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K100 : PC900 Module 8 Volt Regulation Problem [message #21837] Wed, 12 November 2014 10:58 Go to previous message
Shoreline Electronics is currently offline  Shoreline Electronics
Messages: 3
Registered: November 2014
Location: Clinton, CT
Junior Member
Hi Folks !

Got a head scratcher here.

Kustom K100 5 Head

When amp is first powered on, it works great.

After a few minutes both the regulated +8 & -8 Volt supplies slowly drop go down to about 2V & -2V

When this happens... 39.5 & -39.5 rails are perfect.

Pulled all the tantalum electrolytics and tested out of circuit...they are fine.

First thing I did was to disconnect these feeds from the rest of the amp so it's now isolated to just the PC900 module. Same results

Also tried freeze spray on the circuit in case it was a thermal problem...no change

Replaced both Q911 & Q915 with 2N3055's

Not wanting to spend all day on this, I started replacing other transistors in the circuit and check all resistors. I've replaced all transistors except the 2N3638's....those will be here today as I ran out of them

I did replace Q900 and checked the precision resistors in the biasing circuit for it also as these supplies feed that also.

My feeling is it has to be something in common to both supplies to do this.....but I haven't cracked the code yet!

Anyone out there ever had this issue before?

Thanks !


++++++++++++++++++++++++++++++++++++++++++++
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton, CT 06413
(860)-399-1861
fixmyamplifier@aol.com
www.shoreelxandsound.com
++++++++++++++++++++++++++++++++++++++++++++

[Updated on: Wed, 12 November 2014 11:05]

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