Pacman maze curl question...

learpilot2

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I bought a pacman with a g07 electrohome monitor. The picture had two problems. A one inch wide maze curl or the right edge of the maze. The entire maze waved like it was a flag floating on water.

I did the Bob roberts cap kit with a new flyback. I did not change the width coil or the frame transistors. They looked in good condition. I also did NOT do the maze curl mod included with the cap kit.

I turned it back on after the new cap kit and flyback, and the wavey maze floating in water effect was gone! I found 2 leaking caps that most likely caused that. The only problem was that the right side maze curl was still there. I scratched my head for 15 minutes, and then notice the maze curl was completely gone. I turned it back off, then on again, and the maze curl was back. I watched it for 15 minutes, and with every passing minute, the curl slowly irons out. It 15 minutes, the maze is flat and completely normal. I hate to mess with normal even if I have to wait 15 minutes to get it.

Any ideas of what causes this or what to do? Should I do the maze curl mod. I hate to mod stuff. It can't be the monitor warming up because it was just on a couple minutes earlier. It can't be the Hort hold because the maze in centered on the screen.


Thanks for the help,

Rick
 
That has nothing to do with it. Centering is horizontal position, not horizontal freq (hold). tweak it a little and you should be good....
 
tweek horz freq?

I am new to this. The only horizontal pot I can find is on the defection board. Do I power on, get the maze curl, and adjust the horz. freq pot back and forth until the curl disappears? Do I do this while powered on and watching the screen? Why does the maze flatten out after 15 minute warmup, and go back to curled after turned off and back on?

what exaxctly does horz freq. mean or do?

Thanks,

rick
 
The horiz freq is Electrohome's term for horizontal hold. Yes, adjust it with the screen on, preferably using a plastic adjustment tool.

As for why it adjusts itself out - Remember that as the caps age, the adjustments will need to be changed to compensate. When you did your new cap kit, the adjustments are now off a little from where they were when the chassis was new, so you adjust them to get the best picture. When you first turn it on, it's off a little, but as it warms up, the tolerances probably compensate to make the picture look better.

Another thing to check is the B+ setting, as it can cause the same thing if it is off a bit. This adjustment is done at the pot set a little behind the Vertical pots, and the pot faces up from the chassis. Your B+ should be approximately +120vdc. You can measure it with a DMM, putting the black lead on the monitor frame and the red lead on the back side leg of the big white resistor mounted on the left wall. Make sure it is set properly before doing your Horiz Freq adjustment.

And I would have done the curl mod while I had it out, even if I didn't think it needed it. Only takes an extra minute...
 
B+ was way off

I measured B+ after 5 minutes of warnup per the manual. The manual also said to do this measurement with "no signal applied". Should of I pulled the edge connector off the game pcb to cut off the video input signal before measuring B+?

I just measured the B+ with the game fully running after a 5 min. warmup. It measured 113.4 volts dc. I tweaked the B+ adj pot, and got it to read 120.4VDC. I figured that was close enough, and stopped messing with it.

I powered off, and powered back on, and 99% of the maze curl was gone on power up. You could just see a few pixels of minor curl on the two lines of the right tunnel on the mid part of the right edge of the maze. It ironed out on its own 1 minute after powerup. I think I might leave well enough alone. I never touched the hoz freq pot.

If I decided to get real anal, would I re-adjust B+ to exactly 120.0 VDC from 120.4VDC, or would I just start monkeying with turning the horz frq pot?

I hate to mess it up when it is 99% flat, and perfect after 1 minute warmup.

Thanks for all the help!

Rick
 
Leave the B+ alone. That's close enough. Mess with the Horiz Freq if you really want to get it gone completely...
 
B+ adjustment

Thanks, I will mess with the Horz. Freq knob a little!

I am moving on to capping my donkey kong and noticed a B+ adjustment pot. Do you by any chance know where you measure that voltage from, and what the voltage should be? The manual did not really specify.

Thanks,

Rick
 
found tp91

I found TP91 marked in the chassis. It just has a pink wire soldered to the board at that location. How do I measure voltage there when installed and fired up? Do I measure it at the pin marked BJ next to it? They seem to be connected via a pcb trace, or do I check it at the other end of the pink wire where it plugs into the seperate audio board?

Also, the B+ adjustment pot on the chassis board is directly behind the tube yoke. Any tips to adjusting B+ pot when chasis board is installed and running?

thanks
 
Thanks, I will mess with the Horz. Freq knob a little!

I am moving on to capping my donkey kong and noticed a B+ adjustment pot. Do you by any chance know where you measure that voltage from, and what the voltage should be? The manual did not really specify.

Thanks,

Rick

Being an admitted newbie and jumping into a cap kit on an EZ20! Now thats determination! Those monitors usually scare people off because you have to take so much stuff apart to get the chassis out.

I would suggest doing the curl mod on the GO7 as well. Its really easy and solves the problem.

Matt
 
I found TP91 marked in the chassis. It just has a pink wire soldered to the board at that location. How do I measure voltage there when installed and fired up? Do I measure it at the pin marked BJ next to it? They seem to be connected via a pcb trace, or do I check it at the other end of the pink wire where it plugs into the seperate audio board?

Also, the B+ adjustment pot on the chassis board is directly behind the tube yoke. Any tips to adjusting B+ pot when chasis board is installed and running?

thanks

If you trace that pink wire, I think you'll find it goes to the sound board, and is easier to measure there.

Otherwise, attach an alligator jumper to it, with the other end attached to your meter probe, so you can measure it without sticking your hand in there..
 
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