Help needed for Studer A810

[hugo habicht]

Hello,

I have a damaged EPROM on my Studer A810 MP card (1.810.780-00).   The software version is 01/88.   If somebody has made a software backup (something that I should have done myself a long time ago) and could send me a copy it would be appreciated.   I could write the EPROM then and get my A810 back running again.

Kind Regards,
Hagen
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[Ki Choi]

Hi Hagen:

Based on your MPU card part number (1.810.780-00), the firmwas was had been updated.  the MPU card version came with the firmware version 40/85.

Since A810 firmware version 01/88 is the latest official version and your MPU card is somewhat old (-22 is the youngest), I suggest you stay with proven version 01/88 than to upgrade to the last version 25/91 that offers no audiophile related functionalities or default EQ data.

The last time when I checked with Audiohouse, they had 25/91 for sale but no longer stocked the 01/88 chip set.

Ki

[hugo habicht]

Hello Ki,

thank you for the hint with the the CPU card revision.   My paper manual (that came from a different machine) doesn't have newer card revisions included.   I'll get the latest service manual and see what the modifications were.

Kind regards,
Hagen
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[hugo habicht]

Hello Ki,

I compared the CPU card revision 1.810.780-00 with -22.   The differences I found were:

1. Modified battery charging circuit -> has been done on my card.
2. Reset circuit modified from Studer home brewed circuit to reset controller IC -> I may put that in; my A810 sometimes doesn't like to start up
3. More peripheral select and external reset lines -> not needed in the A810
4. Selectable peripheral select timing omitting E-signal for A820 -> not needed in the A810
5. One additional 614.4kHz clock signal -> not needed on A810

That seems to confirm the service manual table that the 1.810.780-00 card can run all A810 software versions.

Kind Regards,
Hagen
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[Ki Choi]

Good work Hagen.  I haven't looked into the details of the MPU version changes but now I know.  The main concern in old MPU card incompatibility with the latest firmware versions is for MPU cards (1.810.752.XX) with 07/83 or older.

Let us know how your recovery work ends up.

After you have your A810 working perfectly, you need to contact the Queen, Eilleen, and get hold of the TP tapes and hear what the fuss is all about!

Ki

[hugo habicht]

Hello Ki,

my apologies for not answering earlier.   Somehow technology seems to be against me at the moment....

Firstly I'd like to thank you very much for your help.   After a bit of trouble with the eprom programmer I got the A810 back to live again.   

But it is still not working properly, so unfortunately it is too early to ring Eileen.   When playing a tape the right tension roller tends to oscillate.   When I dampen it by hand it stays stable but after starting a tape at the beginning the initial oscillation doesn't stop.   The tension rollers move nicely.   I checked the tension springs and they seem to be good within the resolution of my force meter (which is only 0.1 Newton); I don't think that springs deteriorate significantly.   I checked and corrected the electrical adjustment of the tension sensors.   I checked and adjusted the dashpots.   After that I adjusted the tape tension for play, forward, reverse and peaks.   Still oscillating.   My next guess would be to check the compensation network around IC10 on the spooling motor control PCB but I have to make an extender card first in order to be able to do some measurements.   Maybe I simply change the electrolytic capacitors around IC10 and see what happens.  Would you have any other ideas?

Kind Regards,
Hagen
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[hugo habicht]

Hello Ki,

my guess was right!   With capacitances of 54uF, 57uF, 101uF and 680nF(!) for C15 - C18 the phase margin in the controller couldn't possibly have been close to what Willi Studers electronic designers had intended it to be.

It is starting nicely now, not even a hint of oscillation visible any more.

So I think after completely restoring the electronics over Christmas (the cracks in the insulation of the Rifa capacitors don't give me much confidence in their life expectancy) and adjusting all audio parameters there shouldn't be any obstacles left to get my hand on some good Tape Project tapes :-).   Maybe the small but nevertheless important financial side...   But let's see what Santa brings me this year.   I have to get some CDs first anyway; I have to admit that I don't know a lot of the recordings.

Kind Regards,
Hagen
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[Ki Choi]

Hi Hagen:

It's good that you had found the source of the problem and fixed it.  Judging from the electrolytic capacitor issues you had with spoolng motor controller, I would supect you have similar problems elsewhere.

The first area of problem would be the filter caps in the Basis boards.  Although there are many, once you get started, it goes fast.  The next one is the caps in the Power Regulator board.  I have also replaced two electolytic caps in the LED Display board.

The ones that most people miss and I found to be critical are two electrolytic caps in the head preamp board inside the headblock.  I would replace them before you do any audio work on the machine.

Ki

[hugo habicht]

Hello Ki,

I agree 100% with you that at a minimum all the electrolytic capacitors have to be replaced; the odd power semiconductor that has seen higher silicon temperatures during its lifetime will be replaced as well.   The Rifa caps at the mains are also known to go off in smoke (literally) although they should not by design.   I recently treated myself to a nice desoldering station so removing all the caps without stress for the boards will be easy enough.   Thank you for the hint with the head preamp board; this can be easily overlooked.   

With a constant error 001 I don't worry too much about audio performance at the moment.   The battery has found it's way to the recycling center already and I haven't got the new one yet.   I'll have to write a little 6800 disassembler over Christmas and have a look at the software; maybe there is a way getting rid of the battery altogether.   Since the developers kindly left one of the ROM sockets empty I am tempted to plug in a Flash EEPROM for that purpose.   That of course depends how much space they left in the three ROMs and if there is enough time after detecting a power fail to copy all the essential RAM contents.

Kind Regards,
Hagen
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