G08 woes

mcandrewsoun

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Im trying to trouble shoot one of these..
1. Looks like the BIAS on one of the driver circuits is off... In one of the FAQs theres a voltage table.. It lists the Collector voltages for Q600 and Q700 to be 34-35 volts. Im getting one at 42 and the other at 60. Ive replace almost EVERY transistor and checked every resistor.

2. Using my scope. I can verify the inputs to the custom IC are good pins (11 &14). However the output that feeds the bases of Q600 and Q700 is garbage.

3. The schematic shows a resistor from Q604/Q704 to the negative rail.. R738/R638..I dont see it anywhere on the board.

Has anyone seen this?


Andrew
 
Update...Adjusting the H&V centering pots affects that Collector DC value..and a dirty pot will give you 59.5 volts. I was able to adjust those and get a 35 volts. However, Im still seeing garbage on the outputs of the IC. I checked every resistor. Pin 8 of IC 600 is supposed to be 0v, but its reading 7.2v. Its not connected to anything, which leads me to believe something in the IC is shorted or ground is floating in the chip. I think at this point my only recourse is to find another G08 deflection board.

Andrew
 
Hey-

The outputs from IC600- is there ANY semblance of a signal coming out?
Have you tried lifting the bases of Q600,700 to make sure they're not loading anything down?

Are the +/- 9.1V supplies OK? Can you vary the H and V centering from +9 to -9?

I don't think I've ever had a problem with this chip, but it sounds like you've narrowed it down pretty good.

I may have one from a parts chassis, but I'd have to figure out WHERE.

Kerry
 
I'll yank the Q600/Q700 and see what it does..Yes there is signal, it kinda resembles the pic, but not really.. the +-9v looks correct. I need to isolate that part of the circuit..The IC doesnt use any feedback from the output transistors does it? Is there a pinout of IC 600 anywhere?

Thanks,

Andrew
 
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