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Studer A807 Mk 1 Software 30/88

Machine had fault were 50 V fuse kept blowing. I think that was loose reel turntable causing the Reel drive to crossbar the supply, whenever it got out of step. That sorted , but now unable to align the Audio.
Unable to get any change in adjustment parameters in Level , hf for Repro Sync and record. All speed, All eq.
BUT can control bias level.
It was storing tape position. ( Latest test, seem to indicate that no that is not happening , but unsure about the reliability of this test).
My fear is that it a faulty MCM2802. eeprom chip.
I can't even find an readable pdf of this device, let alone a replacement.
Can anyone suggest a source, or equivalent ( Fat chance) .
Also one question.
What is meant to cause the chip to go into write mode.
Dam interesting fault. Almost can't believe it could happen.

Comments

Boswell Tue, 06/15/2021 - 19:33

My experience of those old EPROMS is that they can suffer from one or both of two ageing effects:

1) Degrading of the stored image. This does not necessarily mean that the device is life-expired, simply that it needs re-writing to last another 10 years. The problem may be that of getting hold of an uncorrupted image file from somewhere that you can use to program the chip. It's possible that the Studer web site or user forum could help here.

2) Dirty pins. This is a much easier problem to correct. Gently pry the chip out if its socket and use degreasing fluid to clean the pins. Pushing it back into the socket will wipe the socket contacts.

It's worth trying (2) first. After cleaning the pins and before you re-seat the chip, put it into an EPROM blower and read the contents so you have a copy for when (1) happens (which it will),

Des Amos Tue, 06/15/2021 - 20:40

In reply to by Link555

Was looking along this very option as a worthwhile line.
The studio has 4 of these machines. And they will need to work for another 5 years at least, while organisations still need to achieve any 1/4 inch recordings.
These machines have past they're expected life and components used were only meant to last for 10 years in the case of MCM2802.
It is a simple 16 bit word that is send from processor . In the case of replay only requirement. Only 2 words need to be sent.
Thanks for your response.

Boswell Wed, 06/16/2021 - 04:48

Does any of the other 4 similar machines have the same firmware revision? If so, you could borrow an EPROM from one that does and re-blow your suspect part with the image from the known good one.

There is a temptation to exchange the EPROMs between machines to see if the fault moves, but I would resist that. You don't know what other locations in the memory are used for controlling unrelated functions, and if some of the other locations are also corrupted, it could cause problems. Once the suspect device is re-programmed to have the same known good contents as a working one, it should not matter which part goes in which machine, but I would test it first in the machine it came from.

Des Amos Wed, 06/16/2021 - 19:41

In reply to by Boswell

I can re-burn a new set of eproms.
I cannot remove eproms from going machines. I'm a freelance tech. Can't take that risk with clients property.
But I felt ( Possibly very erroneously) Since I can see some level of bit change at the Dac, but I don't think there is also a write enable. That this is far to small an error for it to be a fault in the firmware and went on the path of looking at the method of writing to the dac .
I think the processor reads the eeprom to write to the Dac. So as you change switch on or change speed,
It needs to load the last used value.
Looking back at what I have written. I think what I though was bit level activity is just other data buss activity.
Would be interested to know if my assumption as to the program operation is correct.

Boswell Thu, 06/17/2021 - 07:51

Your original post did not make clear that you had no access to the boards in any of the other Studers.

I don't see how you can re-blow the EPROM from the faulty machine without an external reference image if you are not certain you can read it correctly in its present state.

I'm sorry, but I can't follow your train of thought about a DAC. Where does the Write Enable come from? EPROMs in old designs like that either have logic-level write enables so that the machine can store last-used settings, or they are elevated-voltage enables that can only be activated by placing the chip in an external programmer. The Motorola part you specified is in the latter category, needing a 25V write enable. It's possible that the Studer electronics produces this voltage for writing purposes, but it would be unusual if it did.

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