WOPL 700B Has more output on the left channel.

[Mohawk]

Hello To everyone,

I Have spent lots of time reading here and I hope someone can point me in the right direction
I acquired a WOPL 700B from a colleague that has an issue of the left channel having more output
than the right side !
I have switched inputs around, switched speakers,switched pre amps and it seems to be within the 700
As far as the guts are concerned, Full WOPL, Full Complimentary output, Light board assembly & Don's relay set up.
The "volume" or what ever you want to call them have been bypassed and the Insulated RCA's go directly to the
driver board via coax.
I have used Room EQ software to input a range of frequencies, if I get the left channel VU up to sit a about half way ,40hz
the right channel VU is maybe @ 1/4 and noticeably less output.
At this point I am getting the impression the VU's are correct in indicating the right channel is muted or the left is boosted
I say possible boosted because I get the impression the louder or left channel is distorted slightly.
This is an issue that has developed, apparently. I'm assuming it was originally ok after the initial build.......
I haven't got to any internal troubleshooting as of yet just confirmed the complaint !
Can anyone think of a reason for this kind of issue ?

Thank you !

 

[WOPL Sniffer]

Call the builder. Some of us don't take a bite of a sandwich somebody else made.

 

[Mohawk]

LOL... In this case we can replace "colleague " with "the builder" ....... One in the same.....

 

[laatsch55]

What revision driver board, what revision backplanes?

 

[Mohawk]

The Backplane boards are Rev "B" and the driver board is Rev "E"

 

[laatsch55]

Have you checked plus and minus 15 volts on the 15 volt test points?

 

[Mohawk]

At this point I have not , Before I open it up I was hoping for some greater power to chime in and say " the only thing that would cause that would
be "_________________________________________" ! ..... Insert magic fix to the left ....... Your thoughts ?

 

[laatsch55]

Not gonna happen like that. Have you checked all rail fuses?

 

[laatsch55]

Is this the amp edroom was involved with?

 

[Gepetto]

At this point I have not , Before I open it up I was hoping for some greater power to chime in and say " the only thing that would cause that would
be "_________________________________________" ! ..... Insert magic fix to the left ....... Your thoughts ?

Insert "that something is broke"

 

[laatsch55]

Check "quick test steps" in the WOPL archives section to isolate the control board from the backplanes and test the bias circuit. Then you'll know where to start. Then we can help from there..

 

[wattsabundant]

Ok, If I'm reading this right , you tested at 40 Hz. If there is a difference in volume level, and both channels have the same input, the likely problem is a failed capacitor in the feedback loop. On the Rev. E board it's C5. Note that the problem channel is assumed to be the one with lower output and the good channel has normal output. C5 determines low frequency response. An open cap results decreasing output as frequency decreases.

To confirm use a "Y" adaptor to feed both channels the same signal. If there is a significant difference in level, at low frequencies, the problem is likely around C5. R11, R13 also affect this.

 

[Mohawk]

Thanks for the feedback ! Yes test at 40hz but that was just a point of reference , the right channel is lower up and down all the test tones.
Again , thanks for the help... I'm gonna make notes here of what everyone has to say and get it opened up !
* The difference in output is not limited to any specific frequency.....

 

[Gepetto]

We could provide a lot of guesses but that is all they would be. You have to get into it for us to provide any real help.

 

[Mohawk]

I'm not sure I follow your last post , I didn't buy this amp at all.... And Yes of course I listened to it....
I mentioned all that in my initial post..... I'm trying to help him out as I see the diagnostics are beyond
his strengths. I don't believe I have implied that he has dumped this on me, Not at all.......
I want to further my understanding and get into it as a favour to a good friend.......
I get the impression you would have me just leave it on his doorstep and split.....

 

[mlucitt]

Easiest check to make is the DC power fuses (this was mentioned above). The next easiest thing to do is to check the test points on the Control Board; set your meter for DC voltage and check the test points in the middle of the board: red and black should be +15V, blue and black should be -15V (this was mentioned above) be careful with your test leads, a slip around the heat sinks can be fatal to the control board. Connect and disconnect with power off (and 15 minutes of capacitor discharge time) if you are not really confident here, or a bit shaky, like some of us.
You can swap the OPAMPs from Left channel to Right channel, another easy check.
Then, with the amp on and warmed up and no inputs connected, measure the Left and Right output binding posts - white to black and then red to black for DC voltage, there should be less than 50mV. Finally, set your meter to measure DC voltage again and measure between the Left channel (yellow) test point on the upper edge of the board and the Left speaker output binding post (white), you should measure about .350V. Then repeat the test for the Right channel (yellow) test point and the Right speaker output binding post (red), you should see about .350V again.
Do this and get back to us.

 

[wattsabundant]

Mohawk, I don't mean to bust your chops, but your first post required careful reading, and for me, several times.

Resist the temptation to start making changes as that may compound the problem. Check the connections to the relay board per the attached page. Pay particular attention to the speaker ground wires.

To point the blame on the relay board or rule it out, do the following:

• Connect a Y cable to both inputs to be sure they get the same signal.
• Set your signal generator to get a few volts AC at terminals 1&2 and 3&4 on the relay board. If you don't have a signal generator download one to your phone.
• The voltage should be the same at both connections.
• If it is the same then go to the binding posts and measure them there.
• You should see the same thing as you measured on the terminal block.

 

[FredR]

you did say you "Acquired" it from a colleague which would "Imply" buying it from him and yeah, you may be better off leaving it on the door step and running. He built it and should be able to work on it better than somebody who has never seen the inside of one.

Perry meant to add a .

 

[WOPL Sniffer]

yep, sorry

 

[Mohawk]

The blind leading the blind ? What's with that ? Apparently I have offended Mr Sniffer in some way ???
If you have no time for my questions and dont care to help then leave it at that.....
I'm only asking for some help and guidance in tracking down a problem......

I DO APPRECIATE any help from any of the other phoenix community members ....
To back this up a bit , the 700 was built maybe ,2 years ago and was just fine until
recently....
The plan was to ask lots of questions, get some ideas, take notes and then open it up
with a plan in mind......

M