Studer A810 on the Blink

Damn my Studer A810 is broken :(

The speed started wandering all over the place and the Phase Lock light started blinking and the capstan would not lock even in stop mode

I removed the Capstan motor and control board and started testing and I have found that one of the Darlington transistors is faulty BU-522, I removed this from the board to confirm it has failed
When I recapped this board I had also fitted a 47nf cap at C7 which was a mistake, that should have been 470nf which I have now replace I also noted that the heat sink connections for the 2 BU-522 transistors were quite loose so may have been getting hot.
I have ordered 2 new BU-522 from Little diode and I am hoping this is all that's wrong?.


https://c1.staticflickr.com/5/4173/3...008e9dfc_c.jpg20170512_092033 by Alan Towell, on Flickr
Alan

:eek::doh::( Fingers crossed Alan

Aye hopefully that's the extent of it Alan.

Does look badly burnt :(

Oh dear not good news, nice when you know how to fix these machines yourself, I can fix silly issues but when it comes
to cct boards etc I would be a bit lost unless it was obvious.

Reel to reel is great until they start playing up.

Hope you get it sorted out.

Alan,

Good luck with this. Fingers crossed for a happy ending.

Best wishes,

Charlie

Thanks guys hopefully the transistors will arrive Mon Tues and I can get it up and running again
Meanwhile a trusty Tascam BR20 is standing in and doing a sterling job it doesent quite have the scale and drama of the A810 but its pretty damn good :D

Alan

The Transistor arrived today so fitted it and reassembled the motor control board with fresh heat sink to both sides of the mica washer and tightly assembled this time checked that there is also good isolation between the BU 522 and the heat sink as it will short if there is continuity.
Leaving the motor and control board out of the machine I ran through the check's in sec 3.5.9 of the service manual using an oscilloscope and multi meter and adjusted the pots to give the required readings, they were a little out of spec so good job I checked.
Reinstalled the capstan and control board into the A810 and its working perfectly now and sounding superb :D happy days !

I believe the cause of this problem could be that the transistors were not tightly fastened to the heat sink and Q1 has overheated or shorted on the heat sink?.
I replaced this with the BD 522B which is a higher voltage rating than the original which may be beneficial as they do get hot in use I noted after the testing.


https://c1.staticflickr.com/5/4177/3...d430d228_c.jpg20170516_175555 by Alan Towell, on Flickr

Alan

Phew!

Quote:

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Originally Posted by topoxforddoc

Phew!

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Absolutely ! :D

Alan