alpha slave troubleshooting...

[chokeyou]

My roommate recently picked up an alpha slave for $40 and was told it worked. 

anyway, we're not getting any output from it through the 215B cab it's supposed to be powering (the cab and cables are fine). we're feeding it from a line output of an alpha 6100 powered mixer (powering a separate 4x10+horn bass cab). He's trying to use it as a biamped (eventually with a crossover) keyboard/synth/bass setup.

anyway, I've got the input sensitivity LED to flicker, but other than that it doesnt do much, and I dont have any experience working on solidstate amps.

I tested the output transformer impedence, and it was something like 13Kohms so I'm imagining it's good... I've traced and checked all the leads from the board to the input/output jacks and they all seem to be fine. the fuses are fine. the pot seems to be fine. how do i go about testing the output transistors? are there any easy to do tests to narrow the issue down without tearing the whole thing apart?

[loudthud]

Output transformer? Solid state amps don't have output transformers except in very rare cases.

The Alpha slave is a lot like the Beta series. There are on board +/- 15V regulators that are zener fed TIP29/30 emitter followers. If one of these fails the amp goes dead. Look for the TO-220 TIP29 and TIP30 transistors. The TIP29 is the NPN for +15. It should have +30 to +40 on the collector and ~+15 on the other two pins. The TIP30 (PNP) has the same voltages except they are negative. I got a Beta lead that didn't make a sound in the store. The only thing that was wrong was the TIP29 was blown. It could really use a small heat sink.

[chokeyou]

my bad, habitual reference to implied parts...and like i said...dont tend to work on SS amps. 

I'll check into it. thanks for the pointers, will report back maybe later tonight.

[chokeyou]

well, the TIP29/30 test out fine.

in other news, tapping around the board i found a transistor that seemed loose in a socket...pulled it out, shot some deoxit on it and cleaned the socket out too, now i'm getting sound out of the amp (progress!!) but it doesnt seem to be working right

I dont get any sound with input sensitivity less than 5 or 6, and then I get sound but it's heavily distorted. bass frequencies only for the most part. the highs you can hear trying to break through but seem to be buried.

This is all with the monitor out on the mixer feeding the slave, and playing around with the other routing schemes i couldnt get any other results... I'm going to try hooking it up to the slave out on my model T and see what happens, but I'm not guessing much.

think its just an issue of input level or do you think there are more problems? tapping on the board with a drumstick i'm not getting any more noise anywhere, so i'm assuming the solder joints are all pretty solid. I'll report back after i slave it to the T

update: slaved it to both my old OD120 slave out and red knob T's 600ohm line out to no avail, gotta crank the shit out of it and all you get is farty fizzle sound. but sound all the same...which is one step closer to where we need to be.

[chokeyou]

anybody know of a schematic with measured voltages i can work off of? i found a copy, but the text is way too small to be legible.

[loudthud]

The schematic I have is a black and white copy of a manual titled Alpha Series P.A. which covers the Alpha Four, Six, Eight and Slave. The circuit board has the number 20-0135 on it. The Beta series used the same circuit board and I don't see any difference in the schematics.


Edit: The one I have looks like these:

http://sunn.ampage.org/site/svcmans/alphaPA/alphpa27.jpg
http://sunn.ampage.org/site/svcmans/alphaPA/alphpa28.jpg

The numbers are a little fuzzy. It will take me a day or two to scan mine and post it.


These are a little clearer:

http://sunn.ampage.org/site/svcmans/beta/betamanual22.jpg
http://sunn.ampage.org/site/svcmans/beta/betamanual23.jpg


and a troubleshooting guide:

http://sunn.ampage.org/site/svcmans/beta/betamanual24.jpg

[chokeyou]

Thanks! I had found the first set but not the second set of the schematic.

That should do, i think...a little rough in spots

I let you know what i find!

[loudthud]

Here's a clean scan of the Alpha Slave schematic. It's a little light but you can read everything.

Keywords: Alpha Beta Poweramp Power Amp Schematic