Studer A807 direct sound only

[cariocaman85]

Dear All,

A regretted friend of mine gave me his STUDER A807 that had been in his attic for a long time.

After gently cleaning it, it is working almost fine, transport is working well, but I can't get no playback sound from the tape.

I sent a reference in the line inputs and it goes right through the output (and inside monitor), even in play mode, but nothing is coming back from the tape.

Looks like the Varispeed, Nab and Insert switch are broken, but I think it shouldn't be this problem, maybe I'm wrong?

I can't see no jumper in the manual that would do that, but I'm surely mistaken.
This is the model without the VUmeters.

By the way it has not been recaped.
I think I will do it, but don't know if it can influence the logical routing.
The fuses are all good and passing.

It seems to be locked in Input monitor mode, but I do not know how to change this.
My version is without the Vu meters and I don't have no Input/repro control.

My guess is there is an automatic switch from input to repro when play is engaged, but I'm not sure.

Enquiring through the service manual tells me that a MC14053 is analog switching between Normal Reproduce path and the input signal. Could be it but as it is doing this on both channels, I suppose it is the command signal of this switch that is not working. I need to find from where this signal comes


Thanks a lot for your help,
Best,

 

[cariocaman85]

Both MC14053 switches from the 2 audio boards are controlled by one 4094 register in the audio control board. Could be it, or could be its command signal...

 

[cariocaman85]

Ok so maybe it is time I write a recap of my findings, so hopefully one of you could chime in and help me...

The A807 is the version without VU.

It is locked in Input mode, so I can hear either PREOUT or MONITOR OUT (which is now also PREOUT, without the possibility of changing). So I'm stuck with a pre out signal.
I checked that by sending the line inputs 1000hz reference signal, hearing it back both from the inside monitor and the line output.
When I play an already printed reel, nothing is played and the 1000hz stays.

So after trying a lot of settings and looking at jumpers, I tried to find what cause the monitor selection to be stuck:

It is said in Manual section 4/1/6 that IC26 (4053) is the one that is switching from one of the 3 lines:
1 Normal reproduce path (I assume it is repro mode?)
2 Reproduce path via repro level control
3 Directly from the insert point of the input amplifier

My guess is that it is stuck in 3.

Please See in 01 A807 Audio electronics schematics attached.

 

[cariocaman85]

What is commanding IC26 is coming from the Audio Control Board (please see 02 A807 AUDIO Control attached).
It is IC9 (4094) that is the 8bits register sending the output control commands. (Please see 03 A807 output control register attached).

IC9 is receiving from the tape Deck
AS Clk
AS Data
AS Str
AS reset

And it is giving for both audio boards:
C Calou
C Uncou
C Input

The thing is that those 4094 are in series so if one is fried I suppose it wouldn't pass AS Data to the next...

 

[cariocaman85]

AS Clk
AS Data
AS Str
AS reset

Are coming from the Tape Deck where logic command lies (see 04 A807 Audio logic control Attached)

It is said that all data is generated in the CPU (IC12) and then distributed to the registers (see 05 A807 TAPE DECK 1/2 attached).

As other fonctions like transport are fine, I suppose that the DATA channel is fine, therefore the CPU is correct.

 

[cariocaman85]

In the second part of the Tape deck schematic (please see 06 A807 TAPE DECK 2/2 attached) we see that Data is distributed to IC28 (HCT574) non inverting Schmitt trigger.

It is it that is feeding IC 9 in the audio control board, so if it's faulty, it doesn't switch from input to anything else, I am right?

 

[cariocaman85]

So... Here are my findings.
I'm planning on buying a few 4094, 4053 and HCT574 as they are rather inexpensive, and replace them.

However I have a few thought:
Before buying is there a way to know which one is faulty?

As I previously said, I didn't recapped the circuits at all, so the capacitors are from the 80's. Could some bad capacitors be the cause of the IC not doing properly their jobs?

Maybe it is a totally unrelated issue ...

Anyone would be willing to help me sort this out?

 

[Ike Zimbel]

Since no one else is chiming in here... That vintage of Studer is loaded with caps that go bad, particularly the Frako branded ones but possibly others. So I would say that before you change any silicon at all, you deal with the capacitors first.
2nd, last time I was around A807's etc they were nearly new, so I don't know if this is an issue with them, but on A-80 series machines I saw plenty of IC's and sockets with a condition I call "black leg", wherein the the pins on the IC's turn completely black from oxidization. I once restored a non-functioning A-80 remote by removing all the IC's and cleaning their legs with a pumice impregnated eraser and replacing the IC sockets. No new silicon was required (although I was careful about static while I was doing the work...still am). So, a 30+ year old 807 might have some of that going on too. Visually, it looks like the IC body, legs and socket are all a uniform black colour.

 

[cariocaman85]

Since no one else is chiming in here... That vintage of Studer is loaded with caps that go bad, particularly the Frako branded ones but possibly others. So I would say that before you change any silicon at all, you deal with the capacitors first.
2nd, last time I was around A807's etc they were nearly new, so I don't know if this is an issue with them, but on A-80 series machines I saw plenty of IC's and sockets with a condition I call "black leg", wherein the the pins on the IC's turn completely black from oxidization. I once restored a non-functioning A-80 remote by removing all the IC's and cleaning their legs with a pumice impregnated eraser and replacing the IC sockets. No new silicon was required (although I was careful about static while I was doing the work...still am). So, a 30+ year old 807 might have some of that going on too. Visually, it looks like the IC body, legs and socket are all a uniform black colour.

Thanks a lot I will check those black legs! Otherwise the boards seem clean, no oxydation residue.

I will recap them when I got the time then. You think they could jam the logic? Only the playback switch seems off. It is recording allright as well.

 

[radardoug]

The first thing you should check is the state of the processor card. The battery on these cards sprays acid all over the board and the board gets corroded. Look for chips with corroded legs.
As others have said, these are also full of caps that go bad, particularly Frakos and Rifas. They all need to be changed.

 

[cariocaman85]

The first thing you should check is the state of the processor card. The battery on these cards sprays acid all over the board and the board gets corroded. Look for chips with corroded legs.
As others have said, these are also full of caps that go bad, particularly Frakos and Rifas. They all need to be changed.

The board looks allright to me, no sign of oxydation, but I might be mistaken. I'll send pictures tomorrow.

I will look at corroded chips and ordering new capacitors.

Thanks a lot

 

[cariocaman85]

Only the lytics, right?

 

[Ike Zimbel]

Sadly, no. I would look at tantalums, too. And possibly film caps as well, but you might leave those to the trouble-shooting phase after you have done the lytics and tants. To be clear, I don't think you should shotgun the film caps, just that the odd one has been known to fail.

 

[cariocaman85]

Sadly, no. I would look at tantalums, too. And possibly film caps as well, but you might leave those to the trouble-shooting phase after you have done the lytics and tants. To be clear, I don't think you should shotgun the film caps, just that the odd one has been known to fail.

Thanks!

Solid aluminium as well?

 

[cariocaman85]

Thats weird, in the manual I can't se no tantalum in the components list
I see electrolytics, Polyesterfoil, Polypropylene, Metal film, ceramic and Solid aluminium.
On the board it looks like there are some tants thought

 

[Ike Zimbel]

About 40 years ago, we used the Philips solid aluminum caps (which were orange in colour) instead of tantalum, in hopes that they wouldn't short if they failed. Since then, I haven't had much contact with them, but I'm hoping we were right back then! I wouldn't change those unless you find a failed one.

 

[cariocaman85]

About 40 years ago, we used the Philips solid aluminum caps (which were orange in colour) instead of tantalum, in hopes that they wouldn't short if they failed. Since then, I haven't had much contact with them, but I'm hoping we were right back then! I wouldn't change those unless you find a failed one.

OK thanks

 

[cariocaman85]

About 40 years ago, we used the Philips solid aluminum caps (which were orange in colour) instead of tantalum, in hopes that they wouldn't short if they failed. Since then, I haven't had much contact with them, but I'm hoping we were right back then! I wouldn't change those unless you find a failed one.

I actually see some tantalums in the Capstan motor control board, the Spooling motor control board and the tape move sensor and the tacho.
In the manual they are referred as solid aluminium but on the board they are clearly tantalums.

Should I change them for new tantalum?

 

[Ike Zimbel]

If the transport is working now, I wouldn't, at least until you know if you can get the machine working. And, before you go down that road...how are the heads? In good condition? The pinch roller? Did you check for the leaky battery on the processor card as Doug suggested?
I would strongly suggest that you make sure that the effort will be worth it before you replace every single cap etc.

 

[cariocaman85]

If the transport is working now, I wouldn't, at least until you know if you can get the machine working. And, before you go down that road...how are the heads? In good condition? The pinch roller? Did you check for the leaky battery on the processor card as Doug suggested?
I would strongly suggest that you make sure that the effort will be worth it before you replace every single cap etc.

Thanks,

The heads are visually allright. Pinch roller seems fine as well, but not sure what to look at.

Here are some pictures of the inside.
Here is the processor board.
I don't think the battery has leaked, don't you?
The white spot is the flash from the phone...
Dirty traces on the center IC look like old glue from a previous sticker.