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MS9-29S low B+ voltage / Heater voltage and no neckglow (voltages slooowly creeping up!).

bytestorm

bytestorm

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Hello!

Just recapped the chassi since the tube was really dim and it took a while to get any picture at all, and even then it looked really wierd.
After the recap its no different, I can hear that the tube "turns on" but I see no neckglow, and B+ voltage started at 56v and slowly creeps upwards.. after a few seconds its av 60v and going up slowly..
Same goes for heater voltage.. starts at 4,5v and slowly goes up to 5v after 15sec..

I doublechecked the cap values, and the soldering, but it looks good, and it was behaving just like this even before the recap.

Reflowed even the faintest hint of crack in solderjoints on solderside..

Heater resistor = 3,3 Ohm resistor mounted.. measuring 4 Ohms. (R532)
Mine is a Toshiba A68KJU96X and the Sega sticker on the tube says "MS9-29S".. there is also a checkbox "interface main pcb", mine is checked "with out"?

Any thoughts on what could cause this slowly creeping up voltages?

Thanks for your time!
 
Did you reflow the solderjoints on the neck board as well?
 
Does the b+ pot have glue on it? I would also do another once over on cold solder joints and or cracks
 
advans14 said:
Does the b+ pot have glue on it? I would also do another once over on cold solder joints and or cracks
Click to expand...
Yes its glued. I am not sure what you mean? I have reflowed every joint even remotely cracked in case..

But yeah, at the same time, slowly rising voltage.. hmm..
 
Sometimes a glued b+ pot can drift even when glued they still go bad. It is something to keep in mind if everything else has been addressed.
 
advans14 said:
Sometimes a glued b+ pot can drift even when glued they still go bad.
Click to expand...
Hmm yeah I could remove the glue and move it a bit back n forth and then back into initial position maybe.. never know.. these creeping voltages seems just like a cracked joint to me but I can’t find any..
 
I can see there´s a crack in the middle of the inrush current limiter, NTH901... it still measures 5 Ohms but I wonder.. Its supposed to get lower resistance as the temperature rises.. wonder if the crack hinders it somehow..

at 96 degrees celcius it stops at 1.4 Ohm when I heat it up with 400 degree soldering iron i get it down under 1 ohm
 
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Wow the more I mess with it the better it gets.. I hate these “repairs” when you have no clue what made it better 😂 .. well I guess the NTC has something to do with it but.. wtf..

Bad ntc or a bad connection somewhere where I haven’t reflowed.. we will see tomorrow 😶

IMG_5194.jpeg
 
Well, a cold start give me this.. B+ voltage starts at 66volts.. hmm annoying as hell but at least I am glad that the picture gets really good after around 10 minutes 😂.. guess the search goes on.. I wiggled the B voltage pot also to check but it’s seems to be working. Perhaps I should measure the voltage drop over the NTC.. what gives this hourglass shape? HOT ?

IMG_5202.jpeg
 
yeah usually the classic "hula" is b+ power related. something in that circuit is jacked.
 
Now it didn’t take more than a couple of minutes and the picture is now perfect 😥 hmm.. damn
 
Oh well, found another Nanao Chassi (26") with the same-ish NTC.. swapped it, and the only thing that differed was that the picture gets better quicker.. B+ voltage still starts at 65volt but ramps up to 70+ in matter of seconds, and after less than 1 min the picture is perfect.. I think ill just let this be the way it is :(... atleast its working. still bothers me that my other NAC with identical monitor and chassie doesnt behave like this.. oh well.

have a hard time figuring the NTC values out.. from the manual :"115-050-41205" I am guessing the ratings are:
115 = 115v? nah..
050 = 5 Ohms (measures 5 ohm and marked 5.0 in schematics" but the last numbers should tell me the max Amperage rating and usually size... the disc is 10mm in diameter, and the bridge rectifier its supposed to protect has a max rating of 4A.

Checking some other NTCs I found a similar code, but then the last number was the max A rating, which wouldnt make sense here since the bridge would die before the NTC.
The markings on my NTC are:

0S
050
52 <-- (the new one from the other nanao chassie has 51..)

any thoughts on the decodings of the NTC?

IMG_5209.jpeg
 
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I think it's not a NTC but PTC, and NTH901 is in the degauss circuit. Can you (with power off) disconnect the degaus coil and see if the hula stops when you turn it on with no coil?
Otherwise its a red herring, and not related to the problem you are seeing. MS9 has a push button to control the degauss, it never fires on its own on my two chassis. Unless someone hacked a wire mod to the push button.

More recent chassis like the PFX fire the coil at startup. It's a 'Chunngnk!' sound. Any sounds when you fire up the ms9 monitor?
 
MS9 can be changed to auto-degauss with a simple loop back wire.

Also, the thermistor isn't part of the degauss circuit. It's an inrush current limiter for the whole primary side.
 
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The NTH901 is not in the degauss circuit, it’s directly connected to the + from the bridge rectifier, there is however PTC in the degauss section, but that one is not causing this issue.

This chassi is trolling me.. it’s a bad connection or solder somewhere.. I am damn sure if it but can’t for the life of me find it…

But last time today I took the chassi out and reflowed all TH components, and bigger SMD.. and after that it cold booted to 72v (no hula)… I give up.. I’ll play until it burns up and then at least I might get to see what’s causing the issue 😂 jeez..

Thanks all for the inputs ♥️
 
Yeah, like, I am so totally over it…



Couldn’t care less…



I have mounted everything back and monitor is ready to go back int the cab…


I’m done with this chassi….


Jeez I hate myself sometimes! I think I am the most annoying person I know.. who never knows when to give up…

F**k here we go..
IMG_5217.jpeg
 
Finally, now it’s boots to 73v and goes up to 76v in minutes. But the picture is perfect from the moment I boot up. There were several pads that had electrolyte leakage at em so I am guessing the solder didn’t really bond.. so I used some wire and also scraped of the solder mask to bond onto the copper tracks on several spots..

NOW we call it a day 😂 phew… although I have 1 more NAC with MS9 monitor to recap… that one already works thou.. but the picture is a bit unstable (small wobbles)
 
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