Monitor buzzes, Blows HOT, then F701 [video]

I finally got back to this & replaced C702/703/704. The buzzing was quieter, but it blew the HOT & fuse again. It did take longer to happen, though.

Continuing along those lines, I picked up replacements for C701. Schematics say that it's a Ceramic 0.1uF 50V. I picked up a 200V also. The cap on the board looks more like a Mylar. Which should I be putting in? (top=mylar, bottom=ceramic)

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I fixed my issue with pin 6 of the flyback to ground, the solder connections on the T1,2,3 connector had excess wire and was jumping pin 1 to 3.

I'm back where I started, monitor buzzes a bit, then the hot goes poof again. Have a look at the updated picture of what I have replaced /tested.

Green is tested good, Purple is replaced, Blue has been verified between both new and old parts.

https://forums.arcade-museum.com/attachment.php?attachmentid=346196&stc=1&d=1522385856
 

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mylar vs ceramic is always mylar being the best when comparing same values. mylar is usually 5% tolerance and ceramic is common to be 10-20% tolerance. i would always use the mylar over ceramic.
 
Just curious if you have made any progress on this TSB?

I had a totally dead XM-1801 that had a blown F702 fuse. So I replaced the fuse, capped it, and put on a new flyback and B+ pot.

When I fired it up, it immediately blew the F701 fuse. (F702 remained intact)

I haven't replace the HOT yet but I assume this should be my next obvious step.
 
Just curious if you have made any progress on this TSB?

I had a totally dead XM-1801 that had a blown F702 fuse. So I replaced the fuse, capped it, and put on a new flyback and B+ pot.

When I fired it up, it immediately blew the F701 fuse. (F702 remained intact)

I haven't replace the HOT yet but I assume this should be my next obvious step.

I think I've got it narrowed down.

What I think happened:
Flyback went bad, putting stress on C701/702/703/704
Replacing flyback causes failing C701/702/703/704 to stress Pulse Amp circuit.
Pulse Amp circuit goes out of spec causing P~P voltage to be too high on HOT Collector.
H.O.T. fails
F701 blows.

Someone will correct me if I've got that wrong, but...

I believe that once C701/702/703/704 have been replaced, C708/709/(maybe 710) also need to be replaced, and maybe D707, ZD701, & SCR701. (H.O.T. & F701 also)

I don't have those parts on hand, though, so I'm on hold until I place another digikey or mouser order.
 
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I think I've got it narrowed down.

What I think happened:
Flyback went bad, putting stress on C701/702/702/704
Replacing flyback causes failing C701/702/702/704 to stress Pulse Amp circuit.
Pulse Amp circuit goes out of spec causing P~P voltage to be too high on HOT Collector.
H.O.T. fails
F701 blows.

Someone will correct me if I've got that wrong, but...

I believe that once C701/702/702/704 have been replaced, C708/709/(maybe 710) also need to be replaced, and maybe D707, ZD701, & SCR701. (H.O.T. & F701 also)

I don't have those parts on hand, though, so I'm on hold until I place another digikey or mouser order.

Holy moly! That's some serious troubleshooting. I'm honestly impressed that you have stuck with it this long.

I've had to disassemble mine a couple of times already and it's already starting to wear on me. I really hope you can figure out your problem. Any info that gets published out there about this monitor, the better. There are not a lot of repair logs out there about this monitor.

Last night, I de-soldered the HOT from my chassis and found it was shorted. (Side note: WOW getting this HOT out was NOT easy. As you know, huge globs of solder holding down screws of all things. What a pita to remove)

Anyway, I reinstalled a brand-new HOT and I'm running out to grab some replacement fuses today. Maybe tonight I'll find out if it was just the HOT causing my problems....or something else.

I wish there was a way to test a HOT while in-circuit. This chassis is just such a pain to take apart.
 
Holy moly! That's some serious troubleshooting. I'm honestly impressed that you have stuck with it this long.

I've had to disassemble mine a couple of times already and it's already starting to wear on me. I really hope you can figure out your problem. Any info that gets published out there about this monitor, the better. There are not a lot of repair logs out there about this monitor.

Last night, I de-soldered the HOT from my chassis and found it was shorted. (Side note: WOW getting this HOT out was NOT easy. As you know, huge globs of solder holding down screws of all things. What a pita to remove)

Anyway, I reinstalled a brand-new HOT and I'm running out to grab some replacement fuses today. Maybe tonight I'll find out if it was just the HOT causing my problems....or something else.

I wish there was a way to test a HOT while in-circuit. This chassis is just such a pain to take apart.

Let me know how it goes. I've thought about using small bolts to install the HOT, instead of the screw. Then I wouldn't have to solder those buggers in.

Bummer to hear about the necked tube (same monitor, or a different one?).

.
 
Let me know how it goes. I've thought about using small bolts to install the HOT, instead of the screw. Then I wouldn't have to solder those buggers in.

Bummer to hear about the necked tube (same monitor, or a different one?).

.

So I dropped a new fuse in this chassis and fired it up. The good news is that neither fuse blew...so that means I must have fixed the HOT issue.

However, this is when I found out the tube attached to this chassis was bad. (necked)

So I moved this chassis over to the other red tent tube (which I think is working). However, this time I fire up the chassis and don't get any picture. I also don't get any neck glow. (neither fuse blows)

The only clue I have to go off of right now is that the B+ is stuck at about 70vdc. And twisting the new b+ pot has no change up or down.

I'm probably going to direct my attention to I701 but I'm quickly becoming a fish out of water here. :(
 
Nice work. I admire your persistence!

I hope you get this worked out.

I think I've got it narrowed down.

What I think happened:
Flyback went bad, putting stress on C701/702/702/704
Replacing flyback causes failing C701/702/702/704 to stress Pulse Amp circuit.
Pulse Amp circuit goes out of spec causing P~P voltage to be too high on HOT Collector.
H.O.T. fails
F701 blows.

Someone will correct me if I've got that wrong, but...

I believe that once C701/702/702/704 have been replaced, C708/709/(maybe 710) also need to be replaced, and maybe D707, ZD701, & SCR701. (H.O.T. & F701 also)

I don't have those parts on hand, though, so I'm on hold until I place another digikey or mouser order.
 
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