Studer A810 on the Blink

[337alant]

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/5/4173/34629399515_e1008e9dfc_c.jpg (https://flic.kr/p/UL5J1k)20170512_092033 (https://flic.kr/p/UL5J1k) by Alan Towell (https://www.flickr.com/photos/69508926@N05/), on Flickr
Alan

[Audio Al]

:eek::doh::( Fingers crossed Alan

[Ali Tait]

Aye hopefully that's the extent of it Alan.

[Audio Al]

Does look badly burnt :(

[Cas]

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.

[topoxforddoc]

Alan,

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

Best wishes,

Charlie

[337alant]

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

[337alant]

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/5/4177/34317971470_06d430d228_c.jpg (https://flic.kr/p/Uhyzih)20170516_175555 (https://flic.kr/p/Uhyzih) by Alan Towell (https://www.flickr.com/photos/69508926@N05/), on Flickr

Alan

[topoxforddoc]

Phew!

[337alant]

Phew!
Absolutely ! :D

Alan

[Audio Al]

Phew x 2 ;)

[Cas]

Nice one, wish I had the ability to do all that.

[Ali Tait]

Good news Alan, must be a relief!

[337alant]

Thanks Guys
Ali yes its a relief that it wasn't anything more serious or one of the ICs that cant be obtained any more or the Capstan motor its self :eek:

Good thing about the A810 is everything is on modular and removable boards and there are still replacement boards available on ebay there is even a Capstan motor on there (at a cost)
I do really like this machine and use it all the time but this has made me think that it would be wise to start limiting the usage of this machine maybe just for recording and use one of the BR20s for everyday playback

Alan

[topoxforddoc]

Studers are built like tanks. As long as you can get heads related or replaced (plenty available from Belgium and JRF in the USA), then these will go on and on. The electronics are very robust, even the caps! Enjoy it Alan :)

[337alant]

I certainly will enjoy it Charlie thanks, its my pride and joy :eyebrows:
As you say they are normally very reliable and superb build quality.
I can't say that the electrolytic caps are any more reliable than any other make as the studers like the revox have a lot of Frako caps the little blue phillips caps and some roe Bakerlite caps
All excellent capacitors in their day but frankly are at the end of the useful life cycle and the frakos in particular have a reputation of failing short circuit and can take out other ICs in the same circuit.
The blue Philips film, wima film and solid aluminium caps are all very robust and should not need to be changed
I have replaced all of the electrolytic caps in my Studer A810 and many were measured out of spec when I removed them the small blue Philips caps being the worst and some of the Roe bakerlight caps had cracked and dried out.
I replaced them with combination of Nichicon Muze KZ, ES (bipolar), fine gold and some Panasonic FC

Example before

https://c1.staticflickr.com/1/720/20767994414_f58282c78d_c.jpg (https://flic.kr/p/xDcpcd)IMG_2389 (https://flic.kr/p/xDcpcd) by Alan Towell (https://www.flickr.com/photos/69508926@N05/), on Flickr

And after

https://c1.staticflickr.com/1/592/20769842603_28f9ef49e0_c.jpg (https://flic.kr/p/xDmSAx)IMG_2487 (https://flic.kr/p/xDmSAx) by Alan Towell (https://www.flickr.com/photos/69508926@N05/), on FlickrAlan