WB Calipers M800

[g1]

Get it back in that working condition with scope hooked up and see if the +66V line has changed. Then you will know if you are dealing with a single problem or multiple issues.
Part of it may be that you are providing a ground connection for the speaker output via the scope.

[Enzo]

you are providing a ground connection for the speaker output via the scope.

That gets my vote.

A simple test, ground your scope at the circuit rather than right at the speaker. If the speaker no longer sounds, the speaker has lost its ground connection somewhere.

[Enzo]

you are providing a ground connection for the speaker output via the scope.

That gets my vote.

A simple test, ground your scope at the circuit rather than right at the speaker. If the speaker no longer sounds, the speaker has lost its ground connection somewhere.

[greenmeanh1]

Did that. I got the same readings as before. -66v on both the orange wires to both top and bottom amp boards but only +44 volts to the blue wires on both. Of course we know the good side of the amp has +-66v to the same top and bottom boards.
I guess the next test i could do is disconnect the 66v lines from the bottom board, the one feeding the ground signal to the speaker and see if the top amp board still works with the scope ground. That would confirm the top amp board is working, i would think, and isolate the problem to the bottom amp board that feeds the ground signal to the speaker. Still have not really ruled out the 66v supply either. Last time i lifted the blue wire off each amp board one at a time the volts only went from 44 to 50 plus volts and not the 66 i had hoped for. This time i will disconnect both and check again.

[bob p]

Enzo keeps at it with the double-posting.

FYI there's a forum error in the php code, where there is a long delay in the processing of a post request, and instead of taking you to the "posted" page, the php script is kicking you back to the "view changes" page. If you're impatient, assume that things did not work, and you click on "submit" again then you'll repost. If you do that quickly, you'll even get the error message that you're only allowed to post once every 30 sec. That should be a dead giveaway that something is wrong.

If you want to avoid the double post thing, you've got to stop clicking on the submit button when you get dumped back to the "view changes" page. One click on the submit button is all it takes, in spite of the fact that the glitch in the board is directing you to the wrong page. Now that you know this, you should be able to avoid double posting.

Works for me.

PS - perhaps this php glitch is related to why the forum keeps going offline every day. It's looking like the forum database needs to be backed up and the LAMP server implementation reinstalled, because the php script errors have been screwing things up for a while now.

[Enzo]

Wait. You said if you connected your scope to the speaker terminals, the amp made sound. All I suggested you do was move the scope ground clip from the speaker to a ground point on the amp circuit. I don;t know from 66v or 44v or blue wires. Is the "ground" side of your speaker not supposed to be at ground potential?

[Enzo]

bob, I am not double clicking anything.

I hit post once, just once, then it spins for a moment or so, yes longer than usual. Then it does one of two things. usually it just puts up a box asking if I want to leave the page, so I click yes. The other common thing it does is to show me the advanced dialog box and tells me I have to wait 28 more seconds to post again. It THINKS I asked to post again, but I did not click any posting buttons. At that point I usually just page back out of it, hoping it will just keep the original post and not put up the duplicate post it thinks I want. In other words it looks like it is asking me to hit post again, but I do not.

I am doing nothing at all different from the way I post all the time on this forum for the last few years. I am not clicking post again in impatience.

Now that you know this, you should be able to avoid double posting.

bob, we can argue about things, and I don;t take it personally. But I resent the condescending tone of this.

This problem has arisen on this board every so often over the years. I don't know what tboy does to clear it, I know I am not the only soul it affects. I don't know why it does not affect others.

[bob p]

No condescending tone intended, but I have the same problem and I've learned to avoid it. I don't know if others have. Rather than hijacking Iv'e started a thread on this.

[g1]

I hit post once, just once, then it spins for a moment or so, yes longer than usual. Then it does one of two things. usually it just puts up a box asking if I want to leave the page, so I click yes.

I think this is what leads to the double post (clicking yes to leave).
When I have clicked 'submit', and get asked if I want to leave the page, I open the 'new posts' page (my bookmark) in a new tab. If I see my post at the top, I know it 'stuck' and just close the tab that is asking me if I want to leave.

[bob p]

hijacker.

[greenmeanh1]

OK, So interesting. Disconnected the lower amp board -66 and the+44 (should be 66v) volt lines and had the scope wired to the speaker as before and the top amp sends signal through to the speaker so i guess that narrows it to the bottom amp board. Power supply still reads +44v after that. Thing is, even though the power supply only has +44 volts it seems to run the top amp just fine. So its gotta be on the lower board im thinking.

[bob p]

Thing is, even though the power supply only has +44 volts it seems to run the top amp just fine. So its gotta be on the lower board im thinking.

44 volts is plenty and will sound just fine ... until you need more than 44 volts.

[g1]

The top amp and bottom amp terminology is very confusing, especially considering there are 2 amps in the unit, 1 good, 1 bad.
Is there any way you can figure out what parts of Doug's schematic you are calling top and bottom amps?
Or draw out an actual schematic for your unit using his as a template?

As far as the power supply issue, check for AC voltage (ripple) on the 44V line and compare it to the working +66V rail.

[greenmeanh1]

So in the M 800 there are four amp boards, two on each side of the amp, or two amp boards on the left and two amp boards on the right. There is a pair of 1216`s and a pair of 2922s on each amp board`. Based on the drawing Doug posted it would appear that they are similar to the amp boards i have in my unit except i have four of them. I haven`t traced out the whole circuit yet for total comparison but they are for sure quite similar.
Now in my particular case there is no common ground for the speaker as in most amps i have tried to work on. The speaker ground output is isolated from the chassis. It appears they pair two amp boards together to make one channel. The output of one of the amp boards ( the bottom one) goes to the ground speaker terminal, the other (top one) to the positive speaker terminal. I guess its like bridging two mono amps but that is a guess. I tested the good side of the amp and the ground is isolated on that side as well. Hope that helps to clear that up. Sorry i really suck at explaining this stuff.

[Enzo]

OK, so the amp is probably two amplifiers per channel and they are bridged. SO an amp for the positive and an amp for the negative. If one of those stops working, the thing will not make sound. But if you ground one of those outputs, then the other working side will power the speaker, though at half level.

In this case then, you should never connect the scope ground to either speaker terminal as it may ground out the output of that amp. It only worked here because that amp side is dead. or so it appears to me. You ground the scope to the ground and view both terminals to see if they have output.