Hello,
i have an Ampeg Portaflex PF-350 on my bench for repair. It works but with very low volume, 1/3 of what you'd expect. Much lower than any 100-150w amp i have around.
It has SMPS and a class D amplification. Looking inside i found two issues:
- found R94 and R98 burned near the Q10 and Q13.
- found that i'm gettin +80v/-80v instead of the +55v/-55v shown on schematics.
The overvoltage is probably the reason why the R94/R98 keep burning. But i cant find what is causing it. the SMPS side seems ok. I'm getting 176v before the transformer.
What i've done so far:
- since Q10 and Q13 were ok, i tried beefier resistors. also burned.
- changed Q10 and Q13 (both 33n25)
What would make the SMSP release 80v instead of 55?
Anyone experienced with this amp?
***
I've annexed the schematics but i could not find the revision I actually have.
Most schematics online do not have R94/R98 in series with C84 and C97 (as per annexed picture).
i have an Ampeg Portaflex PF-350 on my bench for repair. It works but with very low volume, 1/3 of what you'd expect. Much lower than any 100-150w amp i have around.
It has SMPS and a class D amplification. Looking inside i found two issues:
- found R94 and R98 burned near the Q10 and Q13.
- found that i'm gettin +80v/-80v instead of the +55v/-55v shown on schematics.
The overvoltage is probably the reason why the R94/R98 keep burning. But i cant find what is causing it. the SMPS side seems ok. I'm getting 176v before the transformer.
What i've done so far:
- since Q10 and Q13 were ok, i tried beefier resistors. also burned.
- changed Q10 and Q13 (both 33n25)
What would make the SMSP release 80v instead of 55?
Anyone experienced with this amp?
***
I've annexed the schematics but i could not find the revision I actually have.
Most schematics online do not have R94/R98 in series with C84 and C97 (as per annexed picture).
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