PG6 high voltage problem solved

About two weeks ago I started this thread:

http://www.avsforum.com/avs-vb/showt...hreadid=511831


I was convinced something went haywire in the HV power supply. Curt said he had never seen a blown PG6 HV supply. After more troubleshooting I determined I did NOT have a failed HV supply. The problem was that it was never being enabled. Here are the technical details for forum members who do component level troubleshooting.


If everything is working OK you should see these voltages on the HV supply connectors:


PK1=110

PK2=Ground

PK3=+15

PK4=4 or 5mv (ground)


LP1=90mv

LP2=40mv


DF1-5.3

DF2=40mv

DF3=11.5

DF4=4 or 5mv (ground)


There are some timing issues. If LP1 does not go low within 3 or 4 seconds after power-on the HV supply will shut down and DF1 will go low and DF2 will go high to 5.3 volts. LP1 is the HV enabling control line from the deflection board.


The PG6 service manual has an error on the DEF PWB schematic page (3/3), A2 and this confounded me until I understood the circuit better. The table is backwards. It should read HV ON =0.7 and HV OFF=10.


In normal operation the collector of Q5013 is low enabling the HV supply. During startup Q5154 conducts while C5138 is being charged through the internal base resistor of Q5154. With Q5154 conducting Q5013's collector remains high even though horizontal and vertical deflection output is normal which would ordinarily cause Q5013 to conduct once C5138 became charged. Consequently there is no enabling signal to the HV supply.


The root cause of my problem was that C5138, a dumb little 47ufd, 16volt electrolytic leaked just enough current to keep Q5154 conducting. I replaced it and now all is well.


Isn't component level troubleshooting fun?


Regards,