Phase Linear D-500 Low-Z switch not working.

[joec999]

Hi to all,

I am helping a Phase Linear owner up in Canada troubleshoot his Phase D-500 via email. The unit will not switch into Low-Z via the front panel switch.


Earlier, I had the owner take some voltage measurements at pins 11 &12 of the meter board which should be the power source and return path for the Hi-Z/Low-Z relay coil. He was getting about 40 VDC on both sides. I had him remove the wires from the plug at pins 11 & 12 and give me a resistance measurement which showed about 7.9k Ohms (coil resistance). Being that the source is about 40 VDC, I suspected that the coil resistance was too high so I had him remove all three relays and check the part numbers. They were all HG2-DC110V’s and all coils measured about the same at 7.9k Ohms. I’m thinking that the Hi-Z/Low-Z relay may have been replaced at some point with the wrong part. Considering the supply voltage, I suspect that the Hi/Low-Z relay should have no greater than a 48 VDC coil. I would like to know if my suspicion is correct.


Any input appreciated,

Thanks,

Joe

 

[oldphaser]

The Phase Linear Dual 500 service manual states the following on page 29:

6-5.1 Unit will not drop into Lo-Z:
a.) Replace SCR504, D503.
b.) Check wiring to coil of relay K2.

6-5.2 Unit will not stay in Hi-Z mode with an 8 ohm load:
a.) Verify that R505 is 1.5K
b.) Check Q504

NOTE: SCR504 is a 2SC1038, D503 is a Green LED, and Q504 is a TIS97.

Ed