Green line on Astro City monitor

[imjustabill]

I picked up a Astro City cab a few weeks ago, and I'm having some monitor problems. It's got a Nanao ms8 (or possibly ms9) monitor in it. It powers on and shows a thick green horizontal line in the center of the screen, then shuts off a few seconds later. Everything else seems to work, I get sound and can play the game blind, so it seems to be just a monitor issue.

Any suggestions? I've been looking around for about a week and haven't found anyone with a similar problem, so some help would be highly appreciated. Thanks!

[grantspain]

you need to id this monitor correctly first,go to http://www.jomac.net.au/mon.htm

there are a number of ms8 and ms9 variations,it is very important to id the correct one

my bet is that you have a ms8-29a as they were the most common in astro city cabs

the horizontal line is a vertical frame collapse, the model number will point towards the things to check
these monitors will shut down with a frame collapse

[imjustabill]

I found the sticker on the monitor, its a MS9-29S. It looks identical to the MS9-29A / T / SU in the link.

[grantspain]

from my guide over at arcadeotaku
Vertical frame collapse
Q401,Q402 2SD1571
C433 10uf 50volt electrolitic
C437 120uf 50volt electrolitic
R433 0.25W 2K2

also check very carefully for bad solder connections

[imjustabill]

I've disassembled everything, but I cant find any of the parts you mentioned. I did notice your guide is for an MS8, I'd assume it would be different for an MS9?

[grantspain]

sorry mate i though you said a ms8,the ms9 you would look at U401 LA7837

[imjustabill]

Aha! There's a chunk of that thing missing, I bet it's the culprit.

[grantspain]

hopefully only that has died,make sure when you get a new one you have new heat conductive paste on the back

[grantspain]

http://www.audiolabga.com/pdf/LA7837.pdf
this is the data sheet,it would be worthwhile checking the voltage to pin 1 before putting a new chip in
i reckon it should be a nice smooth +12 volts,if not check
c402
d954
d957
u951
c955

[imjustabill]

Yep, we've got 12V, at least until it shuts off. Thanks for all the help!

[grantspain]

should be just a case of changing the LA chip then,good luck

[imjustabill]

Sweet! That did it! Thanks for all the help, it's much appreciated. 

[imjustabill]

I'm also getting some vertical fold-over, are there anything specific I should look for?

[grantspain]

that will be a capacitor and most likely the smoothing cap on the vertical frame ic voltage input pin

[imjustabill]

So I finally got around to replacing that capacitor. I changed out C402(I'm pretty sure thats what it was), which is the 470uf 16v cap on voltage in to the vertical IC. I used a 470uf 50v cap, which I've read is fine, as long as the capacitance is the same and the voltage is equal or higher than the original. The monitor turned on, but the fold over was still there. While adjusting the vertical size, I got the green line again, and it shut off. I tried putting the old capacitor back in, but to no avail.

Do you think the higher voltage cap caused the vertical IC to blow, or perhaps something else? Also, do you have any suggestions on what other caps I should check?

Thanks again!

[grantspain]

maybe your vertical size pot is broken,as for the foldover i will need to look at the schems some more
the cap would not cause that problem of the chip frying

[imjustabill]

Just some additional info:
I had also previously adjusted the pots on the board under the control panel, the pots on the side of the monitor, and  the controls on the very back that seemed to control the power or brightness and the focus. It seemed to be working fine for the last few weeks, until I adjusted the vertical size on the board underneath the last night. Would any of those possibly caused it?

[grantspain]

if you have a break in the vert size pot circuit then that may cause this problem,you would need to meter the vert size traces and check for bad solder joints
are you sure your pot is not broken internally

[imjustabill]

Well, back from a bit of hiatus of working on this, still trying to figure out what happened. I took off the front monitor control panel, and there seems to be a replacement resistor soldered over r296, which is connected to the vertical size pot. However, I metered the connection where the ribbon cable connects to the board,and it read from 1-4V, depending on the position of the pot. Is that good or bad?

[grantspain]

i would consider changing that pot anyway and checking for bad solder joints or bad connection from the remote board

[imjustabill]

Wow, it's been awhile since I've been here, but I finally have this machine at my house so I can work on it more often! I've checked the pot and the connection to the board and they both seem to be ok. I replaced the LA7837 but the screen just powers on to a blank screen for a couple of seconds then turns back off like it did before. Would this possibly just be a bad soldering job on the chip, or something else?

[grantspain]

is it still on a frame collapse?

[imjustabill]

It doesn't look like it. No picture at all, not even the green line from before. You can hear it turning on, then it clicks off in the same way, but no picture.

[grantspain]

try another deflection ic