solid state amp trouble shoot

9 volt · Post by **9 volt** » 11 Oct 2009, 03:00

Hey there, I just bought a cheap solid state amp (mainly for the box) thought I'd try to fix it up first. Trouble is it hums, no sound, no control of hum with volume, I understand tube amps, I thought this may be a filter cap /power problem, no luck so far just wondering if anyone has any advice, thanks

ansil · Post by **ansil** » 11 Oct 2009, 05:12

utilizing some sort of oscilator or a radio through a proper adapator you can feed a signal into it. then using a audio proble you can go part to part to find out where the audio signal is disapearing. but i would guess somewhere along the lines one of your audio devices is dead inside an opamp or the power amp section.

check all your voltages

9 volt · Post by **9 volt** » 11 Oct 2009, 07:31

Thanks I just traced the signal, it's fine right up until entering the output transistors (tda2030) one per channel. Both transistors output buzz/hum. Maybe they are both blown

ansil · Post by **ansil** » 11 Oct 2009, 08:55

did ya check the voltages on the outputs to see if it is nominal

jupagblkxten · Post by **jupagblkxten** » 11 Oct 2009, 15:37

the hum you're hearing is most likely dc voltage being output from the transistors. hook up your meter to the speaker output and see if you can measure any dc voltage. if so, it's sure sign that they're blown and need to be replaced.

9 volt · Post by **9 volt** » 12 Oct 2009, 09:08

This sounds like the trouble, I checked dc voltage and it's coming through the speakers (one was blown-I'm using a dummy load), maybe I should replace the cap the goes to ground (220n) on the transistor output as well as well. Thanks again

royal jelly · Post by **royal jelly** » 22 Oct 2011, 01:23

So did that fix your problem? Your post about the outcome would help alot of people out cause this is a very common problem with solid state amplifiers.Thanks.

teemuk · Post by **teemuk** » 22 Oct 2011, 12:02

What's there to post... usually something like this is a typical case of blown power stage, specifically its power transistors (which often take other stuff with them as well). The transistors short circuit to power rail, the whole DC voltage fed to very low speaker impedance causes tremendous voltage sag of the power supply leading to great increase in ripple, which being AC by nature is heard through the speakers as loud hum... at least for the brief moment it takes for the high power generated by having full DC voltage across the low impedance of the speaker load to entirely toast the voice coil. You usually smell the lacquer burning already, and possible the power transformer will be "howling" in great pain as its trying to muster about a short circuit current. A sustained condition of this kind of fault usually kills the loudspeaker and blows fuse(s), unfortunately in about that order.

The fix is replacing the output transistors, finding out what else failed along with them (sometimes stuff like driver transistors, short circuit protection transistors and circuit, maybe the voltage amp transistor(s) and related components, sometimes the entire input stage, in rarer cases output zobels, feedback loop -related compoenents and so on). Each case is usually slightly different than the other one and repairs have to be made case specifically, so there's no overall guide of what one must do and replace. You check what is still intact and replace the stuff that isn't.

In this specific case, though, the TDA2030 are not power transistors, but integrated circuits containing the entire power amp. So with two of them we're either talking either about a stereo amp, or an amp with bridged or parallel connection of the power amps (latter being very rare an not usually seen in commercial amps). OP says there's one TDA2030 chip per channel so it's basic a stereo amp. So... if both channels just output loud hum and no other signal then both channels have blown. If one of them seems to work to some extent (it may still hum and sound distorted due to enormous ripple and sag of the power supply but it usually will nevertheless output some sort of signal) then only one channel is blown.

In these kinds of repair cases (replacing an entire power amp IC) usually just replacing the blown ICs fixes all the problems, but its still good practice to measure if something else failed along with them, because sometimes something has. Again, the faults are case-specific and each repair has to be treated as an unique process. About the only thing we know is that we have a failed power amp IC or several, which is a good reason to doubt that possibly some power amp or power supply -related components may have failed as well.