G07 driving me nuts !

[Level42]

OK....I have this G07 on my Centipede. And it's driving me crazy. When I got it, Fuse F901 was blown. I replaced it, turned on the monitor and .....nothing happened. I checked the AC coming in. To my amazement, it lowered to about 8 VAC !!!

Then I replaced C511 which is reported to be notorious to let the monitor act as if it's dead. When I fired it up, I could see some nice fireworks going on in the bottom of the HVT.

So....I ordered a capkit and a HVT from Bob Roberts. Installed everything except for 3 minor caps, which I received the wrong value for.

I measured the HOT in diode check on my Fluke. There is no short between the dome and the metal frame, showing a little below 0,5V. I do measure short between the legs, but that is normal AFAIK.
 
I've checked the fuses, they are fine. Checked the fusable resistors, fine.

Now, when I turn the monitor on, I still have the 110VAC going down to almost 0 !!!! Of course the monitor doesn't start, no static sound, no neck-glow...

I was wondering if this could be a problem of the transformer. However, as soon as I disconnect the monitor it goes back to ....110VAC.......

Anyone has an idea ? Grantspain, Ken ?

[grantspain]

i have no experience with the g07 chassis as they were not used in the u.k during my years there.
for your ac to be pulled to 0v there would have to be one hell of a power drain on the transformer and its nothing i have seen before-i have seen transformers go faulty when in operation causing this but only on audio equipment,never on a monitor
in my opinion it may be wise to swap out the transformer first as i just can't imagine anything on a chassis causing this problem without some kind of extreme physical sign i.e fireworks or extreme heat

[qrz]

inspect/check ur ac cables from isolation xformer to pcb .    had this symptom a few times in tv servicing.
was always unexpected ... i.e , ok one minute, DOA the next.   
normally in a loose mains connection , there will be
evidence of arcing around the fault  . but, NOT always .. 

qrz

[Level42]

Grantspain: exactly what you say were my thoughts.....you'd expect at least a fuse to blow   

I could try connecting it to the Galaxian transformer. That one is doing nothing in that cab now, because I replaced the monitor with a (230VAC) TV, and the TL-fixture with a new one (230VAC) as well...
I already planned on using this as my test-isolation transformer, but I never got to removing it from the cab....now there's a good reason

qrz: I've measured the connector coming from the cabs harness. There's a sturdy, constant 110VAC coming from it. I've also checked the corresponing connector on the monitor with continyity check. There are really no breaks from that to the PCB. I even redid the solderings to be sure. I still have continuity further up the PCB traces that directly connect to those leads in the connector. So that is almost impossible....

To be continued.....