Kustom Lead-I Effects Not Working

[Johnrcurry]

I am working on a Kustom Lead I guitar amp. PC boards are as follows:

PC 5129
PC 5033-01 Rev 0
PC 5131-01 Rev 0

Here's an overview of the the three boards:



When it came to me it was blowing fuses immediately when powered on. Someone had spliced in an inline fuse holder, which had fallen apart (see photo).



I traced the short to two small diodes on PC 5131. They were both shorted. I couldn’t find a schematic for PC 5131 to determine the value of the diodes, so I replaced them for the time being with two 1N4007 diodes I had on hand (see photo).





I powered the amp up on a light bulb limiter and the bulb stays off and it has stopped blowing fuses. The amp plays but the reverb, tremolo and pull-bright functions are not working. The controls have no effect on the sound. I can tap the reverb pan and get a “crash” sound, but no reverb effect when playing through the amp. I don’t have the footswitch for this amp, so I can’t see whether switching it in and out makes any difference. I tried using a standard Peavey two-button (“reverb,” “select/effects“) footswitch and it made no difference. With respect to the pull-bright function, the switch itself works.

My questions are:

Should the tremolo and reverb effects work with no footswitch attached?

Should the Peavey footswitch work with this amp?

Is there any part in particular that the failure of those diodes might have ruined?

Any other ideas as to a likely suspect for the faults?

Does anyone have the schematic for PC 5131?

Are those 1N4007 diodes suitable permanent replacements?

What value fuse should I be using (the sticker near the fuse holder says “REPLACE WITH SAME TYPE 1 ½ SB AMP 125 VOLTS.” Does that mean replace with one ½ amp fuse, or replace with a 1 ½ amp fuse?)

Thanks for your help.

John

[Jazz P Bass]

The original diodes, set up in a bridge, where 1N4003.
1N4007 will be fine.
Check the voltages to be sure.
That bridge circuit supplies the + & - 30 volts.
The zener diodes directly below the bridge are the + & - 12 volt ic supply.
Here is a link to the 5129 preamp board.http://music-electronics-forum.com/t15177/
It looks to me as if you do not need the footswitch to enable Rev & Trem.
As to the reverb, the return works (crash)
So check that the ic is sending a signal, IC2 pin 1.
Check the tank cords.
The tank coils should be checked for resistance.

As to the pull bright, that is a switch, a capacitor, wire & connections.
You should be able to tackle that with a meter.

The trem, I would look at IC2 pin 7 to see if the LF oscillator is running.

[52 Bill]

Use a 1 1/2 a slow blow fuse. The original one was a pigtail fuse that was soldered in at the terminal block where the inline fuse was added. Either solder in a new fuse or add a fuse holder. I solder in a basic fuse holder in place of the original fuse, so that regular fuses can be used.

I don't have schematics for the preamp boards in my collection. Did you check the Kustom links in the schematic request section?

Check to be sure that the tank itself is working. Read the resistance across the two RCA plugs that plug into the board. If you hear the tank rattle the output coil is okay. That side should read about 200 ohms. The input coil is usually lower in resistance, somewhere between 50-200 ohms.

The fast test for reverb tanks is to reverse the two plugs and shake the tank. If you heard the rattle with the wires plugged in one way and then switch them and don't hear the rattle, then check the input coil and wire for broken or bad connections. If you do hear the rattle with the wires swapped, then the drive circuit is at fault.

The reverb and the trem should work without a footswitch. If the Peavey one is a plain vanilla one with no leds or internal wiring, then it should work just fine.

[Johnrcurry]

Thanks Jazz and Bill for your helpful replies. When I got back to working on it tonight I found an intermittant short that came and went when chopsticking one of the conntectors between the 5131 board and the 5033 board. I couldn't see any obvious problem on either board, but I reflowed the solder joints on both boards and it cleared up the short and started the tremolo working.

I found a broken wire in the reverb pan and resolder it. That cured the reverb problem. The Peavey footswitch turns them both on and off. As for the pull-bright switch, it turns out it was working all along. It's just more subtle than I'm used to. I replaced the fuse holder, and now the amp is up and running well.

Thanks again for your help.

John

[Jazz P Bass]

Up & running.
Cool.
Personally, when I get an amp as old as this I resolder all of the main connections & large components as a matter of course.

[52 Bill]

Loose parts are a pretty common problem with any amp. Glad you found your problems and got them fixed.

That's the same style fuse holder that I install in these amps. Makes future servicing much easier. It looks like you have the wrong fuse in there.

[Johnrcurry]

Thanks, Bill. You're right about the fuse. It's a 1 amp fast blow, which was the closest I had on hand at the time. I replaced it with the right fuse before I buttoned it up for good.