(Topic ID: 236656)

EBD bridge overheating

By Yoski

8 months ago

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  • 14 posts
  • 5 Pinsiders participating
  • Latest reply 8 months ago by frenchmarky
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20190220_204107 (resized).jpg

#1 8 months ago

I have a problem with an EBD limited ed. bridge rectifier on the power board. Despite heatsink and paste it keeps on overheating. Even after a few minutes in attract mode it gets so hot that I can't touch it anymore without blistering. My EBD doesn't do this. The bridge gets hot to the touch but not anywhere that hot. The consequence of the overheating is that the bridge has to be replaced every 6 month or so. Inside the machine on the aluminum sheet on the bottom there is evidence of heat paste. So the power board was apparently mounted upside down at one time in order to use the sheet as heat sink. So the problem must have been going on for a very long time. Any suggestions? All the boards, except the power board, are original. Otherwise the machine operates as expected.

#2 8 months ago

The original rectifier boards have the two bridge rectifiers soldered under the PCB where they mount to the large metal base plate that provides a massive heatsink.

Sounds like you have an aftermarket rectifier board with the bridge mounted above the PCB and a small heatsink on top.

Guess which solution is going to run cooler.

Are the rectifier boards identical between the two machines?

#3 8 months ago

The rectifier boards are identical but not the rest. The ltd. ed. has everything else original while the other machine has newer boards. Very useful info. Thanks!

#4 8 months ago

Just curious, which bridge is the one getting hot? Can you post a picture of the board?

#5 8 months ago

probably the feature lamp bridge. it usually gets hottest by far in normal conditions.

These transformers found in later bally games run pretty high voltage to the feature lamps. A few games like kings of steel and black pyramid i have picked up had all the lamps blackened and mostly burned out when i got it. There was over 7v going going to the feature lamps. 1volt difference between the two games would result in a lot more heat at the bridge for the higher voltage one.

Stick a big hunk of finned aluminum to it for a heat sink. You can buy one from China for like a buck. Might have to drill a hole to mount, but it will help your bridge survive.


#6 8 months ago

"Just curious, which bridge is the one getting hot? Can you post a picture of the board?"
Can't remember right now. The game is at a friends's place. But one stays luke warm while the other gets super hot. It's a newer Rottendog board (like 2 years old) but the original board was badly burned from all the heat.

#7 8 months ago

Is the game with the hot feature lamp bridge running incandescent lamps while the other game with cooler bridge running LEDs?
Incandescent lamps draw much more current, as a result its bridge rectifier will be more hotter.

#8 8 months ago

Here's a shot of the cooler game. After playing the bridge measures 52.5 Celsius which is noticeably warm. The other game runs at least 100 Celsius hotter, its like touching a frying pan.
Yes Quench, the other difference besides original versus newer boards, is LEDs versus incandescent. I am also wondering if there's a minor short somewhere that draws additional power. Maybe a bad light socket.

20190220_204107 (resized).jpg
#9 8 months ago

Incandescent lamps draw around 0.25 amps.
There are 90 odd feature lamps in this game.
Worst case with all feature lamps on, 90 times 0.25 is 22.5 amps being drawn from the feature lamp supply.
Presuming the diodes in the bridge rectifier have a voltage drop of 0.5 volts, with two diodes in series you lose 1 volt across the bridge.

1 volt times 22.5 amps means the bridge could potentially dissipate 22.5 watts!

Compare to running all LEDs. Standard LEDs draw 0.02 amps. SMD LEDs draw around 0.06 amps.

90 times 0.06 is 5.4 amps.
1 volt times 5.4 amps means the bridge could dissipate 5.4 watts (with all feature lamp LEDs on).

The game with incandescent lamps in the feature lamps is causing the bridge to dissipate 4 times the power compared to the game with LEDs in the feature lamps! That's why it's running much hotter. The thin aluminum heatsink is not sufficient enough to disperse the heat.

#10 8 months ago

Can you post a picture of the rectifier board it'self that shows the bridge. There should be a properly mounted heat sink on that bridge but it's impossible to tell without a close-up of the bridge.

#11 8 months ago

BigAl, the 52.5 Celsius is fine. The one that's overheating is at a friend's place. It has one of those 30x30 mm, cheap $1 passive heat sinks you buy at digi-key and some heat paste underneath. But that's totally insufficient. If I'd to guess I'd say it runs like 150 Celsius, possibly more. It will leave a blister if you touch it longer than 1 second.

#12 8 months ago

The heat sink looks pretty much like the one in this picture:
ebay.com link » New Power Supply Rectifier Module Board Bally Part As 2518 54
Might actually be the same model.

#13 8 months ago
Quoted from Yoski:

The heat sink looks pretty much like the one in this picture:

What brand of rectifier boards have you got? (you mentioned both machines had the same board fitted).
The rectifier board in your picture above has LED indicators for all the supply rails. Neither the Rottendog you mentioned, nor the board in the ebay link has LED indicators.

#14 8 months ago

Decades ago I’d externally wired my EBD bridges to the big mounting plate after the feature lamp one had burned out a second time. I think what must have happened was the bridges had been replaced on top by the previous owner and I didn’t know that was wrong. Can the same bridge work whether soldered onto the top or bottom, I’m not sure. It was before you could find out everything on the internet in two seconds and so long ago my memory is foggy as to how it all transpired. But I recently put in a Rottendog board so now it’s only a memory anyway. 8D

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