Marshall JCM 900 4500 Dual Reverb HELP PLEASE!

[Mike_88]

Hello, assembled the amplifier according to the scheme Marshall JCM900 4500. He earned it immediately, only there is no reverb on the clean channel, there is a revert on the overload. And even when I connect the footswitch, there is no reverb at all, not on a clean one, not on an overloaded one. The clean overload switches well to the footswitch. I believe that errors in the printed circuit board preamp. Co can share photos of the preamp board, JMP52?

[Mike_88]

[nickb]

Welcome!

Switch to the clean channel and turn the reverb level up. Give the reverb tank a gentle tap and you see if you can hear anything through the speaker. That will help to narrow down where the problem is.

What experience and test equipment do you have?

[Mike_88]

In fact of the matter is that the reverb without a connected footswitch only works on an overloaded channel, there's no reverb at all on the clean one, while turning the Reverb knob does not change anything. On the overloaded channel it works well when turning the Reverb knob. I assume that there are errors in the layout of the PCB. If there are photos of the preamplifier board from the side of the tracks please share, I will check for a version of the errors.

[Mike_88]

Here on this I did

[Mike_88]

I would be very grateful if you take a picture of the pre-amplifier board JMP52 from the side of the tracks.

[nickb]

I don't have one to take a picture of. Why do you think the board might be wrong? Isn't this the same one used on 1000's of these amps all of which work?

Either way, the approach to fixing it is the same, a logical series of tests to isolate the problem. Right now, it's not clear to me that you did the very first test correctly (did you tap hard on the tank?) and you didn't answer the question about experience and equipment. Therefore we have made zero progress in 7 posts. It doesn't bode well for the outcome.

[J M Fahey]

I think Mike88 has built in Russia/Ukraine/Bulgaria/Serbia? a Marshall clone, using a non original PCB, and wants to check whether it´s an accurate copy or has errors.

Personally I think the PCB must be fine, the cloner should be really incompetent to practically "photocopy" a PCB, down to the silkscreen (It even says "Marshall Amplification" on it) and miss or move tracks around.

Being also the first build of an unexperienced builder I´d rather suspect a wiring/soldering error way more than anything else.

So Mike88, in principle don´t blame the board, but check wiring, soldering, and do the tests suggested here.
When you answer, we can suggest others.

Good luck and, last but not least, welcome to the Forum

[Mike_88]

J M Fahey, That's right, I'm from Russia, the city of Volgograd. I collected this copy for almost two years. I ordered all the original and printed circuit boards at the Rezonit factory. From my equipment I have only a multimeter and a soldering iron. This is the first amplifier I collect. I like the sound of it. Only problem with reverberation on a pure channel, to exclude the infidelity of times

[Mike_88]

http://music-electronics-forum.com/t41097/ Here in this section wrote, a person has a board that I need. If he helps me and takes a picture of the board from the back, then I will be very grateful to him))

[minim]

[Mike_88]

Thank you very much!!!!!!!!!!!!! Very helped !!!!!! Simply super !!!!!!!!!

[J M Fahey]

Ok, Rezonit made your board and it looks like a serious and large PCB factory (300 employees), the question that remains is: *who* did the artwork/design/drawing of the PCB?

Did Razonit clone an original one and offered it for sale? (in which case I can trust them)
Or somebody at a DIY Forum designed his own copy, and you submitted those files to them for fabrication?
In that case, mistakes are quite possible.

That does not exclude you possible wiring mistakes, of course.

[g1]

Thank you very much!!!!!!!!!!!!! Very helped !!!!!! Simply super !!!!!!!!!

If you found any errors on the pcb, could you please post that information here?
It will help anyone else who may be having the same problem.

[Mike_88]

The board checked, it fully matches the photos of the original board. Errors in the tracks there. I tested the IC7 chip by swapping it with IC4 all good. IC7 working. Jfet 174 and Jfet 111 were punched, dropped 174 and 111 closed the source drain, but the reverberations on the clean channel still do not. I do not know what else might be the problem