M3129DB1-72 Clicking/Cycling

[CrAzYj]

So I picked up an M3129DB1-72 from a guy on FB Marketplace who was discarding it for the Golden Tee cab it came in. He was not aware of anything wrong with it at the time. It came in pristine physical condition and was quite clean. Closer inspection later revealed a burnt resistor on the 31k H. freq board at R17. Other than that it also appeared to have mostly original caps. It did not come with the power cable so I ordered a bunch of stuff from suzo which of course all ended up being the wrong fit. I had some time on my ends so I set out to recap the entire chassis and also to replace that resistor. Ordered decent 105C Nichicon caps from digikey and went to town.

Having the schematic available (attached) seemed pretty clutch until I got into my decapping groove and realized after the fact that my board layout did not exactly match the schematic (rookie move). The schematic and chassis model numbers did indeed match, however I later discovered that my board is revision 6 and I presume this is the reason for the discrepancy. There had been 5 caps on the board that I removed that were unaccounted for on the schematic, and I had failed to write down exactly what their paramaters were. They are C22, C38, C50, C78a, and possibly C90a (might have been empty to begin with). Through pictures I had taken, I figured out what C38 was and replaced it with same. Also of note, C59 had a 220uF 35V cap on it, but schematic showed a 100uF-50V. I replaced with a 100uF-50V per the schematic. C15 also had a 100uF-16V on it, but schematic showed a 100uF-25V. I replaced that with a 100uF-25V per the schematic. All other caps were replaced with what was removed, which also matched the schematic. The only other caveat here is that I failed to physically size many of the caps exactly which resulted in a few tight fits or open spaces here and there. The major offender was C22, which went from a fairly large and uniquely blue "MIEC" cap to a small nichicon about 1/10th the size when replaced (uF and V were identical). All this being said, I feel like I did a fairly good job in soldering with 63/37 Kester 44 and checked capacitance and as many traces as I could for continuity when done.

Having ordered and finally recieved the correct JST VH connectors and crimps, I fixed up a decent power cord, plugged it in and let her rip. It sounded like the chassis was cycling about every 1-2 seconds with a clicking/whirring sound. I could hear static on the screen, and also see some of the finer wires bow in towards the monitor during each pulse. I was not oriented to view the screen or neck immediately upon plugin and did not see any neck or monitor glow afterwards. I also did not smell/hear any burning and did not see any sparks anywhere. The monitor just kept going like this for about 10 or so minutes until I unplugged it. I later tried to plug in an old laptop through the RGB VGA port to see if the cycling had been because it was looking for but couldnt find a signal. I'm not even sure I was sending the correct 31khz signal. My laptop did recognize that it was an analog monitor however, but beyond that the monitors behavior did not change, the cycling continued.

Further research into the issue has led me to consider the HOT or a nearby diode as a prime suspect. I plan on removing the HOT (I've actually read conflicting things on if it is necessary to remove it or not to test) and testing it with my DMM and also testing adjacent diodes. Or could this all just be self inflicted for not replacing a couple "non-existant" caps.

Any thoughts, expertise, or direction are much appreciated. Thank you!

Also, does anyone have the specs for the ghost caps listed above? (C22, C38, C50, C78a, C90a) Recommend replacing?

 

[rewrite]

The major offender was C22, which went from a fairly large and uniquely blue "MIEC" cap to a small nichicon about 1/10th the size when replaced (uF and V were identical).

This cap is definitely wrong then. You need something low ESR (which will be much much larger in size). You're fairly safe just sorting digikey by uF/V/width/height and trying to match the last two as close as possible.

If you're hearing clicking/whirring then you killed a transistor. And yes you should remove transistors to test them. The circuit can affect your readings.


No need to guess that it's the HOT, you can narrow down which transistor blew with good old redneck ingenuity. Get a paper towel tube, put one end over your ear while it's running, and then put it over each transistor on the board in turn until you have figured out which one is clicking, then you know which one has blown. Order another and replace it.

But don't turn it on again until you've sorted the caps (including the big one) as well or you're going to blow new transistors again and again and cost yourself money and time.

Or could this all just be self inflicted for not replacing a couple "non-existant" caps.

Well it certainly didn't help. It shouldn't have been turned on with parts missing.

You're also going to want to find out what the B+ should be set to and get that squared away after the rest before throwing an image at it.

 

[CrAzYj]

Thank you so much for your expertise and the confidence boost!

You need something low ESR

Ahh, this makes so much sense.

If you're hearing clicking/whirring then you killed a transistor.

Is it possible to dump more than one? Or is it kind of protective once one goes?

No need to guess that it's the HOT, you can narrow down which transistor blew with good old redneck ingenuity. Get a paper towel tube, put one end over your ear while it's running, and then put it over each transistor on the board in turn until you have figured out which one is clicking, then you know which one has blown. Order another and replace it.

Love it!

It shouldn't have been turned on with parts missing.

That decision was based on the original design (assuming the schematic is an earlier revision) omitting them intially (at least it seems more plausible then someone coming along later and populating them for whatever reason right?)

Any idea on what specs those caps are?

Also, what are your thoughts on:

C59 had a 220uF 35V cap on it, but schematic showed a 100uF-50V. I replaced with a 100uF-50V per the schematic.

How would you proceed?

Thank you again!

 

[rewrite]

Is it possible to dump more than one? Or is it kind of protective once one goes?

You can kill more if you keep turning it on after removing others depending on how the circuits are setup (learned this the hard way).

I wouldn't have consulted the schematic at all since it's not for the same revision. I'd put the 220/35 back since that was on there to begin with, and we don't know what rev 6 was supposed to have but we can assume it was working with what was on there at one point.

I never throw out caps from decapping until the project is over, that way I can look at them later to narrow down if there's a cap I either overlooked in ordering or wasn't on the list, or whatever have you. So if you did that, you should have those four kicking around and it'd be a good start. If not, it may be a bit of a mystery for a bit here.

I'm not super familiar with makvisions, so hopefully someone else will pipe up about particulars.