Cal Omega CEI Double Up Poker 1982 Troubleshooting - Need Help!

[rokgpsman]

Pulling the motherboard is the most difficult component. If all the voltages are in check, I would rather leave it in place, but I will pull if I have to, not a big deal.

I am considering swapping cap C52 below the empty eprom with cap C45 located above the empty eprom U5/1800.

Is there some damage with C52 or C45?

[RPMcKenna1976]

Pulling the motherboard is the most difficult component. If all the voltages are in check, I would rather leave it in place, but I will pull if I have to, not a big deal.

I am considering swapping cap C52 below the empty eprom with cap C45 located above the empty eprom U5/1800.

Is there some damage with C52 or C45?

Photo 3 in my second last post shows the burned cap.

[RPMcKenna1976]

Just performed the cap swap with the same/similar results. Feels like it is so close to working it's not even funny...

[rokgpsman]

.....
C60 is visible in the first photo. It will be very difficult to test this connection with the mpu plugged in unless i make a lead from it to my multi.
.....

That reddish part is CR60 (I know that's what you meant to type) and the drawing shows that it should have 15 volts ac across it. You might be able to connect two wires to it, one on each lead. They don't have to be soldered, just wrapped a couple of time to hold in place. The 2 wires can run out to where you can connect the meter to them. This is a rig, don't do it if you don't think it can be done safely. We may be able to find the pins on the mpu board connector on the motherboard (backplane) where the 15 vac comes from and measure it there.

[shortrackskater]

I am thinking the next step is to pull the 908 Motherboard/Backplain and check the traces.


Something's not adding up here.

What if there's a quarter wedged behind the motherboard? Just sayin'...

[RPMcKenna1976]

I am thinking the next step is to pull the 908 Motherboard/Backplain and check the traces.


Something's not adding up here.

What if there's a quarter wedged behind the motherboard? Just sayin'...

It's funny that you mention that, while we were hauling the machine into the basement/rec-room I heard that familiar sound of a coin bounce inside the machine, turned out to be a quarter lol. I do not believe that to be the root of the problem though.

.....
C60 is visible in the first photo. It will be very difficult to test this connection with the mpu plugged in unless i make a lead from it to my multi.
.....

That reddish part is CR60 (I know that's what you meant to type) and the drawing shows that it should have 15 volts ac across it. You might be able to connect two wires to it, one on each lead. They don't have to be soldered, just wrapped a couple of time to hold in place. The 2 wires can run out to where you can connect the meter to them. This is a rig, don't do it if you don't think it can be done safely. We may be able to find the pins on the mpu board connector on the motherboard (backplane) where the 15 vac comes from and measure it there.

I just finished lightly cleaning the board with 99.9% isopropyl alcohol. There is a sporous odour in the machine and on the board as I was cleaning, either from humidity that the machine was exposed to or water damage at some point. About to test in a few minutes. If still no luck, that will be my next step. Likely tomorrow though as it's getting to the wee hours of the morning here (3am).. Need some sleep soon as tomorrow is another day.

[Paul]

The green around the cap that looks burned could be leaking acid from the cap.
I would replace all the electrolytic capacitors on the board to be on the safe side.
A shorted cap can bring down the voltage and stop the board from booting.
Plus those caps are around 30 years old and they work like batterys.

[RPMcKenna1976]

The green around the cap that looks burned could be leaking acid from the cap.
I would replace all the electrolytic capacitors on the board to be on the safe side.
A shorted cap can bring down the voltage and stop the board from booting.
Plus those caps are around 30 years old and they work like batterys.

Duly noted. I'll have to check at the local electronics depot to see if they carry the parts and if not, I'll have to locate some online. I have run into similar problems troubleshooting computers through the years and it makes sense.


After letting the alcohol dry and testing, it has the same results.


See ya all tomorrow.


Have a good one!

[rokgpsman]

From reading thru another repair thread the advice from a NLG user named Dormi, who has good experience with these machines, is to make sure that the mpu board is getting 4 important voltages. They need to be measured on the mpu so you are sure they are getting thru the various connectors and wires in the machine to the mpu board. If these 4 voltages are ok and  the 15vac circuit is adjusted as he says and the game doesn't play then it usually means the mpu board has a problem. That means you are looking at figuring out if the mpu is good or not. You'd need to install another mpu board that is known to be good to see if that fixes the machine, or send out your mpu to someone to have them test it.

He lists those 4 voltages to check on the mpu as:
1) the regulated 5 vdc, it can be measured on the thin green wafer caps near any eprom (you've done this)
2) the regulated 12 vdc, you've checked this on the backplane but need to know it is getting to the mpu
3) unregulated 12 vdc
4) 15 volts AC, measured across the MOV that is reddish in color, looks like a diode. This voltage is used by the mpu to know if the 115 vac power coming in from the wall socket is good. This circuit on the mpu can shutdown the mpu and not let it boot up if it thinks the 115 vac is too low. This can be a troublesome circuit on the mpu and cause unintended problems. Since the home user has reliable 115 vac electricity his advice is to turn the adjustment pot in this circuit all the way clockwise so this circuit won't ever shut down the MPU board. If you aren’t sure which way to turn you can try all the way to one side, then see if the machine works. If not, turn the adjustment pot all the way in the other direction and try again.

Unfortunately, the places on the mpu to measure these voltages in that other thread are on a 905 mpu board, you have a 903 mpu board. So the parts designators and locations like C3, R74 and CR25 are called different names on your mpu.

Here is one of your photos with some notes that might help, not sure.

[RPMcKenna1976]

From reading thru another repair thread the advice from a NLG user named Dormi, who has good experience with these machines, is to make sure that the mpu board is getting 4 important voltages. They need to be measured on the mpu so you are sure they are getting thru the various connectors and wires in the machine to the mpu board. If these 4 voltages are ok and  the 15vac circuit is adjusted as he says and the game doesn't play then it usually means the mpu board has a problem. That means you are looking at figuring out if the mpu is good or not. You'd need to install another mpu board that is known to be good to see if that fixes the machine, or send out your mpu to someone to have them test it.

He lists those 4 voltages to check on the mpu as:
1) the regulated 5 vdc, it can be measured on the thin green wafer caps near any eprom (you've done this)
2) the regulated 12 vdc, you've checked this on the backplane but need to know it is getting to the mpu
3) unregulated 12 vdc
4) 15 volts AC, measured across the MOV that is reddish in color, looks like a diode. This voltage is used by the mpu to know if the 115 vac power coming in from the wall socket is good. This circuit on the mpu can shutdown the mpu and not let it boot up if it thinks the 115 vac is too low. This can be a troublesome circuit on the mpu and cause unintended problems. Since the home user has reliable 115 vac electricity his advice is to turn the adjustment pot in this circuit all the way clockwise so this circuit won't ever shut down the MPU board. If you aren’t sure which way to turn you can try all the way to one side, then see if the machine works. If not, turn the adjustment pot all the way in the other direction and try again.

Unfortunately, the places on the mpu to measure these voltages in that other thread are on a 905 mpu board, you have a 903 mpu board. So the parts designators and locations like C3, R74 and CR25 are called different names on your mpu.

Here is one of your photos with some notes that might help, not sure.

Fantastic info, thank you for digging it up!


Do you happen to know where to test for the regulated and unregulated 12vdc? I should be able to manage testing the 115vac a little bit later as I have to step out for a bit. I have already adjusted R33 full clockwise with the same results so measuring CR60 would seem to be the next logical step. I'll report back later with my findings.


Cheers,


Rick.

[rokgpsman]

Fantastic info, thank you for digging it up!

Do you happen to know where to test for the regulated and unregulated 12vdc? I should be able to manage testing the 115vac a little bit later as I have to step out for a bit. I have already adjusted R33 full clockwise with the same results so measuring CR60 would seem to be the next logical step. I'll report back later with my findings.

Cheers,
Rick.

not sure about those 2 voltages you mentioned, that's why I wasn't able to list where to measure them in my earlier post. I trying to go thru the 903 board schematics you sent to be able to advise where to measure those voltages. One idea is that there is a larger capacitor in one corner of your mpu board (see photo below) that may have one of these voltages across it. It looks like a typical filter cap for something like that. If you want to measure the voltage on it we'll see what's there.

Just to clarify, the voltage on the reddish MOV part CR60 isn't 115 vac, it is only 15 vac. But it does represent the 115 vac coming in to the machine on the line power cord from your wall socket. If that line voltage drops then the 15 vac also drops. That's what the circuit on the mpu board watches, to see if the 15 vac drops to a level that means the machine's main input power is unreliable. But it isn't really needed for home users, so best to defeat the circuit by turning that adjustment pot all the way down.

[RPMcKenna1976]

Fantastic info, thank you for digging it up!

Do you happen to know where to test for the regulated and unregulated 12vdc? I should be able to manage testing the 115vac a little bit later as I have to step out for a bit. I have already adjusted R33 full clockwise with the same results so measuring CR60 would seem to be the next logical step. I'll report back later with my findings.

Cheers,
Rick.

not sure about those 2 voltages you mentioned, that's why I wasn't able to list where to measure them in my earlier post. I trying to go thru the 903 board schematics you sent to be able to advise where to measure those voltages. One idea is that there is a larger capacitor in one corner of your mpu board (see photo below) that may have one of these voltages across it. It looks like a typical filter cap for something like that. If you want to measure the voltage on it we'll see what's there.

Just to clarify, the voltage on the reddish MOV part CR60 isn't 115 vac, it is only 15 vac. But it does represent the 115 vac coming in to the machine on the line power cord from your wall socket. If that line voltage drops then the 15 vac also drops. That's what the circuit on the mpu board watches, to see if the 15 vac drops to a level that means the machine's main input power is unreliable. But it isn't really needed for home users, so best to defeat the circuit by turning that adjustment pot all the way down.

After testing CR60 I am reading 13vac, is this too low or is it potentially indicating a motherboard problem? Pot is turned fully clockwise.


The capacitor mentioned in your last post measures 12vdc. Looks to be on par with operating standards.

[rokgpsman]

I don't know how low the 15 vac input to the mpu board can go before the mpu board gets shutdown by that circuit with the R33 pot adjustment. Even with the adjustment pot R33 set all the way clockwise that voltage of 13 vac may be low enough to cause a problem.

Dormi or SolidSilver may know if this is something to be concerned about, maybe one of them or someone else will see this and give advice. Meanwhile I will see if I can find anything on this.

This is a possibility on your problem, glad you found it, we need to run it down.

If you want to try something here is an idea-

Do you see an ic near that R33 pot, it will be marked "LM311" or similar? It should have U37 written on the board near it. This is the circuit that shuts down the mpu if the 15 vac is too low. When you adjust the pot R33 from one end of travel to the other you should be able to measure a change in voltage on pin 7 of U37. If that isn't happening then the 15 vac input is too low. If you can measure U37 pin 7 with the pot all the way to one side, then measure it again with the pot all the way to the other extreme we will know something.

You can use any DC ground for your meter black lead, may have to solder a wire to U37 pin 7 to run it out for your meter to attach to the red lead. I wish it was easier to reach this area of the mpu, can you remove anything like a housing or card cage that is in the way?

Also look for a part labelled U36 near this same area. It is the switch FET that actually does the shutdown. We may do something tricky with it later.

Below is an example of an 8 pin ic and how the legs are numbered. Notice there is a notch on one end of the chip, this is the top edge, pin 1 is on the left corner. Look for the same notch on U37, sometimes instead of a notch there is a small circular indentation by a corner for the pin 1 indicator, I can't tell in the photo what you have. If unsure post a closeup of U37 area. Pin 7 is on the right side, second from the top.

     Forgot to ask earlier, do you have a soldering iron and if so, are you dangerous with it? 

EDIT - I fixed some typos in this post.

[rokgpsman]

What if there's a quarter wedged behind the motherboard? Just sayin'...

It's funny that you mention that, while we were hauling the machine into the basement/rec-room I heard that familiar sound of a coin bounce inside the machine, turned out to be a quarter lol. I do not believe that to be the root of the problem though.

You'd be surprised, we've heard from people that found a coin jammed in someplace causing a problem. These old machines sometimes get hauled in a vehicle laying on their side, or get rolled over sideways, so anything loose inside can bounce all over the place.

[RPMcKenna1976]

I don't know how low the 15 vac input to the mpu board can go before the mpu board gets shutdown by that circuit with the R33 pot adjustment. Even with the adjustment pot R33 set all the way clockwise that voltage of 13 vac may be low enough to cause a problem.

Dormi or SolidSilver may know if this is something to be concerned about, maybe one of them or someone else will see this and give advice. Meanwhile I will see if I can find anything on this.

This is a possibility on your problem, glad you found it, we need to run it down.

If you want to try something here is an idea-

Do you see an ic near that R33 pot, it will be marked "LM311" or similar? It should have U37 written on the board near it. This is the circuit that shuts down the mpu if the 15 vac is too low. When you adjust the pot R33 from one end of travel to the other you should be able to measure a change in voltage on pin 7 of U37. If that isn't happening then the 15 vac input is too low. If you can measure U37 pin 7 with the pot all the way to one side, then measure it again with the pot all the way to the other extreme we will know something.

You can use any DC ground for your meter black lead, may have to solder a wire to U37 pin 7 to run it out for your meter to attach to the red lead. I wish it was easier to reach this area of the mpu, can you remove anything like a housing or card cage that is in the way?

Also look for a part labelled U36 near this same area. It is the switch FET that actually does the shutdown. We may do something tricky with it later.

Below is an example of an 8 pin ic and how the legs are numbered. Notice there is a notch on one end of the chip, this is the top edge, pin 1 is on the left corner. Look for the same notch on U37, sometimes instead of a notch there is a small circular indentation by a corner for the pin 1 indicator, I can't tell in the photo what you have. If unsure post a closeup of U37 area. Pin 7 is on the right side, second from the top.

     Forgot to ask earlier, do you have a soldering iron and if so, are you dangerous with it? 

EDIT - I fixed some typos in this post.

I do have a soldering iron and know just enough to be dangerous! I have already done a little bit of re-work on the board and added the new battery pack.


I am unsure if I will be able to get around to making the measurements tonight as there is some company over but I will get around to it as soon as possible. There is not much that can be done as far as freeing up any space to work on the motherboard in the cabinet. I manages to find a pair of esd (electro static discharge)wrist straps with alligator clips at one end with long enough insulated leads that I am taking the measurements from (thankful I did not get rid of all my tech tools through the years). These esd straps are going to make the job a whole lot easier and safer for taking measurements. I'll post a couple of pics later/tomorrow of how it goes together for anyone interested. Pretty basic but useful.


The components that are closer to the motherboard/backplain have to be measured by:


1.) Turning off the machine
2.) Pull the MPU
3.) Connect leads
4.) Install MPU
5.) Power up machine
6.) Take measurement


The above process has to be repeated for each measurement.


When measuring pin 7 of U37, is it AC or DC thtat we are looking for?


I have worked on thousands of computers through the years, this old arcade machine is not a whole lot different in many aspects and your detailed guidance is like electronics 101. I have learnt a lot being here for the past week or so, and am thankful to you and everyone else for the guidance and support.


Will be back on tonight if possible.

[RPMcKenna1976]

My oversight, measure DC voltage for U37. Should have caught this when you said to ground to DC 

[rokgpsman]

No problem on taking a break anytime you need to or want to. In fact it is sometimes good to get away from a problem, forget about it, come back later refreshed. And if you get tired of my ideas, or someone chimes in with a good-sounding idea you want to try then by all means go for it. I don't want to monopolize this repair thread, I would be ok to be reading and following along while someone else drives this choo-choo, especially someone that is more familiar with your machine.

Yes, the output of U37 is a dc voltage. U37 is an Op-Amp (operational amplifier). It is setup in this circuit to have a logic high output (pin 7) when the 15 vac coming in is good. The 4 diodes nearby to the R33 pot are in a full wave bridge configuration, they change the 15 vac to a dc voltage that runs thru the adjustment pot R33. The wiper of R33 (center arm, pickoff arm) connects this dc voltage to an input on U37 pin 2. This dc voltage can go up or down if the 15 vac coming to the mpu goes up or down and it represents the 115 vac line power your machine is plugged into.

U37 has a second input, on pin 3, and it is a reference for comparison to pin 2. This input on U37 pin 3 is held at a constant voltage of 5.6 vdc by a nearby zener diode called CR61. If the voltage on U37 pin 2 drops below the reference voltage on U37 pin 3 that means the 15 vac input voltage has dropped too far and the U37 output on pin 7 now goes to a logic low. This will cause the mpu to be shutdown. The R33 adjustment pot is used to set the voltage on U37-2 so this circuit operates properly when the ac power to the machine is ok. You want the voltage on U37 pin 2 to be as high a voltage as possible, that's why you turn the R33 pot all the way one direction. I'm not sure which way clockwise is on R33, I suppose it is with you facing the front of R33. Is that how you did it?



 

[RPMcKenna1976]

U37 = 2.8-2.9vdc


What a pain in the butt rigging that lead cable from pin 7...

[rokgpsman]

If the wire to measure U37-7 is still attached can you turn R33 all the way to opposite direction and measure U37-7 again?

[RPMcKenna1976]

I'm not sure which way clockwise is on R33, I suppose it is with you facing the front of R33. Is that how you did it?

That is how I did it.