5150 Combo problem

[Wailin]

The head I am discussing does not have the reverb problem as it has no reverb, I was referring to the wide open volume control issue

[Enzo]

I know, I was being facetious.


The discussion is still relevant, you need to trace the signal and see where the loss of voltage division occurs. His also has no EQ action, do your EQ controls work still?


By the way, welcome to both you new members. Wailin, may I suggest if your amp needs ongoing discussion that you start its own thread. It can get confusing having two concurrent discussions over similar problems.

[oegoeh]

Any suggest what suppose to check? cause I don't have either tone generator or osciloscope

[Enzo]

Without a tone generator I use something else. Got a keyboard? Set a weight on a key so it sounds continuously and use the keyboard as a generator. Of connect a CD player to the amp. And if you have no scope, then use the AC voltage function of your meter.

[JerryP]

I've had several 5150 heads come thru the shop with non functioning post volumes and EQ. I repaired them by replacing filter cap C37.
Jerry

[oegoeh]

I've had several 5150 heads come thru the shop with non functioning post volumes and EQ. I repaired them by replacing filter cap C37.
Jerry

Thx Jerry,

I'll try, but for now I've send the amp to my friend for repair.

[oegoeh]

I've had several 5150 heads come thru the shop with non functioning post volumes and EQ. I repaired them by replacing filter cap C37.
Jerry

Jerry,

BTW the filter caps C37 base on 5150 combo or head schematic...?

thx

[oegoeh]

all,

I've replace filter caps C57 and C58. I can hear that the EQ is working. But the output is very low now and post pots is no affect until turn to max will give more volume a little.

Measure from filter caps C56 is 478 V, C57 is 328 V, and C58 is 310 V.

[oegoeh]

I'm has put back the old filter caps, now they give same result. The output became low and eq is working now, post pots still no effect until turn to max and give more a little volume. Reverb doesn't working yet. Should I replace Q1 and Q4?

[Amp Kat]

I think we are confused which schematic you have with the combo. C-37 on the 5150 is the 1st filter cap on the HV after the rectifier and there is a 10k resistor and another filter cap. Is that what you have ?

[oegoeh]

I think we are confused which schematic you have with the combo. C-37 on the 5150 is the 1st filter cap on the HV after the rectifier and there is a 10k resistor and another filter cap. Is that what you have ?

hi,

yes correct in 5150 head C37 is 1st filter caps HV (V2+) and 10k resitor after that. But in 5150 combo is C57 for 1st HV filter caps. In 5150 combo C37 is caps 100nF on leg 2 TRIAC.

[oegoeh]

Gents,

After replace filter caps C57 and C58, also remove Q1 and Q4 my 5150 combo working normal on post pot and EQ. I think Q1 and Q4 is broken, because no +20V on the gate while the amps is ON also at CR9 and C12.
removing Q1 and Q4 give +10V on Q1, Q4, CR9 and Q12, this is normal??
For now is enough for me, only no reverb, I guess Q7 is broken . I can't find J174 in my little town, must buy to other town.
I can use my reverb pedal using FX loop.
Thx everyone for helping me.

best regards,