g1176 vu pegging in gr mode

So. It's all together, voltages look to be right. I figured I'd calibrate the vu in GR mode. I turn the switch to GR. Meter pegs. I twist the trimpot this way and that. Meter pegs. I'm not sure what to try next.


A little more: It's a Modutec VU. In its former life(in a tape duplication setup) this VU had a resistor & a cap attached between the + & - terminals. Might I need to reinstall this?

Thanks
Tom

Tom,

You need to verify that your meter is an actual VU-meter, and that it's sensitivity is 0VU=+4dB over 775mV with a 3K6 series resistor.

If it's not, you'll need to do some thinking to make it work..

Jakob E.

Well, I spoke too soon about the voltages being good. I'm seeing 30.1 volts off the 7824, which is fine, but at the junction of cr9/10 and R86(referring to the schematic on Jakob's site) I see -16 volts, then -8 or so at the junction of R86 & R85, & then 0V on the other side of R85. I'v checked all my caps & diodes, & they're all facing the right way, no solder blobs or bridges.
Short of taking everything off the board & starting again, I'm not quite sure what to do. Any thoughts on where to start the diagnosis?

Thanks
Tom

> 0V on the other side of R85.

DEAD-zero? Not 0.6V? Not even 0.010V?

R85 should only be feeding C24, CR6, R52, R56, R57, IC1, R82, R45

Check, re-check, and triple-check those resistor values. 10K and 10 look the same when you are tired or frustrated. Have someone else look it over, especially some ignorant person who has to work out the colors with a chart.

If you were wise enough to socket IC1, take it out (disconnect the GR meter first). Hey, be sure you got IC1 in the right way round: I once put an 8088 CPU in backward, and it didn't work. Sucked the power supply WAY down too.

If still no error found, lift one end of each of those parts. Save CR6 for last. Re-check every few parts and see if the voltage has popped up-- if so, one of the parts you lifted was the problem. Figure out which and why. If you get all those parts lifted and still no joy, you have a short that you have not found. Bad PCB, mounting screw, solder-blob.....

As I was going through rechecking resistor values, I noticed that R56 was making contact with the case of my Lundahl output xformer. I bent R56 a bit away from the Lundahl, powered up, & found my -10 volts.

So there it is. Ridiculously simple, but it had me pulling my hair out.

Thanks
Tom

Glad you got that one fixed... :thumb:

Jakob E.

I also had a pegged VU meter in GR mode.

If your using a Mnats board and you connect your interconnect 18 to the wrong 18 hole on the mainboard your VU will peg. There are 2 hole 18's and you must select the appropriate hole for the trimpot located next to it. See Mnats wiring guide for more help. I wish I would have read that before I interconnected!

Will