(Topic ID: 180430)

GamePlan Sharpshooter: boots halfway

By Alan_L

7 years ago


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  • 18 posts
  • 2 Pinsiders participating
  • Latest reply 7 years ago by Alan_L
  • Topic is favorited by 1 Pinsider

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#1 7 years ago

I'm getting back to my "bete noir", a GPN Sharpshooter after a year because I have some people interested in it and I can't just let it sit there.

I get three of six flashes on power up which indicates a bad 6810 IC. I have replaced the 6810, Z80CPU and a half dozen other chips, still three flashes.

When power on the CPU I found that I have 2.18 VDC on TP5, and only millivolts on TP3. The wretched schematic that comes with this thing really does not show what the readings should be for these TPs.

Looking for ideas as to why I have no voltage at TP3 and if 2.18 at TP5 is correct. Also, any other suggestions as to why I have only three flashes with a good 6810.

Let's hope that we have an exiting game tomorrow.

#2 7 years ago

See the explanation below for the indicators on the MPU schematic for TP3 and TP5:

TP5 is a clock signal that swings at high speed between 0 and 5 volts so it doesn't have a static voltage to measure. You'd need a scope to properly see it but since the game is going through the Power On Self Test, the CPU is operating meaning the clock signal should be ok.
This signal spends almost half the time at 5 volts and the other time at 0 volts. If you measure with a volt meter you'll get an average about half way.

Both voltages you measured on TP3 and TP5 look ok.

Is the 6810 socket in good clean shape?
What other chips did you replace?
Does the board have any battery corrosion?

GP_TP.jpgGP_TP.jpg

1 week later
#3 7 years ago

Sorry for the long time to reply, got called away to another project,

I found a lifted pad underneath the 6810 socket, fixed and reinstalled it. I have replaced the Z80 CPU and about a half dozen others. No battery corrosion.

However, when I went to reinstall the MPU, for some stupid reason I had the game turned on when I plugged the J1 power supply connector. Zap! I blew the 5amp fuse and something else. Just nanovolts at TP1. I have replaced the LM323K voltage regulator and still no 5 volts, even at the regulator. I noticed a component labeled L60V5 on the power supply board schematic, but I can't find it on the board. Is this an inductor that's behind the board where I can't see it? Where else should I look to get my 5 volts back?

Thanks for your help.

#4 7 years ago

You'll need to isolate the problem and move through the voltage chain.

Is there around 12V on both sides of the 5A fuse?
Does the LM323 regulator have about 12DC on the input pin (violet/red wire)?
Does it have 5V on the output pin (red/yellow wire)?

Not sure that the L60V5 is. Would need to see full pictures of the area and power rectifier board.

#5 7 years ago

I only have less than 1 VDC at all these locations. The LM323K is on the back side of the metal plate above the rectifier board. See pic. Could I have blown the 15K uf cap?

20170218_090707 (resized).jpg20170218_090707 (resized).jpg

#6 7 years ago
Quoted from Alan_L:

I only have less than 1 VDC at all these locations.

You have less than 1VDC even at both sides of the 5A fuse?
If you take a step back up the voltage chain, maybe the bridge rectifier is blown (open circuit).
If you set your multi-meter to read AC voltage and measure across the AC pins on the bridge rectifier that's connected to the 5A fuse (I think it's the bridge rectifier closer to the LM323 and one of the AC pins look to have a white/blue wire, the other AC pin will be diagonally opposite), what voltage do you get?

#7 7 years ago

8.85 VAC.

#8 7 years ago

The schematic says 10.5VAC, but we'll take 8.85VAC for now.

Disconnect the machine from the wall and remove the 5A fuse to isolate the bridge rectifier.
If you know how to test diodes with your meter, check that bridge rectifier (it's basically made up of 4 diodes). You might need to disconnect one side of that large capacitor so it doesn't affect your readings.

#9 7 years ago

Removed 5 amp SB fuse and 1 leg of cap. All 3 bridges give the same readings at diode position when testing bridges, roughly .423 to .654

#10 7 years ago

With the 5A fuse still removed, power the machine on. What are the DC voltages you're getting from ground to each side of the fuse clips?

#11 7 years ago

9.45VDC on the top clip and 9.40 on the bottom. I thought the outside fuse (nearest the cap) was the 5 amp as it had a 5 amp fb fuse in it. Should have been a 3 amp SB. All fuses are now correct. Sorry 'bout that. The large cap is still unhooked.

#12 7 years ago

So you've got about 9.4VDC at the 5A fuse but less than 1VDC at the input pin of the LM323 regulator? Check the ceramic 0.5 ohm resistor, it might be open circuit.

#13 7 years ago

I have continuity between the legs of one of the 0.6 ohm resistors with the power off. With power on, I have a null reading. The other resistor reads null either way

#14 7 years ago
Quoted from Alan_L:

I have continuity between the legs of one of the 0.6 ohm resistors with the power off. With power on, I have a null reading. The other resistor reads null either way

By "null reading" do you mean no voltage or something else?

What voltage are you reading on each side of the 0.5 ohm resistor with the machine on? Looking at the third picture of the first post on this thread, the 0.5 ohm resistor is probably the bright white one right in the middle of the circuit board:
https://pinside.com/pinball/forum/topic/game-plan-sharpshooter-voltage-issues

Pull the circuit board out and see if any traces have burnt/blown off the back.

#15 7 years ago

A null reading to me is when the DMM says "OL" , out of limits, the opposite of .000: an open circuit.
With power on I get 10.19VDC at the end nearest the fuses and no volts at the other end. Removing board now.

#16 7 years ago

No damage to traces on the back of the board.

#17 7 years ago
Quoted from Alan_L:

With power on I get 10.19VDC at the end nearest the fuses and no volts at the other end.

Then that resistor must be open circuit (faulty).

Being 0.5 ohms, it's value is such a low resistance that it's practically a short circuit so a good one will measure almost the same (10VDC) on each side when the machine is powered. It's essentially there as a fuse.
Unsolder it and test it out of circuit to confirm.
The schematic says it's a 0.5 ohm, 5 watt resistor.

BTW, hook up the capacitor again if you haven't.

#18 7 years ago

Thanks, Quench.

I will R&R it and let you know what turns out.

I'm heading out to the Snowbrawl pinball tournament at Crabtown in Glen Burnie, MD. Going to get a chance to see some real pros play.

Thanks again for your help,

Alan

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