(Topic ID: 307002)

Can you solve this GI mystery?

By RobAquinas

1 year ago

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#1 1 year ago

The mystery: A Bally Lost World has no general illumination lights on the playfield. Coin door and backbox GI are working. 6.8 VAC is measured at rectifier board J1 pins 1,2,5, and 8. 6.8 VAC is measured at every single socket. GI bulbs in the playfield have been switched out with known working bulbs. Sockets have been cleaned. Continuity checked between transformer and all sockets, GI pins on rectifier board, and ground straps. Fuse is good.

J1-2 to 5 GI circuit worked. J1-1 to 10 circuit worked intermittently. Headers were reflowed and trifurcons installed. Now, nothing except 6.8 VAC and no lights.

Can you solve this mystery? I can't after about 4 hours of testing.

#2 1 year ago

The GI circuits is fairly simple. Approx. 7vac from transformer to the light sockets and then to ground. I don’t remember there being anything that switched the GI on and off other than the main power to the transformer. Therefore, if you are actually getting 6.8vac at your GI sockets, measuring from socket to ground… then the problem is between the socket and the ground. Check j1 GI return pins 1 &2… make sure those are actually grounded. Then check that there is continuity from the sockets to this pins…. Somewhere you have the GI return disconnected from ground. My 2 cents.

#3 1 year ago

Keep machine turned off and apply 5-6vac to one of the GI bulb sockets on the PF, if all the GI lights on the PF come on, remove your 6vac supply and run a jumper from the GROUND on one of the PF GI's to one of the backbox GI's grounds and turn the machine on, if the PF GI's now come on look for the missing PF ground to the source.

#4 1 year ago

Double check the J1 connector at the power supply. May be shifted over one pin.

#5 1 year ago

MMGB I think you are on to something with J1-1 &2 not grounding. I hooked the J1-1&8 GI Bus and Return to the J3-2&11 GI Backbox GI Bus and Return and the correct half of the playfield GI lit up. I also measured voltage on backbox return and it is 300 mVAC which makes sense. The playfield GI return shouldn't be 6.8 VAC. I also measured the return side of each of the backbox sockets which measure 300 mVAC. The playfield shouldn't be measuring 6.8 VAC across each socket.

I triple check the solder joints on the back of the rectifier board and everything looks fine. I reflowed them again. No change. What could I possibly be missing?

#6 1 year ago

tomtest I unplugged J1 and jumped the backbox GI Bus and return to J1-1&8 and the playfield GI lights came on. That would mean the problem is on the rectifier board, right?

#7 1 year ago

Picture of back of rectifier board for reference.

PXL_20211230_193245792 (resized).jpgPXL_20211230_193245792 (resized).jpg
#8 1 year ago

Like MMGB said, the PF GI ground is missing, is their a braided ground wire coming from the cabinet to the center front of the backbox that usually has a wing nut to connect to the braid, is it missing? In any case the PF GI ground to the backbox is missing.

#9 1 year ago

tomtest MMGB turns out the ground to playfield return is on the front side of the board under the plastic that holds the pins. I let some solder seep through and it finally grounded. When I turned on the game all playfield GI lit up, but no playfield lights are on. I checked voltage at TP1 - nothing. The fuse blew.

I did some tests and noticed that I have continuity between J1-7&8. I looked at the schematic, and it doesn't look like that should be happening. I looked all over the front and back of the rectifier board, and I don't see any splashed solder.

I removed the male pins from J1 to check the front side for a short and don't see anything. Any help is appreciated. Before I put the male headers back in, should J1-7&8 have continuity? Is that what is causing the new problem? This has been the most frustrating rectifier board I have ever dealt with.

#10 1 year ago

Glad you found the problem with the ground trace for pins 1&2. Pins 7 & 8 are two separate circuits, you don’t want those to come together… if they do you will blow something. Pin 7 is 5vdc, pin 8 is 7vac. So, no, you definitely don’t want continuity across those two pins.

#11 1 year ago

Interesting development: my DMM reads continuity up to 30 ohms resistance. It was reading through the 25 ohm resistor that connects the 5v circuit to ground. Therefore, the 7v circuit was showing continuity with the 5v circuit because they were both grounding. I found this out by testing resistance at varying points to try and figure out where the short was. Turns out there wasn't a short. Put everything back together and all lights are working perfectly. I'm not certain why or how the 5v circuit fuse blew, but it is fine now.

Thank you MMGB tomtest and JethroP for your help and suggestions.

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