i got this amp the other day with 1 bad channel, the outputs (TIP35/35) were shorted between all 3 legs. i checked the drivers (TIP41/42) out of the circuit and they seem okay, the emitter resistors are within tolerance, and the base is getting 38v/-34v. i replaced the outputs and powered it up, now all 4 channels are kind of tappered down on the top half of the output. if i turn it up into clipping the top half will start distorting. i was just wandering if i should look further into this channel or something that all four channel have in common.
the pic is before clipping.
the pic is before clipping.
Attachments
Both +/- regulated voltage on all of the op-amps?
Clean signal coming off of the preamp board?
DC voltage on the base of Q149 and Q150? Place the black probe on the emitter of the transistor on which you're measuring the voltage (red probe on base). I'm assuming that this is like the 800.4. These transistors would be near the outputs and there would be a pair for each channel (249, 250...). The Qx50 transistors would likely be near large green film caps. Both should be C945s.
Clean signal coming off of the preamp board?
DC voltage on the base of Q149 and Q150? Place the black probe on the emitter of the transistor on which you're measuring the voltage (red probe on base). I'm assuming that this is like the 800.4. These transistors would be near the outputs and there would be a pair for each channel (249, 250...). The Qx50 transistors would likely be near large green film caps. Both should be C945s.
well i got readings from all the Qx50's and they were all at 0.225v from e-b. then i got a phone call and when i came back the amp was off and now it wont come back on. pins 8 & 11 have 1.4v and pin 12 has 0v on the tl494. i never noticed any parts getting hot especially the power supply fets or the outputs. i was out of the room for about 1-2 minutes and now i regret it.
if i removed the power supply rectifiers would that isolate the problem to either the power supply or the audio side of the amp. it was powering up fine but all the sudden it turned off and now i'm kind of lost. i know the TLx94 is not getting 12 volts but could it be something related to my previous problem (distorted output) which i believe is more probable or maybe something in the remote circiut?
I was using a similar but different amp as a reference so the J513 may not be the same. Follow the circuit back from the muting transistor with 0.6v on the base (vbe). The base resistors for all of the muting transistors will go to one trace which will then go to the power supply circuit. Break the connection between the muting transistor base resistors and the power supply muting drive circuit. The simplest way will likely be to remove a wire jumper.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.