MS2933 going into protection

[Cycl0ne]

Hi,

my MS2933 is going into protection. I send it to a technician here in Germany, but he kind of doesnt know where to look because of missing diagrams (anyone have something for this chassis type?). Here the text from him, maybe somone has a clue for him:

I m familiar with fixing monitors.
But this time its tricky, above there is no diagram available.

The fault:
The unit powers up after one second getting the line voltage, takes normally current from the 115V
transformer, then in the same moment the high tension is very too high. It sparkles around the connector or the crt and also i can see sparks within the system of the crt! Then immediatly shut down.
Very strange, the caps are ok, i tested them with my esr-meter.
Nearby the flyback is a little pcb located with a murata-ic and also two caps on it, these little smd caps had bad esr, i swapped them and now after power up there was a huge loud spark, worse as before!!
On this chassis the h-deflection and the high voltage generator are built separated.
At least i interupted the voltage source to the flyback, then it powers up until the protect-line works.
Thereby i can see the h-defl. with my scope for this short time, may be ok. Also the v-defl. may be ok.
Is this a well known prob?
Now i have the idea, to power up the high voltage section while reducing its operating voltage....
This weekend i will be busy, but in the coming days i want to finish this building site.

Thanks
C.

[Asayuki]

Sounds like the lopt has a couple shorted windings on the primary, but hopefully I'm wrong.

[Cycl0ne]

From my tech guy:
"Two years ago I have had a similar prob with the 2931 chassis....the high tension was very too high and that killed the tube.
Heavy sparks inside the neck and the tube was destroyed. Later i recognized, that the pot for adjusting the HV was interrupted.....too late.
The high tension output stage has a regulator circuit, that is located on a little pcb upright beneath the lopt. This weekend i will finally try to fix it by voltage controlled supplying the hv-stage.
Has anyone a schematic.....?!?"

[mufunyo]

There are a few service manuals available on the wiki. Even though you might not be able to find the service manual for your specific model, your technician will probably be able to work out the differences between the different chassis and still find the manuals useful.

[xga]

Yeah, I was just about to say that it is my understanding that the MS2933 is a slightly revised model of the MS2931 (both are tri-sync's). Therefore the service manual for the MS2931 might provide the information your technician requires. http://wiki.arcadeotaku.com/images/3/34 ... l_full.pdf

There are service manuals for the MS2932 and MS2934 (both 31KHz only) in the Wiki, but I have never seen a service manual for the MS2933 ever.

[Cycl0ne]

Thanks this gave him a hint. but now he noticed the sparks broke his testing tube

While he is at it, i was considering to buy a new chassis and found a Wei-Ya 3129A. But this thing wont work with my Blast City. The picture is 10cm to wide (the h-pot is on max value) and the neckboard makes strange noise (it changes when the h-pot is regulated).

So my question is, what number is the best replacement chassis for my monitor? i saw at arcade spare parts a 3129DSS with the comment: for blast city. But i dont want to buy it for 300$ (180+tax+shipping) and it wont work. On the Wei-ya Page they have alot but not the 3129DSS. so i am confused on what to do:

http://www.weiya.com.tw/products_detail ... %20CHASSIS

So anyone can tell me which chassis works perfect for me as a replacement of the nanao 2933?

[grantspain]

3129a won't work on a blast as nanao ms2930 to 2934 use a 0.195mh yoke
the 3129a uses a 0.300mh yoke

for a blast you need a wei ya 3129b or rodotron 666b1

[Cycl0ne]

thanks, i posted the link to wei-ya, can you tell me which one i need to order?

[grantspain]

i would need to know the yoke tolerence of the chassis on that list
wei ya should inform of what you need,you have a semi curved crt single focus witha 0.195mh yoke-the same as the old 3129b they used to sell

[xga]

Hey Grantspain,

Not to hijack Cyclone's thread, but on the topic of his tech's tube breaking due to sparks, have you seen or heard of this happening before?

I remember hearing someone destroying a tube when testing it with a MS2931 chassis that was being repaired and left running for 24 hours. The way it was described it sounded like the tube imploded, but that might have been an exaggeration and it could have been a spark arcing in the neck, killing the electron gun. How would this happen? Would it be the over-volt protection failing and the B+ sending too much voltage to the flyback and then anode?

What's the safest thing to do before connecting a suspect chassis up to a tube and avoid destroying a tube? Is it just a matter of measuring the B+ voltage before connecting it to a tube?

[Cycl0ne]

Hi Grantspain,

got first reply from rodotron:
"Thanks for your inquiry.
Sorry to inform you that we had stopped to supply chassis CH-666B1 for a while.
But if you don't need to use for CGA/EGA (15K and 24.8K) mode, we have another chassis CH-2948A (31K~48K) to replace it."

now i need to start singing: "its the end of the world as we know it".

Lets see what wei-ya tells.

[Cycl0ne]

Ok news from the technician, the tube didnt take any damage, he just repaired 4 other chassis with it, still working, but the nanao is still broken, i copied his text, maybe one of you could give him a hint?

Hi folks, im back again
The fault is located in the HV-producing-circuit.
In the meantime i got the manual from the 2931, it seems to be similar to the 2933.
First i separated the HV-circuit from the power-supply and inserted a 300 Ohm / 30W as current-limiter.
Now the sparks were gone and the normal sound charging the tube with HV was to hear.
The waveform at the drain of the HV-switch looks normal and clean, a few hundred Vpp.
But after two or three seconds the protect-line shuts down the supply. Everytime.
The manual says the HV regulation depends on the voltage-feedback at the bottom of the HV-windings.
Similar like the beam-current-limitation at the cold end, there is nothing bad to see with the scope.
A third wiring is used to deliver a voltage for the X-protect, after rectifiing and smoothing 24V.
This is exactly the same as in the manual described and leads to the x-protect input from HV-reg.
Interestingly this 24V should be the reference voltage for correct setting the HV!
All secondary voltages from the switch-mode-supply are fine without ripple and in the correct range.
Looking with the scope at the vertical and horizontal deflection pulses showed no unusual things.
The H-defl. pulse only was ca. 700Vpp, in the manual it should be aprox. 1000Vpp.
Also i changed the yoke from 320µH to 200µH, as suggested few days ago and then i got the 1000Vpp.
This action didnt stop the protect-line from shutting down every time, unfortunately Dead

Here comes the special:
When i lower the current limitation for the HV-regulator and take instead the resistor only a 60W bulb:
After powering up there comes little sparkling noise and HV immediatly shuts down.
Interrupting the x-prot-line will give little longer sparking from top of the tube, but nothing is to see.
The Lopt works, i think. I cannot imagine that it is defective. Flyback condensor is also in spec.....
Without the limitation i do not trust myself to power up the set......until yet nothing is damaged!

Or is this a significant note, that the Lopt is dead...........i cannot believe

[xga]

Read this repairers comments re : Nanao flybacks on monitors over 20" in size

http://www.aussiearcade.com/showthread. ... ao-ms-2931

[Cycl0ne]

hmm but i have no "Black Goo of Death" on my chassis. So i dont think its corrosion here.
but what i found:
http://www.aussiearcade.com/showthread. ... protection

So from my email, Rodotron has no chassis anymore, arcadespareparts no chassis anymore, last one is Wei-Ya. If they send me: sorry.. i have then a blast without a working monitor.. damn.

[Cycl0ne]

Wei-ya just responded. this chassis is also not available anymore. so i have to hope for my chassis guy to repair it.

Wei-ya offered me a new monitor 29" from them, how are they?