Hot rod deluxe RevA channel switching

[nevetslab]

What Enzo said ^^^^^^^ as well as the relays K1 & K2 showing their pin numbers. You'd sort of have to have a data sheet on the relays to make sense of those.

[Oldmactech]

I ordered replacements for K1, K2. Repeating continuity and touching up solder joints has not given me any progress. Stumped.

[The Dude]

FWIW: You can check relays with a battery, a couple clip leads, and a DVM. I think it's counterproductive to start shot guning.

[Enzo]

It is difficult to get on the relay pins to take readings. But every relay pin connects to something nearby, like a resistor or something. SO put your meter probes THERE. They don't have tp be right on the relay.

[Oldmactech]

Testing question: I’m going over some of the test points on the schematic (had to enlarge it since my eyesight isn’t too good).
Ovals are AC, right? What about an oval with an expected mV reading? For example TPS 14, 15 expect 66mV on an AC scale?

Im using an old Sears DVM (not auto-ranging), my AC scale doesn’t seem to include mV.

Goofy Question, enlighten me please.

[glebert]

Testing question: I’m going over some of the test points on the schematic (had to enlarge it since my eyesight isn’t too good).
Ovals are AC, right? What about an oval with an expected mV reading? For example TPS 14, 15 expect 66mV on an AC scale?

Im using an old Sears DVM (not auto-ranging), my AC scale doesn’t seem to include mV.

Goofy Question, enlighten me please.

Set your scale to the lowest range and then 1mV = 0.001V

[nevetslab]

While I had a Fender Hot Rod DeVille 410 open, I looked at the two relays K1 & K2, both Omron parts, and they had the pin-out/schematic diagram silkscreened on the top of the relay. I took photos of those, and parked them here, just for reference.

[Oldmactech]

Thanks. I might take some close up pics, Seems easier to see the traces that way.
Looks like a cap has fried, right next to R22.

[Pedro Vecino]

Looks like a cap has fried, right next to R22.

It has a series resistor installed to slightly reduce the gain.

[nevetslab]

That's right. There's a 602 ohm resistor in series with that cap, and another off screen, both used in reducing the excessive gain used in stock More Drive mode.

[Oldmactech]

Ok so I’m back with some TP readings. Many of these are not close to what should be so I am minority concerned my old Sears DVM is broken but here goes.

(all taken with the amp on and in the state called for on the schematic) Drive engaged, pots at 50% etc. expected reading is listed first, actual after.


TP 2 R4 1.8mv 0 (pretty loud pop when probing)
TP 3 C1 +1.72v 0 (tested 3.0 at one point recently)
TP 4 R41 13.0mv 0 (hums when probed)
TP 5 R11 252mv 0 (hums, previously tested 442VAC)
TP6 (Incorrect, measured R10 accidentally)
TP7 R8 33mV 0
TP8 R16 850mV 0
TP 9 C8 1.72 mV .90-.150 and wanders.
TP10 R20 580mV 0
TP11 R22 13.3v 440VAC
TP12 R21 1.72 1.74
TP13 R28 20v 0
Tp14 R28 66mV 0
TP15 C12 66mV 0
TP 16 R48 39.mV 0
TP 17 Op amp U1 pin 7 1.28 VAC 0
TP 18 R51 1.14VAC 0

Despite these odd readings, clean channel works as advertised.

Guidance is greatly appreciated.

[g1]

Are you putting in 4mV 1Khz signal at input jack #1 as specified on schematic? Can you measure it with your meter?

[Oldmactech]

No, I don’t have a signal generator. Is there a way to do that without one?

[glebert]

No, I don’t have a signal generator. Is there a way to do that without one?

You can get an audio generator app for your phone and then go out from the headphone jack with an adapter to 1/4". You only need to do this for the AC measurements. Also, some DVMs can't measure 1kHz signal amplitude.

[Oldmactech]

Great, I’ll rig something up with my phone.