Edison Professional Powered Speaker System

[bsco]

Hi there. Trying to find a schematic for this powered speaker. The owner replaced the fuse and installed a 10 amp fuse....needless to say it blew up....Now he wants this unit repaired.....I changed out all the blown parts that I could find and re-installed the burnt traces..It works now but when you increase to volume to a loud level, the unit distorts....when the volume is low it sounds nice and clean........Any help on a schematic would be great...Searched the net and found nothing so far......
Cheers,
Bernie

[Jazz P Bass]

So is the input being overdriven?

[soundguruman]

Seems like your speakers may be blown....
but why did they name the speakers after a douche bag?

[Steve Conner]

Yup, should have bought a Tesla-powered speaker system instead.

If it distorts at high level, it's usually because the power amp is only half working. Look for burnt emitter resistors, output transistors with loose connections and so on.

[soundguruman]

Yeah, when it's half working, it turns quarter notes into eighth notes. Wrt dsoton psible.

[bsco]

No the input is fine...I have the other matching cabinet here and it works great......I swapped out the input board as it was easy to do just to check...There has to be something that is still weak on the output board....but not completely gone.....I had replaced all the burnt components and melted traces and another speaker was hooked up to this cabinet and the same problem....I will check into the power supply section to see if one side is lower than the other when you increase the volume....thanks for the help....
Cheers,
Bernie

[soundguruman]

No the input is fine...I have the other matching cabinet here and it works great......I swapped out the input board as it was easy to do just to check...There has to be something that is still weak on the output board....but not completely gone.....I had replaced all the burnt components and melted traces and another speaker was hooked up to this cabinet and the same problem....I will check into the power supply section to see if one side is lower than the other when you increase the volume....thanks for the help....
Cheers,
Bernie

Just replacing components that are burned, will not find all the problems.
You need to take all the semiconductors, etc...and test them individually.
A part that looks fine, could be blown.

[bsco]

Actually I have already done what you just described....Couldn't find anything gone.....I just checked out the supply rails...both are measuring plus and minus 49volts....and with the system cranked up, the readings are steady...Also the 2N5401 and the 2N5551 tested ok in the transistor tester section of my meter.......which now I have to ask.....are they reliable as they are supposed to test the gain of the transistor....too bad i can't find a schematic.....
Cheers,
Bernie

[soundguruman]

Actually I have already done what you just described....Couldn't find anything gone.....I just checked out the supply rails...both are measuring plus and minus 49volts....and with the system cranked up, the readings are steady...Also the 2N5401 and the 2N5551 tested ok in the transistor tester section of my meter.......which now I have to ask.....are they reliable as they are supposed to test the gain of the transistor....too bad i can't find a schematic.....
Cheers,
Bernie

Use an analog meter set on high ohms.
Check for base to emitter and base to collector junctions, as usual.
BUT then reverse the meter polarity, and check for reverse leakage. Transistor testers frequently ignore small amounts of reverse leakage.
Check the diodes the same way.
I prefer the analog meter, because reverse leakage is revealed, and otherwise ignored.
I replace transistors, diodes that show reverse leakage. Many other techs do not. But in audio quality, thermal, reliability, it can make quite a difference, or all the difference.

[bsco]

OK then. I will check all the transistors with my analog ohmmeter...will let you know what I find.......My meter's highest range is 10K....is that going to be high enough???
Cheers.....

[bsco]

Checked out those smaller diodes and transistors with an analog meter....found one transistor that was leaky between collector and emitter and leaky between collector and base...everything else checked fine. Checked this same transistor with a transistor tester and a DMM and it tested good with these two pieces of test equipment....but the analog meter picked it up....so that is something else that I have learned....always have an analog meter on hand just in case...Thank you very much for this tidbit of information...I will have to pick up the part.....2N5551 transistor tomorrow and hopefully they will have this in stock....if not I will have to order it......Once I get this and install it, I'll let you know how I made out....
Cheers,
Bernie

[soundguruman]

Checked out those smaller diodes and transistors with an analog meter....found one transistor that was leaky between collector and emitter and leaky between collector and base...everything else checked fine. Checked this same transistor with a transistor tester and a DMM and it tested good with these two pieces of test equipment....but the analog meter picked it up....so that is something else that I have learned....always have an analog meter on hand just in case...Thank you very much for this tidbit of information...I will have to pick up the part.....2N5551 transistor tomorrow and hopefully they will have this in stock....if not I will have to order it......Once I get this and install it, I'll let you know how I made out....
Cheers,
Bernie

You may be delighted to find that an analog meter tells more than many fancy test equipments. The fancy meter totally missed the leakage.
My favorites is Simpson 280 or RCA Volt Ohmist. Vacuum Tube Volt meter / big analog scale rules, of course.
I just scored an RCA at an estate sale for $5....

[bsco]

Yes you were right..The fancy test gear missed the transistor leakage..I had to order the transistor...had nothing hear to substitute so in is on order...I'll let you know how I make out...great score on that estate sale....Actually i have an old Micronta analog meter here I picked up at a yard sale awhile back...model #22-210There is a rotary switch which selects -DC or (+DC.AC.Ohms) so it is a two position rotary switch....When the switch is in the -DC mode and you select the CONT function it generates a tone as if your meter leads were shorted together, and if you select X10K range the needle pegs backwards. If you select the +DC, AC and ohms setting and then select CONT, the needle pegs backwards but there is no audible sound and if you select the X10K range the the needle again pegs backwards..Also, the X1,10 and 1K ranges are dead also. When shorting the test leads together there is no meter movement.....SO I guess I will have to figure out what is wrong so I can have a couple of analog meters to use....I am going to search for a schematic first to see whayt I can find....Once again, thanks for the analog meter tip...
Cheers,
Bernie

[bsco]

To Soundguruman......just got a chance to get on line again....I had ordered those transistors in and received them a while back.....2N5551.......I tested them with the analog meter and guess what....I have the same leakage readings as the original one.......I had ordered in four of them and they all test the same....I also tested all the diodes in the circuit for leakage as well and they tested fine(out of circuit).......I haven't powered it back up yet as i have to reinstall the board and bolt it to the heat sink.....I wish somebody out there had a schematic for this.....I did find a bad solder connection that I had missed previously so later today I am going to fire it up again....I'll let you know how I make out with this.....too bad the owner replaced the 4A fuse with a 10 amp one...
Cheers,
Bernie

[bsco]

Well...guess what I just discovered.....I took the 2N5551 transistor out of a MM4D powered mixer and tested it...The is NO reverse leakage.......the transistors that I had ordered in ALL have a reverse leakage and they read the same amount of leakage on the analog meter....so I guess I ended up with a bad batch of transistors......so I will have to order a few more.....what a piss-off..........because all the transistors I had ordered showed a reverse leakage I figured that was normal......but now I know for sure that they are all bad.....hope this helps somebody else out so that they don't end up chasing their tail like I did.....
Cheers,
Bernie