Crown XLS1000 Amplifier Low input channel

[scott2000]

I have a Crown XLS1000  with a low input channel...
Anyway, I traced the issue to the display board/input board and specifically to U500B....At pin 6, it's all good, then it all but disappears at pin 7....... very low signal........ (for comparison  .06v at pin 7 u500 and .4v at pin 7 u600....)

There's some deal about the Y-input in this area too which I'm not sure if it may have anything to do with my issue............this is the section I'm in on the board and the picture is attached....

ANALOG INPUTS:
The input to the APM can accept 1.4Vrms input and drive the resultant APM output
to a level that drives the amplifier to full rated power into 8G. The differential analog
inputs come from J700 which connects to the MAIN board of the amplifier. The
input XLR, ¼”, and RCA connectors tie directly to this point on the MAIN board.
The following will be for CH2, with CH1 being identical except for the analog Y
input switch (U601).
U600-A,B form a differential to single ended gain stage with a gain of -3.54dB. See
Gain Block Diagrams below. The output of U600B drives the input of U601, which
is a unity gain amplifier that selects either the ‘A’ input (CH2) or ‘B’ input (CH1)
dependent upon the INPUT_Y drive from the microprocessor (Q600 to U601-1).
U601 provides the Input Y audio routing. The output of U601 drives front panel pot
R610 that feeds single ended amplifier section U600-C. This stage has a maximum
gain of +13.86dB as shown.
For CH2, the output of U601-5,6 drives a comparator, U700-B, that lights the front
panel SPI LED when the input signal is >-40dBu. R600/601 provides the DC bias

////////////
Should I just be suspect of U500 or could there be an issue somewhere else.....????

Checked a ton of the surrounding components and they seem good..../////

I appreciate any direction......The replacement board is $120

Thanks!

 

[JohnRoberts]

I have a Crown XLS1000 that I sold on the bay a while back and it was returned to me with a low input channel....I never realized it had a problem but, the guy said he was trying it with y-input low pass which I'd never tried..... Come to think about it, I ran it in mono or stereo no problem so, I think something went goofy after the sale from a mistake. But I hadn't used it in a while before I sold it so who knows......

Anyway, I traced the issue to the display board/input board and specifically to U500B....At pin 6, it's all good, then it all but disappears at pin 7....... very low signal........ (for comparison  .06v at pin 7 u500 and .4v at pin 7 u600....)

Pin 6 is a virtual earth so should have no signal at that node... pin 7 is the actual output.

Symptom suggests bad op amp or missing PS rail, while if other op amps in package work we can assume PS is good.

JR

There's some deal about the Y-input in this area too which I'm not sure if it may have anything to do with my issue............this is the section I'm in on the board and the picture is attached....

ANALOG INPUTS:
The input to the APM can accept 1.4Vrms input and drive the resultant APM output
to a level that drives the amplifier to full rated power into 8G. The differential analog
inputs come from J700 which connects to the MAIN board of the amplifier. The
input XLR, ¼”, and RCA connectors tie directly to this point on the MAIN board.
The following will be for CH2, with CH1 being identical except for the analog Y
input switch (U601).
U600-A,B form a differential to single ended gain stage with a gain of -3.54dB. See
Gain Block Diagrams below. The output of U600B drives the input of U601, which
is a unity gain amplifier that selects either the ‘A’ input (CH2) or ‘B’ input (CH1)
dependent upon the INPUT_Y drive from the microprocessor (Q600 to U601-1).
U601 provides the Input Y audio routing. The output of U601 drives front panel pot
R610 that feeds single ended amplifier section U600-C. This stage has a maximum
gain of +13.86dB as shown.
For CH2, the output of U601-5,6 drives a comparator, U700-B, that lights the front
panel SPI LED when the input signal is >-40dBu. R600/601 provides the DC bias

////////////
Should I just be suspect of U500 or could there be an issue somewhere else.....????

Checked a ton of the surrounding components and they seem good..../////

I appreciate any direction......The replacement board is $120 and the amp isn't even worth that any more.....It is to me but so is my house......

Thanks!

 

[abbey road d enfer]

Anyway, I traced the issue to the display board/input board and specifically to U500B....At pin 6, it's all good, then it all but disappears at pin 7....... very low signal........

It shouldn't be good at pin 6, since, as JR mentioned, it's a virtual earth, but it should be good at pin 7. You may replace this IC with a 5532 or 4559, even a TL072 would make it as a temporary fix.

 

[abbey road d enfer]

Thanks!

guess I could dead bug one on to see.....

I don't have any soics except some tl064......

Would those work as replacements??????

TL064 is a quad; I believe 33709 is a dual...

 

[abbey road d enfer]

Ok I see the confusion....

The 33079 is a quad... I posted the 33078 sheet that has all versions......

I thought you were saying I could bypass half of it with the 5532......

Being a quad, any issues/dangers putting the 064  in place????  I know it's not bipolar but does it matter here?????

I happen to have some soic versions here.......

Thanks!

I don't think there's any serious issue with replacing with a TL064, however the TL06x is not very fast and quite noisy, so you may not want to keep it. That would be a corroboration that the 33709 is actually faulty, though, I think you'd want to wait for a better opamp.