Hot Rod 3 Bright Switch squeels

[Enzo]

Caps OK, then also verify that the negative end of each has continuity to ground and that the B+ is on the + end of each. A good cap is same as a baqd cap if the connections to it have failed.

Just a query, the two OT primary wires, the blue one is on TP19, the one between the two tubes?

If the bright switch does anything in the dirt channel something is wrong. The relay K1b completes the path to ground for the bright switch. But only when in clean. With bright switch OFF, measure R102 below it. DO you get 1 meg when it dirt channel??

I have no reason to suspect C4 of anything, it apparently switches in and out OK and increases the gain of the stage.

When it does this, push on the gray ribbons connecting the main board and the tube socket board. Does that do ANYTHING?

When it is doing it, does pushing the MORE GAIN switch change the noise in ANY way?

I must need drugs, I am starting to imagine a cockamamie feedback path through the C8, C9 and the JFETs.

In the clean channel the drive control should have no effect, volume control works. In the dirt channel, the volume control should do nothing while the drive control works. Is that the case?

[beezerboy]

Caps appear to have good grounds (within the resistance of the meter leads). C36 had 331vdc, C35 had 380 vdc, C33 had 420vdc, so all a bit low.

Output Xformer wires are as you said.

did not check K1 action but I did check R102 out of circuit and grounds early on and they were good... may revisit that. I got distracted by noise that the amp makes when my hands get near the ribbon cables from V1 and V2.... both make noise when I get close.... don't have to touch them, I get my finger 1/2 inch away they make noise. closer I get the louder the noise. moving the ribbons makes noise too (I poked them with a stick). looks like I will need to deal with them? I already hit all the solder joints

switching to gain channel lowers the noise when on the bright mode. more gain lowers the noise even more

clean/drive/volume/master seem to work normal (as you describe)

[Enzo]

Close enough on grounds, I was concerned about opens, not resistance.

Understand why I ask these things. I was not concerned that R102 was bad, but one end is grounded and the other will be grounded or not depending on the relay switching. SO you measure across the resistor while it is in circuit. Now it should measure 1 meg or whatever in one mode and zero in the other. If it toggles one to the other, then the relay contacts are working. if it stays zero all the time, then either the relay contacts are stuck shut or the relay is not energizing when it should. The push switch is OK, because it switches between two conditions.

[beezerboy]

yep.... I understood where you were going on the relay, I got sidetracked by the ribbons & forgot to do that check until I posted that last bit. and you are right.... the 1M never switches in, contacts must be stuck. it has 16vd, I hear the relay click & the LEDs come on when switching channels. I would take it to mean the driver circuits are probably OK & its all on the relay

[Enzo]

You hear "the" relay click? Relay K1 has its coil in parallel with the other relay,, so you need to determine if BOTH relays are clicking or just one.

When you say the coil has 16v, that is half the story. The relays should all have 16v on at least one end all the time. That is the end connected to the supply. The other end sits at the same voltage when relaxed, and then goes down in voltage when the thing is energized. You could measure the voltage across the parallel snubber diode, but that won't tell you how many relays are clicking. Some relays you can see into, and you can see if something moves or not.

[beezerboy]

yes, I hear them click (have doctor's stethoscope). have 16V (to ground) at the coil, have 21.6 across the coil of K1 when drive is selected. heres the weird part, when I select Bright and Drive, when I measure R102, I get 90k instead of 1Meg. I could swear the last time I measured that it did not change with the relay & got zero ohms both channels (indicating K1 not switching). anyway, appears I have a parallel path around R102 but I don't see it. maybe cooties inside the relay?

btw, this amp had a lot of spotty residue on the PC boards. not very pronounced, but all over... something that kinda looked like maybe it had been doused with water, possibly even under water. the main PCB is vertical, so not the kind of stains you would see from sitting around. I took pix before I cleaned it but its hard to see

[Enzo]

When you are testing a switch, either a relay contact or a regular push switch, the very fact it changes something in the circuit tells you it is functioning.

R102. Look at the schematic. If the bright switch is open and the relay too, you get like 1 meg, right? Now close the bright switch. Now look at the circuit. The bottom end of R102 is ground, the top end connects through the switch to the top of 100k R43. The bottom end of R43 is ground too. SO the result is the 100k is now in parallel with the R102. Right? Top ends connected together, and bottom ends connected to ground, and thus together. So what is 1 meg and 100k in parallel? About 91k. Like your reading.

remember, it is all about the circuit, not the parts.

[Jazz P Bass]

btw, this amp had a lot of spotty residue on the PC boards. not very pronounced, but all over... something that kinda looked like maybe it had been doused with water, possibly even under water. the main PCB is vertical, so not the kind of stains you would see from sitting around. I took pix before I cleaned it but its hard to see

In my experience that 'residue' may be just that.
Flux residue from the wave solder process.

It's supposed to be cleaned off by the board assembler.

Not too sure that it impacts the board performance but it sure looks ugly.

[beezerboy]

ya... could be that.

as for the parallel read.... rooky mistake from doing too much too late at night.

any other input???? works as advertised except on Normal channel, on Bright... that sounds like a shorted input jack. every other channel/Bright combination is fine