Monitor buzzes, Blows HOT, then F701 [video]

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This thing has been kicking my butt... I've replaced the Caps, Flyback, HOT, transistor, and a couple burnt resistors.

Here's what it's doing now:

 
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I have the exact same issue as you. HOT keeps blowing then F701 goes.

I've replaced the Flyback and all the caps on this monitor. Before F702 would blow after some arcing in the neck and picture would fluctuate on the screen. Replaced the flyback (it was cracked) with a new one from security. Now the HOT and F701 blows.
 
yup. most common problem of all time with this monitor, yet it comes up and gets posted
here over 100 to 1000 times and still no definitive answer on the one and only solution to
solve this... even the flowchart is unhelpful here. will the fix for this never be told???
 
yup. most common problem of all time with this monitor, yet it comes up and gets posted
here over 100 to 1000 times and still no definitive answer on the one and only solution to
solve this... even the flowchart is unhelpful here. will the fix for this never be told???

I'll check my magic 8ball... "outlook good"


For what it's worth, I've lifted a leg of nearly every component that I could test while following the traces.

Everything that tested within spec was circled in green;
the components that had failed with the first flyback are circled with red;
the items that failed AFTER I installed the new flyback are circled in orange;
and the Caps (which were summarily replaced) are circled blue.
It is also NOT the tube, as I have tested them both with my solitary working chassis.

PLEASE correct me if you see something else to check, but the only thing I can see left
to test is I601, I701, and the new flyback (though the other flyback that I purchased at
the same time is working well on the other chassis).

I601 = 1X0065CE = NTE Equivalent NTE1550 = Hitachi HA11235 = Panasonic ECG1550
I701 = 1X0137CE = NTE Equivalent NTE1751


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OK so, my SCR is good, my IC701 and my replacement flyback is good as well (tested in my other good chassis). I'm stumped on where to go next. All the capacitors in the HV section checkout. Anyone else out there have this issue?
 
OK so, my SCR is good, my IC701 and my replacement flyback is good as well (tested in my other good chassis). I'm stumped on where to go next. All the capacitors in the HV section checkout. Anyone else out there have this issue?


I was reading up on CRTs and came across this: www.repairfaq.org/sam/deflfaq.htm#dstwk
"Blowing up the HOT after minutes is due to bad base drive, or (much more rare) due to LOT core saturation. Blowing up a HOT immediately is due to too high collector pulse."

It seems like the issue is somewhere in-between. Not really immediate, but on the early side of "within minutes".

I started testing all the components on the Drive side, and found that all of mine were within spec ( -| |- caps were not shorted). That leads me to believe that the issue is I601.

Attached an updated schematic with what tests good on mine.
 

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I socketed and replaced I601, but it did not resolve the issue.
I'm moving on to check components that connect via the sync amp.
D501, D502, D503
Q501, Q502
Etc.
 

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I've gone through more of the board, testing what I can. It's still "in progress" but I've got to step away for a few days and thought I'd post an update for anyone who's following this repair.

See attached pic showing how far along the testing is. Testing -||- caps has just been to verify that they are not shorted (I don't have access to an ESR meter).
 

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It's still "in progress" but I've got to step away for a few days and thought I'd post an update for anyone who's following this repair.

I'm definitely following your updates on this repair. I'm sure others are too!

Thanks for keeping us all posted! :)
 
I've replaced IC601 and 701. No change. Same issue. I have an ESR meter now and will test every single poly cap and will report back...

Edit:

Could T602 be the culript?
 
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T602 has been on my list to find a replacement for. They don't normally go bad, but it is possible. I don't think you can test it without current flow (correct me if I'm wrong).
 
Are you monitoring the B+???

to high will cause the HV P~P voltage to go to high.

if the meter means you were checking HV then its to high!

Its should be around 25KV.

Driver transformer should not be the issue here.

The flyback were an issue in the tv models and a common problem

but if your replacement is as good and the same part number.

I would confirm the B+ is not running to high at startup?
 
Thanks for looking at this with us ohmerone! I've seen some of your posts on other monitor threads.

The meter on the video is measuring B+, and it peaked around 90ish before the HOT failed.

Something seems to be oscillating, causing a humm/buzz. I was initially thinking it would be a diode/zener. I haven't found a bad diode yet, but I don't have a way to test the zener breakdown voltages, either.

Are you monitoring the B+???

to high will cause the HV P~P voltage to go to high.

if the meter means you were checking HV then its to high!

Its should be around 25KV.

Driver transformer should not be the issue here.

The flyback were an issue in the tv models and a common problem

but if your replacement is as good and the same part number.

I would confirm the B+ is not running to high at startup?
 
is the HOT insulated?

I'm still new to repairing arcade machines; however, I'm going to ask anyway.. Is the components, of the High Output Transistor i.e., the base, emitter, and collector totally insulated? Do you have a Mica insulator in place? You would have to have a new HOT reinstalled, before any power was applied and with a multimeter, in order to confirm, or deny that your HOT is not shorting out to ground.

I've noticed some HOTs have an additional insulator on the emitter that if not reinstalled leaves an opportunity for a sort to ground.

>is the HOT shorting to ground?

>is there a mica insulator installed?

>if the original design intent was to have a insulator on the emitter then, is there one installed?
>>if the HOT is not shorting to ground then a insulator on the emitter won't be an issue.

As an inexperienced newcomer to arcade repair, the above listed questions really stand out to me.

That's my 2 cents!

Good luck, most sincerely, John
 
This thing has been kicking my butt... I've replaced the Caps, Flyback, HOT, transistor, and a couple burnt resistors.

Here's what it's doing now:


I have the exact same issue as you. HOT keeps blowing then F701 goes.

I've replaced the Flyback and all the caps on this monitor. Before F702 would blow after some arcing in the neck and picture would fluctuate on the screen. Replaced the flyback (it was cracked) with a new one from security. Now the HOT and F701 blows.

Thanks for looking at this with us ohmerone! I've seen some of your posts on other monitor threads.

The meter on the video is measuring B+, and it peaked around 90ish before the HOT failed.

Something seems to be oscillating, causing a humm/buzz. I was initially thinking it would be a diode/zener. I haven't found a bad diode yet, but I don't have a way to test the zener breakdown voltages, either.


B+ Maybe working Ok.

I would suspect the HVsafety caps or bad connection, you might reflow

pins and trace.

The arcing is the reason for the short of the hot.

You would need to replace the parts again and confirm the B+ supply

is not low to ground, each time your fuse blows.

then try it again.

the bussing you might disconnect the deguasser coil during trouble shooting.

If the B+ is stable and you are getting excessive high voltage cause arcing

everywhere including SG on neck board.

If I have the symptom right?

I would suspect the caps just replace them..
 
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