Hot Rod Deluxe channel switch problem

[Brad1]

My friend's Hot Rod Deluxe no longer switches channels. He said when he pushed the control panel button last week, it seemed like it was switching back and forth quickly, the LED flickered with it, and then it just stayed where it stopped, which is the LED is off.

The amp still works fine, as far as playing it through that one channel.

I used the footpedal switch from a DeVille to test it, figuring that maybe the panel switch was whacked, but the pedal might work. No go. The foot pedal LEDs both change (channel and drive) but nothing happens in the amp.

Apparently, the "More Drive" switch isn't functioning either, but is that because it doesn't work unless the non-working channel is kicked in?

Having looked at the schematic, I see that both switches are in the same circuit. What I can't figure out, yet, is how exactly it works. I assume that circuit somehow switches the relays (K1 & K2?) to change "channels" and kick in "More Drive"? I am also guessing that since neither seems to work, it may not be the relays, but something in the switching circuit (that is disconnected schematically from the main circuit)? (I'm trying to follow the logic through this thing, and am not even sure, yet, if those relays do a task each, or both work together. If the More Drive circuit isn't engaged until that channel is engaged, I suppose a bad channel relay would prevent both?

Anyway, before my head explodes, has anyone run into this before, or does anyone have an idea of the (or some of the) likely culprits that may cause this?

Thanks in advance.

[trem]

Take a look at R78 and R79. The HRDx has a long history of channel switching troubles. You could just try re flowing the solder joints for these resistors and that may fix it. The resistors themselves might be bad. A lot of times the leads were over stressed and became open inside the component. I have replaced quite a few of those 5 watt resistors in the last few years.
Or I could be wrong, and you may have a different problem entirely. But it is an easy, quick fix to try.
Good Luck

[Brad1]

Thanks Trem,

I'll try that first. I'll post back with the results.

Brad1

[Brad1]

Trem, I just looked at the schematic. So you think it could be the 16V/-16V supply? I suppose I could measure the voltage at those two points and see what happens before I tear it apart.

Thanks,

Brad1

[trem]

Yes, that +/- 16V hits the channel switching, and has been a source of trouble in the HRDx for a long time. Some guys are dripping the value of those two resistors by 100 ohms each. Not sure if that has any long term proof behind it. But it was suggested to me several times. I always just stuck with the stock values. A lot of times it is just cold solder in that little circuit that throws it into lethargy.
Good Luck

[StratBrian]

Same symptom - slightly different

Hey guys, I have a similar problem. My Hot Rod Deluxe switches channels randomly without pressing the channel switch button or hitting the foot switch drive button. It's been happening when I'm playing in the clean channel. It will then randomly switch to the drive channel for 10 seconds or so, then usually switch back on it's own. No buttons or pedal were pushed. Any idea? Could it be the pedal, pedal chord, or the same resister problem you mentioned? I need to fix this quick before my next gig. Thanks for any help!

[Albert Kreuzer]

Could it be the pedal, pedal chord, or the same resister problem you mentioned?

Yes.














All of the above applies.
Most probably the resistors.

HTH
Albert

[Enzo]

And the footswitch jack itself. if the cutout contact on it is not clean, things like this can happen.

And to get real esoteric, the switching circuit is voltage sensitive, so the little diodes, LEDs and zeners in it can get off spec and confuse it.

[Amblingtee]

Another channel switching problem fix

My channel switching was messed up too and switched randomly. After reading one of the entries here about the 16V inputs I removed the spade lugs where 16V comes in on CP15 and CP16. When removing I noticed that one of them seemed a little loose. The voltage checked out ok, so I crimped the loose lug so it would fit tighter and the problem was fixed. It was getting flaky 16V because one of those 2 spade lugs was not a tight fit.

[mikeboone]

I had a HR Deville with that problem and the channel LED had a fractured solder joint. I noticed it would switch when I touched that area of the board. After poking around a bit, I found the bad solder joint and reflowed it.

[Enzo]

Part of the deal is that the LEDs are not just passive little indicator lights, they are part of the circuit, and the voltage drop across it is important.