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PL 400, PL700 Power meters, How to test?

laatsch55

laatsch55

Super Member
I have restored several 400's and a 700B, Im fairly new at this but wth generous advice from Echowars on Pioneer and d3imlay on Phase Linear the restorations went well.
I have neglected to ask this question since I haven't had any that didn't work. Can they be tested?
Thanks, Lee
 
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Should be calibration procedures in the service manuals.
 
Avionic, I reviewed the manuals after your post and there is no mention of meter failures or calibration procedures.
 
That suxs..Nice thing about Yamaha-they have meter cal procedures.:scratch2:
 
Should go the usual way - put the output on a 8ohm dummy load, get in 1kHz sinus, check on the scope, when it starts to clip or slightly below, adjust the trimpot of the VU to 0db.

LIX
 
Make sure your load is capable of handling the power.KEY..
 
No trimpot on the meters. I would like to know if they can be checked out of circuit and what kind of signal to use. AC obviously, but do i need a current limiter?
 
Phase 400? not series II?? Lame meters. Not worth cal'ing. If you pursue it, cal at clipping for "0dB VU". as said before. and make sure you've got the big loads so they don't roast. Although the accuracy on the meters is poor enough that you can run to clipping, monitoring with a scope, and set the meters for "0dB VU" with an open load. Use a 400 Hz tone, in case the meter circuit is frequency sensitive.
 
I do have a pair of 450 watt 8 ohm dummy loads. No problem there. Yes series 1. I do agree they are lame, I'll fire up the scope and signal generato and see what i can come up with, Thanks guys.
 
The Phase Linear meters read O db at about 30volts output and are buried at continuous sine wave full power testing. This accounts for the response time of the mechanical movement and the fact that music is not a continuous sine wave. Calibration would require removing the front bezel and adjusting the movement. Considering that the only replacement meters available are from scrapped out units, I don't think it' worth the chance of damaging one by opening it up. If one meter reads high the series resistor on the board could be increased or replaced with a pot.
 
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