Matsushita TM-202G Horizontal Sync Repair Log

LyonsArcade

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This has been documented before, but I thought I'd make a separate post because I couldn't find all the info in the same place and just had to fix one of these.

If you have a Matsushita TM-202G that the Horizontal Hold won't lock in, here's why:

1. you may have the sync on the wrong pin, this monitor only takes Negative Composite sync, and only on pin 5. Pin 6 isn't hooked up to anything. Many Atari games have two video connectors to accommodate this monitor.

2. Once you know the sync is correct, if the monitor's B+ is off, the vertical will sync and the monitor may work but the Horizontal will drift out of sync if you can get it to sync at all. At this point doing a capkit is the next step. There are 4 Bi-Polar caps on the monitor.

3. After a capkit, you may still figure out that the B+ is nonadjustable (stuck around 144v instead of 123v) because resistor R811 is burnt up. You can easily measure the B+ on either end of fuse F002 (right near the edge of the board). If the B+ will not adjust, check R811, but you have to remove it to test it. It should be a 47k 1% resistor (half watt).... if the resistor has drifted anything more than about 1k the 500ohm B+ adjustment pot it's tied to will not work. 46k, or 48k, will not work. Mine for instance was measuring 68K, way out of spec.

Once you get the B+ right and the capkit done, the horizontal hold will literally snap into place when you adjust it like it does on most monitors. Hope this helps people save this monitor, because they have great pictures if they're working.
 
Very good info. Gives a little more hope for Matsushita owners. I'm looking forward to diving into mine. The tubes I have bumped into are almost always minty. So hard to give up.

Thanks
Blake
 
To further add to this thread, since some of us are so stubborn that we will try everything to save this very unpopular monitor... I, for one, am an advocate for practicing on this monitor. If you can rise to the challenge of repairing one, then most other monitor jobs can be done with confidence. The documentation on this site for repair of this chassis is very comprehensive and helpful.

4. The horizontal adjustment pot is at location r505 - near center on the main pcb... right under the yoke... right in the static zone... use a long plastic screwdriver to adjust.

5. Use deoxit spray in a can on all the pots before reapplying power and adjusting. Found the horizontal adjustment pot was stuck it place and was the main culprit in not getting a signal after doing a capkit and B+ filter cap. After freeing it up, the signal which looked like a sync issue because EVERYTHING was so maladjusted, the picture dialed right in. Then it took only 17 days to get the colors right...j/k

I am currently repairing a tm-202g that worked slightly when I got it. The chassis is in very good condition with little to no discoloration on the boards from heat. I can tell that it has been serviced before and badly at that. I applied a cap kit with a new filter cap. B+ adjustment works when the brightness is turned midway. When it is turned up all the way it pops the 1.5amp slo-blo I use on my isolation transformer. It will pop about five minutes after powering on. If the brightness is turned down it will run forever without popping the fuse. Following the instructions in the manual it seems that the most I can get is 98vdc at the test point (D91) and the pot seems to do nothing in either direction. 811 was replaced during the cap kit installation. Going to replace the brightness pot and Q802 (2sc1941 transistor) to see if this makes any difference.
 
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Monitor now works fine... not quite. The service switch renders a pink horizontal line across the entire center of the screen and the B+ still acts squirrelly. I used a test pattern generator built into a scrap board to align the monitor. However, the colors look great, the picture is good and stable and a 16 hour test later it still was working perfectly without any problems. Now it can sit, for eternity, in the stack of monitors I have amassed. I do not have the confidence in this monitor to actually put it into full time service because there were obvious signs of someone else's work prior to mine and some shoddy jumper work on the back of the board. I repaired all those locations on the board and applied hot glue to some locations out of necessity. But it is a great test monitor for my purposes.
 
3. After a capkit, you may still figure out that the B+ is nonadjustable (stuck around 144v instead of 123v) because resistor R811 is burnt up. You can easily measure the B+ on either end of fuse F002 (right near the edge of the board). If the B+ will not adjust, check R811, but you have to remove it to test it. It should be a 47k 1% resistor (half watt).... if the resistor has drifted anything more than about 1k the 500ohm B+ adjustment pot it's tied to will not work. 46k, or 48k, will not work. Mine for instance was measuring 68K, way out of spec.

I've got another TM-202G on my workbench. A visual inspection revealed nothing of concern, and it appeared this chassis had been recently recapped, so I proceeded to fire it up for testing. I saw the same symptoms you described here (no image on tube, cannot adjust B+ below 144v/145v. So I pulled R811 and it measured 55k ohms out of circuit, so I installed a new one. No change. Any further suggestions?
 
I've got another TM-202G on my workbench. A visual inspection revealed nothing of concern, and it appeared this chassis had been recently recapped, so I proceeded to fire it up for testing. I saw the same symptoms you described here (no image on tube, cannot adjust B+ below 144v/145v. So I pulled R811 and it measured 55k ohms out of circuit, so I installed a new one. No change. Any further suggestions?
If the resistor is in spec (I assume you checked it), did you check the adjustment pot?
 
If the resistor is in spec (I assume you checked it), did you check the adjustment pot?

Yes, it's fine. I've pulled & tested the four resistors in that circuit:

R811 expected: 47k ohms 1% actual: 47.02k ✅

R812 adjustment pot expected: 500 ohms actual: 5.4-477.9/3.3-476.4 ✅

R813 expected: 5.3k ohms 1% actual: 5.326k ✅

R815 expected: 270 ohms 5% actual: 265.5 ✅
 
It seems like R814 can't be accurately measured in circuit, but it looks fine out of circuit…

R814 expected: 220k ohms 5% actual: 219.1k ✅
 
Ok, I made some progress. I replaced the 4 small caps (3x 1uF & a 3.3uF BP) missed by the person who previously installed a cap kit, replaced the voltage regulator, and reflowed a TON of stuff… and now I'm getting an image, but the B+ is quite low and I can't adjust it, plus I've got very little brightness control from both the BRIGHT and SCREEN pots.

I know this model draws more current than most monitors, so I tried it with two different isolation transformers. With the standard 120V iso from APAR I'm only getting 100v on the B+, and with the iso from a Pac-Man cabinet I'm getting about 113v. Obviously both of these are far less than the expected 123v, and turning the B+ adjustment pot has no effect.

I'm not sure what to try next. Maybe swap in a different OEM flyback?

Tagging @mecha because I know he's very concerned about this, and apologies to @LyonsArcade for necro-hijacking his thread.
 
Ok, I made some progress. I replaced the 4 small caps (3x 1uF & a 3.3uF BP) missed by the person who previously installed a cap kit, replaced the voltage regulator, and reflowed a TON of stuff… and now I'm getting an image, but the B+ is quite low and I can't adjust it, plus I've got very little brightness control from both the BRIGHT and SCREEN pots.

I know this model draws more current than most monitors, so I tried it with two different isolation transformers. With the standard 120V iso from APAR I'm only getting 100v on the B+, and with the iso from a Pac-Man cabinet I'm getting about 113v. Obviously both of these are far less than the expected 123v, and turning the B+ adjustment pot has no effect.

I'm not sure what to try next. Maybe swap in a different OEM flyback?

Tagging @mecha because I know he's very concerned about this, and apologies to @LyonsArcade for necro-hijacking his thread.
your filter cap may actually be bad
 
your filter cap may actually be bad

I had to pull the original metal can filter cap to remove/replace the voltage regulator, and I was looking to replace the filter cap too, but I didn't have the correct value on hand. I'll try that -- thanks!
 
Tried that. Didn't help. Got any other bright ideas??

we didn't factor in an ancient edict known as "user error"

you're effectively like the guy that doesn't understand what 'blooming' is on the Golden Axe title screen
 
I've pulled all of the resistors & diodes in the B+ regulator circuit and confirmed they're all in spec. What else should I try?
 
Well, I fixed it. And I take back everything negative I've ever said about @mecha even though his advice didn't make any difference here…

sigh The isolation transformers were the final problem. I've noticed in the past that Matsushita monitors draw a lot of current — far more than a typical 19" color raster. My benchtop isolation transformer struggled to power my first one years ago, which is why I would use the Irish Kangaroo cabinet to power it while fixing it. However, I seem to recall it working fine with my benchtop iso when I was testing it for @security0001 a few months back. While working on this other Matsushita, I recalled that issue, so I had been using the iso in my Pac-Man upright to power it on the workbench… but even that was apparently not putting out enough oomph, as once I hooked it up to the iso in my MKII cabinet (meant to power a 25" K7000), it started working perfectly. I can now adjust the B+ voltage and dial it into 123V as expected.

IMG_2694.jpeg
 
@CharlieG
Worked on my first Matsushita 202g this week. Did full capkit and filtercap. Powered on and had display, but it was very bloomy. B+ was 118v and would not adjust. All resistors in that circuit were good. I was using my bench ISO from apar. I did notice it humming louder than normal.
I recalled your post above and just hooked it up to the atari brick transformer and bam, perfect picture and I could dial in the B+ to 125 So thanks for the discovery lol
 
@CharlieG
Worked on my first Matsushita 202g this week. Did full capkit and filtercap. Powered on and had display, but it was very bloomy. B+ was 118v and would not adjust. All resistors in that circuit were good. I was using my bench ISO from apar. I did notice it humming louder than normal.
I recalled your post above and just hooked it up to the atari brick transformer and bam, perfect picture and I could dial in the B+ to 125 So thanks for the discovery lol
All this info is good to know as I am about do do my first Matsushita rebuild and I too have the APAR ISO on my bench rig
 
@CharlieG
Worked on my first Matsushita 202g this week. Did full capkit and filtercap. Powered on and had display, but it was very bloomy. B+ was 118v and would not adjust. All resistors in that circuit were good. I was using my bench ISO from apar. I did notice it humming louder than normal.
I recalled your post above and just hooked it up to the atari brick transformer and bam, perfect picture and I could dial in the B+ to 125 So thanks for the discovery lol

Glad I could help -- but I just hope I don't develop a reputation as "the Matsushita guy!"
 
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