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Is my amp dead for good?

#186
Well, it seems that the amp has taken a bit more of a hit than just the burned thermistor!
i used the amp at rehearsal for the first time since i "fixed it" and I noticed that it has lost quite a bit of power. I usually had the volume set between 8 and 9 o'clock but now it is more like 11 to 12 o'clock. Now, the power output is still more than I'll ever need but I worry that some components are not working properly and that the amp could drop dead anytime again. Any advise what to look for?
 
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#192
subdude67 said:
Any advise what to look for?
Click to expand...
A new amp?

Given the lack of available of parts or repair techs where you live, you might want to set this one aside for fixing at a later date, if and when you are so inclined.
The amp took a 400 volt hit, you replaced the thermistor and kind of got it going again.
That is a herculean effort on your part even without the other challenges. You did a good job.

However, it is apparent that the over-voltage event went further than just the thermistor.
I am not surprised at that one bit.

If you are gigging, this amp may not be reliable for you as is.
You should be looking for something else.

It sounds like this amp can be good for practice.
Or you can further explore your inner technician without being under some time line to have it back together for the next show.

If you do get it fixed, then you have a nice backup amp when (not if) the next time the power grid goes wonky.

Best of luck to you.
 
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#193
subdude67 said:
I am not sure that I understand the question, where would I find the info on the voltage of the power supply?
Click to expand...
Sometimes it's labeled on the board near the connectors or a test point. Just be very carefull working on it powered on. Very high voltage. I haven't done much with SMPS. I wouldn't bother if it's not labeled. If SMPS and its powering at all, the heart of the supply is probably good and it could be a filtering or regulation issue.

Filtering is usually accomplished on the power supply, but regulation can be on other boards.

If you are not comfortable around high voltage or there are no labels indicating voltage, the TV shop you mentioned should be good at SMPS.

I don't consider myself a good amp tech. If an experianced tech comments, you should probably list to them over me :D

If you decide to measure supplies, don't get dead!
 
#194
There are several mechanisms used to govern the power supply (SMPS) that depend on feedback to control various performance aspects. It's possible that one of these mechanisms has failed, but they are difficult to troubleshoot (even for an experienced tech) with a real shop bench full of test equipment.

It could also be something else, even corrupted software in the case of that amp.
 
#195
subdude67 said:
Yes, sound, controls, Tone Print, all working fine, it's just less power coming out of the amp.
Click to expand...

Check that the line voltage is normal.

I assume that this is into the same speaker cabinet as before. A higher impedance cab would result in less volume. Just to rule out the speaker cabinet and speakon cable, try the amp into another cabinet.

Next, test all amp functions:

Is the active-passive switch working. If you have an active bass, is the battery good.

Does the amp have the latest firmware installed. If yes, if you feel comfortable doing so, download the firmware and reinstall it. Before you do, TC can tell you if this is a possibility based on your amp’s symptom.

Does the headphone output sound normal or does it have a lower volume level as well. Oxidation on a shunt in the headphone jack can cause a proble as it mutes the speaker output. Vigerously cycle a plug in and out of the jack repeatedly. This can sometimes remove anything that is interfering with the signal going to the speakon.

Test the preamp out into a mixer. If this level is normal, it could indicate that the problem is in the power amp.
 
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#199
Thanks for all your input!
I have tried different cables to amp and speaker, no change. I don't have any other speaker to test with. What I haven't done yet is using another bass, I will report back when I tested with another one on Monday. .
Like I said, as far as the controls go, every pot and switch, TonePrint and tuner works just fine. And despite the apparent loss of power there is still plenty for my needs, I guess I just keep on using it.
 

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