I got this amp in for repair.
When powering it up it draws excessive current. SO i unplugged the output board from the power supply board and amp idles fine.
I checked the outputs all seem fine. Wondering where i need to check next.
When powering it up it draws excessive current. SO i unplugged the output board from the power supply board and amp idles fine.
I checked the outputs all seem fine. Wondering where i need to check next.
That amp is so old even I would need a internal pic to tell you where and how to roll on this one. Plus Tim is most likely remembering the PQ amps that I remember which used UPC1270AH or UPC1225 driver chips for each channels set of outputs. I recently did a channel repair on a Alpine using these and everywhere wanted $12.00 each for a $2.25 part. I am guessing due to their age and lessening availability. Glad i found my private NOS stock pile from yester-year...
By chance have you ohmed the outputs yet, or does this amp use large STK modules. ADS did use these way back a very long time ago on their Power plate series as I recall.
Plus I do recall some of these PQ amps being 12 volt powered and not using a switching power supply at all and these were all bridged discrete device channels as I recall also.
Your asking a lot mike with out posting a snap or two of the inside to jog a old timers memory😱🙂 Give us a hint if you could of what it looks like please ? I have been in all of them but the I am drawing a blank with your model number duh ...thx...C😱
Clamp the transistors to the heatsink, connect your meter to one of the emitter resistors and power up the amp. Find the emitter resistor that has more than ~0.000v DC across it. That will show you the channel that's passing too much current.
Perry and Tim are correct Mike. The UPC1270 is your channel driver, and they fail and usually so does a output or two. Should not be too complicated for a tech like yourself ..thx for the pic, it all came home right away...🙂
THanks Perry,1moreamp,and Tsmith for the help ill order the parts and replace the defective ones.
I also found the UPC1270H for $2.24 each
I also found the UPC1270H for $2.24 each
I found them at a place called matchaknob i order parts from there time tio time and have had no problem with the parts at all.
Match-a-knob Electronics Wholesale Distributer
Match-a-knob Electronics Wholesale Distributer
I order the parts for this amp.
I clamped everything down and put a current limiter in line.
I measured the voltage across the emitter resistors . I dont get anything over 0 volts on any of them.
Wondering is it still probably 1 of the upc1270h's??
I clamped everything down and put a current limiter in line.
I measured the voltage across the emitter resistors . I dont get anything over 0 volts on any of them.
Wondering is it still probably 1 of the upc1270h's??
If all read 0.000v DC, it could be...
rectifiers
transformer
power supply transistors
power supply drive circuit fault
rectifiers
transformer
power supply transistors
power supply drive circuit fault
Everything in the power supply section tests fine.
What do i set my scope at to look at the gate's on this amp??
What do i set my scope at to look at the gate's on this amp??
Looking at the gate signal isn't as easy as it is in a supply that uses FETs. Pull the rectifiers. Does it power up?
Twist the transformer. Does the current draw change?
Twist the transformer. Does the current draw change?
I pulled the rectifiers and seems to power up and not draw current.
Since there is no power light on this amp.
If i leave the rectifiers in the amp that when it draws excessive current
Since there is no power light on this amp.
If i leave the rectifiers in the amp that when it draws excessive current
Are the rectifiers shorted or leaky?
Measure the AC voltage on the outer legs of the rectifiers. Do you read any voltage?
Measure the AC voltage on the outer legs of the rectifiers. Do you read any voltage?
If that's on diode-check and they only read in one direction, they seem to be OK.
When I wrote:
Measure the AC voltage on the outer legs of the rectifiers. Do you read any voltage?
I meant to measure the AC voltage on the rectifier pads (rectifiers out of the circuit).
When I wrote:
Measure the AC voltage on the outer legs of the rectifiers. Do you read any voltage?
I meant to measure the AC voltage on the rectifier pads (rectifiers out of the circuit).