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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 11th Aug 2020, 6:46 pm   #61
Trigon.
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

I'm afraid that i.c. appears to be a 24 pin bespoke device, likely a mask programed microcontroller or logic array - certainly not a user programable PROM.

Cheers

edit: Just found this:-
http://boginjr.com/electronics/old/revox/
Quote:
The internal differences are mainly, but not exclusively, on the digital tape drive circuit boards: the MKI variant uses a mask-programmed gate array, the Motorola “SC10429”, whereas all MKII variants use 74xx-based TTL logic coupled with an action bitmap stored in a 32-byte, one-time PROM, to actuate the TRIACs and brake relays of the tape transport.

Last edited by Trigon.; 11th Aug 2020 at 6:53 pm.
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Old 11th Aug 2020, 7:18 pm   #62
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

I've been off on a little safari. I found the service manual on Elektrotanya.

First image, the overall motor drive with IC4, lower centre.

Second image, closer in on IC to make the pin numbers more visible, although some still aren't. They can probably be solved by following the relevant tracks on the layout diagram, if that is possible.

Third image, an interesting footnote suggesting that IC4 can be substituted with a logic PCB, so that seemed like great news, especially as the service manual also includes the circuit diagram of the substitute logic PCB.

However, when you look at that diagram (image 4), it turns out that the substitute logic board also has a PROM on it, the contents of which would have to be obtained somehow.

Edit: Just caught Trigon's post which seems to confirm that the original device is a mask-programmed gate array. In that case it is unlikely that it can be replaced with a single device like an EPROM.
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Last edited by SiriusHardware; 11th Aug 2020 at 7:26 pm.
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Old 11th Aug 2020, 8:46 pm   #63
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Hi,

The proms in the later B77 Mk1's, Mk2 and all PR99s are 32X8 (82s123) bipolar proms and indentical. These are the same type as used in the Studer A807 that this thread started for. I'm afraid you have the early B77Mk1. Good news all the later boards will work in your machine and are not hard to find. Quick look on Ebay and they start at $30us. If you had a later board I could dump a good one and either I or SiriusH could program it. In fact I have 2 in for service right now so I will try to dump the prom for future use.

Jim
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Old 12th Aug 2020, 1:00 pm   #64
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

hello jsantoro,

I've looked on eBay but the only boards I found were for a PR99 with the part number: 1.177.317.13. From what you've said, I assume that these boards would work in my machine but they're rather expensive!

Regards,

Dave.
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Old 12th Aug 2020, 1:55 pm   #65
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

I've attached a photo of the board, although it's probably academic now. It is a 1.177.315-12 (1), the last number is in a circle.

Regards,

Dave.
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Old 12th Aug 2020, 2:34 pm   #66
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Amraduk, how sure are you that IC4 is really the cause of your problem? The reason I ask is that I went looking and found a 'repair kit' for your version of the board which includes the power semiconductors and a full set of replacement capacitors, including conventional replacements for the Tantalum bead capacitors, of which there are quite a few on your board. These are notoriously temperamental parts which have a tendency to fail low resistance or short-circuit.

There are at least -eight- capacitors directly connected from pins of IC4 to 0V, so I would try checking them in-circuit for very low resistances or short, if any seem suspect desolder one end and check the capacitor by itself. Or just replace them and keep and identify the original capacitors by position so you can put them back in (if you wish) if they do not fix the problem.

Last edited by SiriusHardware; 12th Aug 2020 at 2:51 pm.
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Old 12th Aug 2020, 6:25 pm   #67
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Amraduk,

I'm with SiriusH on this one. Try fixing the board you have. What are the symptoms?Don't assume it's the Prom. I've never seen one just go bad.

And yes any Pr99,B77 Control board will work. 1.177.317.xx. Keep a look out and also outside the UK, I've seen then for $30-$40 if you catch it right.

Also those 2 gold Frako's have to go. Replace any of those you see in the deck and also any of the rectangular Rifa caps.

Jim
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Old 13th Aug 2020, 8:19 am   #68
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Hello Jim,

Good to know that other boards will work in a MKI.

I accidentally shorted out something on the EOT device which blew the 24v supply fuse, it was after that when the problems started. Does anyone know what type is the phototransistor? The LED seems to be OK as I can see some illumination from it, though I suppose it could still be faulty.

The symptoms are that when attempting to play a tape, it runs backwards! I suppose it could be insufficient pinch wheel pressure and/or too much back tension on the supply reel.

I do intend to to check it out but it's not easy to work on the boards when they are 'in situ'.

I've seen lots of component kits on eBay for these boards at around $30 US but no actual boards at that price.

It would be good to have a back-up board just in case something does go wrong with the one in the machine.

Oh yes, I know about the Rifa and Frako caps, the Rifa across the mains socket gave up the ghost soon after I got the machine but I didn't know there were others in it. I'll certainly change them when I get some replacements.

Regards,

Dave.

Last edited by Amraduk; 13th Aug 2020 at 8:25 am.
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Old 13th Aug 2020, 1:11 pm   #69
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

If you really did hit the EOT device with 24V (it runs on 5V) then I agree it is possible you may have damaged anything on the 5V rails including IC4.

Rather than search for / spend real money on new parts which may not fix the problem, try a little bit of fault tracing. With the power on, compare the difference in the voltage on IC4 pin 3

-When there is no tape in the EOT sensor
-When there is a tape blocking the light path in the EOT sensor.

The way the EOT opto device is wired to the following transistor, I would expect the voltage on IC4 pin 3 to be low (logic 0 / around 0V) when there is nothing in the EOT sensor and high (logic 1 / around 4-5 volts) when there is something (ie, tape) blocking the sensor light path.
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Old 13th Aug 2020, 3:41 pm   #70
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Quote:
Originally Posted by SiriusHardware View Post
If you really did hit the EOT device with 24V (it runs on 5V) then I agree it is possible you may have damaged anything on the 5V rails including IC4.
I don't think that's the problem. From the manual:-

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Obviously shorting the +24v pin to chassis would blow the fuse - but I can't see shorting any pins together on the EOT would do any damage.

With the sensor blocked, pin 3 sees 24v via 6k8. All the '24v' sourced inputs are likely clamped to the +5v supply internally and may well sit at around 5.7v.

Cheers
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Old 13th Aug 2020, 3:45 pm   #71
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Thanks, I really need my eyes tested or a better copy of the diagram. I thought the EOT sensor was powered from +5V, so obviously shorting +24 to that would have been potentially catastrophic. Those blue tantalums are still #1 on my hit list.
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Old 13th Aug 2020, 4:39 pm   #72
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Does the roller energize against the capstan? Capstan turning? Did you have anything else apart beside playing with the EOT sensor. Might be helpful to start form the beginning from the last time you saw it working. This board is still reviewing my posts for some reason so it takes a while to respond.
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Old 13th Aug 2020, 7:02 pm   #73
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

Quote:
Originally Posted by Amraduk View Post
Some additional info. I've just looked at the PROM IC (IC4), it has the 'M' symbol for Motorola followed by 7803, below that is 'STUDER' and below that is 50.05.0143.
SC10249 is a Motorola custom type number, so that seems to confirm the M symbol.
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Old 16th Aug 2020, 10:24 am   #74
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Default Re: Studer / Revox etc BiPolar PROMS! Question and concerns!

When I first saw the tape running backwards, I had assumed that the capstan motor was running normally, however, while making some more tests, I found that it was actually running in reverse. That was my fault because, despite making a drawing of the connections, I found that I had two of the three capstan motor wires swapped! After changing them back to the right way, the tape now runs forwards. Sorry about that. I think it was this that made me think it might be IC4.

I think what must have happened was that I shorted the photo-transistor, thereby putting 24V (actually about 27V) on the base of Q9 (shown on the circuit as a BC107A but was actually a BC547B), thereby blowing the b-e junction of Q9. Also, the photo-transistor is O/C. As the LED (coloured red) is giving a fair amount of visible red light, I'm wondering if it, and the photo-transistor are, actually, visible light devices rather than infra-red?

The 5V supply is a bit low at 4.77V, the zener diode (D5) is correct at 5.6V, I don't know if that's normal but I'd like to get the 4.77V nearer to 5V, if possible. The 5V supply is just a simple zener-biassed emitter follower (Q5, 2SC496), so the emitter ought to be just under 5V, maybe the transistor is faulty or the 100uF across the 5V output? I've not yet checked them.

Does anyone know of a suitable replacement for the photo-transistor? Thanks.

Regards,

Dave.
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