Edison Professional Powered Speaker System

[g1]

Sounds like a wild goose chase to me. Reverse biased junctions are supposed to measure high resistance, there is nothing anywhere that says they have to measure "open" (no reputable sources anyway). There may be a range of resistances that are acceptable for this type of transistor.
Have you tried the one from the mixer in this unit? Or one of the new ones in the mixer?
You have a meter that says they are good, and one that MAY indicate leakage, or maybe not.
I would not wage any bets that it is the source of your problem.
What resistance are you measuring and which junction? Can you list the readings from your various meters?

[bsco]

I installed the other 2N5551 transistor...the one that didn't show any reverse leakage...G-gone...you were right....it didn't make any difference....this is beginning to be one bastard to fix.......and I can't find a schematic anywhere.....the boards are glued in place with this black type of super hard epoxy and can't get them out to swap them with the other cabinet that is working......what a pits......and not only that,, if i do get it fixed I can't guarantee the realibility because there was a 10 amp fuse installed where it should have been a 4 amp fuse and then powered back up.......I checked all the small signal diodes and transistors and there is nothing gone......so the problem has to be elsewhere but I don't know where.....anyway that's it for this one.....thanks for all the help anyway guys....I had somebody bring me in another powered speaker system that had tinfoil wrapped around the fuse...I laughed and just refused to take it.....

[J M Fahey]

Please quantify "lower output" or whatever is bothering you.
Inject 1V 1KHz at the input, scope the output, what do you see?
If you can post a picture, please do.
What power do you measure at clipping?

Besides that, try to draw the schematic yourself.

Maybe not all of it, but the most important part.

Start backwards: power transistors/their drivers/the predriver stage , because these are the parts that suffer most in a short.

FWIW last night I repaired the "1200W" (actually 350+350W RMS) power amp from this mixer , without schematic:



Found 3 of 4 NJW0281/32 shorted, and don't trust the remaining one, so replaced all with much beefier MJ21193/94.
Also replaced 2SA/2SC Japanese TO220 drivers with trusted MJ15031/32 , the 2SA something predrivers with MJE340/350 and smaller transistors with 2N5401/5551 as needed , plus some blown diodes, and all visibly burnt resistors.
Also 2 of 4 0.5 ohms 5W ballast resistors were blown, I replaced all 4.

Since it has a stiff SMPS power supply which does not allow for series bulb lamp limiters or raising it slowly with a Variac, the classic "play it safe" approach , I hooked the module to one of my own 100W SS amps power supplies, which uses a conventional EI transformer and can be lightbulb limited with ease.

It supplies +/-40V instead of +/-63V original SMPS but if the amp works with the smaller one, it will work with the large one too.

It started fine, didn't show a short , output voltage was very normal 15 mV DC .... but music showed horrible distortion

Scope showed only the positive halfwave was being reproduced.

Further searching showe 2 10 ohms resistors in series with power transistor bases were open.

They looked ***perfect***, not even slightly browned (unlike others covered in soot or cigarette type ash) .... but they were open anyway.
Replacing them restored amp to full glory.

It was used successfully today at my Son's Church.

So in a nutshell, approach must be 4 sided: replace all visibly burnt stuff + unpowered (resistance) measuring + static DC voltage measurement + dynamic (audio signal) checking.

Good luck.

[Darkman042]

Hi there! bsco, did you ever fix that Edison powered speaker? I have one now that I am experiencing the same problems with. About a year ago I purchased 4 of them. 3 of the 4 didn't work. After some "googling" I decided to replace the output transistors (toshiba 2SC5200 AND 2SA1943). This made the 3 dead speakers work just fine until recently. One of them is behaving exactly as you described. I hope that someone has found a fix!

[Darkman042]

So far on mine through swapping boards with one of my speakers that still works, I have narrowed the problem down to what I call the "input board." (the board that has all of the inputs and outputs for the speaker) I have replaced two bad 470uF 16v capacitors on it, but the problem persists! I have to turn in for now, but if anybody has any ideas to offer me I would really appreciate it.