Skateball MPU resistor (TECH)

tomdotcom

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Skateball MPU resistor (TECH) UPDATED almost there...

Hey guys I just got my new rectifier board installed on my skateball.
I got the board from pin-logic.

But, I'm still having an issue with my MPU board. R113 resistor on the
MPU is heating up and burning in the middle basically. I did replace
the old one because it was doing the same thing. It's value is 2k 1/4
watt.

I believe it's +43vdc on connector J4 on the MPU.

Any ideas what might be causing this to happen?

The game lights power up and the machine powers up, but the displays
don't come on and that rectifier burns up on start up. Where do I go
from here?

Thanks!

Tom
 
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Little bit of info I've found so far, still not sure where to go with this:

This resistor takes the 43 volt DC coil power to the zero-crossing detector circuitry and
normally runs hot. Hence it may eventually go open, so check it if
only 5 flashes from the LED are seen.

Interesting...R113 and R16 are part of the Zero Crossing Detector
circuit and go across the 43VDC and ground...for them to go up in
smoke you have to somehow put a LOT more voltage across them...like
200VDC or so...
 
Little bit of info I've found so far, still not sure where to go with this:

This resistor takes the 43 volt DC coil power to the zero-crossing detector circuitry and
normally runs hot. Hence it may eventually go open, so check it if
only 5 flashes from the LED are seen.

I'm pretty sure I already mentioned that, though you will get 6 flashes. The 7th flash is the zero crossing detector. I've seen this before and I replace the 1/4 watt resistor with 1/2 watt but I don't suggest you do that in this case until you fix the other problems. A larger wattage resistor in this case could actually make the problem worse.

Interesting...R113 and R16 are part of the Zero Crossing Detector
circuit and go across the 43VDC and ground...for them to go up in
smoke you have to somehow put a LOT more voltage across them...like
200VDC or so...

Amperage is what will burn stuff. You could run 200V though a 1/4 watt resistor with no problem at the right amperage.

If R113 is burning you've probably got something shorted in the zero crossing detector circuit opening a path for way too much current to go through R113. I would suspect R16, CR49 or the gate in U14. You could have some other problem like traces shorted on the board but I would check those things first. I wouldn't be surprised if R113 is acting as a fuse for a shorted gate in U14 (U14a or U14b). If none of that stuff is shorted I would check R17 and R18. I would expect whatever is shorted to get hot too.

Does the MPU boot? Do you get the 7th flash?
 
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I haven't run into this before myself, but just thinking about it:

R113 and R16 form a voltage divider, halving the voltage, which is fed to U14 via R17. If R17 isn't running hot, then the excessive current isn't heading toward U14, it's all in the divider. Both R113 and R16 being 2k each, at 43 vdc, the total current draw of the divider portion of the circuit would normally be about 1/4 watt on each resistor. If either one of the resistors is shorted, then the total circuit resistance would drop to 2k (instead of 4k) putting 1 watt on the non shorted resistor.

Ok, so there's the description of how the resistors could burn without excessive voltage.

To isolate your problem, see if R17 is hot too. If not, check both R113 AND R16. If either of them is less than 2k, the other will fry. If R17 is hot/warm, then the current is heading toward U14. Did you already verify 5vdc to the board? If the 5vdc is missing or really low, the zero crossing circuit may be trying to power the 5vdc rail via CR49.

If all that is ok, it would be a good time to back up and re-evaluate the board for other issues, with no flashes at all, you may have bigger problems. Back the 43v wire out of the connector and see if you get any flashes or avtivity at all. If not, you might want to try and see why the board isn't booting before you go any further.

D
 
I measured test point 3 on the MPU. The schematic says it's supposed to be 21VDC but my meter came up as 148.

Ratz, my other post came at the same time as this one.

148 !! Man, nasty short somewhere in the power chain. UNPLUG That MPU now before you get any other damage and go back over the power chain, something has to be miswired or plugged in incorrectly.

D
 
Hopefully I tested it right. I just put my meter on DC volts. Put the red lead on test point 3 and the black to ground. That's the proper way to do it right?

So if I'm getting 148 there I must have something wired wrong on the rectifier board somehow? I wired it all according to the instructions. The old rectifier board was causing this same issue. Maybe I have something wrong with the transformer itself or the wires on the transformer lugs maybe are shorted or something?
 
Ratz, my other post came at the same time as this one.

148 !! Man, nasty short somewhere in the power chain. UNPLUG That MPU now before you get any other damage and go back over the power chain, something has to be miswired or plugged in incorrectly.

D

Yeah... that's not good at all. I would isolate the rectifier board and test it.

Time to trace the power though the machine. You definitely should have tested the voltages at the rectifier board when you installed the new one.

I assumed you had checked that (solenoid voltage at MPU). Silly me :)
 
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Ya I'm not the greatest with a multimeter by a longshot. This is all pretty new to me.

I replaced the resistors again, this time I replaced r113 and r16.

How exactly can I test my rectifier/power? Probably not a simple answer.

MAybe I need to go read some guides that explain how to test my rectifier/power supply.
 
Okay I've read through marvin's guide a bit more.

I tested all the test points on the rectifier board (with j1 & j3
unplugged)

Here are the results:
test point 1
6.15

2
149

3
11.22

4
6.6

5
44.4
 
Here is what the specs are from the manual/repair guides:

* TP1 (on AS2518-18) = 5.4 volts DC +/- .8 volts (4.6 to 6.2
volts). Fuse F1, bridge BR1. Used to power the "switched
illumination" (feature lamps).
* TP1 (on AS2518-49 & -54) = 6.5 volts DC (5.8 to 7.2 volts). Fuse
F1, voltage regulator RP1 and RP2. Used to power the "switched
illumination" (feature lamps).
* TP2 = 230 volts DC, +/- 27 volts (203 to 257 volts). Fuse F2,
diodes CR1 to CR4. Used to power the score displays.
* TP3 = 12 volts DC (11 to 16 volts). Fuse F3, bridge BR2. Used to
power the regulated +5 volts DC for the game's logic circuits.
* TP4 = 7.3 volts AC, +/- 1.0 volts (6.3 to 8.3 volts). Fuse F5.
Used to power the general illumination.
* TP5 = 43 volts DC, +/- 5.4 volts (47.6 to 48.4 volts). Fuse F4,
bridge BR3. Used to power all the coils.
 
Okay I should now be testing ALL the wires that go into j1 & j3? To
make sure the proper wire is going to the right place?

How do I test the wires coming into j1 & j3? I have a chart that says
all the proper voltages and what not. But I'm not sure where to put my
multimeter exactly to test each wire individually..

I know alot of my questions sound stupid. But I
am trying. I've got this far, no use stopping now :)
 
bstnguy is sending me a Solenoid driver board. Mine had issues before the pin died on me. So maybe something is shorted or screwed up on my old one...not sure if that could even have anything to do with it at all though...
 
I would offer to have you send me all the boards for repair but shipping the transformer might be kind of expensive. Let me know if you're interested in doing that.
 
Ok I traced all the wires by hand and using the schematics. All the
wires line up for connector J3 on the transformer board going to the
all the other boards. Except for one exception.

I have the transformer wire from a2j3-13 going to Solenoid Driver
board a3j3-5. The plug connector schematic says its supposed to go
from a2j3-13 to SOL. BUSS

I have no wire at a2j3-9. The plug connector schematic says its
supposed to go to a3j3-5, a8j1-9.

Thoughts? Would this cause my issue possibly?
 
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