Dead GO7-CBO

hazmat1234

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Hello all, after years of working great the monitor in my Centipede decided to die. Blank screen and no neck glow. I have installed numerous cap kits over the years and this one has me completely stumped... Needing HELP... This is what I know.

Pulled the chassis out and started replacing all the caps from the kit including a new flyback. During the process I discovered that the fuse 901 was blown. I thought "ahhh there was my problem" New capkit, new flyback, new HOT and new fuse, problem fixed." NOT!! After installing the chassis back into the machine, still dead. After numerous times in and out checking things, solder connections, traces, cap orientation, etc. Still finding nothing that jumps out. This is what I do know:

B+ out 125v (when first plugged in) Drops to 120v after 5 min of warm up.
166v into the resistor (same cold or warmed up)
166v on the case of the voltage Reg. Ground to chassis positive lead to button case
123v on the case of the HOT. Ground to chassis positive lead to button case
Don't hear the monitor cracking or warming up when plugging in.
No heater voltage when I take the leads and check H9 -H10 However if I take the black lead to chassis and red lead to either H9 or H10 it shows 54v.(strange, am I missing something here??)

After hours of frustration, numerous installs/removals of the chassis I went to bed last night. Turned off the room lights, machine was still on and in the darkened room, low and behold Centipede appeared on the screen ever so faintly. I checked brightness and it was all the way up.

Lost on which way to go now??

Thanks for your help. Haz
 
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things i have seen personally are the neck pcb with cold solder joints/crack traces and there are wires on the posts of the neck pcb and i have had them break off or barely holding on with a strand or two.
 
I should document this better (on paper, I certainly try to do it in my threads), but I think I've seen this happen for a number of different reasons personally.

Bad flyback-still got the 120vdc but when I changed the flyback (again, even though it was new) it fixed the problem. (from the run of flybacks a few years back from BR).

Bad solder connection-lifted pad or traces on C511 I think. I almost always use the legs of C511 now and jumper them to the nearest point even if the chassis is rock-solid

minor cracks coming from the flyback. Test all of the points coming from the flyback. Push on the chassis a little as you test to see if the connection becomes intermittent. (again can't remember if I had a blank screen and good B+ with this or not)
 
Thanks gentlemen... I will check both of those. Tron, you bring up a good point on the flyback being bad. (that thought was in the back on my mind) This was a new flyback that I had with the capkit that has been sitting on my shelf that I got from BR several years ago... Now wondering if it came from the same batch you mentioned???? Ordering a new one to try. Will let you know when the new one is in and installed...

Haz
 
Also check resistors R516 (150k @ half watt) and R517 (180k @ half watt). If either of them go bad you will have a dim picture. If both go bad, you will have a very very dim picture. I have noticed lately more and more of those resistors are failing due to old age and heat.

I have also seen instances of the tube socket on the neckboard developing bad solder joints. I've had to repair some neckboards where a customer performed a capkit himself and lifted the foil on electrolytic capacitor C107 which can affect brightness.
 
Thanks gentlemen... I will check both of those. Tron, you bring up a good point on the flyback being bad. (that thought was in the back on my mind) This was a new flyback that I had with the capkit that has been sitting on my shelf that I got from BR several years ago... Now wondering if it came from the same batch you mentioned???? Ordering a new one to try. Will let you know when the new one is in and installed...

Haz

if you need a flyback i have plenty in stock along with the 150K and 180K resistors Ken spoke of.
 
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