Thanks Phil.

Yep. Plugging into the power amp input, signal clean as a whistle. Nice way to quickly eliminate suspect components.

Next step replacing all electrolytic caps on the preamp board, and the logic board as well, for good measure.

16 in total:

1 16V 100uF
2 16V 10uF
7 25V 10uF
6 50V 1uF

Here is an audio clip of the noise, if this helps anyone to ID an obvious problem.

The noise is happening regardless of whether anything is plugged in, knob position, i can even have the volume down all the way and it is still audible.

https://drive.google.com/file/d/1ZGVHAwuoPCNL8kdBITldN0QJwp078zU7/view?usp=sharing


Anyone familiar with this and its cause?

Success! Well mostly. Channel switching now works.

Thanks for the recommendations on replacement parts!

When you replace cabling, you really have to replace ALL of it. The wiring, the connectors, the sockets, every bit of it. Also IC7 and IC8 had to be replaced. (CD4013BE).

So it's in a working state now, as far as channel switching goes, but there is one last issue...

There is a light distortion tail when playing clean, accompanied by intermittent crackling and pops. This happens on both channels- I'm hoping the last bit of cable/socket replacement will take care of it but I fear its in the caps.

I'm going to replace them all regardless, but does what i'm describing sound like a capacitor problem?

Thanks, this info about the replacement TL604s & 607s- immensely helpful.

I was planning on replacing all capacitors as well, I was asking someone at amprepairparts.com for a kit, and the told me that the 11000uF/60V capacitor was no longer being manufactured. I'll likely need to find that one as well if I want the job to be a complete restoration.

Hopefully within the week i'll be able to post a follow up with how things are going.

@DrGonz78

I see that you soldered an orange wire directly to IC2.

Can you explain this?

EDIT: nevermind, I saw your other post, I wonder what they heck they were trying to do?

I updated the link to the PDF.

To the best of my knowledge I have confirmed that all the connector cables are working (they have been replaced) but i have not confirmed that the pins they are attaching to are actually making a connection to the board. Some may have corrosion or wear.

That will be my next step!

Hi,

I have a 1983 Fender Showman, a solid-state amp from the Rivera era, and it has an interesting problem.




On the front panel, Channel 1 works great. However, I cannot switch to channel 2.

So I tried plugging in the footswitch to see if it was a bad switch on the front panel, and this is where it gets interesting. When I plug in the footswitch and hold down the Reverb button, I CAN switch channels, and play thru it with all channel 2 controls working, but only as long as I hold the Reverb footswitch down. As soon as I let it go, nothing.

So the switches themselves appear to work but somewhere there is a problem. The only thing i have done so far is to replace the input jack with a generic alternate- I'm not sure if that would affect channel switching or not.

On the schematic you can see where the front panel switches and the footswitch paths merge, so i have to assume that the issue is happening on the preamp board and not the logic board (but honestly i have no idea)

I'm attaching link to a PDF of the schematic- if anyone can help me trace the signal path and recommend some possible solutions that would be greatly appreciated!

https://drive.google.com/file/d/1N5OFU8sjBvo5nWdV8ukadsTESLImRg8U/view?usp=sharing

So far I have tested IC's 1 (the schematic seems to indicate this is involved with channel switching) with a multimeter in diode mode. I don't know if this is useful info or not, i dont have an o-scope and a multimeter is all i have.

Here is IC 1 and the values I got:




Hopefully someone can give me an inspiration or two on this. Thanks in advance!