Toshiba D29CR55 blowing HOTs

[MonMotha]

I've got a Toshiba D29CR55 (common in DDR and similar Konami "BEMANI" games made in Japan and AKA PB6643 by PCB IDs) that's eating HOTs.  Original failure was from a dying power switch that caused a slow "droop" of the AC input voltage.  The monitor did not shut down as this happened and exhibited a slow horizontal collapse before eventually biting it with a shorted HOT.

Replaced the HOT and tested for about 15m with no input signal (displayed good raster) with no issue.  Reinstalled in the game, and it ran for ~15m before dying again with another shorted HOT.  Tested all the electrolytic caps and other caps in the horizontal area and found none bad.  Damper diode accompanying the HOT tests fine, but was replaced as well the first time around just in case.  Also tested all the other power transistors, and they're reasonable.  Flyback tests the same as another unit.  Yoke seems fine and tests the same as another unit, as well.

Any other ideas before I blow another $5 "fuse" (aka HOT)?

I don't have a manual or schematic (but would very much like a copy if anyone has one), unfortunately.  Ridiculously detailed pics at http://quasared.net/D29CR55/ (TXT file at the top has a description of the pictures, and the ZIP file is all the images + TXT file together as one big download).

[grantspain]

i would test it without signal for 24 hours first
this chassis i have not seen,is it a auto switching multisync?

[MonMotha]

It's a dual frequency but it does not auto switch.  There's a 4 conductor plug near the center of the board to set it to 15K or 24K.

[lilshawn]

i'm no expert, but has this diode on the HOT heatsink been replaced? is this after or before replacing... the symbols on the board don't quite match the symbols printed on the component...

http://quasared.net/D29CR55/IMG_4523.JPG

[MonMotha]

The diode was replaced along with the HOT the first time around.  It's the exact same part as the OEM part and with all the same leadforming, etc..  The symbols look like the match up to me...

The removed diode did appear to test good, but I didn't exactly feel like swapping it back in.  Now that the second HOT has blown, I tested the diode, and it again seems to still be good.

[lilshawn]

The symbols look like the match up to me...

now that iv'e looked at it longer maybe your right... a schematic would definitely help.

[Gray_Area]

No signal is fine. That board is not. Have you tried another source?

[MonMotha]

The game the monitor was installed it wasn't the game the monitor got pulled from.  The machine the monitor originally came from has been happily running for months with a replacement (identical model) monitor.

I don't know much about the setup the thing was in when it blew the second time.  Somebody else had an urgent need, so I shipped him off the freshly repaired boardset for him to use.  It's entirely possible his yoke is screwed up or something, though that has been checked (and the signal source is fine - it works on other monitors including ones of this very model).

I can just run the thing again, but I have a feeling it'll just blow another HOT.  It's just annoying because they're a somewhat unusual Japanese part that run like $4-5 each plus MCM's outrageous shipping.

[MonMotha]

OK, I finally got around to looking at these things.

Note that pics of the boardset still up at http://quasared.net/D29CR55/
There's no schematic for this sucker that I know of anywhere, but believe me I'd like one!


Here's the story:

1) I have one of these.  It died due to known causes (massive AC input droop).  Shorted HOT found.  Replaced along with accompanying damper diode.  Powered up, ran, tested w/ no signal for about 15m no problems.

2) Friend has one of these, too.  His died as shown in this pic:
http://quasared.net/IMG_0515.JPG

3) I sent him my (repaired/somewhat tested as above) chassis.  He installed on his tube/yoke.  It ran for "a couple minutes" then died.  He claims it "collapsed" (direction not specified) then nothing.

4) I have both boards in my possession now.  Found both with a shorted HOT.  Replaced.  Also replaced accompanying damper diode.  Checked all caps in Hout area and all electrolytics.  They're good.  Checked all major power electronic devices including pin amp, vert ic, vsize amps.  They're at least not shorted, and the BE junction behaves reasonably (gain not tested).

5) BOTH boards now exhibit the same behavior as follows when testing on my (believed good) tube/yoke:

When powered up, there's a somewhat loud buzzing noise.  I'm not talking "Woah, what's that?  I can't hear you over it!", but it's not something you'd expect to hear in typical operation.  I can't quite tell where it's coming from, but it's either the power supply or the HOut area; I think the latter.  The degauss coil is not hooked up.

The power supply (SMPS) is running.  I measure 121VDC at what seems to be a reasonable place on the supply output.

There's no HV, and I don't get the 15k squeal (I can hear it fine on working monitors).  The HOT does not seem to sustain damage (which seems to be the normal failure on these things).  Nothing seems to get hot.  I don't see any heater glow, but these particular tubes are difficult to see into normally.

Any ideas?  I do have several more of these things (that work).  I can get one some time and start taking measurements off it if I have to.

Given the similar failures, I'm inclined to suspect a signal, tube, or yoke issue at my friend's end.  I'd like to get both of these working on my (believed good) tube/yoke with no signal then move on from there to identify other issues.

[MonMotha]

Current suspect is the MOSFET on the other side of the pulse transformer used to drive the HOT.  Need to order a replacement then replace and test.

[MonMotha]

Well, that's not it.  Any other ideas?  I've got activity from the sync processor to the MOSFET gate.  There's activity at the drain of the FET (it's a low side switch with the source grounded).  I get nothing on the other side of the pulse transformer at the HOT base.

[lilshawn]

argh.... this would be so much simpler with a schematic.... i hate when they hold out on stuff like that.

maybe you can e-mail someone at Toshiba and get lucky

i had to do that with a monitor in a house of the dead. i had to actually call sega and get them to fax me a schematic.

[boardjunkie]

The horiz retrace tuning cap could be leaky. That is right after the horiz output in the circuit going to gnd. If that gets leaky and starts drawing current, the HOT will get taken out. It'll be a big HV job, rated 1200v or more. Other than that, the flyback could be the fault. This has been known to happen on Wells 7000 chassis.

[MonMotha]

OK, I got one of these to start up again (the one that is mine and died from the bad power switch).  Ran it for a couple minutes but haven't done a long run on it yet still trying to figure out if the failures between the two monitors are related.

I'm not entirely sure what all was wrong with the one that's working again.  HOT was definitely blown, but it didn't come up immediately after replacement.  While checking all the other components, I essentially took my iron to every major solder joint on the darned thing, so it may have also had a cracked solder or something, maybe from all the handling it's undergone.

Still no luck on the other one.  I know about where the failure is, but I can't find an actual bad component.  Doing this without a schematic is a pain.