Nanao MS8-25FTB vertical collapse / shutdown issues + red bleed/flicker [fixed] - cap list

[MagicianLord77]

Hi, I've got a Nanao MS8-25FTB chassis that has vertical collapse, tube is Toshiba A59JMZ193X, yoke readings (not perfect) are:

• 0.4 ohm / 0.360mh
• 6.4 ohm / 25.47mh

While I'm trying to repair the chassis (difficult), could something worse than odd geometry happen if try the tube with a Kortek KTX26 chassis? (game is 15khz)
The usual Zenith monitor yoke readings that work well with Kortek are:

• 0.7 ohm / 0.750mh
• 27 ohm / ??

Investigated old threads but couldn't understand if lower impedance could mean risk of burning the yoke or something?
Thanks!

 

[trashedcabs]

Do not try to use the Kortek chassis, it is made for a standard NTSC yoke (high inductance), where the Nanao uses a high-res yoke (low inductance). The resistance doesn't matter as much as the inductance value, as far as "blowing up my chassis". If you try it, your HOT will fail or worse.

Dead vertical deflection issues are usually pretty easy. If you've done caps, you can look at replacing the vertical IC, looks like an LA7832 in this. Common failure and cheap part to replace.

 

[MagicianLord77]

Got it, I won't try the Kortek then, I guess I'll try it in the future with a TV tube+yoke since you mention it's could be a good fit for standard NTSC yoke (measuring inductance before), but that'll be a different topic, thanks!.

About the MS8-25 vertical collapse issue, this is what I had done with it before bringing it again to the workbench:

• Chassis looks in good shape, no signs of anything broken or previous repairs, haven't recapped it yet. Besides the vertical collapse it was shutting down by itself after some seconds - not sure what's the cause of that.
• Replaced IC401 LA7832 with LA7833 - arcadepartsandrepair says it's compatible.
• Installed socket and replaced IC103 HA11423 just in case (not sure if it could be related)
• Measured a bunch of components around the vertical area (ZD401, ZD501, both 6.2v zener are good), and after desoldering and closely measuring 2 transistors that seem related to vertical, multimeter displays some voltage (diode test) between C-E, got replacements, they don't have that weird reading, put them into the chassis but nothing changed:
  • Q402 PNP 2SA1408 Y - only found an O one to replace it with but hFE looks quite similar, maybe it doesn't even matter.
  • Q401 NPN 2SC3621 Y

So now I brought the monitor again to the workbench, and this time it doesn't even power on, I hear a slight "psu on" noise, but it is clearly not on, like if it was on shutdown protection or something?, hopefully after recap it'll work again.

Now I was doing a bit more of research since it seems the MS8-29 is quite the same (unlike the MS8-26), and there are an amount of threads about it. Found this one https://www.aussiearcade.com/topic/98425-nanao-ms8-29fsg-no-hv-or-shutting-down/ , mentions the same odd transistors readings that I had, and then his issue was a bad fusible resistor R438, so went and checked mine, it is bad too!, measures megaohms.
The weird thing is that he mentions "It's supposed to be 2.2 Ω", I guess because it's a MS8-29, mine is red/violet/green/green, so 2.7 Ω? (not sure what's the green/green). I'll update once I get to replace it

Thanks!

 

[MagicianLord77]

This is more difficult than expected, I can't find 2.7 Ω 1/2w fusible resistors anywhere, tried mouser/digikey, ebay and arcadepartsandrepair. Also I'm not even sure if it is 1/2w or 1w? measures 8.5mm length, 3mm diameter, so it matches a usual 1/2w carbon but that does not guarantee it.
Also found a parts list but it's from MS8-29, and not complete: https://wiki.arcadeotaku.com/images/2/2e/MS8-29FSG_manual_partlist.pdf

Power rating	Body length (l)	Body diameter (d)	Lead length (a)	Lead diameter (da)
Watt	mm	mm	mm	mm
1/8 (0.125)	3.0 ± 0.3	1.8 ± 0.3	28 ± 3	0.45 ± 0.05
1/4 (0.25)	6.5 ± 0.5	2.5 ± 0.3	28 ± 3	0.6 ± 0.05
1/2 (0.5)	8.5 ± 0.5	3.2 ± 0.3	28 ± 3	0.6 ± 0.05
1	11 ± 1	5 ± 0.5	28 ± 3	0.8 ± 0.05

https://eepower.com/resistor-guide/resistor-standards-and-codes/resistor-sizes-and-packages/

Closest I could find is a 1W 2.7 Ω one, I wonder if it would be safe to use it? it is curious that it is 1W but smaller (6.5mm length)
https://mou.sr/4lrf9rc Vishay PR01000102708JA500
Also I don't even know if it's really fusible, only thing it says in its datasheet is "defined fusing characteristics" but not classified as fusible

Closest one that is really fusible is 2W 2.7 Ω (10mm length), so it would be clearly above the required wattage, this could mean it could not fuse when needed
https://mou.sr/3I4JQnF Vishay PR02FS0202708KR500

Could a fusible resistor be made somehow by combining a regular resistor and a fuse in series?

 

[MagicianLord77]

This monitor has been fixed

• Replaced R438, with the Vishay PR02FS0202708KR500 2W 2.7 Ω, fits nicely, and recapped it, but nothing changed, it was good to do it anyways, probably fixed other unseen issues, one of the capacitors had 90ohms ESR!
• Then I could not make it turn on again, but that was due to me having inserted the HA11235 chip upside down
  
• After reinserting the chip, the vertical collapse was solved. Shortly afterwards found unadjustable heavy red bleed/smearing, pots did adjust the color but not the bleed.
• Went to check neck board transistors with a multimeter, the MS8-26 schematic is quite similar, red related components are named 30X, green 31X and blue 32X. One of the small red related transistors gave an odd voltage reading between its legs, sometimes can happen due to a diode being around, etc. so went to check for the same in the blue related transistor, that reading wasn't there. Upon closer inspection, D301 (1SS133) connected to the transistor looked suspicious, had a 1.8v forward voltage reading, while other diodes have 0.6v. Took it out, checked that still was the same off-circuit, and also it had a frosted glass look. Replaced it with a 1N4148, turned the monitor back on, issue solved
  

I wonder what's the appropriate B+ for this chassis? only know that MS8-26 is 92v and MS8-29 is 94v. Kept it at 92v just in case

Here is the cap list of all the original capacitors the chassis had minus the filter:

Code Capacitance Voltage Note
C560 0,47uf 160v Flyback area
C909 100uf 160v
C906 100uf 160v
C448 100uf 35v
C442 100uf 10v
C432 100uf 35v
C440 10uf 35v
C332 10uf 250v Neck Board
C580 1uf 50v Flyback area
C577 1uf 100v Flyback area
C561 1uf 200v Flyback area
C552 1uf 50v IC102
C501 1uf 50v
C445 1uf 50v
C443 1uf 50v
C420 1uf 50v IC102
C401 1uf 50v
C913 220uf 16v
C911 220uf 25v
C910 220uf 50v
C570 22uf 250v Flyback area
C521 330uf 16v
C574 33uf 35v
C449 33uf 16v
C446 33uf 16v BP
R566 4,7uf 100v over resistor
C565 4,7uf 100v
C562 4,7uf 25v
C576 470uf 16v
C573 470uf 16v
C431 470uf 35v
C422 470uf 16v
C908 47uf 16v
C572 47uf 16v fb
C447 47uf 16v
C438 680uf 25v

 

[MagicianLord77]

The monitor was running alright, but after 5-10 minutes red color would begin to flicker, sometimes went full out, and sometimes went normal back again for a while, quite weird, very unstable.

So began by checking:

• Connection from board to monitor, tried something different (TPG) - no change
• Gain/bias pots - no change

Took the monitor to the workbench, I suspected the issue would be at the neckboard but wanted to be sure, so using the cheapo battery powered scope measured the red color and black (gnd) wires that go to the neck board:

Having a crosshatch pattern on screen I could see certain "square" wave, because red had always the same intensity. When the flicker issue began to happen and then red was out, the wave did not change at all. I think if the issue was on the mainboard (circuit previous to neckboard) that wave should have changed in some way too, so that confirmed I should really check the neckboard.

Measured around the red related components, found a voltage difference when measuring in circuit in reverse D302 (red) vs D312 (green), later I found it wasn't the diode, a resistor R306 (100 ohm, fusible) was open.
Replaced it with a regular 1/4w one (may later get a fusible one), I think the worst that could happen would be it burning to a crisp.

Fired it up and nothing changed - how did the monitor work with it open? not sure.
Measured diode voltages of all red related transistors/diode compared to other colors, found nothing. Then remembered I had a similar issue in the past, it was a zener diode: https://www.arcade-projects.com/threads/nanao-ms8-26sg-green-color-noise-what-to-check-solved.18787/

So took out the only zener from the neck board: ZD301 15v.
Tested out its zener voltage with a bench supply, all good, that had me puzzled, but decided to try and put a new one there just in case (a bit larger but same).

That fixed the issue! - had it on for 3 hours now, not a single flicker

Also, used the schematics from @Franck 78 https://www.arcade-projects.com/threads/nanao-sanwa-schematics.34709 - thanks again!