Reverberocket reissue channels wont switch

[tpw]

I did a big dumb dumb with this amp. I cleaned all the contacts to the channel switch toggle. I F'd up and connected one of the wires that goes to the toggle to J20 instead of J33. This blew the fuse and killed channel switching. Now the amp will only work in normal and the switches (toggle and footswitch) do nothing. looking at the schematic I realized J20 is the 230vac terminal.
I cant figure out what it actually did.Nothing sounded like it burnt out and nothing smelled like burning anything.
Im not familiar with channel switching in general and im having trouble locating the problem.
the reverb still works and the light on the footswitch lights up. The dirty channel doesnt work and the footswitch doesnt light up.
when i turn the amp on and off I can hear the relays clicking.
this one must be an early reissue since it has e34l's
thanks for any help

[tpw]

This might help
http://www.schematicheaven.com/ampeg...brocket_ri.pdf

[Enzo]

Well, I am inclined to help you, Bro, but I have a serious bad cold and can't think for squat. Next week maybe...

I would not be surprised if all the JFETs are dead.

[Ray Ivers]

tpw,

Since the amp blew its fuse and the relays still work, you may have gotten lucky and just shorted D3, the 3.3V Zener at the switching circuit input. I would check every component both upstream and down from D3 - from the jack to IC2 - to make sure everything else in that vicinity is OK.

Ray

[tpw]

will a zener check like a regular diode on a tester?
my votages on IC2 legs 8 and 4 are good (8=+15V, 4= -15V)

[Enzo]

Zener will test like a plain old diode on a meter, adn that is usually good enough to see if it is shorted or not. But it won't test it for "zene" at the proper reverse voltages. If it is working as a voltage reference, then it is OK.

[tpw]

the d3 in the circuit measures .000. The voltages are 1mv on one side and .5mv on the other when the amp is on.
Q3 shows -15 on two outer legs and -14 on the center
Q1 shows +14 on the center leg and 0 on the others
Q2 shows -14 on the right leg and 0 on the others
maybe this helps

[Enzo]

So lift one end of D3 and find out if it is shorted or not. SOunds like it is, but on the other hand if the panel switch is on and nothing is in the FS jack, then the normal circuit path will be shorting across it.

The schemo shows voltages at the channel switching circuit. So what is on pin 1 of the 5532? Does teh channel switch change it? Does it toggle between +14 and -14 with the switch? get that before you expect anuthing else to happen.

Is Q3 shorted?

Ignore Q1,2 for now, they are just switching mutes.

[tpw]

OK
D3 is shorted when lifted from the circuit and reads .000 on diode tester.
pin 1 of 5532 doesnt switch and stays at +14.
all legs of Q3 are shorted when the amp is on but not when its off.
Also D6 and R49 show paths to ground from both leads when amp is on but not when its off.
I guess i need to order some parts. Is there anything else i should suspect?
thanks

[Enzo]

If the zener is shorted, then the control input is grounded off by it, so you need to replace the 3.3v diode. If you just remove the diode, it might even work.

Look at the schematic and verify every resistor around that circuit - R47, 48, 69. And 10 ohm R67 while you are there. Make sure D4 is not open or shorted

With power on, is there 15-16VDC on the upper end of R47, 48? And are the +/-15VDC present on the IC2? If so, then pin 1 of the 5532 ought to go from +14 to -14v when the channel switch is toggled.

Until we get that happening, nothing further along will happen.

[tpw]

I tried without D3 and it works.
Ive got the new part coming tomorrow.
all the other resitors and diodes tested fine.
I guess i got real lucky.
Thank you very much for guiding me through this.
Now I understand a little more about these channel switching amps.