Studer A810 fails to power up

mab

Well-Known Member
Sep 10, 2011
10
3
908
Hadn't turned her on in a few months and when I tried last night my friend said he saw the lights come on for a second but then no power. No smoke or pop or anything. Is anyone willing to help me diagnose? If I could repair myself that would be great!

Thanks,
Matt
 

mab

Well-Known Member
Sep 10, 2011
10
3
908
blown fuse

I took off the back cover and discovered this blown fuse Slow Blow 5A Supply 5,6V + 24V.

20150906_145700 (1).jpg
 

amirm

Banned
Apr 2, 2010
15,813
37
0
Seattle, WA
The key moment is when you put a new fuse and it stays on or burns that one out too. Be sure to use the same rating and slo blo.
 

mab

Well-Known Member
Sep 10, 2011
10
3
908
Yeah, my guess from a brief skim of the service manual is that something out of spec would be the cause for this fuse to blow. My hopes are low and I'm a little worried about risking powering it up again with a new fuse.
 

amirm

Banned
Apr 2, 2010
15,813
37
0
Seattle, WA
A visual inspection would be good before repowering. Smell around and see if anything is burnt.

The problem with slo blo fuses is that they let things cook good before opening. So you could make it worse but all in all, I would change the fuse and see what happens if visual/nose inspection comes out clean. :)
 

Ki Choi

Member Sponsor
May 13, 2010
764
29
1,590
Seattle WA area
Matt

Got your PM and for the benefit of the other members, I will attempt to give you pointers. Unfortunately, I am not at home and don't have the manual handy to reference exact details on parts.

As you had guessed, the slow blow fuse blew for a reason, and you shouldn't just replace it. It would do more damage if the new fuse doesn't blow...

The first area of troubleshooting would be to mark the cards from the bottom rack and remove them all. Then disconnect the Molex connector that feeds DC outputs from voltage regulator board to the Basis Board. I would visually inspect for an axial filter cap for 5.6VDC in the voltage regulator board that is mounted on the left side metal frame as you look at the machine from the back and the basis board where the cards were plugged in before. If you see the dreaded yellow/gold colored Frako type caps, I would replace them first before you go any further.

There's a small chance one of the large can bolt mounted type cap could be bad but it is less likely (unless your machine is the typical eBay sourced A810 had been resting for the last thirty years).

After removing the Molex output connector from the DC Regulator board (or Studer Stabilizer), you put the replacement fuse and power up the machine. Be careful to measure the output voltages from the board pin outs. Check the manual for proper output voltage spec. My guess is that the Stabilizer would be good in supplying the +24V, +5.6V, and +/- 15VDC. If not, I would go back to checking out the input voltages from the power transformer/rectifier/bolt mounted filter caps to the Stabilizer. If input supply voltages are good, then you know you have an issue with the Stabilizer board.

Otherwise, if you get good output voltages from the Molex connector pins from the Stabilizer board, the most likely cause for your trouble would be that you have shorted filter cap(s) in the following boards:
1) basis board - again if they are yellowish Frako type with known 100% failure rate, you would need to replace all of them anyway.
2) LED control panel - if you had Frako caps elsewhere, you are sure to have one there as well. Replace it. If it is shorted, it will blow the SB fuse.
3) Although not related, you should also replace two axial filter caps under the headblock for +/-15DC supplies to the head preamp.

After recapping, you should power up and measure the voltages from the back of the machine at the top section of the basis board's solder side that is marked with proper voltage numbers. After verifying you have good voltages at the back of the Basis Machine solder side, I would power down and insert only the transport cards first. Measure the voltages again at the back of the Basis board. If good, then insert one channel of audio cards and check again...and next channel, etc.

You should be good to go by then.

Hope it helps. Good hunting.

Ki
 

mab

Well-Known Member
Sep 10, 2011
10
3
908
Thanks Ki! Debating now whether I want to take this project on or try to find someone to repair. :) Very kind of you to spend the time to help describe the procedure for troubleshooting this problem. Many thanks!
 

Curt Palme

Well-Known Member
Jan 25, 2012
86
1
83
A bit late, but just to add, all Studer machines should be fully recapped. The blue Frako caps short out for no reason, which is most likely what's happened here. If there are still original blue Frako electrolytic capacitors in the deck, then you can either troubleshoot to find the bad one.. and then expect to do this once a year as others short, or recap completely, and be trouble free (most likely!) for a few years.

Depending on where you are, I can take on the project, as can a couple of other techs here, I don't want to take business away from anyone else..
 

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