Quote from: rens on November 06, 2018, 02:16:59 PM
Reverb: 7-8 measures around 700 ohms when connected, but I guess it has to be disconnected to know for sure?

Take a look at the schematic. When measurung DC resistance, any cap can be considered "no connection". There is no DC path between 7 and 8, so you don't have to disconnect it. 700 ohms is fine, the reverb tank seems to be ok.

Quote from: rens on November 06, 2018, 02:16:59 PM
Pin 10 does hum, but I could not hear if the hum went into the tank.

My bad, I overlooked that that junction is also the input of the gain stage around Q4, so this is certainly inconclusive.

Quote from: rens on November 06, 2018, 02:16:59 PM
Tapping the tank with something does give an echo to the signal, but not the guitar signal.

This means that the reverb pickup and recovery amp(Q16/17) are fine.
So there is not that much left,  either driver amp TA7200P does not work or there is a broken trace/solder joint around its output/C49/R96.
15VDC at pin 3 are present?

Quote from: rens on November 06, 2018, 02:16:59 PM
Chorus: R137 does not give significant hum when touched, some faint crackling can be heard though when touching it.
The connection from R188 to point 20 of the channel 1 PCB looks fine and measures fine.

Ok, so you should check the return path of the chorus first. Does touching one of the legs of R31 give any hum? It is the input of Q19, the switching FET. Touching it and switching the chorus or vibrato in and out should make an audible difference.

Indeed, a TDA2007A, and the SGS-Thompson is the only available datasheet as it seems. If you take a look at the reference schematic on page 4, you can see an electrolytic cap C3 for ripple rejection. I would take a look at that one first. The DC at the speaker seems odd, but it could just be a weird multimeter readout of the buzz.

Quote from: rens on November 06, 2018, 05:19:18 AM
Question on the reverb: should point 7 be connected to 13 and 8 to 15?

No, not at all. Point 7/8 are the input of the reverb tank, basically a speaker with springs attached instead of a cone.
Point 13/15 are the output, sort of a dynamic microphone with the other ends of the springs attached instead of a membrane. So you should measure some resistance between 7 and 8, if they are open, the tank itself is the problem.

In your particular JC, the left speaker always puts out the clean signal, if you engage chorus/vibrato, it gets switched into the right speaker's signalpath only. So your signal gets lost somewhere in the chorus/vibrato section.
It could be the BBDs clocking oscillator, as a BBD will not pass signal without clocking(P1 and P2 in the schematic), but there's quite a few other possibilities.
Touch one of the leads of R137 with chorus or vibrato engaged and see if you get some hum from the right speaker.
Oh, and there is some sort of noise gate in the chorus/vibrato circuit, which checks for signal at the 'dry' speaker, to the very right in the schematic, around Q34 and Q35. If the connection at the end of R188("*2 1CH 20") is missing, it won't open.

Looks like you just fixed someone elses incompetent fix.
So obviously you now have two different faults, one on the reverb driver side and one on the stereo chorus/vibrato output.
As there are no dangerous voltages in the reverb section, you could try touching pin 10(IC1) to induce some hum, and check the input of the reverb tank for continuity(point 7 and 8 in the schematic). There's not that many possibilities here, signal is taken from the volume pot, goes into driver TA-7200P and directly to reverb tank input.

Now if you turn the chorus/vibrato switch to the center position(off), both speakers work, right?
I will take a closer look at the schem after work. Should not be too hard to weed out your remaining problems.
You did a great job so far, just keep going, that amp is definitely worth it.

That IS an amplifier problem, isn't it? And it looks like a chip amp, so I don't think you've come to the wrong place.
What is the device on the heatsink? Would be helpful to have a reference schematic from the manufacturers datasheet.
Does the device still pass signal or is the buzz the only sound it makes?
The sound in the video would suggest a PS problem, sounds like 120Hz from a bridge rectifier to me.

Congratulations, I also think you found the original problem. :dbtu:
I would just re-solder IC5 and see what happens. If it is dead and you have to desolder it, it is a good idea to put in a socket. A 5532 should work in that spot, but you never really know until you try.
You still have a local electronic parts guy? Be grateful, treat him nice and make sure to send some business his way - I find it really annoying having to wait several days for a few components that cost next to nothing plus several bucks shipping...

If you measured 43V across R195 it surely must have got hot. 43V/2700Ohms x 43V are about 0,66 Watts, already over its rated 1/2Watts. Even at 20% tolerance, 2160 Ohms are the lowest acceptable value for it - replace it!
Oh, and don't power up the amp without the zener in place...
How did you test the diode? Some failures occur at higher voltages, so replace it, too.
Zero volts at the junction D14/R195 means a direct short to ground. If we look at all the -15V connections in the schematic, there's not that much left: R52/R55 - 390k. R109 - 1k. R111, R114 - also 390k. Q32 - highly unlikely a pathway to ground. R173, R176, R177, TR8, C121 and R181 are also quite unlikely.
If the zener diode really works, I would look at IC5 next.

Sorry for not being clear enough: voltage drop across a resistor is measured in parallel. So R195 looks good, you can confirm that by measuring its resistance, just make sure all the caps are discharged before you do that.
Quite likely something is shorting your -15V to ground. I will take a look at the schem and possible culprits again during lunch break.

Edit: After a quick look I'll take a wild guess here. From experience I know that zener diodes very often go short when they fail. Additionally, there is no other 'easy' pathway to ground(ok, IC5 maybe), so D14 is the main suspect now.
The original part 05Z-15A is not available anymore, just put in any suitable 15V zener diode, it doesn't make any difference. Be careful not to put it in the wrong way.
If you pull the board, take a close look at its solder side and reflow everything that looks questionable. Considering the age of your amp, you could also swap the electrolytics as a preventative measure while you're at it.

OK, it looks like you're on the right track. It is absolutely normal to have some deviation from the voltages in the schematic, 14pointsomething volts are fine.
No -15V would explain why your FX section does not pass signal. Now you should find out where those -15V get lost. It could be R195, but a short further down the line or a broken trace/solder joint are also quite common.
The next logical step in this game of divide and conquer would be to measure the voltage drop across said R195. Take the measurement directly at its legs. Zero volts would confirm a broken resistor. 43 volts would suggest a short, with C145 and D14 being the closest suspects.

Sorry for the late reaction, I hope you found out how this particular Cembalet works in the mean time. If not:
In this model, there is no DC across the reeds, as you already found out. But how does it work?
The first transistor in the schematic, the AF101 to the very left, is used as a single transistor high frequency oscillator. The inductor across the reeds that seems to give you continuity is actually a secondary winding on that transistors collector inductor(making it a transformer actually). So you have a high frequency AC voltage across the reed assembly. If you hit a key, this HF gets modulated by the then "oscillating" capacity of the reed assembly.
Diode OA79 and capacitor 500pF demodulate it, just like it is done in a detector radio. The derived audio is then amplified by the following AC101 stage. The 1M trimpot in parallel to the LDR is used to adjust the intensity of the tremolo effect.
So if your instrument only puts out hum, you shpuld first check if your HF carrier is present/if your oscillator is working properly. I hope this helps.

A bit more information would be helpful, most of us don't have a working crystal ball...
Which model FUC is it? The FUC DSP?
What does the distortion sound like? Farting out?
Does the dirt channel sound ok? (As it used to)
What about the signal from the FX send? Also distorted?
Did you try feeding signal directly into the FX return to see if the PA section works without distortion?
And why did you change the ps filtering caps? Did you have hum problems recently?

You don't really need to understand the schematic in full detail, take a look at the signal flow first to narrow down possible causes for the problem.
Just to make sure: Both (input) channels are passing signal/working ok, just no effects? This suggests that either:

a) the whole effects section doesn't get any signal
or
b) the signal from the FXS does not make its way back

Is your multimeter capable of measuring AC millivolts? Do you have anything you could use as a makeshift signal generator? You could even use a CD/MP3 player with sinewave files...

The FX section is located on the lower left of the schematic, starting with the reverb around IC1, next to the footswitch connectors. The signal is fed through R91(47k). if you trace that back you see it is directly taken from the VOL pot VR4. You say the channel passes signal, so we can rule out the reverb input. At the end of the reverb section, signal is taken from the wiper of the REV pot and fed back to the gate of Q4 via R22.
The chorus section(the delay part to be precise, as the LFO does not matter at the moment) input is R121, output C97 behind Q25, and finally routed back into the main signal path before the "main ins".
The switching is done slam-to-ground style, so there is no relay or sophisticated FET switches(which is a good thing IMO).

So, what would I do? Considering that reverb and chorus get their signal from different points in the schem and also feed their output to different stages, I can only come up with 2 possible reasons:
Either both happen to be shot or there is a problem with their supply, which is the only thing they really share. At least, if the 15V were not present, neither of both would pass signal.
So I would check if +- !5V are ok at C144/C145.

You're correct, D114 and D115 are the ones you're looking for. If you find the dirt channel level still to be lacking, R19/R20 form a voltage divider, you could replace R20 with a jumper and R19 with 100k to double that channels output level.

Quote from: jcmbro on September 27, 2018, 05:51:20 PM
Don't have any experience with SMD soldering but there's a first for everything right?

It is actually pretty easy once you get the hang of it. And the SMDs Mikhail chose are not the gazillion-of-tightly-spaced-micro-legs type anyway, so everybody should be able to do it.

Quote from: jcmbro on September 27, 2018, 05:51:20 PM
What did you use for a power supply? I'm having a hard time finding something that can supply +80V,-80V,-12V,+340V on the cheap.

You have several optios:
- Have a transformer custom made
- Look for a transformer with 2x~60V sec and get an extra one with 12V sec. Add a third small 230V(2x115V)/9-10V in reverse, secondary connected to 12V. The preamp draws only a few mA, so that would be an acceptable solution.
Or use the step-up powersupply Mikhail suggested and adapt it for the higher voltage. But be warned, the devil is in the PCB layout, you may encounter all kinds of noise and oscillation if you have no prior experience with that kind of stuff.

Quote from: jcmbro on September 27, 2018, 05:51:20 PM
Also what are your output transformers specs? I got some trannies from a broken SS poweramp that i'm going to have rewound by a buddy of mine.

I only built the MicroPA and used the suggested Xicon trannie, which is available from Mouser, for about 5 bucks IIRC.
If you are going to rewind an existing trannie, make sure to get the measurements done to guestimate the core's specs before you take it apart!
If you need help with that, KMG made some excellent posts and also has software to make the calculations more convenient on his webpage.

I have built KMG's LND150 JCM800 as well as his E530 and his microamp for a friend.
Aquiring the components was easy, except for a few semiconductors that I had to order from Mouser(together with the transformer for the microamp).
You will have to make your own design for the HV-supply, if you don't have any experience designing proper layouts for SMPSs I recommend you use the 12VAC-into-backwards-transformer variety. It is a bit bulkier and less efficient, but you only need a few milliamps anyway.
Also, you will have to etch and drill the PCBs yourself, which is rather easy with KMGs single-sided designs, but certainly is some effort compared to just sending away gerber files and waiting for the PCB to show up in the mailbox.
Soldering SMDs was a real pain until I realised I needed new glasses and a finer tip for my soldering iron.

Don't forget that you will have to have the output transformer manufactured (or wind it yourself), it is a good idea to get in contact with the transformer guys before you start! In my experience they are usually very helpful, and having transformers wound to spec is often cheaper than buying off the shelf (...and you won't find anything for your PA there anyway).