Makvision/Wei-Ya 3125B chassis trouble

yaruni

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Hello, I've been working on one of these monitor chassis for an arcade i volunteer at, I did a full recap and it stopped the old issue of the relay clicking on steady loop. I was told it was left operating for six days and stopped working, now clicking with a short pulse of 15khz noise about every second. I brought it home by itself to troubleshoot further over the week. I measured the low voltages 7 12 25 +V B+, wrote what i read in an image to help keep track of test;points. At some point I hear something happen and the relay started clicking slower, about 2 seconds now an being on slightly longer, and all the voltages that were below half what they were meant to be went back to normal. I don't remember what the voltages on the lower right winding are currently (like +V), if what i wrote was before or after the sudden change while troubleshooting.
After the noise i hear and recheking low voltages on the diode pins, i checked the HOT which i didn't before, and wrote what i read. I haven't gone this in-depth with troubleshooting a chassis and i'm not sure if the HOT is just dead or if there might be some other component leading to the input that could be the problem. I've heard of these boards blowing replacement HOTs instantly too so I'm afraid of simply replacing it and hoping. Since I'm uncertain, does this seem like a blown HOT in the readings i noted? Pin 2 is at 15khz like pin 1 but slightly lower voltage and a more distorted pulse than 1, to clarify. Mainly unsure if the input(?) is meant to be ~2.4Vpp.
If new measurements or pictures are desired I can check them. Also i haven't cheked HV, i don't think i can/should with my standard probes, i know 2 volt Horiz deflection isnt right...

Forgot to add, using this schematic: https://na.suzohapp.com/pdf/service_pdfs/makvision/makvision49-3056-00_schematic.pdf
Thank you!
 

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Update for my board.
Ive been continuing working on this on and off for a while, and ive finally found an issue. I believe the small sound i heard before the relay started clicking slower was this PP cap blowing. Its C86, value says "0.36J 400MPP", body is marked with "F364J W 400MPP1", and im not able to identify exactly what value it is searching online. I couldnt find a bill of materials for this chassis either, and i obviously cant measure it anymore. Is anyone able to make sense out of these codes, happen to know the value, or would be willing to measure it from their board? There dont seem to be any other PP caps sharing its value in this chassis.
Thank you!!
 

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Online research suggests the following:

F364J = 360nF (0.36uF)
400 = 400 Volt
MPP = Metallized Polypropylene Film

Available here: https://www.mouser.com/ProductDetail/667-ECW-F4364HL

You might want to check the lead spacing. The part listed above is 15mm lead spacing, but I'm sure it can be made to work even if that is not an exact match for your application.
 
Oh thank you, i couldnt for the life of me figure it out for some reason (J through me off, like "Joules? What?") I figured the PP in the value meant Polypropylene but there were other values in the schematic that ended in "MPS" and "VPPS" and such, so i wasnt sure.
There are two holes for one end of the cap so pin spacing shouldnt be a problem
 
Does the poly cap read shorted out of circuit?

These had really shitty HOTs in them and the worst caps created, a cap kit is a kust on all Makvision chassis, take it out of circuit and measure it, in mine I replaced them with the FJL6920s. All tri-sync monitors seem to eat HOTs like crazy.

 
Oh yeah i forgot to mention, i did try replacing the HOT (with the same part, new old stock from ebay) and didnt stop the clicking, but i think the cap already blew and i didnt notice it (its obscured partially by the 31khz relay board) and the Vout was higher than the Vin (though my scope was reading 24khz..? idk if the time base was wrong or something isnt working due to the cap, im just going to wait to test it with a new PP cap)
The cap measured 0L in resistor mode and the capacitance mode on my scope didnt change from the low 0.0xx nF that it sits at idly
I read about this chassis being harsh on HOTs and i sent that replacement one to the arcade owner to buy for the monitor, i found out about the better HOT after having bought the originally used part on ebay
A recap was the first thing i did and he told me the monitor ran for a few days and then died again, either the HOT dying or that cap blowing. He said the relay started clicking rapidly and that cap is connected to the switch in the relay so i imagine it was on the fritz, from how much ive looked at the schematic i cant exactly tell what those pp caps and the relay are for and how its triggered exactly
With the incorrect H frequency being measured, despite hearing 15khz from the flyback and B+ being correctly +74V for 15khz, i did check the resolution switching ic (IC5, erroniously called IC6 in the schematic) and its digital outputs to its transistors and the inverted output of the transistors was correct, looking at IC5's truth tables
 
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Came back to the chassis again, i replaced the HOT now (i was going to but it hadnt been ordered yet) and found a 520nF cap (rather than 360nF, hoping its close enough) and still clicking as usual. Im real stumped with this, though i did check B+ and before the 1ohm resistor it goes through, it looks fine as it should, 72 ish volts, but over it its almost dead? I took scope pictures and labeled them. I think the input to the HOT is right but the out also looks dead. They go to pin 2 and 1 of the flyback respectively, could it be a flyback thing?? Should i check the collector with it lifted from its hole on the board?

I still dont exactly understand what the main relay and the one on the 31khz board are even for, i dont know whats exactly wrong going into it thats causing it to shut off on loop.

Also checking frequency of the H drive, it keeps reading 22khz rather than 15khz.. Could that be causing it?, and why would it even be 22k... B+ is supposed to be 110V for 24khz and 72V for 15k, which it is.

Do let me know if theres anything else i should measure.
 

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Oh thank you, i couldnt for the life of me figure it out for some reason (J through me off, like "Joules? What?") I figured the PP in the value meant Polypropylene but there were other values in the schematic that ended in "MPS" and "VPPS" and such, so i wasnt sure.
There are two holes for one end of the cap so pin spacing shouldnt be a problem
J indicates the tolerance of the capacitor value is + or - 5%
 
Came back to the chassis again, i replaced the HOT now (i was going to but it hadnt been ordered yet) and found a 520nF cap (rather than 360nF, hoping its close enough) and still clicking as usual. Im real stumped with this, though i did check B+ and before the 1ohm resistor it goes through, it looks fine as it should, 72 ish volts, but over it its almost dead? I took scope pictures and labeled them. I think the input to the HOT is right but the out also looks dead. They go to pin 2 and 1 of the flyback respectively, could it be a flyback thing?? Should i check the collector with it lifted from its hole on the board?

I still dont exactly understand what the main relay and the one on the 31khz board are even for, i dont know whats exactly wrong going into it thats causing it to shut off on loop.

Also checking frequency of the H drive, it keeps reading 22khz rather than 15khz.. Could that be causing it?, and why would it even be 22k... B+ is supposed to be 110V for 24khz and 72V for 15k, which it is.

Do let me know if theres anything else i should measure.
Since the original cap had a 5% tolerance, and is used for matching the impedance of the horizontal output circuit to the yoke, a 520nF cap is way too far out of spec to be useful.
The horizontal drive frequency is determined by the frequency of the sync input signal to the monitor. The no-signal default may be 15kHz, but I have never checked that.
Don't try to use a standard scope probe to measure the horizontal output signal. That is several hundred volts peak-to-peak and may destroy your probe and the scope. You are lucky that the horizontal output was not functioning.
If you have a flyback/yoke ringer, pull the flyback and check it. Many of these seem to be failing.
 
I wasnt sure what the cap was for with the whole relay circuit, that is good to know, thanks. I was pretty sure it was 15khz by default and i can hear the 15khz ringing the brief moment the relay turns on, so i was confused and that stood out to me. I knew to definitely not use a normal scope and probe for the HV, but was under the impression at least 10x to measure the Hdrive was okay, thank you for letting me know. I wont test further without the proper value cap, i just wanted to get close to what was there to be able to continue measuring and see if the new HOT was helping at all, but i wont continue till that cap is replaced. I dont have any crt specific equipment but considering i am having more opportunity to work on them i will consider investing them now, there are some things with this and other projects i dont think i will be able to diagnose without.
Considering its an arcade machine and not a television i would not be surprised that there really were that many failing parts (buldging electrolytic before the full recap, likely bad original HOT, popped PP cap, maybe the flyback now.)
If you have a flyback/yoke ringer, pull the flyback and check it. Many of these seem to be failing.
Do you know one i would get? Just any i find on ebay? I dont have any connections so i dont have anyone i can ask to borrow equipment.
Thank you!
 
"I knew to definitely not use a normal scope and probe for the HV, but was under the impression at least 10x to measure the Hdrive was okay"
My mistake. I misread your post and thought you were looking at the collector of the HOT.
There were a couple of the Heathkit and other brand yoke/flyback testers on ebay awhile back. If there is an old TV shop anywhere near you, you may be able to find one there. It was also built into the Sencore VA-62. Might also want to check in there is a ham radio club nearby. Lots of old TV techs are also hams, and they may have a lead on one.
Best of luck.
 
Sorry should've specified, i was measuring both sides of the HOT, i mean the anode HV, i'll be more careful.
Thank you for the leads! i'll look around and try searching those brands and models. I definitely want the tools to be able to properly test flybacks and yokes, i have one old TV i can only theorize has a short in the flyback and would like the tools to be able to test the suspected flyback and potential replacements
 
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Sorry should've specified, i was measuring both sides of the HOT, i mean the anode HV, i'll be more careful.
Thank you for the leads! i'll look around and try searching those brands and models. I definitely want the tools to be able to properly test flybacks and yokes, i have one old TV i can only theorize has a short in the flyback and would like the tools to be able to test the suspected flyback and potential replacements
STVDST-01 is what you want, id like to have one myself

 
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