Studer A807 direct sound only

[cariocaman85]

And other pictures:

Audio Board

 

[cariocaman85]

And motor / Captsan controls:

 

[guy_4]

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.

Hello, there is no battery in the A807. There is a battery in the A810, 812, 820.

 

[guy_4]

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.

Hello, how can you say " record is alright " but you can't playback the tape ??? Does it mean the A807 can go into Record Mode ? And if so, can you listen back to the tape you have just recorded ?

 

[guy_4]

Hello, how can you say " record is alright " but you can't playback the tape ??? Does it mean the A807 can go into Record Mode ? And if so, can you listen back to the tape you have just recorded ?

What serial number is your A807 ?

 

[guy_4]

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.
View attachment 89551

 

[guy_4]

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,

Hello, can you post a front pic of your A807, please ?

 

[guy_4]

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,

Varispeed, NAB/CCIR and Insert can be active while pressing SHIFT at the same time. Speeds too. These are software programmable switches. They can be changed.

 

[guy_4]

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.

Hello,my advice would be to first find the problem ( no audio from Playback head ) and later you'll replace the caps. I don't think it is a problem now coming from old caps or oxidized iC's pins.
( still have four A807's to fix in my shop now ... )

 

[guy_4]

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?

Hello, I will try to help you...I fixed Studer stuff for decades... and still do...

 

[zonkers31]

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,

no, there is no automatic switching. You should have switches on the front panel that say Input, Sel-rep, Repro. you must select one to change the status of playback.

 

[mjrippe]

Here are some pictures of the inside.

Dirty traces on the center IC look like old glue from a previous sticker.

Well, that IC looks like an EPROM, which should have a sticker over the quartz glass window. These chips would be erased by putting them under UV light. It is possible that the data has been corrupted. Not the most likely suspect, but something to check if all else fails.

 

[guy_4]

no, there is no automatic switching. You should have switches on the front panel that say Input, Sel-rep, Repro. you must select one to change the status of playback.

Hello, no need to have that switching front panel. I have serviced many A807's that had no panel, and worked well. I have no time now to do a search to fix this " no playback ' problem but I will do ASAP. Cheers.

 

[guy_4]

Well, that IC looks like an EPROM, which should have a sticker over the quartz glass window. These chips would be erased by putting them under UV light. It is possible that the data has been corrupted. Not the most likely suspect, but something to check if all else fails.

Hello, I don't think the EPROM is " erased " . If so, the A807 would not turn on . Cheers.

 

[cariocaman85]

Hello, I will try to help you...I fixed Studer stuff for decades... and still do...

Hello,
I'm so sorry, I was on the road for a few weeks and did not see your messages... I feel bad...

I check today everything you asked and come back with answers!
Sorry for the very late reply...

 

[JohnRoberts]

Do you have a scope or any way to look for the missing audio signal?

JR

 

[cariocaman85]

Do you have a scope or any way to look for the missing audio signal?

JR

Yes I do have a small scope available

 

[JohnRoberts]

try to carefully follow the signal... you mentioned some part numbers for CMOS transfer gates, one of them may be faulty, it could be almost anything, but basic troubleshooting is to follow the signal until it goes astray.

JR