) sound to come out
of your old box. Is the problem with the new box now solved?

Divide and conquer.

All the best fortune,
Chris Hornbeck

[David Nebenzahl]

On 1/1/2009 9:39 PM Kevin McMurtrie spake thus:

> In article >,
> David Nebenzahl > wrote:
>
>> Thanks for your reply. Any other ideas?
>
> I found an image of your deck and it has a pretty cool retro-tech look.
> I'd save it. Pretty much everything I owned in the 80s died from having
> solder evaporate off the leads of power components. Circuits back then
> had new high temperature components but they didn't have copper sheets
> in the PCB to improve dissipation. Resolder areas of the board that have
> discolored from heat aging.

Checked the PWBs; all the solder connections look as bright and clean as
the day they left the factory. Dunno how solder can "evaporate" (sounds
like the urban legend about glass flowing?), but in any case the unit
seems well-designed, with a monstrously-large heat sink for the output
transistors (4).

So, any other ideas? The demolition tools are at the ready ...


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

[Chris Hornbeck]

On Thu, 01 Jan 2009 21:44:57 -0800, David Nebenzahl
> wrote:

>On 1/1/2009 9:39 PM Kevin McMurtrie spake thus:

>> Some older decks have tape and EQ loop jacks. There'd be jumpers across
>> the jacks in case you had nothing to put there.

>It's a receiver, not a deck.

Nonetheless, that was good advice. If you'll post the labels
of all the RCA/phono jacks on the rear panel, we can rule out
this (good) possibility.

All good fortune,
Chris Hornbeck

[David Nebenzahl]

On 1/2/2009 6:42 PM Chris Hornbeck spake thus:

> On Thu, 01 Jan 2009 21:44:57 -0800, David Nebenzahl
> > wrote:
>
>>On 1/1/2009 9:39 PM Kevin McMurtrie spake thus:
>
>>> Some older decks have tape and EQ loop jacks. There'd be jumpers across
>>> the jacks in case you had nothing to put there.
>
>>It's a receiver, not a deck.
>
> Nonetheless, that was good advice. If you'll post the labels
> of all the RCA/phono jacks on the rear panel, we can rule out
> this (good) possibility.

Alright. I *know* there's no such jumper as someone postulated, but just
to keep you happy, here's what's on the back panel:

Input/output jacks:

o phono
o CD/aux
o video 1
o video 2
o tape 1: record
o tape 1: play
o tape 2: record
o tape 2: play

In addition, there are:

o the usual antenna connectors (AM & FM)
o the phono ground connector
o main speaker connectors (A & B), w/impedance-selector switch
o "surround" speaker connectors, with on/off switch
o 3 switched outlets
o remote connector (2 jacks)

There are front-panel input select buttons for each source listed above.
In addition, Tape 2 can function both as a source and a monitor (its
state is shown in the front-panel display).

I've tried everything in all possible positions. No sound.


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

[Ron]

On Jan 3, 12:12*am, David Nebenzahl > wrote:
> On 1/2/2009 6:42 PM Chris Hornbeck spake thus:
>
> > On Thu, 01 Jan 2009 21:44:57 -0800, David Nebenzahl
> > > wrote:
>
> >>On 1/1/2009 9:39 PM Kevin McMurtrie spake thus:
>
> >>> Some older decks have tape and EQ loop jacks. *There'd be jumpers across
> >>> the jacks in case you had nothing to put there.
>
> >>It's a receiver, not a deck.
>
> > Nonetheless, that was good advice. If you'll post the labels
> > of all the RCA/phono jacks on the rear panel, we can rule out
> > this (good) possibility.
>
> Alright. I *know* there's no such jumper as someone postulated, but just
> to keep you happy, here's what's on the back panel:
>
> Input/output jacks:
>
> o phono
> o CD/aux
> o video 1
> o video 2
> o tape 1: record
> o tape 1: play
> o tape 2: record
> o tape 2: play
>
> In addition, there are:
>
> o the usual antenna connectors (AM & FM)
> o the phono ground connector
> o main speaker connectors (A & B), w/impedance-selector switch
> o "surround" speaker connectors, with on/off switch
> o 3 switched outlets
> o remote connector (2 jacks)
>
> There are front-panel input select buttons for each source listed above.
> In addition, Tape 2 can function both as a source and a monitor (its
> state is shown in the front-panel display).
>
> I've tried everything in all possible positions. No sound.
>

A lot of pictures here, also notice the price. http://tinyurl.com/73wkqo

[Chris Hornbeck]

On Fri, 2 Jan 2009 21:21:39 -0800 (PST), Ron >
wrote:

>On Jan 3, 12:12*am, David Nebenzahl > wrote:
>> On 1/2/2009 6:42 PM Chris Hornbeck spake thus:

>> Alright. I *know* there's no such jumper as someone postulated, but just
>> to keep you happy, here's what's on the back panel:

>> I've tried everything in all possible positions. No sound.

Excellent. Please don't be offended. This is Usenet; almost nobody
knows each other, and many/most such issues are simple matters
of hookups, and what-not. No way for responders to know unless
you tell...


>A lot of pictures here, also notice the price. http://tinyurl.com/73wkqo

I'd guess that the age estimate of late 80's/ early 90's is about
right.

Because the speaker relay fires, and no obvious operational gotcha's
seem to apply, the next best guess is that the input switching IC's
are damaged. These could be 40xx family, but are more likely from
the data-bus family.

David, you've ruled out all the obvious non-failure issues, so an
actual failure is next up at bat. The input switching IC's are
MOSFET devices, fairly fragile in overvoltage fault conditions,
and very exposed to the outside world. Failures there are common.

Repair will require a schematic and some troubleshooting. Or, you
could just replace the switching IC's and cross your fingers. Sorry to
be a wet blanket, but probability of (blind) success is maybe 25%,
give or take a lot.


All the best fortune,
Chris Hornbeck

[David Nebenzahl]

On 1/2/2009 9:46 PM Chris Hornbeck spake thus:

> I'd guess that the age estimate of late 80's/ early 90's is about
> right.

I think I remember reading 1988 somewhere in my search for info.

> Because the speaker relay fires,

Actually, don't know if it's operating correctly or not. Strange: it's a
2-pole (DPST) relay, but both poles are wired together, so it's just a
SPST switch here, looks like it switches AC power (xfmr secondary), not
the speakers directly??!?. In any case, I jumpered the contacts, and
still no joy.

> and no obvious operational gotcha's seem to apply, the next best
> guess is that the input switching IC's are damaged. These could be
> 40xx family, but are more likely from the data-bus family.

Purty good guess; there are 3 LC4966s (quad bilateral switches) there.
One nice (and unusual) thing about this unit is that the boards are
liberally labeled as to function (the radio board is divided into "AM
RF", "FM RF", "AM IF", "FM DET", etc., sections). Looks like a nice unit
to work on, if one has the schematic and the right test gear.

> David, you've ruled out all the obvious non-failure issues, so an
> actual failure is next up at bat. The input switching IC's are
> MOSFET devices, fairly fragile in overvoltage fault conditions,
> and very exposed to the outside world. Failures there are common.
>
> Repair will require a schematic and some troubleshooting. Or, you
> could just replace the switching IC's and cross your fingers. Sorry to
> be a wet blanket, but probability of (blind) success is maybe 25%,
> give or take a lot.

That sounds about right. Not worth it to me. Probably going to just
salvage the fairly enormous power transformer and whatever other parts I
can reap from it. I've got other, better amps & receivers here.


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

[Dave Platt]

>Alright. I *know* there's no such jumper as someone postulated, but just
>to keep you happy, here's what's on the back panel:
>
>Input/output jacks:
>
>o phono
>o CD/aux
>o video 1
>o video 2
>o tape 1: record
>o tape 1: play
>o tape 2: record
>o tape 2: play

#snip#

>There are front-panel input select buttons for each source listed above.
>In addition, Tape 2 can function both as a source and a monitor (its
>state is shown in the front-panel display).
>
>I've tried everything in all possible positions. No sound.

At this point, I think you're going to have to start the "inject a
signal at some point, follow it downstream, and see where it
disappears" method of tracing.

Since Tape 2 is able to act as a tape-loop monitor, it's probably the
"latest" injection point available - when the switch is in the monitor
position the "tape 2 play" input would bypass the rest of the signal
selection logic and go fairly directly to the controls. If you can
get output when you inject signal here and set the "monitor" switch,
it would indicate that the fault lies prior to this point (e.g. in the
rest of the input-selection circuitry, or even in the Tape 2
monitor/source switch itself). If not, it's a "downstream" fault - in
the controls, amp stage, or output protection circuitry.

[According to a web search I did, a not-uncommon reason for "no
output" or "can barely hear anything with the volume turned all the
way up" is a Tape 2 switch accidentally set in the "monitor"
position. TURN THE VOLUME DOWN before changing this switch back to
the "source" position, or you may damage your speakers and/or ears!]

If you've got no sound at all, in any control setting, with any signal
injection point, on either channel, then I'd tend to suspect that the
speaker-protection circuitry is involved (assuming this receiver has
such). Protection logic is often a relay which only closes (and
allows output to the speakers) if there's no over-current-on-output
situation detected (e.g. short circuit) and if there's no DC offset
voltage present at the amplifier output stage.

If there is such an output-protection relay, check to see if it
"clicks" a few seconds after the amp is turned on. If it doesn't,
this suggests that the fault protection circuitry is operating. A
shorted output connection could make this occur. So could a DC offset
at the amp outputs... this could occur if an output transistor was
shorted, or if a fuse in the DC supply to either channel has blown
(which might happen due to accidental amp overload, to a shorted
output transistor, or just to old age... fuses do degrade with time
and use).

--
Dave Platt > AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[David Nebenzahl]

On 1/3/2009 1:15 PM Dave Platt spake thus:

>>There are front-panel input select buttons for each source listed above.
>>In addition, Tape 2 can function both as a source and a monitor (its
>>state is shown in the front-panel display).
>>
>>I've tried everything in all possible positions. No sound.
>
> At this point, I think you're going to have to start the "inject a
> signal at some point, follow it downstream, and see where it
> disappears" method of tracing.
>
> Since Tape 2 is able to act as a tape-loop monitor, it's probably the
> "latest" injection point available - when the switch is in the monitor
> position the "tape 2 play" input would bypass the rest of the signal
> selection logic and go fairly directly to the controls. If you can
> get output when you inject signal here and set the "monitor" switch,
> it would indicate that the fault lies prior to this point (e.g. in the
> rest of the input-selection circuitry, or even in the Tape 2
> monitor/source switch itself). If not, it's a "downstream" fault - in
> the controls, amp stage, or output protection circuitry.
>
> [According to a web search I did, a not-uncommon reason for "no
> output" or "can barely hear anything with the volume turned all the
> way up" is a Tape 2 switch accidentally set in the "monitor"
> position. TURN THE VOLUME DOWN before changing this switch back to
> the "source" position, or you may damage your speakers and/or ears!]

As I said, I've tried all switches in all positions, including the Tape
2-as-input one. Nothing works. But your advice is good nonetheless.

> If you've got no sound at all, in any control setting, with any signal
> injection point, on either channel, then I'd tend to suspect that the
> speaker-protection circuitry is involved (assuming this receiver has
> such). Protection logic is often a relay which only closes (and
> allows output to the speakers) if there's no over-current-on-output
> situation detected (e.g. short circuit) and if there's no DC offset
> voltage present at the amplifier output stage.

As I explained in another post, that relay is kinda weird. There are two
relays in the unit, one on the power supply board which is obviously the
one for the "soft power-on" function. The other one is on the board with
the surround switch and surround speaker connectors (separate from the
main speaker connectors). Strange thing is that it's a 2-pole (DPST)
relay with both poles wired together, so it's really just an SPST
switch. It's also connected to one of the power transformer secondaries,
so it seems to be acting in some indirect way.

In any case, I tested it by wiring across the switch contacts and still
got nothing, so I'm suspecting that the output stage is blown.

> If there is such an output-protection relay, check to see if it
> "clicks" a few seconds after the amp is turned on. If it doesn't,
> this suggests that the fault protection circuitry is operating. A
> shorted output connection could make this occur. So could a DC offset
> at the amp outputs... this could occur if an output transistor was
> shorted, or if a fuse in the DC supply to either channel has blown
> (which might happen due to accidental amp overload, to a shorted
> output transistor, or just to old age... fuses do degrade with time
> and use).

The unit has only one fuse, which is good, on the primary side of the
power transformer. Someone else pointed out that there may be fusible
resistors in the output stage: these appear to be present, biggish
ceramic-packaged resistors very close to the output transistors. Maybe
these are open. Kinda hard to test w/o a schematic, as the resistors are
in packages with multiple leads.

It's looking like the parts bin for this guy.


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

[Chris Hornbeck]

On Mon, 05 Jan 2009 11:17:44 -0800, David Nebenzahl
> wrote:

>The unit has only one fuse, which is good, on the primary side of the
>power transformer. Someone else pointed out that there may be fusible
>resistors in the output stage: these appear to be present, biggish
>ceramic-packaged resistors very close to the output transistors. Maybe
>these are open. Kinda hard to test w/o a schematic, as the resistors are
>in packages with multiple leads.

These resistors have three legs? White flat rectangular package?
2 X 0.22 Ohms or somesuch small number?

If so, these are the output transistors' emitter resistors.
You should measure very close to, but not exactly, 0 Volts DC
from all legs of each to chassis ground. This is a very
good test of the output amplifier stage. Let us know.

All good fortune,
Chris Hornbeck

[jakdedert]

David Nebenzahl wrote:
<snip>
>
> The unit has only one fuse, which is good, on the primary side of the
> power transformer. Someone else pointed out that there may be fusible
> resistors in the output stage: these appear to be present, biggish
> ceramic-packaged resistors very close to the output transistors. Maybe
> these are open. Kinda hard to test w/o a schematic, as the resistors are
> in packages with multiple leads.
>
> It's looking like the parts bin for this guy.
>
>
You've done a lot of messing around, but it seems you've yet to
systematically test the unit from front to back...or even from back to
front. Either can be a valid method, although conventional wisdom is to
start at the input and trace signal forward through the circuit.

In your case, I'd at least test the outputs, as suggested many times in
the thread. Inject a signal--it could be anything, like the output of a
DVD player--into the output section. If you get sound out, then the
problem is before there...the preamp, or its switching.

If not, the outputs could be blown, although it's not the only
possibility. The protection circuit is the other main potential
culprit. Output devices (I believe you said they were discrete) are
usually easy to check with a DMM.

Test the preamp by plugging another amplifier into the tape outs with
the tuner selected as source. 'Another amplifier' could be one cheap
powered computer speaker, with appropriate 3.5 mm > RCA adapter...or it
could be another working hifi amp. The same computer speaker can be
used as a signal tracer to track the signal through the entire circuit,
with a suitable probe (consisting of a tinned bare wire and an alligator
clip for ground.

In any case, what good is a parts bin with suspect parts in it? If
you're really determined to ditch it, just do so; but you've gotten a
lot of advice that you've apparently not followed.

jak