Checking...
Here are the results of the Predriver voltage checks, all on Left Channel with Dim Bulb in place:
Connection ............................ To Ground ..................... To Output Post
Q6 B .......................................... +0.653V ............................ +0.710V
Q6 C .......................................... +84.7V .............................. +84.6V
Q6 E .......................................... +0.145V ............................ +0.221V
Q9 B ......................................... -1.197V ............................. -1.104V
Q9 C ......................................... -84.7V ............................... -84.6V
Q9 E ......................................... -0.665V ............................. -0.592V
For fun, I tested the SOA Protection transistors:
Connection ............................ To Ground ..................... To Output Post
Q7 E .......................................... -0.055V .............................. +0.015
Q7 B .......................................... +0.606V ............................ +0.674V
Q7 C .......................................... -0.048V ............................. +0.22V
Q8 E ......................................... -0.062V ............................. +0.008V
Q8 B ......................................... -0.269V ............................. -0.197V
Q8 C ......................................... -1.115V ............................. -1.025V
While looking at the PL14_PL20 Rev E BOM and Schematic together, I saw where I might have made some errors. Could you help me verify the correct values for the Control Board Left Channel for Fully Complimentary units:
On the Schematic .................. Currently on the Control Board and listed in the BOM
R20L, R26L 13K ....................... 56K
R21L 22.1 ohm ........................ 56 ohm
R36 56 ohm ............................. 1 ohm
I think these values, as built on the board, might change the bias voltage felt at the Q6 backplane transistor? I have verified that the parts to be left off the fully comp Control Board are omitted.
Finally, I traced the source of the 3-3.1V Emitter to Collector voltage across the bias transistor. I have the full rail voltage at R31L (10K) and on the other side it drops to 22.11V. This voltage is sensed on one side of R20L (3.32K) and then drops to .986V on the other side to feed the Collector of Bias transistor Q6.
This seems low, is it possible that the Q6 Bias Collector voltage is being pulled down by something common to both channels such as a shorted capacitor or a missing ground on the backplanes?
On the Emitter side of Bias transistor Q6, the voltage is negative (-1.168) is this normal?
Still searching...
Mark