Crate GT1200H won't switch to Solo channel.

[Duncandod]

Hi. Just inherited this Crate amp, made in St. Louis. It works well on Clean and switches to Rhythm channel okay via front, but no solo channel. Rhythm/Solo switch tests okay. Also, will not switch between clean/rhythm via foot switch, although the switch tests fine on other amps and LED lights up. No measurable signal to the foot switch and no LED.

I have the schematic and have tested Q5, Q11, Q15 and Q23 at my friend's suggestion and they test to spec on Mouser website on the board. No visual indication of heat damage or bad solders, although Q9 loos like it may have been re-soldered at some point. Anyone have an idea of what else I should be looking for? My expertise is in computers, but I have a very fundamental understanding of electronics, a good meter/ IC tester and can solder a board.

Thanks in advance for any suggestions

[g1]

Please upload the schematic.

[Jazz P Bass]

Crate GT1200H Schematic

Sounds like a bad jfet.
Here is the schematic.

You will need to take a few voltage measurements around Q29.

[Duncandod]

Sounds like a bad jfet.
Here is the schematic.

You will need to take a few voltage measurements around Q29.

Will do. The schematic notes that I am to have a specific wave signal into the insert Jack. Do I need special equipment for that? Thanks.

[Jazz P Bass]

As you do not have a specific 'waveform' problem, for now you need to get the switching function working.

[Duncandod]

I'm getting 15V on pin 8 on all ICs. No reading on pin 1 on any. Supposed to be -15V?

[Jazz P Bass]

Pin 8 should read +15 Vdc.

I thought that you had a switching problem?

Q29 is jfet that switches the Solo channel in & out.

Measure the dc voltages on all three pins.

You could even compare those readings to Q4 & Q21.

[Duncandod]

Pin 8 should read +15 Vdc.

I thought that you had a switching problem?

Q29 is jfet that switches the Solo channel in & out.

Measure the dc voltages on all three pins.

You could even compare those readings to Q4 & Q21.

I've examined both the schematic and the pcb and I cannot find a component labeled Q29. Could you be so kind as to give me an x/y coordinate on the schematic? Thanks for your help :-D

[Duncandod]

Nm....found it. I'll get back to you on the results.

[Duncandod]

Measuring from P1 to P3, Q4 and Q21 read: 0/0/-14. Q29 reads 0/11.8/0. This is with OD channel on, and reads the same with Solo channel.

[Jazz P Bass]

Sorry about that, Chief.
C-2.

[Duncandod]

Measure C2 or replace? C2 measures 0V on both ends. in all settings.

[g1]

C-2 is the coordinate on the schematic where Q29 is located.

[Jazz P Bass]

Whew.

[Jazz P Bass]

This may be a can of worms.

From looking at the schematic, it appears that #1, you have to be on the OD channel for Solo to work.

Is there a Solo LED?

If that is true, you will have to signal trace the schematic to find out where it is failing.