Anyone have a DC-10 schematic?

[brandx73]

I used the search and saw there was a few peopel asking for one but I didn't want to revive long dead threads or hijack anyone. I'm having trouble with my dc-10. Ive ensured that the problem is not my tubes, replacing one preamp at a time and checking the power tubes in the same manner. Channel 1 is not passing any sound through either the clean or pull out rhythm, using channel selector switch or footswitch. Channel 2 plays just fine. I did notice however, with channel 1 selected, after a few moments it sounds like something is switchng/clicking on and off. I was going to replace the VTL5C9s and the 4N33 optoisolators in hope that would fix the problem. Caps look fine, no leakage or bulging, no burnt areas on the board. Had an issue where the channel was cutting in and out using a beat buddy pedal, thought that it was the pedal. Happened today and I plugged in a guitar to ensure I was getting signal and I was not. The issue seemed to be remedied by switching to 60 Watt mode at first, but then it cut out and channel 1 has not come back on line since. Anyone who has experienced this, any help would be greatly appreciated. I'm an electronics tech by trade so I'm pretty handy at fixing things, just need a point in the right direction before I start shotgun troubleshooting. I've had these isolators go out in a crate amp before and was the fix, hopefully this is the same thing and not a bunch of troubleshooting needed. Thanks in advance. I appreciate any help.
V/r,
Will

P.s. Also, are there any direct replacement for the VTL5C9s? Only ones I am seeing online are from China, and trying not to support that if I can help it. US distributors? Thanks again.

 

[brandx73]

New update. Powered on to try to troubleshoot a bit. Channel 1 was working for a minute or so. Heard a high pitch click and it went out again. Sounded like a relay switching. Have a video of it as it happens for anyone interested that may be able to help. Thanks.
Will

 

[brandx73]

Video of channel 1 cutout.

 

[brandx73]

Also now when switching off and on sounds like metal crumbling or a spring being expanded...

 

[user 21540]

This is from the Tube Store via Wayback Machine:
https://web.archive.org/web/20160228085350/http://www.thetubestore.com/Resources/Mesa-Boogie

 

[brandx73]

@wildschwein
Thank you for the response. I have been in comms with bandit. I wasn't sure if there was any major differences between the 5 and 10 variants. This amp went from amazing to wonky very quickly. As I have mentioned to bandit, I have replaced all the preamp tubes back to what I received it with, all 12AX7s. I had replaced V1 with a 12AT7 and Reverb (V3? still waking up. lol) with a 12AY7. Anyway, now, Channel 1 is completely bypassed somehow. Even when switching front switch manually or using the foot switch, only channel 2 is operative and channel 2 controls only the volume on channel 1. Maybe a bad relay? I was going with the opto-isolators but it seems to be switching just not outputting through the correct channel. I will take a look at the DC5 schematic and see what I can figure out. Thanks, and if anyone has any similar dealings, please let me know. Thanks again.
Will

 

[Monsta-Tone]

Without looking at the drawings, going from memory….. DC5 B preamp should be the same as the 10

Try replacing the 4N33 optoisolators
They control most of the switching in these amps

Every time I have had weird inter channel issues, it has been the 4N33’s

 

[brandx73]

@Monsta-Tone
Thanks. That was the plan to replace the 4N33s and also the VTL5C9s. That way they all have a same replace date and I can try to minimize assembly/disassembly. Just hoping I wont have to completely remove the board in order to get those components replaced. Anyway, going to replace all optoisolators. The other thing that has me concerned is the audible/amplified click in the video when ch1 stops working. To me it sounded like a relay. The fact that it works then cuts out makes me think it is a failing relay or maybe the diode controlling the relay switching after a while has a failing junction, maybe overvoltage or some other damage. Since I have it open and will be soldering, may as well replace those too. If you have any other insight, would be glad to hear your input.
Will
edited: Need more coffee. For some reason i thought i saw the upper chain of block diagram as the rhy channel.

 

[user 21540]

Without looking at the drawings, going from memory….. DC5 B preamp should be the same as the 10

Try replacing the 4N33 optoisolators
They control most of the switching in these amps

Every time I have had weird inter channel issues, it has been the 4N33’s

Yes I believe the DC5B documentation has info in it about the DC10.

 

[brandx73]

Quick update. Replaced ldrs the 4n33s and the relays (just read a thread today in another forum about the relays getting stuck open or closed), and she works on all channels. Now my 6khz on geq not working. Checked wiring and everything looks solid. Will have to check schematic but thinking it's freqs inductor. Can anyone confirm before going any further? About to head out for a bit why I'm asking. Thanks guys for all the help so far.
Will

 

[bandit2013]

Sounds like you are making progress. Good to hear it.

When it comes to the GEQ, more than likely it may be the slider pot. Try measuring its change in resistance when you move it before digging into the inductor. It is possible but the mechanical part is more likely the issue.

If you can measure the inductor resistance, it will be a very low value. Inductors can short (windings are burned) or open circuit but will tolerate more electrical current than the resistive element on the slider pot. Since there is a capacitor in that circuit, it would be signal current, so I doubt the inductor had failed due to any surges. Then again it is not ruling out a solder joint weakness if such exists.

 

[brandx73]

@bandit2013 Thanks for the info. Will definitely check the resistance. I did replace all the sliders within the last year since buying the amp. I didn't replace the inductors though and i thought maybe that was what was going on. I have already ordered the replacement and waiting on mesa to ship but will still check the resistance values on the sliders to make sure they are all in tolerance since i will have the GEQ board out anyway.

For all those following, the yellow arrows indicate the components I replaced.

 

[brandx73]

Mesa has shipped the 33mH inductor and should be here Saturday. Will update on slider resistance readings and success/failure of inductor replacement then. I appreciate all the help received from everyone who has contributed in this repair. Good bunch of knowledgeable folks here. Cheers!
Will

 

[brandx73]

So I replaced the inductor today. I ohmed out the old inductor and it came in at 1.2 ohms, same as the new. Checked the sliders and they were all reading 50k (I removed them from the circuit individually). In case someone attempts this repair and forgets to take pics, with amp facing pcb up (resting on transformers) and geq to the rear left quadrant from top to bottom wiring should be brown top, blue middle, and green bottom. If you connect it, brown top, green middle, blue bottom, the eq will be reversed polarity, down will be boosting, up will be cutting, so be sure to get your wiring right. Must have been a cold wire joint or something like that. Amp is working great now! Forgot how loud that sucker is. On about 5 my sinuses began to hurt...lol. Thanks everone for the info and help. I appreciate you all and this great group. Have a good 1.
Will

 

[brandx73]

Back in business!!!!