What's new

gigasturtz

Professional
Joined
Jan 26, 2021
Messages
235
Reaction score
256
Location
Louisville, Ky
After successfully recapping another cabinet I decided to be proactive and recap the ms8-26a chassis in my candy 26. The kit I got was a little wonky, with a typo in the part reference and an apparent extra cap. I was cautious and thorough while replacing, making sure that the values matched with the board references (in some cases the voltage rating on the new parts exceeded the original parts but my understanding is that should be fine). When I first returned the board to the cabinet I had an apparent problem with the red gun.
8FEC8907-8DAB-426B-8225-3BEFB9DAA2EB.jpeg

This is the best I could get it looking, if I turned up the brightness the red would be scattered more than just horizontally.

I pulled the chassis back out, reflowed the solder on the neck board, reconnected everything to see if that helped and this time nothing. The monitor didn’t turn on at all, no sound like the tube is getting energized. I pulled the chassis again and reflowed the main chassis partially, focusing on the daughter boards, headers, flyback, and anything that looked suspicious when visually inspecting it. I hooked it back up to the same result, nothing.

Any suggestions would be greatly appreciated!
 
At this point it feels like there’s either a broken trace or a part has burnt out. Or there’s a cold joint that broke after all the handling.
 
You've shorted something if the HOT is blown. An easy mistake to make is putting in a cap in the wrong way. Double check your work before turning it on again with the new HOT.

EDIT: although cap polarity wouldn't explain why you had it partially working between tries.

Can you take some pics? Both component side and solder side of the chassis.

26A has some differences compared to 26SG, and a lot of differences compared to 26SE and 26SU. I wouldn't trust a cap kit with this chassis.
 
Last edited:
The last photo (ended up in the next comment) shows where the board cracked a little when I put it back into the plastic frame. I scraped the coating up and globbed some solder on, it’s got continuity across the traces (where they should be that is) but it’s definitely an area of concern.
FF853B42-4C31-4F26-A915-255B1D5DCD58.jpeg
4132E2B9-2EC9-426E-B6C2-F454FDAC5257.jpeg
E52278B6-2163-414F-9D40-E95D02DA8AF4.jpeg
FB6B4BE7-C34B-4F83-AB2B-BEB015044358.jpeg
29AFA44D-C3DC-428C-8AA7-9757A8FB4723.jpeg
88035525-8A3F-4428-8A69-19C06F29C248.jpeg
E1ED496E-881A-4318-8B21-298D154FC5C8.jpeg
8B1F167A-6559-4A16-8CE1-F3B3B7F5F988.jpeg
9FE848C3-033B-43C0-8E4B-45A85D86FEAA.jpeg
2BDF5ECE-6B54-4B02-8389-9BD49F0B232F.jpeg
 
Yes, that side of the board breaks often.

Your soldering looks OK and your board is clean. Unfortunately, nothing really jumps at me -- apart from the vertical position pot. It's missing the cover, but it's not damaged otherwise, is it? One side of that is ground.

Also, C560 and C908 haven't been replaced (above the filter cap). C560 is a 0.47uF 160V which is known to go bad. Sega replaced it with a ceramic capacitor on 26SU. However, I doubt it's your issue.

EDIT: The problem with this chassis is that there's a crap load of different revisions. All have slight variations. You really need to be careful when replacing caps. Don't trust lists.
 
Last edited:
Swapped out the HOT and the C3306, still no dice. There was a light burning component smell when I turned it on, which is certainly disconcerting. I might be suspecting the thermistor, it was the only thing that was getting warm at all but my understanding is that is not unexpected given it’s function. But it looks a little burnt on the board underneath it.
95679152-D5EB-4890-B52C-01A98F60A25A.jpeg


Is the degaussing coil header polarized or can it go either way? I may have had it the wrong way if it is polarized.

The vertical position cap keeps falling off, not sure what to do other than maybe glue it but that feels like a bad idea. It was working when the monitor was last powering on.

Here’s the list for the cap kit I used, I ended up with an extra 470uf35v cap. I checked most of the values before swapping them and all that I checked were correct but I don’t think I checked every single one.
Current behavior is still nothing in power up other than the thermistor getting a little warm. No tube glow, no sound like it’s energizing the tube at all.

Any suggestions for test readings I could make on the board while it’s powered on to identify where the problem is? I’m still fairly new to working on monitor chassis and have a healthy respect for the risks so would appreciate advice for what I can safely test/interact with while the chassis is connected.
 

Attachments

  • 431FCF25-8EF8-420B-9FC3-2340F1265163.jpeg
    431FCF25-8EF8-420B-9FC3-2340F1265163.jpeg
    296.6 KB · Views: 53
Is the degaussing coil header polarized or can it go either way?

It's not polarized.

Thermistor looks fine.

See if you have B+ voltage? You can measure it from the F902 fuse. Black meter to ground. Flip the board over before measuring to look for a nice ground spot. I use J144 which is a jumper to the right of the fuse, but looks like yours might be under some glue.
 
I’ll check that now.

In addition to the new HOT I did order a replacement filter cap so if there’s no B+ voltage I will replace that as well I guess.
 
B+ voltage started around 111v and slowly climbed to 125.5v BUT when I turned it back on to double check I was getting a reading of only a few volts.
 
The board indicates 125v by the fuse, is that supposed to be the rating of the fuse or the reading at that point?
5C41ED78-C9FF-4118-ADBB-BD12468E00D5.jpeg
 
Swapped out the filter cap and it’s still only reading a few volts at F902. Is there anything that would explain why I saw the higher reading when I first measured then it dropping on the second? I suppose a part dying might explain that…

Since I replaced the filter cap I did notice a new little sound up by the tube, like maybe it was trying to energize this time?
 
My personal advise:
- Recheck the work yet again especially around the HOT connections and the B+ power supply and anything on the way between them. If you take the extra time check any passive diodes or resistors in those two circuits while your looking around doesnt hurt to just measure them really fast.

-Check solder joints and the polarity on the newly installed caps. Anything that was ever reflowed or touched. If you want to take even more time I would test continuity or check for broken traces at the pads of anything reflowed/touched/questionable.
Its happened to me and sometimes the micro cracks in the traces hide really well on the board. You can narrow this down to the circuits of the PSU and Horizontal Output for now.

- The HOT may have been on the fritz or its last legs before the recap and either handling the chassis or the fresh caps created a condition where the HOT just died some how. Your chassis's HV will not run without an HOT (at least from what I know) its an integral part to boosting and operating the FBT and some of the higher voltages (outside of actually being responsible for operating the horizontal scan)

-When you install your new HOT and retest you need to put a multimeter somewhere appropriate to measuring the B+ voltage. Watch that meter the very moment you turn the chassis on as within seconds you may be able to notice an odd behavior such as an extreme spike and voltage drop etc, or it may just stabilize. If its stable keep watching it for a few more moments to be sure its actually stable. The voltage may increase or drop up to a volt or so this may be normal behavior while the power supply reaches a more stable condition.



If what Nem says is correct and nominal B+ is 92~VDC for this chassis then entering the 100+ VDC threshold is honestly gonna be a little uncomfortably high imo.
Usually from what I recall B+ can usually range on CRT sets between like what 80 to 180VDC or so but its entirely dependent on the circuit design and chassis so you cant just assume.

I cant recall it happening in the past to me but I have read that technically changing the capacitors especially around the B+ supply may affect the B+ output (especially if the B+ was for w/e reason re-tuned with aging capacitors installed; AKA you need to recheck that B+ and readjust if needed.

The B+ voltage could be spiking and taking something out or causing the chassis to enter a shut down.
Leave the chassis off for 10 to 30 mins, attach a meter on the appropriate B+ testing point (or some acceptable point to test B+) then turn the chassis back on and monitor the B+. Things can happen very quickly so it may spike back up to life then Immediately shut down in the blink of an eye and the entire process starts over. That is if there's a problem with the SMPS B+ output or something faults the B+.

You need to double check your work, which I think you already have done. Filter Caps replaced that's fine.
I wouldn't really mess with the B+ adjustment pot much yet until AFTER you replace your HOT and reverify the B+ output though it may be possible to run the chassis with the HOT removed and you can test the B+.

If you are really trying to pull out your magnifying glass and troubleshoot this guy deeper I would advise buying at least a second HOT if you didnt already because what ever the fault condition is may not be the HOT but rather something else in the circuit killing the HOT or killing something that's in circuit with the HOT and that causes the HOT to burn out / short.
A simple broken trace or solder connection may be all it takes to create a condition that kills your HOT or passive.

The rabbit hole gets deep you have to really sleuth eventually if you rule out all the easy fixes and checks.
Also just a quick warning, the HOT also deals in really crazy voltage swings while its live that will destroy standard multi meters, so as far as I have been aware you cant directly meter that easily with out special equiptment but thats an entirely different subject and information needed to troubleshoot. So unless you know what your doing do not measure the HOT and you shouldnt measure something live unless you have a decent understanding what its actually doing and rated around.
 
B+ output is staying low. Would a high B+ burn out the new HOT? Would a dead HOT explain the reading I saw (ramping up to 125 then staying there, turned off for a few minutes, then staying at 3-5v after powered back on) or is it possible that the chassis is going into shutdown immediately now?

I ordered three HOTs just in case but I’ll have to go over that circuit before putting in a new one (and test the current new HOT).
 
Realized I did something really stupid. I swapped in a new C3306 when I replaced the HOT… but I didn’t solder it, just screwed it to the heat sink. Soldered it in and now I’m getting ~92v on the B+ line but otherwise the same behavior.
 
Reflowed solder on the whole board, had a promising hum on power up quickly followed by a fuse blowing…

Thinking one of the solder joints that looked like they should be connected shouldn’t have been.
 
Last edited:
Back
Top