Studer A820 +/-15v +24v stabilizer

[jtvrdy]

Hi,
I’m refurbishing a Studer A820 tape recorder,
recapping the the old electrolitics capacitors I have a problem with the 1.820.873.00 stabilizer +/-15v+24
with the old caps (C20,C21,C23,C24)(Philips 118 2200uF/16v) it is working ok but with the new ones don’t work…. it goes up and down swinging the output voltages…
tried 2200uF/25V Nichicons PW, Rubycon ZLH and Panasonic FC, only with Vishay 021 it works but it is ringing with high pitch tone…

 

[sahib]

I tried to find the data sheet for the Philips cap but it is like looking for a needle in a haystack.

The new capacitors seem to have higher ESR than the original ones used. This means less damping, hence ringing at best, oscillating at worse.  Try capacitors with lower ESR.

Edit. I have just checked Vishay 021 against Panasonic FC. Try two Vishay in parallel instead of a single one and see if that helps.

 

[jtvrdy]

http://www.vishay.com/docs/28334/118aht.pdf

 

[jtvrdy]

it could be contrary,that needs higher esr?

 

[radardoug]

Are you testing with a load. Not the Studer, bad idea!

 

[sahib]

it could be contrary,that needs higher esr?

No. 

But the radardoug has a  good point.

 

[jtvrdy]

made the tests in the machine.

 

[Michael Tibes]

made the tests in the machine.

You should probably get a dummy load...

Michael

 

[Michael Tibes]

Do you have the full information on the psus? I remember 2 machines on which the red Wimas on the switching supply pcb cought fire back in the day. There might be some service bulletin concerning that, maybe it also contains useful information on the other caps on the board.

Michael

 

[radardoug]

Did you just recap it because you thought it was a good idea? Did you measure the caps as you removed them?
Caps are often not as bad as people think, particularly good ones like the old Philips blues.
Having said that, change the Frako caps, especially the one on the counter pcb under the front panel. They are know to be bad.

 

[jtvrdy]

Do you have the full information on the psus? I remember 2 machines on which the red Wimas on the switching supply pcb cought fire back in the day. There might be some service bulletin concerning that, maybe it also contains useful information on the other caps on the board.

Michael

I have all the service manuals from the Studer ftp side, but don't find any info about this caps...

 

[jtvrdy]

Did you just recap it because you thought it was a good idea? Did you measure the caps as you removed them?
Caps are often not as bad as people think, particularly good ones like the old Philips blues.
Having said that, change the Frako caps, especially the one on the counter pcb under the front panel. They are know to be bad.

I just recap this stabilizer because on the other stabilizer 1.820.872.83 (5v,+/-26,+/-24v)found one cap shorted(the same type) and replaced them all on the 872 is working fine but not on the 873...
The Frako are all changed

 

[jtvrdy]

the original caps are Philips 118 series 2200uF/16v , on the data sheet of Vishay 118series the ESR 100Hz is 0,205 and Z 10kHz 0,18 Ohms ,the 021 series 2200uF/25v  are 0,132 and 0,07 and the other caps are much lower than that, for some reason with caps with low esr is unstable.

 

[radardoug]

Its more likely that when you changed the caps you ripped out a via or something similar. You need to check all the pcb where you changed the caps to make sure you have continuity between the top and bottom of the board.

 

[jtvrdy]

Its more likely that when you changed the caps you ripped out a via or something similar. You need to check all the pcb where you changed the caps to make sure you have continuity between the top and bottom of the board.

yes, checked all the pcb traces and all are ok, the continuity is ok, right now I put back the old ones and is woking fine, so the only variant are the caps.

 

[radardoug]

Well if its working fine with the old caps, leave it alone! Did you measure the value of the old caps at any time?

 

[sodderboy]

Perhaps the 3 can pins of the Frako's are completing a circuit that is not completed with only one leg of a radial cap? 

Those stabilizers are ugly when they blow.  I had one melt the connectors at the 40V supply.  Really ugly.
Mike

 

[mgrisoli]

I have a Studer 827 with a buzzing sound on the +-15v 24v stabilizer board.
I found a bad cap, replaced it, but now it is oscillating.
This is a long shot but if any of you who worked on this thread is still around, can you guide me through what you have done?