RetroHacker
Well-known member
Well, I've been round and round with this monitor. I'm really getting sick of looking at it...
You may remember my previous thread about the HV shutdown - that one got derailed with another user's problem, so I'm starting a new thread about this monitor.
Previously, I could get a raster on the screen, but I couldn't dial the B+ up over 95v, any higher and the monitor went into shutdown. I just received the new IC 601 from Bob Roberts, and I installed it. Now, the problem is even worse - it goes into shutdown immediately, regardless of how the B+ pot is set - just a quick burst of HV, then shutdown.
Some history on this monitor:
As found, it was totally dead. Quickly checking with my meter revealed that the 300ma fuse was not blown. I recapped it. Still dead. Notice that the large 180ohm 20W resistor gets REALLY hot - and it was cracked down the middle. Further investigations revealed that the HOT was shorted, and closer inspection of the 300ma fuse revealed why it had not blown - some joker had replaced it with a 7A fuse at some point. (I never even knew that they made 7A fuses that small). Carefully inspect flyback and see some evidence of seepage along the seam at the top. Replace the HOT and the flyback with new parts from ArcadeCup, and replace the 180ohm resistor with a 25w one scavenged from another chassis. After that, I can get a raster, but adjusting the B+ results in shutdown. Replace flakey B+ pot. Find that it shuts down at right around 95v. Replace the current limiting transistor as IC601 was still on order. No change. Replace IC601 - now monitor goes immediately into shutdown regardless of B+ pot setting (quick flash of HV). Replace C606 for the heck of it - no change.
So... I've gone over the board looking carefully for shorts, cracked traces or cold joints, and I can't find anything. All the caps are installed the right direction, etc. I've already changed all the parts I've ever seen fail on these monitors. Now what?
-Ian
You may remember my previous thread about the HV shutdown - that one got derailed with another user's problem, so I'm starting a new thread about this monitor.
Previously, I could get a raster on the screen, but I couldn't dial the B+ up over 95v, any higher and the monitor went into shutdown. I just received the new IC 601 from Bob Roberts, and I installed it. Now, the problem is even worse - it goes into shutdown immediately, regardless of how the B+ pot is set - just a quick burst of HV, then shutdown.
Some history on this monitor:
As found, it was totally dead. Quickly checking with my meter revealed that the 300ma fuse was not blown. I recapped it. Still dead. Notice that the large 180ohm 20W resistor gets REALLY hot - and it was cracked down the middle. Further investigations revealed that the HOT was shorted, and closer inspection of the 300ma fuse revealed why it had not blown - some joker had replaced it with a 7A fuse at some point. (I never even knew that they made 7A fuses that small). Carefully inspect flyback and see some evidence of seepage along the seam at the top. Replace the HOT and the flyback with new parts from ArcadeCup, and replace the 180ohm resistor with a 25w one scavenged from another chassis. After that, I can get a raster, but adjusting the B+ results in shutdown. Replace flakey B+ pot. Find that it shuts down at right around 95v. Replace the current limiting transistor as IC601 was still on order. No change. Replace IC601 - now monitor goes immediately into shutdown regardless of B+ pot setting (quick flash of HV). Replace C606 for the heck of it - no change.
So... I've gone over the board looking carefully for shorts, cracked traces or cold joints, and I can't find anything. All the caps are installed the right direction, etc. I've already changed all the parts I've ever seen fail on these monitors. Now what?
-Ian