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Main => Monitor/Video Forum => Topic started by: cruppel on May 16, 2020, 04:27:03 pm

Title: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: cruppel on May 16, 2020, 04:27:03 pm

Hi all!  Im here humbly requesting some help with my Makvision 29" (27") tri-mode arcade monitor.  I had everything running perfectly yesterday until I tried to move my arcade cabinet back into its corner while it was on (yes, I know...).  As I moved the cabinet, I saw a flash from the fuse area and the monitor turned off.  I checked and saw that the fuse was blown so I ordered new fuses that matched (F4AL250V).  I just tried the new fuse and it blew immediately.  I know my way around a circuit board, but not a CRT.  Can anyone please help direct my next debug steps?  I'd really appreciate it!

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: grantspain on May 17, 2020, 05:58:28 am

if you moved the cab then the chassis has either moved from its home and is shorting or some wiring is shorting

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: cruppel on May 18, 2020, 10:58:12 am

Ok so I got the monitor out of my cabinet.  I dont see any obvious damage except for the fuse.  After poking around with my meter, it looks like AC/N and A/C are shorted.  Any tips for me?

One more note, FG is also shorted to the chassis.  Not sure if this is how it is supposed to be.

Heres the schematic: https://na.suzohapp.com/pdf/service_pdfs/M3129DF-TS.pdf

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: grantspain on May 18, 2020, 12:24:06 pm

i know this chassis very well, i doubt the ac is shorted as such
first thing to check is the bridge rectifier and FET in the power supply
you can also check the PTC for a short

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: cruppel on May 18, 2020, 12:45:07 pm

Thanks for the advice, grantspain.  Just to be sure, you're talking about DB1 and Q1 in the schematics, correct?  From what I've googled, it seems like the HOT may be the issue (which I think is Q1).  Also... apologies, but what is the PTC?

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: grantspain on May 18, 2020, 01:09:17 pm

yes DB1 and Q1
q36 is the HOT, when that fails chassis goes into ocp
PTC is the component for the degauss, its marked on the schem
immediately blowing a fuse is a dead short

disconnect ac power input connector when you read the bridge

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: cruppel on May 18, 2020, 04:45:06 pm

MOSFET and all 4 bridge diodes are passing the diode check (0.45V ~).  I'm not sure how to test PTCs, but when I checked the three pins they all showed as shorted.  This was all done in circuit with the ac cord detached.

Edit: ooh my Q36 base to emitter is not showing voltage drop.  That must be it.  When the HOT goes, are their other things I should check or just replace that? 
Edit #2:  Hmm now Im reading that its difficult to test HOTs with a digital MM....

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: grantspain on May 18, 2020, 05:45:10 pm

hot won't blow fuse on this chassis, only a dead short on the primary psu will do that- anything after primary will put the chassis into ocp

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: cruppel on May 19, 2020, 02:28:51 pm

Ahh I see.

How do I test the PTC?  Any other thoughts on how I should progress?  I really appreciate your help.

Title: Re: Makvision 29" (27") tri-mode arcade monitor - Fuse blows on replacement
Post by: grantspain on May 19, 2020, 05:07:54 pm

prove ptc by desoldering from circuit