Driving game display issues

[robm]

Guys,

Just picked up the Sega Cool Riders driving game, mostly working. (This is the 1st time i've every opened one of these up, so i'm making it all up from here....unfortunately i can't find any circuit diagrams etc for the game)

Everything seems OK, sound is a little scratchy but both displays are really pixelated - see pic.

I've reseated all the cables (as i would on a pin!) and thats about it.  There is a note on the main CPU that says "As discussed, i could find no fault (on both video outputs) ran OK for 20 hrs, Steve"

So from this, i assume "Steve" knows far more than me (and was sent the CPU for testing) , and it seems the CPU and other boards are all OK, which indicates the problem is most likely between the CPU and the monitors

Anyone got ideas where to start looking....

Thanks

Rob

[MartyJ]

What I don't know about arcade stuff could fill a warehouse..BUT I did have a Rave Racer with a similar problem.

Mine ran off a JAMMA power supply and the voltage was out (can't remember if too high or low) on the +5V.

Not sure if yours even has the same PSU but worth a look.

[robm]

Marty,

you may be onto something here - dunno about my logic BUT

When i test on the PSU (the silver one - is the black one a PSU as well????) there is a good 5V and 12V on the appropriate lugs IF i put the -ve lead of the multimeter on the GND tab of the PSU

However, 

If i put the -ve lead on some of the earth screws (green wires in the pic) i get only millivolts - does this mean there are some potentially bad earths and they all need a good clean or am i wandering down the wrong path all together and i shouldn't be getting a reading off these screws anyway?

[Strangeways]

+1 - What Marty said - Check +5 V, and edge connectors.

[MartyJ]

The black one sure looks like a PSU too.  Check the voltages on that one as well.  Do both machines have 2 x PSU?

There looks to be some funky wiring with the tape around the silver one too.  I'd be careful around those and make sure the repairs are OK.

The 5v should be checked at the PSU and at the corresponding wire at the JAMMA edge connector as well.  WIth machine off - make sure your earth's are clean and not rusted.  I think you can use a DMM on ohm and check the earth points to the earth on your power plug (unplugged).  In the back of my mind I have a figure of less than 2ohm is what it should be - but I really am running out of RAM on that so I'd check with someone who's got more experience in that area than I.

[narf]

there both PS

id check the voltage straight at the connector. you be surprised the voltage drop is along the way

[robm]

On the board connector i have 5.02, 5.03 for the 5v and 11.94 for the 12V - is this OK?


Do both machines have 2 x PSU?

One machine has all the CPU, PSU and boards in it - the other just has some plugs going into the back

[shansta]

Looks like the video ram is being corrupted?

You will have better luck on AussieArcade - lots more guys on there who play with these things...

[FirePower]

I have no experience with these style of machines, so offer the following just as food for thought or avenues for investigation.

It's not unusual to have the earth of a system commoned to the 0V.  With two independent power supplies as you have, notwithstanding it looks like one has been added later or repaired, it would not surprise me to see the 0V of both supplies and the earth tied together.

You could most likely confirm this just by visual examination of the wiring.

If the second supply has been added as a bodge to beef up the supply they would almost certainly want to have a common 0V.  I can't read the labelling on the silver psu, but I'd be verifying how it is wired in relation to the black one. Maybe as the +12V on the black psu is not wired it has failed and this is the function of the silver one, to provide the failed 12V?  The black "looks" more original to me.  What do the terminal labels of the silver psu read?

With the power off and unplugged I'd remove the yellow / green wire to the PG (protective ground) terminal on the black psu and measure the resistance between this PG and the terminal labelled GND.  Try this with the silver one too if you can find 0V and ground (earth) terminals. I'd expect close to zero ohms.  (The two ohms mentioned elsewhere is the wiring standards maximum resistance between the earth stake and any other point on your house wiring, so not that directly relevant here) Maybe then report back and the results of your visual wire tracing.

In any case cleaning up the rusty earth cannot do you any harm - but WORK WITH THE POWER OFF! And ensure the outlet you are using it on is rcd protected. This is good advise for any of us amateurs playing on this forum.

[narf]

jomac does board repairs also

not sure if joey is on here though

[robm]

Thanks heaps for the info so far

All my points are on a RCD, and am very particular about unplugging.

Dunno if another angle will help at all

The black PSU is                          silver PSU

 +12                                          +5
 -5                                            GND
 GND                                          GND
+5                                             +12
+5                                             NC
FG                                             FG
AC                                            ~
AC                                            ~

GND's are connected
+5's are connected
FG's are connected
AC's to ~ are connected

there is no connection between the +12, and this would be due to the fact that there is no +12 on the black PSU - spot on Firepower - it seems the silver one is an add on.

When i took the FG off the black PSU there was no reading for resistance (or continuity) between FG and GND - same on the silver one.  Resistance between the FG and the earth screws was around 0.5 ohm

[robm]

OK, i'm almost certain this is a power supply issue now (after some great help from one of the guys at Jomac)

The machine has 2 power supplies - one is not giving  12V (the black one)  - they were bridged together, so i disconnected the faulty one and terminated the wires going to it.

So the power supply in use (silver one) is giving 11.97V and 5.05V at its output pins, when i test at the pins going into the main board interface, the 5V ones range from 4.96 to 5.02 V (there are about 6).  The guy at Jomac said to test either side of the pink coloured capacitors at the end of each IC, when i read there i am only getting 4.86V - which may be the cause of the pixelation....

I pulled all the boards apart and cleaned the connectors with electrical contact cleaner, what else can i do or check to try and get 5V at the board?

[robm]

And 2 hrs later i certain its NOT a power supply issue - adjusted the voltage and got 5.02V at the board with no change to the displays.

Had a chat to Jomac and he said it is definitely a board issue, so will send it to him if the arcade repair fairy does not turn up tonight and magically fix everything...

[MartyJ]

Well, ruling out a power issue its always the first step.  Joey @ JOMAC is a great guy and super knowledgeable about just about everything arcade related.

His service is A1.