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Nanao MS7-18 sync issue

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Blue0524

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I need some help! I’m trying to get the monitor in my Sega City all set up and it’s just not syncing. the volatages are at 4.72 and 12.13 but they won’t adjust evenly. The ground and sync wires are hooked up properly to the harness. Not sure where to go from here.
 

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nem said:
There's no sync pot on the chassis?
Click to expand...
that was my first thought. or the pot is broken.

if you adjust the v-hold or h-hold pots does it make a difference? if it has no effect then the pot could be cracked or you have a broken connection to the pot.
 
you shouldn't need to pull it out to adjust v-hold and h-hold. usually those are on a remote adjustment pcb or along the edge of the chassis and easily accessible since they need to be able to be adjusted with the monitor powered on.
 
looking at picture of the MS7 the hold pots should be right on the edge of the chassis:

Nanao-MS720L.jpg

looks like they're on the bottom right in this image.

if you turn it and the screen makes no reaction then the pot is bad. if you turn it and the screen reacts then it's probably good and the problem might be somewhere else.

check that first and if you think the pot might be bad then pull it and replace. after that do a cap kit then re-evaluate.
 
Blue0524 said:
The screen does react but it doesn’t fix anything
Click to expand...
if it reacts then it's likely still good and the problem is elsewhere.

a cracked pot will often not react at all (as if it was removed) One that is partially cracked will act like it's changing positions rapidly when just touching but not necessarily turning the pot. Though usually a partially cracked/jumpy pot will become fully cracked and non-functioning very quickly.

it couldn't hurt disconnect and reconnect the video connector on the chassis (with the power off) and then with the power on wiggle the connector on the chassis to see it changes. you can also test continuity of the video pins between the JAMMA edge and the connector on the chassis. to rule out any bad wiring or corroded connectors.

after that a cap kit may or may not fix the problem but it's a good next step.

while doing that it'd be a good idea to check/reflow any suspect solder joints as well as those under the hold pots and under the input connector to ensure that they're solid.
 
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Alright. I’ve check continuity from the jamma edge to the point where it connects but not all the way up to the chassis. Will probably have to do that this weekend.
 
twistedsymphony said:
looking at picture of the MS7 the hold pots should be right on the edge of the chassis:

Nanao-MS720L.jpg

looks like they're on the bottom right in this image.

if you turn it and the screen makes no reaction then the pot is bad. if you turn it and the screen reacts then it's probably good and the problem might be somewhere else.

check that first and if you think the pot might be bad then pull it and replace. after that do a cap kit then re-evaluate.
Click to expand...
Think i may have figure out whats going on with the monitor. If you look at the pic of the chassis there is 6 pins for the video connection but in my picture there is only 5 wires coming down. Im going to pull the monitor when i get home and follow the wires all the way to the chassis. Hopefully it wasn't cut.
 
there's normally only 5 wires for video on a typical JAMMA setup
red
green
blue
ground
sync


a lot of video connectors have 6 or 8 pins though for additional sync connections
-V sync
-H sync
+V sync
+H sync

you only need to use -H sync, though on some monitors you want to split the sync wire to both -V sync and -H sync.
 
I guess I misunderstand what someone else way trying to tell me. Anywho I’ll get some more work done on it this weekend.
 
Hi,

Another question: what is the difference between CN501 and CN502.

Looks like I can rotate the screen by 180.

I found the answer just put the plug in to CN502 to CN501.

Thanks
 
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Blue0524 said:
I need some help! I’m trying to get the monitor in my Sega City all set up and it’s just not syncing. the volatages are at 4.72 and 12.13 but they won’t adjust evenly. The ground and sync wires are hooked up properly to the harness. Not sure where to go from here.
Click to expand...
Hey : )

what is the model monitor with Nano MS7-18 ?

(In my city : chassis Sanwa 1745 v21 with monitor Goldstar : sega model 18V21SK )
 
Push.
We have a SEGA Blast City here with this chassis. The picture is great when it works.
But after some time (a minute, or several hours) the screen goes completely whacked. Superficially it appears to be losing sync. However it appears to randomly insert blanking on the video signal AND on the sync lines. Thus, the screen becomes more black and loses sync. If you leave it running like that, it can happen that the picture goes completely normal again. The defect's appearance is binary, there's no fading from working to broken and back. However it can be different kinds of broken with just very shaky sync and a bunch of scan lines missing, or a completely black screen.
If you turn down +B, more and more of the picture reappears. The picture also doesn't fade. The scan lines just completely go black or return to full brightness with nothing in between.

Methinks intermittent bad voltage regulator or intermittent bad Zener.
Problem: There appear to not exist schematics for this monitor on the entire internet, I don't even know where to start working!
(I've already tested and replaced some of a select few capacitors in the sync section)
(also helps that the waveforms on the vertical don't look much different between working/non-working state)
 
That'll have to wait for two weeks as I don't have immediate access to the machine. Next weekend are two repair cafes, so I'm next at the museum on 22nd.
On first and second glance, the chassis looks identical to the one in the photo above. But I kinda remember that blue gain pot being populated on ours, on the one in the photo there's just a jumper wire.
Maybe the machine is called SEGA City and not Blast City, I'm not familiar with their naming scheme. The machine looks mid 80s from the inside. Fact is, the label on the monitor says NANAO MS7 (no dash anything though) and it looks like the one on the photo (and I've seen more than two monitor chassis in my life).

From my testing yesterday it also looks like the fault has become permanent-ish. I'm trying cold spray next.
 
I fixed it. On the photo way up there (from 7.3.2018) in the bottom left corner are two hybrid "IC"s (small circuit boards with SMD components. The left one (facing left, oriented vertically) seems to be the sync separator/blanking shaper/whateverIdontknow.
Let's number the pins starting from the bottom, which is connected to ground, pin 2 should have the vertical sync pulse output, instead there's some weird oscillating garbage (at least at clean TTL levels).
The SMD transistor on that hybrid "IC" outputting that signal (with you looking at the component side and the pins facing down, it's in the bottom left as well) was bad.

TL;DR
The monitor works for a minute or two when cold. If it's left off for less than a few days, it won't even last two seconds.
Now - freeze spray didn't work. Spraying the area that turned out to have the faulty transistor did little to nothing to the picture. Spraying the area where the yoke connects actually did more, but not much either.
So I started looking at signals and you could see the sync hybrid had some weird needle pulses on nearly all outputs, but most pronounced on pin 2. When you unplug the monitor, you can see the waveform on the scope go from garbage to normal while the signal fades, and when you let it cool down for a day, you could see it start normal, stay normal for a second or two and then go to garbage.
Disconnecting that pin brought back the picture, but no vertical lock, the picture would roll. Connecting the pin to a pull up resistor showed the signal to look normal, but as soon as you connect it, it would go to garbage. Without it, there was no garbage on any of the other pins of the "IC".
I took that "IC" out and looked at what's connected to pin 2 and there's a transistor. Just from looking at it I was pretty sure it's a garden variety NPN and I could see that emitter is ground, collector goes to pin 2 and base connects to a resistor on the board. Just to be sure, I desoldered that transistor, soldered on legs and put it in the component tester and sure enough, what I read is pretty much the same any standard NPN like the BC547 would give, so since I had lots of BC548 and that's pretty much the same, I put in a BC548 and that fixed it. Just to be sure, I scoped the output and it looks fine. It's not getting warm either and I ran it for most of the day with no issues.
That monitor has a crisp and bright image and is capable of a painfully bright image with superb contrast (which required some fiddling with the base and gain pots) and crisp sharpness. I had to turn it down some.
 
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