Bally MPU voltage issues: Insanity ensues

FireSlash

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Bally voltage issues: Insanity ensues

So, at the moment my Flash Gordon isn't booting. The LED on the MPU is dim,and does not flash.

voltage at the MPU is 4.1v (well below the minimum to start booting). The same voltage is found on the A3 solenoid board.

Originally it was also blowing F1, so I totally rebuilt the rectifier board. All voltages here look fantastic now.

This fixed the feature lamps, but the MPU's problem is unchanged. So, following a tip, I replaced the C23 capacitor. At the moment, it's still on order but I rigged up a couple of 450uF caps in parallel to see if that was actually the problem, and it's not. Same symptoms. low +5v rail. I'm out of ideas now, and I've not seen anyone else address a low voltage issue like this one before.

So perhaps someone else has an idea?
 
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Assuming that the voltage at TP5 is within range (10-12VDC) and the voltage at TP1 is well below +5VDC on the regulator/driver board I would suspect a bad +5V voltage regulator on the regulator/driver board. If the +5 checks out at the driver board you've got a voltage drop between it and the MPU most likely caused by bad connectors.

I've also seen bad solder joints or loose mounting screws at the voltage regulator cause low voltage.

More information:
http://www.pinrepair.com/bally/index1.htm#ps

EDIT:

Saw this in the other thread

If I short 40/39, the LED brightens up properly, and seems to start flashing.

That indicates a problem in the reset circuit on the MPU but you've still got a low voltage issue that needs to be dealt with.
 
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Tp5 is low as well, 9.4v

edit 2: Ok, I had a bad ground. Output on the rectifier is 11.7v DC. it's down to 10.1 by the time it gets to Tp3 at the solenoid board.

edit 3: Cleaned the contacts on the solenoid board, up to 11.0v DC. Still looking at a .7v drop from the solenoid board though.
 
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ok, went back and cleaned up a few solder joints, checked resistance between all connections, everything looks good on the rectifier now.

Tp3 reads 15.4v idle, 11.23v load (with J3 connected). This varies a bit, probably due to weak connections to Tp3 and gnd, but the highest I've seen it is 11.7v. Voltage is down to 10.98-11.1v by the time it gets to Tp5, which is well under range and explains the 4.23 at tp3.

Connectors have all been cleaned, not sure where to go from here.
 
Voltage is down to 10.98-11.1v by the time it gets to Tp5, which is well under range and explains the 4.23 at tp3.

Well... not really. You should still be seeing +5VDC at TP1 and TP3 (with harness connected) with TP5 down to about 6-7V. Assuming the jumper wire at J3 has good connections. I would be checking the +5VDC at TP1 and solder a jumper wire on the board between TP1 and TP3. This is explained in greater detail on pinrepair.com.

If you're still seeing ~4VDC at TP1 I would suspect a bad voltage regulator or bad connection at the voltage regulator.

I won't be surprised if you still have an MPU problem when the +5VDC is fixed but it needs to be fixed anyway.
 
Checked the MPU with a computer PSU (as outlined in that doc... great info). It gets 6 flashes. (I think. One flicker, then a flash, a pause, and 5 more).

TP1 and TP3 both read similarly low (4.45 and 4.53). I jumped them anyway, but it didn't improve the situation.

Interesting to note that if I unplug the MPU, the +5v rail settles in right at 4.98v (and +12 at 12.01v). However, the reverse is not true, the rail still sits at 4.5ish volts with the MPU plugged in, even if I pull the light and aux light boards. So I'm guessing it might be a grounding issue, or a problem with Q3 like you said. I'll clean the contacts and if that doesn't help, I'll start hunting up a replacement for q3.
 
Checked the MPU with a computer PSU (as outlined in that doc... great info). It gets 6 flashes. (I think. One flicker, then a flash, a pause, and 5 more).

TP1 and TP3 both read similarly low (4.45 and 4.53). I jumped them anyway, but it didn't improve the situation.

Interesting to note that if I unplug the MPU, the +5v rail settles in right at 4.98v (and +12 at 12.01v). However, the reverse is not true, the rail still sits at 4.5ish volts with the MPU plugged in, even if I pull the light and aux light boards. So I'm guessing it might be a grounding issue, or a problem with Q3 like you said. I'll clean the contacts and if that doesn't help, I'll start hunting up a replacement for q3.

The test before the 6th flash checks U11 and the display interrupt (generated by U12). You could use a logic probe or oscilloscope to check the output of the 555 timer (U12) but if you're seeing that much of a voltage drop with the MPU connected the offending component might be getting hot enough that you could find it by feel.

You could also swap the PIAs and see if you get more or less flashes. That would tell you you've got a bad PIA or PIA socket.

If you're going to do any serious work on the MPU it will be easiest to do it out of the machine. Your voltage regulator might be fine.
 
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I checked http://www.youtube.com/watch?v=IVB6A4CDGjk and verified that I was indeed seeing 6 flashes. The light then goes out, but doesn't come back on for the 7th. THe pause between flash 1 and 2 seems normal. And getting only 6 flashes on a computer PSU is normal, since the 7th requires an extra voltage connection that the PSU doesn't provide.

From that, I don't see how it could be anything BUT the voltage regulator. the MPU power draw is a bit suspect, but the low draw on the lamp driver is likely because most of the feature lights aren't lighting (only the drain special, 4x, and low bonus lights 1 and 4 are lighting. This may be normal during boot, or may indicate an issue with the lamp driver, or might be a side effect of it being underpowered. The number of lights vary, sometimes none at all light up, other times I only get the special lights. Also interesting to note that the 1 and 4 will turn off after a while of being on, and stay off for a period of time until it's left off for about an hour. I've since disconnected the primary and aux lamp driver boards.
 
I checked http://www.youtube.com/watch?v=IVB6A4CDGjk and verified that I was indeed seeing 6 flashes. The light then goes out, but doesn't come back on for the 7th. THe pause between flash 1 and 2 seems normal. And getting only 6 flashes on a computer PSU is normal, since the 7th requires an extra voltage connection that the PSU doesn't provide.

That makes sense. I thought you had 5 flashes and the MPU in the machine.

If you're testing the MPU out of the machine you can jump the display interrupt output to the zero cross input to fake out the 7th flash. This is explained on pinrepair.com.

Bally MPUs can be flaky when powered with a PC power supply. I've found that I have to do manual resets to boot MPUs on the bench when the same MPU will boot fine in a machine. My guess is that the switching power supplies take longer to become stable.

A longer reset is not necessarily a bad thing. You can add a cap (described on pinrepair) to lengthen the reset but I don't use that method personally.

If you need to rebuild the reset section I suggest using a Dallas DA1811 or equivalent instead of replacing the whole original circuit. Ed should have these:

http://www.greatplainselectronics.com

From that, I don't see how it could be anything BUT the voltage regulator.

Quite possible. Keep in mind that bad connections or loose mounting screws here can cause this problem. The case of the regulator needs to have a good connection to the trace on the back of the board. A lot of these screws have been soldered on the back of the board. If the solder cracks or the screw comes loose you won't have a good connection to the regulator and you'll see a voltage drop under load.

Or you could just have a bad regulator but I would check that stuff first.

the MPU power draw is a bit suspect,

The only way to really tell if it's really drawing more than it should would be with an ammeter, though I would have to test a "good" one to tell you what would be typical.

but the low draw on the lamp driver is likely because most of the feature lights aren't lighting (only the drain special, 4x, and low bonus lights 1 and 4 are lighting.

The lamps won't put much draw on the +5VDC supplied to the lamp driver board other than to turn on the SCRs to light the lamps but that shouldn't be much of a difference from no lamps on to all lamps on. The lamp current is flowing through the switched illumination circuit. I have never measured how much current each board draws (should do that) but I would suspect the lamp driver board will draw less than the MPU regardless of which lamps are on.

This may be normal during boot, or may indicate an issue with the lamp driver, or might be a side effect of it being underpowered. The number of lights vary, sometimes none at all light up, other times I only get the special lights. Also interesting to note that the 1 and 4 will turn off after a while of being on, and stay off for a period of time until it's left off for about an hour. I've since disconnected the primary and aux lamp driver boards.

I wouldn't worry about that until the MPU is booting consistently.

What I would do is fix the MPU out of the machine, then fix any power supply issues remain after fixing the MPU and go from there.

If you would like to do more thorough testing of your MPU I still have a couple of these available:

http://warpzonearcade.com/?p=356

I'll also have a better version coming out in the near future, but it will cost slightly more.
 
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I'm throwing in the towel on that board.

The front looked good so I hadn't pulled it until now. However, it's much worse than it looks. Several traces had burnt up and were jumpered. The high voltage line has crept completely out of control and is putting out +251v... which might explain why all but two of the displays are cooked. I'm not entirely sure (this is listed as in line in some places, others say it should be set to 170-180v) Furthermore the voltage adjust seems to do nothing. the 5v rail is still screwy after reflowing all of the shady looking solder joints, and I suspect by the time I've ordered all of the parts to progressively fix it (after figuring in shipping), it'll be cheaper to just buy a known-working rebuild.
 
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I'm throwing in the towel on that board.

The front looked good so I hadn't pulled it until now. However, it's much worse than it looks. Several traces had burnt up and were jumpered. The high voltage line has crept completely out of control and is putting out +251v... which might explain why all but two of the displays are cooked. I'm not entirely sure (this is listed as in line in some places, others say it should be set to 170-180v) Furthermore the voltage adjust seems to do nothing. the 5v rail is still screwy after reflowing all of the shady looking solder joints, and I suspect by the time I've ordered all of the parts to progressively fix it (after figuring in shipping), it'll be cheaper to just buy a known-working rebuild.

The display voltage starts out at 250VDC (give or take)....it then gets regulated down to the 170-180VDC on the driver/regulator board. Something in the high voltage regulation section has bit the dust and letting the full 250VDC pass through to your displays. This is also explained in detail in the pinrepair link Lindsey is linking :)

Edward
 
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