Malfunctioning amp woes (Acoustic B200H)

[Basstovsky]

So while I am very familiar with doing wiring for basses, I have never actually taken apart an amp, and I figure posting here first would be best before I manage to inadvertently make my amp worse so here goes.

Playing a gig last night, and without warning my amp just cuts out, sounded great the few songs beforehand, I didn't change anything, it just suddenly was not working. Played the rest of the show with only the amp's DI through the PA. Today I take a closer examination and it seems pretty odd.

If any rig details are important: I run my bass to a pedalboard that splits my output so I have a dry output running into the "passive" input on the amp and I send the effects signal to the "active" input. Hadn't even used any effects at all in the set when the amp failed. It's running to an 8 ohm 400 watt 1x15 cabinet.

This morning I take closer examination, I remove all the variables; using a different power cord, speaker cable, speaker cabinet, bass, and instrument cable to make sure none of those caused my problem and I get the same result. The amp powers on perfectly fine, but when I play a note, it cuts the note off after a split second with a sharp (but not very loud) click-click from inside the amp (not through the speaker). When I unplug the speaker cable, it does not make that noise when I play a note, which is why the DI worked alright last night (I unplugged the speaker and just had the XLR from my DI) though it did seem to cut out a tiny bit here and there.

Any ideas on what is causing the cutoff and click noise? It's action reminds me of a circuit breaker. I play a note, trips the breaker (or whatever it ACTUALLY is) on the first click , it resets with the second click, then the note is audible for a split second again, and it repeats the cutoff and clicks.
Any help is much appreciated, I have another amp I can use but much prefer the sound of this B200H!

[5port]

If you are the original purchaser of this amp take it to the nearest Guitar Center and they will replace it for free. If you are not the original owner its time for an amp tech (repair).

[B-string]

You need to try a different speaker cab. The cab may be shorted and tripping the amp protect circuit?

Sorry just re-read and you said you tried that.

[grendle]

Yeah it sounds like something is shorted in the output section if your OK out the DI. try a different cab and cable first. If not, see what your warranty options are, if none , you can look at it your self but it's kinda tough without schematics. Your looking for a short, most likely either in a transistor , fet, or cap. the click your hearing is most likely a protection relay or internal breaker.

[fdeck]

The click might be the output protection relay, indicating that the amp has gone into fault mode.

Quite some time ago, somebody posted pics of the insides of this amp. The power amp is a large hybrid module -- essentially an IC. If you look up the part number for this module, you should be able to find a datasheet with the recommended application schematic. The production circuit probably would not stray far from that diagram. There is a Kustom amp, 200HD, with the same innards.

Of course it's dangerous to open line powered gear if you're not a qualified tech. There is a small but hopeful chance that the problem is due to something visibly "mechanical" such as a loose wire or dodgy solder joint.

Warranty service is definitely your best option.

[Basstovsky]

Originally Posted by fdeck

The power amp is a large hybrid module -- essentially an IC.

To sound stupid, I have no idea what that means but your click explanation definitely sounds right to me

Warranty is not an option, I am the second owner and it is something like 4 years old so my current 3 options are fix it myself, take it to a tech and see if the repair price is reasonable, or buy a replacement if the tech is too pricey (I only paid $200 for it used).

Thanks for the input so far everyone! Can't see anything specifically wrong after opening it, there's quite a lot of residue around a few of important contact areas, looks like the buildup you get on car battery terminals that I'm gonna see about cleaning off, its possible there is something causing a short.

[poorbassist15]

My little 260 is doing something similar...I'll get it fixed because I love the little thing to death.

[RickenBoogie]

It seems you really only have 2 options- take it to an amp tech, or buy another amp. Best of luck.