Marshall JCM 900 4500 Dual Reverb HELP PLEASE!

[J M Fahey]

You will have to inject signal at the reverb circuit output, listen to it through the speaker, and work backwards, until you find the stage where it gets lost.
Then you have a relatively small area to check.
Replacing parts at random, can take 1000 years.

One suggestion: we are having a communications problem, please also post the Russian original text, it might be easier to decode.
When writing, please use standard "dictionary" words, for example "amplifier" instead of "amp", "electrolytic capacitor" instead of "Electro" or "can", etc. , I mean the equivalent standard Russian words, translators do not understand slang.
Double check for proper punctuation and accents, make it easier for the translator.

EDIT: just one example:

The board checked,

You may be saying: "I checked the board" (no comment on results) or "I checked the board and it is fine" ... not the same meaning.

it fully matches the photos of the original board.

Then the board design is good.

Errors in the tracks there.

then the board design is wrong.
Which one is true?

and so on.

[g1]

If IC7 is good, then jfet TR2, TR3 should not matter, as they are same for both channels and OD reverb is working.
How about clean reverb pot or it's solder connections?

[Mike_88]

Board design is correct

[Mike_88]

Everything is sealed, the track was ringing with a multimeter

[g1]

You have no scope?
How about an audio signal tracer? You can make one with any small amp and a capacitor to block DC.
Or you can inject a constant tone and measure AC volts with your multimeter. Compare levels from good channel to bad channel.
Check at outputs of IC7, and inputs of reverb pots.

[Mike_88]

soldered everything is good, I checked all the tracks to call multimeter and details of all piping circuits IC7 serviceable

[Mike_88]

[ATTACH=CONFIG]43777[/ATTACH]

minim, in the channel switch on your photo you can not see how the tracks are done. Look please at my preampboard, are the tracks right here brought to the switch as well as on your preampboard?

[minim]

Yes it looks the same to me:

[g1]

I have attached a picture of the only components that are different for the clean channel reverb, circled in red.
All other parts must be good because OD reverb works.
The only other possible problem would be the switch command that goes to pin1 of IC7.
Does DC voltage at IC7 pin1 change when you switch channel from clean to OD ?

[Mike_88]

Voltage changes on 1 contact, as well as on other microcircuits

[mikepukmel]

Cold solder joints?

Voltage changes on 1 contact, as well as on other microcircuits

Hi Mike!
Awesome looking build! Looking over your board photos, looks like you might have a few cold/bad solder joints. I don't know if these are in the part of he circuit that isn't working as expected, but you might want to rework these joints anyway.

Also, might be intermetallics on some of the discretes. I ran into that ages ago, at a job in a factory that made discrete rectifiers.

Best.
Mike

[mikepukmel]

Ages ago, I worked for a company that made leaded rectifiers. Mostly for power applications. They had some engineers go to high rolling mil spec soldering courses, some came back and gave lectures. I recall one very interesting lecture on pre-tinned component shelf life. I would never have believed before that, that leaded components have a shelf life. Anyway, once lead/tin solder is applied to a copper lead, intermetallic compounds start forming right at the layer where lead-tin meets the copper. For a fairly long period of time, depends on heat and humidify in the environment, you can take the component and solder it into a circuit, no problem. At some point, the intermetallic compounds grow and consume both copper and solder. Eventually you get a mix of this awful stuff that nothing will solder to. What we had at the factory was a customer complaint that a bunch of components they bought rolled right off the board when they tried to solder them on. This was the problem.

Anyway, I doubt that is your problem if you bought your components from a 'good' dealer. But you might have at least a few cold or bad joints. Sometimes they conduct for a while, and cause a crackle or hiss or pop, sometimes it happens if you give your amp a bump or a tap.

If you have a magnifying light fixture, maybe its a good idea to do a thorough visual inspection of all of your solder joints.