Studer A807 - erase calibration

[jpmorris]

I noticed the other day that the A807 isn't quite erasing the previous material. Adjusting this has proved a bit harder than I thought.

Firstly, mine is a 2-channel machine with a full-track erase head. The manual gets a bit vague about this, though it seems to be suggesting that the full-track head wants a drive voltage of about 75 volts between TP2 and TP3. This is not happening on either channel. In fact, there doesn't seem to be much across the erase head itself either.

So, I guess my questions are:

1. What kind of voltage should I expect across a full-track erase head? If someone can quickly check on theirs that would be much appreciated. Come to that, is it DC or AC (the manual doesn't say)?

2. The manual says that jumper W1 on the audio electronics board (GR40) should be removed. This is... interesting because RG40 is the audio control board and not the audio electronics card, but more to the point I have not yet been able to locate W1 on the schematics, ridiculous though it sounds.

Any ideas?

Thanks,

[jpmorris]

Well, I've played around with it and determined empirically that the erase head is functioning. The A807 has a lever which allows the erase to be defeated, and the result is pretty conclusive - it is erasing most of the program material, just not all of it.

At the end of the day, I think I need to know three things:

1. How to figure out which of the two audio cards is controlling it

2. Where W1 is on the audio control board (seriously, I cannot find it!)

3. Precisely how the erase circuit is supposed to be adjusted. The manual says this:

* Turn R139 to minimum (fair enough)
* Put a meter between TP2 and TP4
* Turn T3 to obtain minimum voltage
* Put a meter between TP2 and TP3
* Adjust to 75v "with the aid of R139"

...this is where I get a little lost. Ignoring that I'm getting more like 5v prior to any adjustments, it seems to be saying "Turn T3 down and leave it there" . Is that right? Or when it says "with the aid of R139" does it really mean "Adjust both T3 and R139 until it works"?

If anyone out there has done an erase calibration on one of these machines before, I'd greatly appreciate some help with it. If it was just the one trimmer I'd be tempted to do it by ear, but there two per channel and I don't know which channel is actually driving the erase head anyway :roll: