WG 4600 main board problem simplified

Doughbroz

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Starting a new thread on this, the other one got too confusing. Have the same identical problem with two 4600 main chassis boards, one of which has been totally recapped with no improvement, both have new HOT, good solder connections, etc. Problem is, at startup no HV, volts on big resistor start at 90 and 70, iso transformer is rattling. After a couple of minutes voltage drops to 50 and 10 and rattling gets louder. Leave it on long enough, HOT blows but fuse never does. All three daughter cards, flyback, and neck board are from a working monitor, hooked up to a game that works fine with a third main chassis board. So, the problem has to be in the main chassis boards. Tested every diode I can see, solder is good, wiring is good, etc, etc. Any ideas what is left to try? I am at the point where I would gladly pay to have these things fixed because they are really pissing me off. And does anyone know where I can find a 4600 flow chart. Thanks
 
Why was the horizontal output transistor replaced? Did you install a mica insulator between the transistor and metal frame? Did you put on silicone grease too? Is it connected properly?
 
No Riptor, I haven't tried the two bad ones on a different tube. The tube I'm using works fine with the third chassis, and the recapped bad chassis came off this same tube. Ken, I replaced one HOT that was definitely bad and the other just because I presumed it was too. The HOTs only fit the frame holes one way, I cleaned off the old and installed new insulators with the proper heat compound. White wire goes to the upper pin of the HOT on all three chassis. I'm curious about something else though. I have several of each of the daughter cards. One of the power cards, the ones with the big ceramic resistor, is marked MV-3 Sound/Power. This one has a transistor at the top of the component board with its tab screwed to the metal frame of the daughter card. The rest are all MV-13 Power and all have an outline for that transistor, but it was never installed on any of them. One of the middle cards has the plug that goes to the neck board facing toward the tube, the rest are all vertical. I assume they are all interchangeable since they all work with the good chassis. Finally, one of the bad chassis has a small transformer, an electrolytic cap, and two other caps in the corner next to the tube, behind the filter cap. The others never had these parts. This business of the rattling iso just baffles me, especially since the rattle gets louder when the voltage drops, and it does the exact same thing with both of the bad chassis. That seems to say something is pulling too much power, but the 3A fast blow fuse doesn't blow unless I leave the power on for several minutes after the voltage drop, and I suspect that's because the HOT goes out first. I'm so curious to know the solution that I would gladly pay to have them fixed just to know what the hell the problem is with both of them. Any ideas where I could send them? And I'm still looking for a 4600 flow chart, I have several others, but missed that one. Thanks for the replies.
 
Thats fine, as long as you verified the tube is good.
There were a few different revisions of the 4600 chassis. I noticed that a few weeks ago when I repaired two back to back. I noticed the little transformer on one but not the other.
 
WG 4600 main board problem simplified *SOLVED*

Just in case anyone was curious, I finally figured it out. My mistake was ASSuming the flyback I pulled off the shelf for testing was good. Either it wasn't or it poofed at startup. That had me chasing shadows for hours on end afterward. Finally, Occam's Razor came to mind and I swapped the fly I knew for certain was good. Bottom line, three of the five flybacks I had to work with were shot in one way or another. But I did learn a few things about the 4600 along the way.
1. With a bad fly, you can blow 5 or 6 HOTs and never blow a fuse. (yes, it's the right fuse)
2. You can be getting high voltage to the tube with a fly that is defective in some other way.
3. A bad fly can result in either high or low voltage at the large resistor.
4. I should change my flow chart. The part that says "This [flyback failure] is very rare in this monitor" should read "With a 30 year old monitor, flyback failure is damned likely".
5. The 4600 is a very good monitor. I still have 2 or 3 that have been working pretty regularly for 30 years and still look very good.
6. Whoever designed the clip under the anode cap and the horizontal width coil mount should be boiled in oil.

Happy troubleshooting
 
6. Whoever designed the clip under the anode cap and the horizontal width coil mount should be boiled in oil.

Even if we have to dig him (them) up to do it!!!! :goodnight:

I second your praise of the overall design though. I would love to see some of these LCD monitors in 30 years. :15:

ken
 
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