Intermittent missing red. [Pac-Man]

matman

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My pac-man is intermittently missing red. It is as if no red comes through, although at times it does and when it does it looks perfect. It doesn't appear to be weak red, it looks like missing entirely. ( Blinky is black with just the eyes showing. )

It could be one of the following:

1. no red signal off the pcb
2. red not working on monitor
3. other issue that someone on here could help identify ;)

Out of curiosity, could this be a ROM thing? I plan to swap the red and green wires off the pcb to see if I am then missing green and red is showing, but I haven't had a chance to yet.

thanks!
M@
 
I just did some further investigation. It appears that even when swapping green/red wires, the red will not come through. So I have isolated it to somewhere in the monitor..(sigh).

To figure this out i pulled out some pins from the molex that connects to the monitor chassis and swapped them around:

All tests keep blue, ground and sync in their proper place. (Note: each step required turning off the machine and unplugging it to set up the next test, i didn't do this with the machine on and was careful not to touch many parts on the chassis)

1. pulled out both red and green. result=blues (expected)
2. put green wire into red slot. result = blues (not expected)
3. put red into green, green into red. result = yellows. (not expected)
4. put red into green slot, pull out green wire entirely. result = yellows (expected)

The above tests show that voltage is running fine along all wires, meaning the fact that red isn't showing is somewhere in the G07. What i don't understand is why is it intermittent. I wonder if this thread needs moving to the monitor forum... :/
 
try swapping the red and another drive transistor on the neckbord , see if the problem migrates, but first I would try touching up the solder joints on the neckboard first
 
I will investigate the transistor swap..I do have 2 questions tho.

A GO7 flowchart I have recommends on missing red to replace:

neck board:
x102 (in the manual its x3102 = 2sc1514vc obtainable from bob roberts)

main board:
x101 (in the manual its x1101 = 2sc1685(r) )
x102 (in the manual its x1102 = 2sa673(c) )

bob roberts has for x101:
2SC1685 [85] Sub 1815
or
2SC1815 LF Amp (NTE85)

not sure which one to get, i think it would be the second (NTE85) if i am reading this page correctly:
http://nte01.nteinc.com/nte/NTExRef...9147b2a2aec42c0785256a78007a3f47?OpenDocument

I see no 2sa673 from him..I'm guessing the replacements is NTE290A according to this:
http://nte01.nteinc.com/nte/NTExRef...586a7a76a6f8349285256a78007a083d?OpenDocument

However i don't see Bob Roberts having this..unless its this one?
2N5365 (NTE 290A) K4900 color

hmmm..any thoughts on this? I mean, is the mainboard really something to consider replacing x101 and x102?
 
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well, now i'm frustrated.

i took the neck board off to find that it is cracked...could be a good reason why red doesn't always work..or hasn't worked much..so i put on another neck board i have from a GO7 that needs rejuvenating...when i hook this thing up, i get nothing at all...

so i hooked the cracked board back up and sure enough, it works - but with no red...

so i hook the 'good' board back up...nothing..just a blank screen...sigh

i've done this two or three times now..i don't get it.
 
I guess third time is a charm...now it works...although the red is still missing..which leads me to the monitor main board now....

at least i'm making progress :)
 
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If you have a multimeter, you can figure it out too. Just check continuity from the red wire all the way up to the red pin on the neck socket. If it shows a resistance of 8.4k or something, check and see what the resistance is on the green and blue, if it's the same or close, it's probably a tube thing. If it's different, go backwards a little bit and see where the signal is changing. Of course you can check the transistors and resistors too, it's pretty easy to do because you have two good colors to compare everything to. You'll see of course that every part that the signal runs through, there's a set for the other colors as well.
 
well, today i was able to put in the spare main board and the color and vibrance is awesome! I've noticed two things tho and I could use some advice (reference article: http://arcadecontrols.com/BBBB/go7-1.html#vcg07 ):

1. the picture is horizontally left (i'm using the true horizontal, not pacman left right.) so it results in the picture being shifted up on the screen..it gets a little clipped by the bezel which theoretically could shift up, but I would rather adjust the pic so it is centered on the monitor.. I'm not sure how to correct this. The full picture is on the screen, just not centered. I've
a) moved the jumper wires from "right" to 'center','left','right' but it doesn't seem to have any affect on the position.
b) measured the B+ and it is coming in at 119.6V...is that close enough to 120? Does adjusting this even do anything for centering?


2. my 'screen' knob is very binary. I can't get all black to show up anymore and its either a perfect picture or its washed out (when turned all the way)..there doesn't seem to be an in-between..if i leave it in the middle..it eventually washes out and then i can adjust again to the perfect pic. I do have the yellow wire going to the neck board through a molex connection..not sure if that might have an impact on it.


Any help is appreciated...
 
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