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Revox Stopped working

jt45

jt45

Super Member
I have a Revox B790 that Ive had running for a few months with no problems thru my Mitsu compacts separates system . Today I hear a small pop, like a bad record pop while playing an older LP and now Im getting nothing (no sound).
Ive hooked my Mitsu TT up to eliminate the pre-amp/amp amd checked the rca cables, so could this be a cap or resistor issue ? Ive replaced some things when I restored the revox so I have been into it before (with some help from a local AK member) Ive checked the fuse and the TT still runs and appears to be tracking so the issue seems to be purely output related. The cartridge and stylus appear OK as well the connections to those.

So has anyone had a similar issue and what troubleshooting tips might you have?
 
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HI,
I've never worked on the Revox arm so take what I offer carefully. I'm guessing that the arm, like many arms, have a muting function and this has failed thus breaking the signal path from the cartridge. Often this is a photo detector working in conjunction with a relay. It won't be an active amplifier because this would potentially degrade the audio signal. Without specific experience with this arm I can't say more. You may need to get a service manual (you should have one anyway) to troubleshoot the problem.

Sparky
 
Hi; There is a muting relay that is controlled by the arm solenoid circuit. How to fix? It is that clear plastic box on the arm control board. One thing you might want to check is that the cable for your RCA connectors is plugged into the arm control board properly.
 
jim249 said:
Hi; There is a muting relay that is controlled by the arm solenoid circuit. How to fix? It is that clear plastic box on the arm control board. One thing you might want to check is that the cable for your RCA connectors is plugged into the arm control board properly.
Click to expand...

Thanks I will give that a look as well as a few other things, I replaced some resistors the last time I was inside it as well as the RCA leads but I will check that plug also, the odd thing was that it was playing fine up until the 3rd track or so with a little bit of dirty record noise and I was just about to pull it and give it a spin in the cleaner when it went dead.

Thank god I have the Mitsu DP-EC20 ready, to keep the music going.:D The old Shure V15 IV is keeping me sane for the moment.:music: But I wont let the
Revox stay down for long if I can help it.
 
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There must be some way to do a temp bypass of the muting relay to check to see if that is really the problem. Any help out there?!
 
The relay is wired in as a "dead man" default and cannot be conveniently defeated without removal. The most likely defective components will be capacitor C1, diode D5, and/or transistor Q3 if not an open K1 relay coil.
 
Pio1980 said:
The relay is wired in as a "dead man" default and cannot be conveniently defeated without removal. The most likely defective components will be capacitor C1, diode D5, and/or transistor Q3 if not an open K1 relay coil.
Click to expand...

I found a bad lead connector on the Blue and white lead to the cart. I fixed that but when I put everything back together a resistor (R15) went up in smoke so now Im back to square one and dont think Im doing it much good.

Anyone know who might repair those. I would be better off just sending the board to someone but I wonder what might be causing it fry those. This same resistor was shot back when I first fixed this table with some help from another member here.

I think you (PIO1980) commented to the fact that these were a PITA to solder back then. Now Im stuck wondering whats causing the problem to repeat itself after several months.
 
R15 47^ is associated with the large e'lytic cap C5 next to it. Replace R15 and C5 if it hasn't already been changed out and check D10 with diode check function of DVM.
 
If you haven't done so already, replace all the caps that say Fraco on them. They are junk and cause most of the problems with this table. If you are ready to throw in the towel, JM Technical Arts services Revox and they are in Knoxville, I believe.
 
dr*audio said:
If you haven't done so already, replace all the caps that say Fraco on them. They are junk and cause most of the problems with this table. If you are ready to throw in the towel, JM Technical Arts services Revox and they are in Knoxville, I believe.
Click to expand...

Thanks I may give them a call if I decide not to fix it myself (price allowing of course). Their number looks to be in Nashville unless they have a branch here also.
 
Pio1980 said:
R15 47^ is associated with the large e'lytic cap C5 next to it. Replace R15 and C5 if it hasn't already been changed out and check D10 with diode check function of DVM.
Click to expand...

Parts espress has a 1000uf cap with a +-20%
The original was 1000uf -10% +50% wouild that matter?
 
J-M Technical Arts are in Nashville. No Knoxville branch. Jack Clark, the company head was director of service for Studer ReVox America in Nashville prior to their shutdown. He's Swiss trained by Studer/ReVox and expert on their gear.
 
Are you talking about the arm control board? Are you looking at R-13 which is at the end of C-5? Please provide update to this thread.
 
jim249 said:
Are you talking about the arm control board? Are you looking at R-13 which is at the end of C-5? Please provide update to this thread.
Click to expand...

Your right it is R13 those trace lines threw me off, thanks for pointing that out for me. Here is a pic of that smoked R13 and a big cap I have been running for awhile that needs to be replaced as well as the whole layout. I think im gonna replace all those caps if what im reading is correct they cause alot of issues.

IMG_1006.JPG

IMG_1017.JPG

IMG_1023.JPG
 
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I can see your problem right now. My print copy of the service manual shows that R-11 was changed from 33K to 3.3K with the reasoning "Prevents Q5 and Q6 from ( can't read) conduction at insufficient saturation of Q2. Protection of R-13." R13 was mostly fried in my table too, so I did the upgrade. R-11 is the middle resistor of three in the top picture at the bottom left. It has orange orange orange banding. It should be orange orange red. The parts on the power supply board are not that hard to change but the ones on the arm control and motor control boards are difficult because of the double side traces. All those gold colored caps are Frakos and need to be replaced. There is a lot of info in other threads about this upgrade you need to do.
 
I noticed that the specs list those resistors at .25w. The ones Im seeing at parts express start at 1/2 w would those be ok or should I use something different? Also the one cap on the ACB is listed as a 1000uf@63v
parts express only has a 50v version. Is there a better source for those caps, so far it seems every source is missing at least one I need, seems like a waste of money paying shipping for split orders.
 
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