Peavey microbass blowing fuses

[Lownotebb]

Well...had rail voltages at 3 and 5 respectively, obviously had output, obviously, (hum). Input measured like 3v constant, no signal on amp input, with signal on amp input, same....and then....accidentally shorted 4 and 5 together.....now no output....I just keep taking 1 step forward and 2 steps back.🤯

[Lownotebb]

Any ideas besides replacing amp ic? Sorry for setback...

[Jazz P Bass]

What I implied for pin #1 is an ac signal from the preamp.
If you had voltage at that pin then either the IC was indeed dead or you have a preamp issue.
I would remove the ic and carefully check pin #1 for a Volts ac signal from the preamp. (obviously you must inject a signal into the input jack & turn up the controls.)
There should not be any Volts dc on that pin.

[Lownotebb]

I'll check preamp output....Thanks Jazz P Bass

[Lownotebb]

Preamp does put out upwards of.5v ac with passive bass as signal source, does this sound sufficient?..

[Enzo]

Yes. Pretty much any signal at pin 1 should be heard through the speaker, that is if the amp IC is good and the speaker and wires are good.

[Lownotebb]

Well...I did short pins 4 and five earlier and lost all output when investigating hum.....so while waiting on replacement amp chip, trying to check power and signal coming into ic....checked speaker independently, checks good....

[Enzo]

I rarely have to do any more than replace the IC on all the little amps of the world.

[Lownotebb]

Wanted to make sure I didn't damage anything else

[Lownotebb]

👍good to know...Thanks

[Lownotebb]

Hey guys! Long time....back into this Peavey microbass. Replaced output amp, have signal, but seems to fart out with any kind of input at all. Tried external speaker, bypassing speaker out jack, all same. Signal good and strong with headphones....Could chip still be faulty?
. Thanks for help...

[The Dude]

If you look at the schematic (https://www.thetubestore.com/lib/the...-Schematic.pdf), the headphone jack is in the same spot as the speaker- the ground is just elevated 100 ohms to knock the level down. If the headphones sound good, so should the speaker, unless there's something hinky right there at the ouptut. You said you tried a different speaker, so maybe the switching part of the headpone jack is bad and the speaker isn't making solid connection through the switching part of the jack when it's empty. Check for continuity from pin 4 of the output IC (cathode of CR6 or anode of CR5) to speaker +. Maybe even temporarily run a jumper wire and bypass the headpone jack to see if there's any difference.

[Lownotebb]

Bypass headphone jack....of course!...I'll try that...thanks The Dude

[Lownotebb]

Update.....hopefully closing in on closing this amp up..Although still have an over modulation or distorted sound with any kind of real pluck of the string. Much less noticeable with headphones but still there even with an external speaker. Replaced headphone jack, cleaned ext. speaker jack. Could there still be a bad component on-board, could cheap ass tda2040 be to blame..any other ideas? Thanks for all your help you guys, appreciate this forum and hope I can return the favor to someone else one day..

[Enzo]

Or it is simply clipping.