Nanao MS8-26A/MS8-26AK Nothing on screen

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jeston
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Nanao MS8-26A/MS8-26AK Nothing on screen

Post by jeston » November 10th, 2019, 7:23 am

Hi,

I got issues with 2 different chassis but on the same tube.
Both used to display picture, so it's not the tube, nor the chassis being already dead.

MS8-26A :

Just fitted a cap kit on it, no picture on first power ON. Was working before.
CRT seems to hold no charge, no tube glow.
I tried to adjust the B+ to 92V (was 76V) by measuring TP1 and TP2, it blew the secondary fuse.
Waiting for replacement fuse right now.

Edit : seems D1880 is toast.
to do : change the fuse and replace D1880

MS8-26AK :

This chassis is from what I know unheard of. Supposedly the original chassis model of my Konami Domy H.V.
Worked on first power ON, but picture upside down.
My bad, I didn't plug the yoke connector to the right connector (it has to be plugged on REVERSE on the Domy HV to display properly as the tube is mounted upside down).
Turned OFF the cab, switched the connector.
BAM, no picture, no glow, tube seems to hold no charge. NOTHING on screen.


Now, it seems both chassis have similar symptoms :

- No glow
- the CRT doesnt' seem to have charge

So, the common point between both chassis is the tube.

I noticed the yoke connector wasn't always connecting properly, the pin connectors would slide up, out of the plastic housing.
I then highly suspect the chassis have been powered ON without proper yoke connection and it blew something on both chassis.

Am I right suspecting the HOT ?

At this point, I'm a bit lost...

I'd really like to get this cab running...

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grantspain
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Re: Nanao MS8-26A/MS8-26AK Nothing on screen

Post by grantspain » November 10th, 2019, 9:40 am

check the value of C560, it should be 0.47uf 100v
read b+ by using a capacitor ground and the secondary fuse, 92v is correct level. Before repowering this chassis turn the b+ pot back to its original position
if the 2sd1880 is short then check the regulator circuit 2sc3306 and 2sa1091

do same checks on chassis with bad yoke connector and replace yoke connector

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jeston
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Re: Nanao MS8-26A/MS8-26AK Nothing on screen

Post by jeston » November 10th, 2019, 11:37 am

First, thanks for your help. It's much appreciated. :)

On the MS8-26A :
The value of C560 is 0.22uf-160V.
It's the ONLY cap I didn't change. Actually, it's impossible to find the same values.

I followed the cap list from This threadon Neo-Arcadia .
It was matching my orignal values except 2 of them :
C433 : listed as 10uf-50V, was actually 10uf-25V. Upgraded to a higher voltage, no issues there.

C909 : listed as 47uf-250v, was actually 22uf-160v

Note : my values seems to match the cap list from this website

In all cases I stuck to my original values, therefore I was not able to find a replacement for C560.

The B+ pot is back in its original position (not to make the matter worse).
I'm waiting for fuses and transistors replacement to measure the B+ again from the fuse.

On the MS8-26AK
Still no clue for now...

The yoke connector issue was on the cable side of it.
I just had to make sure the metal tab of the pin would secure it inside the gray connector.
It should be good by now.
Last edited by jeston on November 10th, 2019, 12:30 pm, edited 1 time in total.

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nem
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Re: Nanao MS8-26A/MS8-26AK Nothing on screen

Post by nem » November 10th, 2019, 12:20 pm

jeston wrote:
November 10th, 2019, 7:23 am
I tried to adjust the B+ to 92V (was 76V) by measuring TP1 and TP2, it blew the secondary fuse.
Did the fuse blow from adjusting B+ or did you short TP1 and TP2 together?

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jeston
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Re: Nanao MS8-26A/MS8-26AK Nothing on screen

Post by jeston » November 10th, 2019, 12:49 pm

Most likely from B+ adjustment.

I used alligator clips with insulated sleeves and was pretty afraid of that scenario.
I of course positioned them before turning the monitor ON.
Plus the fuse didn't blow right away...

If I remember well, the multimeter didn't show any short either when on continuity test with the clips still in place.

Very unlikely from a short.

Some things I forgot to mention in my initial post regarding the MS8-26A.

- I was able to see a fainted vertical line at some point (no video source connected at that time).
- The B+ voltage was fluctuating (+-5V), I don't know if that's normal. I couldn't get a stable measurement like I would on a PSU.

My uneducated guess would be :
Yoke poorly connected =>vertical line (no deflection)
B+ too high=> burned D1880 and fuse blew as well.
or yeah, same scenario with the blown fuse being the result of a short on TP1 and TP2.

we'll see clearer when the new fuse arrives.

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nem
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Re: Nanao MS8-26A/MS8-26AK Nothing on screen

Post by nem » November 10th, 2019, 3:35 pm

jeston wrote:
November 10th, 2019, 12:49 MP
yeah, same scenario with the blown fuse being the result of a short on TP1 and TP2.
I blew the HOT doing this once. Easy enough to check, look for a dead short between the outer legs and the middle leg.

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jeston
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Re: Nanao MS8-26A/MS8-26AK Nothing on screen

Post by jeston » November 18th, 2019, 9:57 am

Here are the updates

MS8-26AK:
I replaced the regulator c3306 and the HOT, which seems different on this model, it's a C5296

All of them are short, again :problem:

I didn't look at the SA1091 and I suspect it could be that... silly me... (Q902, Q903, Q904. by visual inspection)

No neck glow, no picture, no blown fuse.
Haven't checked the B+, I should have...

MS8-26A:

Replaced the HOT D1880.
Adjusted the B+ It is now 92,1V at F02. So this is at least out of the way.

No neck glow, nothing.
I don't know what to do.

note that C560 is still 0.22uf-160V and not 0.47uf-100V as mentioned by grantspain

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jeston
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Re: Nanao MS8-26A/MS8-26AK Nothing on screen

Post by jeston » November 19th, 2019, 5:31 am

MS8-26A:

The culprit was C909!
The capacitor is listed as 250V-47uf on Neo-Arcadia (on a chart that matched my monitor for everything else).
However, the cap installed on my chassis was labeled as 160V-22uf.
Anybody with common sense would stick to the original values when replacing the caps...
But what got me suspicious of this particular cap was that C570 is also labeled as 160V-22uf but is much smaller...
I kept my original C909 (the big one labeled 160V22uf), I soldered it back in place and BAM, VoilA... picture is back. :awe:

At this point I'm not sure what's supposed to be the correct value for C909, I guess I'll stick with the original one.

MS8-26AK:

I'll have a try at replacing
Q902 (A1091)
Q903 (C2610) (the surrounding diodes seems okay)
Q901 (C3306)
set proper B+ to 92V
replace the HOT (C5296)

I hope I'll get something out of it.

The board is not in great shape, hasn't been well kept and had several repairs before it got into my hands...
One of those chassis is meant to be a backup of the other

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