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SS64 30th July 2009 11:08 PM

Had a Stupid Moment PC2150
 
OK I finally got around to buying the Mjl21193's and 94's for my 2150.. I pulled all the 35 and 36's and pre bent all the leads on the 93 and 94"s... needless to say someone distracted me and I didnt know it at the time but I installed the 94's in the 36's place and the 93's in the 35's place.. so my dumb self reversed them.. i powered it up and ofcourse no sound.. by then I realized what I had done.. I took the 93's and 94's and put them in there right place...
Powered it up and the right channel works perfect. Left channel has distortion at low volume.. Took out the 93's and 94's and checked them.. they where good.. so i replaced the drivers.. still the same noise.. so the guy down the street from me that used to work at ppi told me it was probably the driver boards.. So i replaced the big surface mounts on the board with no improvement... and I replaced the smaller parts above the larger ones.. still no luck..
So where do I go from here??? .. nothing on the driver boards looks burnt..
Anybody have any ideas? Or does anybody have a driver board?

Perry Babin 31st July 2009 12:06 AM

Do you have clean audio getting to pin 3 of the driver board?

Do you have a scope?

SS64 31st July 2009 01:53 AM

ok I will check the signal tomarrow.. i left the amp at work,, and yes i have a 10mhz tecktronic.. what should I see on the scope?

Perry Babin 31st July 2009 02:31 AM

Compare the signals on the input of both driver boards. If they're essentially the same, look at the speaker output signal on the scope. Is it missing the top half or bottom half?

If not, how is the signal different, compared to the other channel?

Have a speaker or some other load on the output. Be careful. The outputs may overheat when testing. This could cause them to fail. Monitor their temperature the entire time it's powered up (on both channels).

Also, the regulators in those amps tend to heat up quickly. They're likely 2N6488/91s (Q16, 17, 68, 69?). If they overheat and short, it could destroy all of the op-amps in the amp.

SS64 31st July 2009 11:20 PM

The waves on the good channel are completely different than the hurt channel.. I dont know a whole lot about wave forms but I can tell there is something very wrong with the left channel.. And the driver board gets very hot very quick.. and it looks like it may be missing the top half of the wave form..

Perry Babin 31st July 2009 11:32 PM

With no power applied to the amp, measure the resistance from the pads where the overlaid resistors make contact. You should read 100 ohms. Compare to the good driver board. Do you read 100 ohms for each resistor?

http://www.bcae1.com/temp/ppidriverb...roverlay01.swf

The overlaid resistors are not actually going to be there. The 100 ohm resistors are printed under the large SMD resistors. The ones on the photo show where to make the connections if the ones on the board are open or well out of tolerance.

SS64 31st July 2009 11:48 PM

Yep One reads 100 ohms like is should the other reads over 300 ohms..

Perry Babin 31st July 2009 11:57 PM

Well... Ideally, you should cut the 300 ohm resistor so it's completely open but the boards are easily damaged (don't recommend removing SMD transistor to cut the resistor) so I'd suggest simply installing a 100 ohm resistor between the two points to see if the problem goes away. You 'could' use a higher value resistor to make it 100 ohms with both the printed and new resistor in parallel but the printed one probably isn't reliable. A slightly lower overall resistance shouldn't hurt anything.

SS64 1st August 2009 01:36 AM

Damn well ok .. I'm going to try and locate some here locally.. otherwise I'm going to repair it and pray..
Thank you again Perry

SS64 26th August 2009 02:13 AM

Ok perry I found the driver boards.. I put it in and still the same problem.. Had my ppi guy look at it and he said that with the signal generator on it everything looks good on the scope.. I tried different head units, rca's, tested in and out of the car and the distortion still persists.. Any ideas?


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