Hi,
Normal hum from amp, controls seem to work eg increasing Gain or Vol increases hum.
Plugging directly into either of the effects loops works, the guitar sounds OK.
Plugging into input jacks get no sound other than hum already present.
Wiring at input jacks and controls looks OK.
I've lifted the board (GP1) and all traces, solder joints look OK
I recapped in December last year, amp has worked fine since then. Replaced all electrolytics, a few resistors and new E34Ls.
Any advice please. I'm comfortable with DMM, also have a cheap cap meter and ESR although not used them in anger.
Thanks.
No Signal through Input Jacks 112RP
No signal on either input jack, but amp works with input into the effects loop? Is the shorting lug fully disengaging on the input jack when you plug in?
Also...never work on an amp in anger...they react badly to such negativity.
Hi Steve, thanks.
Hi Steve, thanks.
Yes the shorting lug fully disengages. I have tested (not) continuity from the guitar hot wire to ground on the amp, on both input jacks.
Have tested that none of the lugs on the control pots are going to ground (except the green wires)
Checked all the components between input jacks and 100mV socket;
Resistors - a few seem well out of tolerance, but I'm measuring on the board with a DMM so caps may be interfering with the value.
Caps - the higher value electrolytics I have tested with ESR meter, but then they were new anyway. Lower value caps I have tested for continuity using DMM. All OK except C4 which I desoldered and checked with my cheap cap meter.
IC1 - I don't know how to test, and don't want to fry it.
Is there a way to test IC1 (MC1458CP) without desoldering from the board?
Assuming there's a fault between the input jacks and the 100mV is there a way to check roughly where?
Thanks again.
Faulty IC1
Hi, spent an hour or so with jumper leads on resistor legs to pinpoint it was IC1. Then two minutes to swap over the IC4 (tip from another post). Issue solved. Thanks for a great site.