[Gareth Magennis]

Hi,

I reluctantly took on a Studer B67 that "only had one channel missing, the rest of it is fine, honest".
Fixed that problem, changed the op-amps on the Mono/Stereo board.

It unfortunately has a speed problem, where the speed is modulated, i.e.the recorded tone warbles when monitored in real time off the tape.

This only happens on 15ips, the 2 lower speeds are rock solid.
It has the 10-turn Varispeed fitted, the warbling happens exactly the same with Varispeed in or out.

Once the machine has been on a while the fault dissapears though - it did this yesterday and has just done it again today. I can't recreate the fault now by tapping, pulling looms or anything.

Maybe this is a common problem, I don't know, but I don't fancy wading through the Service Manual to find out how the machine actually works.

Any time saving hints would be greatly appreciated.



Thanks,


Gareth.

[Mike Rivers[_2_]]

On 12/1/2015 6:15 AM, gareth magennis wrote:
I reluctantly took on a Studer B67 that "only had one channel missing, the rest of it is fine, honest".
Fixed that problem, changed the op-amps on the Mono/Stereo board.

It unfortunately has a speed problem, where the speed is modulated, i.e.the recorded tone warbles when monitored in real time off the tape.

You might sign up for the Studer Mailing List and ask there. They're
mostly into the multitrack recorders but someone might have a hint for you.

http://bach.pgm.com/mailman/listinfo/studer/


--
For a good time, visit http://mikeriversaudio.wordpress.com

[Scott Dorsey]

gareth magennis wrote:
Hi,

I reluctantly took on a Studer B67 that "only had one channel missing, the rest of it is fine, honest".
Fixed that problem, changed the op-amps on the Mono/Stereo board.

It unfortunately has a speed problem, where the speed is modulated, i.e.the recorded tone warbles when monitored in real time off the tape.

Before even applying power to that machine again, replace every Rifa capacitor
and every Frako electrolytic that you see. They are all bad. If they have
not failed yet, they will fail soon.

There is a capstan motor servo alignment procedure in the manual that you will
want to go through, but don't do it until you have replaced all of the
electrolytics in the transport control.

Also check the supply reel brakes while you have the thing apart, put on
a new pinch roller, and lube the motor bearings, just because these are
normal routine maintenance items that need to be done every couple years
and likely have been neglected if the machine has been in storage.

There is a Studer mailing list out there which will be filled with helpful
people but the first thing they'll ask is if you changed out all the
electrolytics.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[John Williamson]

On 01/12/2015 14:26, Scott Dorsey wrote:
gareth magennis wrote:
It unfortunately has a speed problem, where the speed is modulated, i.e.the recorded tone warbles when monitored in real time off the tape.

Before even applying power to that machine again, replace every Rifa capacitor
and every Frako electrolytic that you see. They are all bad. If they have
not failed yet, they will fail soon.

The fact that the speed stabilises as the machine warms up (And the
capacitors, especially the electrolytics, stabilise in value) agrees
with this diagnosis.



--
Tciao for Now!

John.

[Phil Allison[_4_]]

John Williamson wrote:


Before even applying power to that machine again, replace
every Rifa capacitor and every Frako electrolytic that you see.
They are all bad. If they have not failed yet, they will fail soon.


The fact that the speed stabilises as the machine warms up (And the
capacitors, especially the electrolytics, stabilise in value) agrees
with this diagnosis.


** And the fact it works absolutely fine at both lower speeds *contradicts* it.

The vast majority of tape recorder faults are mechanical in nature, change over time and can be intermittent too. So, chances are this is one of them.

The electros can be tested in a few seconds with an ESR meter, if they read OK then they are not causing the fault.



.... Phil

.... Phil

[Gareth Magennis]

On Wednesday, December 2, 2015 at 3:50:07 AM UTC, Phil Allison wrote:
John Williamson wrote:


Before even applying power to that machine again, replace
every Rifa capacitor and every Frako electrolytic that you see.
They are all bad. If they have not failed yet, they will fail soon.


The fact that the speed stabilises as the machine warms up (And the
capacitors, especially the electrolytics, stabilise in value) agrees
with this diagnosis.


** And the fact it works absolutely fine at both lower speeds *contradicts* it.

The vast majority of tape recorder faults are mechanical in nature, change over time and can be intermittent too. So, chances are this is one of them.

The electros can be tested in a few seconds with an ESR meter, if they read OK then they are not causing the fault.



... Phil

... Phil



I think now this might be a Tacho signal problem. It's gone away now so I can't confirm until tomorrow.



Gareth.

[Gareth Magennis]

On Wednesday, December 2, 2015 at 10:51:17 AM UTC, gareth magennis wrote:
On Wednesday, December 2, 2015 at 3:50:07 AM UTC, Phil Allison wrote:
John Williamson wrote:


Before even applying power to that machine again, replace
every Rifa capacitor and every Frako electrolytic that you see.
They are all bad. If they have not failed yet, they will fail soon.


The fact that the speed stabilises as the machine warms up (And the
capacitors, especially the electrolytics, stabilise in value) agrees
with this diagnosis.


** And the fact it works absolutely fine at both lower speeds *contradicts* it.

The vast majority of tape recorder faults are mechanical in nature, change over time and can be intermittent too. So, chances are this is one of them.

The electros can be tested in a few seconds with an ESR meter, if they read OK then they are not causing the fault.



... Phil

... Phil



I think now this might be a Tacho signal problem. It's gone away now so I can't confirm until tomorrow.



Gareth.


Sorry, talking rubbish.
Motor appears to be free running, but seems to have speed modulation on high speed, tacho confirms this.
I was thinking the tacho might be loose/vibrating or modulated by PSU rippple, but that wouldn't then modulate the motor, I guess.



Gareth.

[Scott Dorsey]

Phil Allison wrote:
John Williamson wrote:

Before even applying power to that machine again, replace
every Rifa capacitor and every Frako electrolytic that you see.
They are all bad. If they have not failed yet, they will fail soon.

The fact that the speed stabilises as the machine warms up (And the
capacitors, especially the electrolytics, stabilise in value) agrees
with this diagnosis.

** And the fact it works absolutely fine at both lower speeds *contradicts* it.
Not really. The servo loop might be just stable enough to work at lower
speeds but not stable enough to work properly at 15. As the caps age, the
poles and zeroes move around.

The vast majority of tape recorder faults are mechanical in nature, change over time and can be intermittent too. So, chances are this is one of them.

It might be, that's why I suggested doing pinch rollers and checking the
brakes, both of which can cause some weird problems (although both of which
will cause problems at all speeds). As well as doing the motor lubrication,
which is also just a thing that needs to be done on schedule.

One of the nice things about these machines is that there is really not that
much mechanical stuff to go wrong. Unfortunately there is a lot of electronic
stuff to go wrong, and it does.

The electros can be tested in a few seconds with an ESR meter, if they read OK then they are not causing the fault.

It's a B67, few of them are going to test good except for the four big ones
on the power supply board. It won't hurt to test them... but any of the
ones that test good won't be testing good for long.

It's possible that none of these have anything to do with the actual problem,
but you need to do all these things in order to get the machine up to the
point where you can diagnose the actual problem.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

I was thinking the tacho might be loose/vibrating or modulated by PSU rippple, but that wouldn't then modulate the motor, I guess.

If this is a closed loop servo system, then yes it would modulate the motor.

That is what makes troubleshooting noise in closed loop feedback systems challenging,

Unwanted noise injected __anywhere__ into a feedback loop travels around the entire loop..... so that makes it difficult to determine the point of origin of the noise.

There are two useful stratagies to troubleshooting noise in loops.

1) If you can open the loop and still have it operate (maybe have to inject a signal to fool it) then you can simply find the origin of the noise.

2) Use a dual trace scope and observe the polarity changes of the noise as it travels around the loop.

Mark



Mark

[Scott Dorsey]

gareth magennis wrote:

I think now this might be a Tacho signal problem. It's gone away now so I can't confirm until tomorrow.

It is a servo problem... could be in the tachometer, could be in the
differential stage or the integrator. The servo cal procedure will
tell you for sure but I'd change caps before I did that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

gareth magennis wrote:

Sorry, talking rubbish.
Motor appears to be free running, but seems to have speed modulation on high speed, tacho confirms this.
I was thinking the tacho might be loose/vibrating or modulated by PSU rippple, but that wouldn't then modulate the motor, I guess.

If the tach gets dirty, the waveform coming out of it can be soft instead of
having nice crisp edges, and then the PLL has a hard time locking. There
really isn't a whole lot going on with that servo circuit; it's not like an
ATR-100. But it's going unlocked and your goal is to find out why.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Gareth Magennis]

"Scott Dorsey" wrote in message ...

gareth magennis wrote:

I think now this might be a Tacho signal problem. It's gone away now so I
can't confirm until tomorrow.

It is a servo problem... could be in the tachometer, could be in the
differential stage or the integrator. The servo cal procedure will
tell you for sure but I'd change caps before I did that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."



This is actually more interesting than I at first thought it would be,
thanks to all.


There is more than one Capstan drive card for this machine.
The one I have does not have the adjustment capability I think you are
referring to here, though this process is detailed in the manual.
(Schematics for both cards are in the manual, one has the required preset,
this one doesn't)

I believe there is yet another card for 30ips capable machines.

I have no idea if the current card is the original.




Cheers,


Gareth.

[Scott Dorsey]

Gareth Magennis wrote:

This is actually more interesting than I at first thought it would be,
thanks to all.

It always is with these machines! It will make you wish you had an Ampex
with a synchronous capstan motor after a while.

There is more than one Capstan drive card for this machine.
The one I have does not have the adjustment capability I think you are
referring to here, though this process is detailed in the manual.
(Schematics for both cards are in the manual, one has the required preset,
this one doesn't)

There's an adjustment on the tach, there's a pot on the board (and that
might well be missing on some units), but most importantly there are waveforms
along the signal path and you can look at them on a scope and compare them
to see where things are going pear-shaped.

I believe there is yet another card for 30ips capable machines.

I have no idea if the current card is the original.

Shouldn't matter. Check caps and do the motor lube.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."