Hot rod deluxe RevA channel switching

[Oldmactech]

Sure would appreciate some more advice?

[Jazz P Bass]

Right off the bat I can see a few that are off.
I have attached the TP's for easier reference.
Go through the chart and identify the odd men out.
Then post those points.

Quote: "Skipping normal readings."
Please include the Normal readings as per the TP chart.

Have you tried with the factory FootSwitch?
Note: TP 31 is only for the FtSw and also that the FtSw will override the FrPnl switch functions.

[Enzo]

And really, aside from not skipping. Please tell us settings, not in or out for the switch. The TPs all refer to DRIVE, MORE DRIVE, or NORMAL. Not in and out. And while we may be concerned with DRIVE switching, it matters if it toggles to some other state for NORM or not.

[Oldmactech]

Thanks. Sorry, I do not have a foot switch but these are the readings I took for TP31-36.

31 norm 1.05
Drive .83
More Drive .83.

32 norm .53
Drive 9.80
More drive 9.80

33 norm 5.06
Drive 2.14
More drive 2.14

34 norm - 12.21
Drive -12.21
More drive -12.21

35 Norm .53
Drive .53
More drive -9.86

36 Norm -15.99
Drive -15.99
More drive -15.99

thanks very much.

[nevetslab]

It appears your 5.1V zener diode CR22 is bad, as the voltages shown at TP 34 aren't changing as the Fender voltage chart shows. And, I also think the op amp U3 is bad NJM4560, as the voltages at TP36 aren't switching to +16V in More Drive mode.

[Oldmactech]

Thanks, I think I have a spare zener and a njm4560, will report back after swapping.

[Jake Trout]

Also switch back to the 470 ohm 5W resisters. I did the Fromel upgrade a few years back had the same problem pop up soon after. The change to the 330 ohm resisters were based on a Fender warranty station fix for the Hot Rod DeVille. I switched them back and replaced the three legged LED lights and haven't had a problem since.

[Oldmactech]

Mine has 470 ohm 5W resisters installed. Source for the LED lights?

[Oldmactech]

Replaced cr22 5.1v zener diode and the switch 4560 and no change.
stumped.

[glebert]

Have we verified that the +16V supply is correct? Maybe I missed it.

[Oldmactech]

Thanks, measure that at the 470 ohm 5W resistors?

[glebert]

Thanks, measure that at the 470 ohm 5W resistors?

Since we are looking at the switching issue I would start at R91 and pin 8 of U3 and if it isn't right there work back to the 5w resistor.

[nevetslab]

Have you checked/replaced Q3 & Q4? I forget off hand where I had found the 3-pin bi-color LED's. RED and GRN are the two colors, and with both lit up, I believe that's what yields YELLOW. Generally, when your Test Points are measuring like those shown in the chart on the schematic, the channel switching is correct. More Drive requires both JFET's Q1 and Q2 to be switching, and that the two relays K1 and K2 are working. I have had to de-solder and re-solder the relays, though I don't recall having to replace any relays. Only a couple times have I had to replace the JFET's Q1 & Q2. The voltages at the test points in the chart is key to getting the switching to work. And, of course, having reliable +/-16VDC on the supplies.

[Oldmactech]

Thanks. I’ll check out the JFETS and the switches.
Does the fact that the yellow drive light lights even when in standby mode mean anything?

[Oldmactech]

R 91 Normal Drive More Drive

1.0/4.3 .8/1.3 .8/1.3

pin 8 U3 4.3 1.3 1.3