Gottlieb Solved El Dorado City of Gold (Gottlieb, 1984) Playfield Lights "flickering"

[njPinWiz]

Just picked up an nice, very clean El Dorado City of Gold. Everything seems to function as it should, with one bothersome exception. During play, and only occasionally - the play field lights "flicker" in unison. It might last a few seconds, or up to a minute or so. When a new game is started, the lights behave normally...then a few games later, the flickering occurs again.

I tried to re-seed all the connectors, but that didn't resolve it. I am hesitant to touch any other connectors until I can isolate which ones might be the cause - I don't want to cause other problems in the process.

Anyone familiar with Gottlieb System 8A, and can suggest which specific connectors/boards might be the culprit? Thanks!

 

[pinballdaveh]

have you checked out the T (tilt relay)? there are 2 NC switches that controll the GI lights and the playfield score lights. with power off clean and adjust these 2 switches. dirty or pitted switches may cause this flickering.

 

[njPinWiz]

Thanks pinballdaveh. I located the tilt relay, but there seems to be only 1 switch. I cleaned it & it appears to be gaped properly (normally closed, then opens when tilt is triggered. I then removed connector A3J3 from the Master Driver board & cleaned the contacts...still didn't resolve the problem. Any other thoughts or suggestions? Always appreciated. Thanks.

 

[pinballdaveh]

it might be a data loss from the control board to the driver board. check and clean those connections.

 

[njPinWiz]

while I was at that - I cleaned and inspected every connector on the driver board & the control board. Nothing seemed out of the ordinary. So far, haven't detected the "flickering" occurring, but since it has been intermittent will play more games on it & see if it reappears. will keep you posted, and if you think of anything else I can try please let me know. thanks.

 

[njPinWiz]

A service tech mentioned this could be caused by the LEDs under the playfield which had been put there by previous owner in replacement of #47 bulbs. Anyone ever hear of that possible cause of lights flickering? Might try and go back to #47s just to see what happens.

 

[Coil_Smoke]

Normal LED's are not perfect replacements for incandescent lamps. They can ghost and flicker dimly when they should be completely dark. They respond to stray voltages in solid state circuits that would not light an incandescent. I see newer LED replacements for pinballs that have built in circuitry to better simulate the bulbs they are replacing at a cost of dollars more. LED's in strobed lamp matrices strobe right along with them. They blink so fast the flicker is not directly noticeable but they make a fast moving pinball hard to spot as it strobes along it's way. It sounds like your playfield lights are acting up in groups. So I don't think replacement LED's are an issue.

P>S> Here is a link to previous discussion of LED issues amongst other trippy waddle ... LED'S ??? - Pinball Nirvana Forums

 

[njPinWiz]

Coil_Smoke, thanks for the comment. The flickering lamps are across the top where there is a 10 drop target bank, and middle-right side where there is a 5 drop target bank. Could they be wired as two distinct groups & flickering occurring as a group? Any other thoughts on what might be the problem? I heard about Lamp Driver Boards potentially causing this problem, but I don't think this machine has one.

 

[pinballdaveh]

my next guess would have been loose sockets to their straps until you said about using LED'S. a anti-flickering mod that i have heard about is using 470 ohm resistors soldered across the sockets(see pic). resistors across all sockets may not be needed to solve problem. this mod was done on a bally, and i dont know what kind of results will happen on other manufacturers.

 

[Coil_Smoke]

Coil_Smoke, thanks for the comment. The flickering lamps are across the top where there is a 10 drop target bank, and middle-right side where there is a 5 drop target bank. Could they be wired as two distinct groups & flickering occurring as a group? Any other thoughts on what might be the problem? I heard about Lamp Driver Boards potentially causing this problem, but I don't think this machine has one.

This is where a schematic would really help. I am very curious about what is in your lamps circuits. There must be more to them than just relay contacts. Are there game controlled driver transistors ? Are the lamps in parallel in the groups that act up? My gut says your problem is in the back box. Are any of your connectors overheating , turning brown or smelling hot?
PS> That Game looks like many other early machines with grounding issues. Any improvements or doubling up ground connections will make for more reliable play.

 

[njPinWiz]

Coil, thanks. Starting with what I know: the connectors seem OK, I cleaned them & there is no browning, nothing that looks like any of them are overheating, and no odd smell. I checked schematic & it appears all the lamps for both 10 drop target bank & 5 drop target bank are on the same parallel circuit. I also found that there is a group of transistors called the "lamp driver transistor" which outputs from Master Driver Board A3. I located those on the driver board, solder looks good, no discoloration on any of them. Am thinking of doing this: (1) replace the LEDs on playfield with #47s, (2) replace the molex connector between Control Board & Driver Board, (3) Replace Driver Board with a newer technology board entirely, (4) live with it...lol. Any other thoughts? Thanks guys.

 

[Coil_Smoke]

I suppose putting #47's in could make the thing settle down. There is no load on those circuits when the LED's switch off ...That 'inter connect' cable between mpu >driver board is notorious for internment gremlins. I think newer after market boards may have controller and driver on one board. Hope you can get your factory bits working .

 

[njPinWiz]

An update, for what it's worth. After replacing the LEDs (with #47s) corresponding to the top bank of 10 drop targets and the right side bank of 5 drop targets the flickering stopped. I didn't replace those for every lane or the bonus ladder. Maybe that was the solution. Am continuing to experience some occassional scoring problems and drop targets resetting prematurely, but that is a different issue. Thanks for the advice!