Zaxxon RAM failure

[Luigi]

Hi.

I have an original SEGA Zaxxon PCB. When starting it only shows garbage. Pressing the test switch starts an internal test procedure. It says ROMs are ok.

But then it says: RAM 1 NG

Can anybody tell me what ICs I have to check or replace?

Thanks

[SirPeale]

I'm not familiar with Zaxxon boards, but I'm guessing RAM 1 would be the first place to start.

[SirPeale]

Oh yah, try here:

http://www.arcadedocs.com/vidmanuals/Z/Zaxxon.pdf

[Luigi]

Hi Peale.

Thanks for the link.

I already downloaded the manual but I'm not sure what RAM is meant.

In the manual it says, that the test is verifying the WORK RAM so  suppose it must the one with the CPU.

The second picture shows the position of U70 and U71.

Is "2114" the IC number what I must look for??

[Kevin Mullins]

That's where I'd start at...... U70 & U71
Skimmed through the manual and came to the same conclusion you did.
Should be two identical narrow chips side by side.
Which one is which I'm not sure. (RAM1 or RAM2)

Can you read the numbers right on the chips themselves at those locations?
Or swap them around with eachother and see if the test results change. (they are identcal chips) At least you'll know it's one of the two if the results change.

[RayB]

The first thing I would do is measure voltages.

[Luigi]

Hi.

I received the pcb like it is: non working. It's the pcb only, no cab around it 'til now.
What do you mean with "extension cord"

Both ICs have the +5V.

I will take a look at the "real" chips what numbers are written on them.


I will also go and get two sockets and solder them in. So I can swap the two ICs.

[Ken Layton]

2114 is definitely a ram chip. I just replaced one on a Pole Position yesterday. There might be some additional numbers/letters on the chip too which indicate speed or low power type.

NTE 2114 will work as that's what I used on the Pole Position board.

Jameco Electronics (www.jameco.com) has these versions of the 2114:
# 38957CH    2114N Static Ram chip, 1k x 4, 450ns $2.29 each

# 38973CH    2114N-2 Static Ram chip, 1k x 4, 200 ns $2.49 each

# 38981CH    2114N-2L Static Ram chip, low power, 1k x 4, 200ns, $2.49 each

Any one of the above will work in your application. Oh, by the way, these are 18 pin chips so if the existing chip is not socketed, then please install an 18 pin dip socket in case of future failures the chip can be replaced without having to unsolder it.

[RayB]

What do you mean with "extension cord"

you feeling ok?

 

[Luigi]

What do you mean with "extension cord"

you feeling ok?

 

[Kevin Mullins]

hmmmm ... I guess the extension cord bit was slightly misunderstood.
But who needs one of those anyways if you have an all mighty cord stretcher.

(fact is: an old or very long extension cord could give bad, weak, unstable voltage causing game isues of many types)

Anyways,
Luigi.....keep us posted on what you find out.
The RAM info would be good to know.

[Luigi]

hmmmm ... I guess the extension cord bit was slightly misunderstood.
But who needs one of those anyways if you have an all mighty cord stretcher.

(fact is: an old or very long extension cord could give bad, weak, unstable voltage causing game isues of many types)

Wait a minute: are we talking about power cords???
I never heard of faulty games caused by using bad or old power (extension) cords.

Did you?

[Kevin Mullins]

Power cords..... sorta.... but not the one attached to your machine.

For instance:
You have your machine sitting there and need to plug it into the wall.
But the cord won't reach the plug outlet in the wall.
Then you would use an "extension cord".

Usually orange, yellow, brown....and some of the new ones are all kinds of funky colors. I guess people can call them different things. I've even heard them called pigtails....let's throw that terminology in the mits of this huh?

And yes....... it is possible to have problems with power cords and extension cords.
Corrosion, resistance in the wire, and a few others. Usually affecting older machines because they aren't stable to begin with.
But it was just a suggestion to check. IF you were using one.

If you have 5v at the RAM... start there.... swap the RAM around. (with sockets of course)
Anxious to here the results of the test.

[grantspain]

hey perhaps your not too far out talking about cords,when i first started work we had shed loads of faults caused by ribbon connectors on the game boards

[Luigi]

aargh....this thing will have to wait for while. Trying to unsolder the first chip I discovered that soldering a Jamma-adapter isn't like unsolder a chip 

I will need a little more practice on this if I don't want to kill my Zaxxon PCB 

Any hints for a lamer on how to unsolder a chip?

I've read that it might help to add new fresh ......ehm..."L

[SirPeale]

Suggestions?  Yup.  Practice on something you don't care about.

Use a solder sucker.  And/or solder braid.

[Luigi]

Suggestions?  Yup.  Practice on something you don't care about.

Use a solder sucker.  And/or solder braid.

I think getting some practice will be the best way.

I already have a solder sucker, what misses is the braid. I will go and get some this afternoon and do some "exercises" on garbage boards

Meanwhile I will go and get some sockets and the 2114s

[Kevin Mullins]

Yes indeed..... practice , practice, practice.
Get as much solder off ALL the chip legs as you possibly can.
You may even have to solder-suck from the top side of the chips.
I have had many that need the soldering iron to heat AND the solder-sucker at the same time.
Heat the solder on each leg from the top side of the board with the iron and suck the solder from the bottom side.
But even after that you may need to apply gentle upward pulling pressure and run your soldering iron down all the legs again to keep any leftover solder free to move while pulling the chip up. Gently, otherwise you may pull some traces off the board.
Experimenting and practice is the key.
Can be very frustrating......that's why everyone recommends sockets after you actually get them off.
 

[grantspain]

the best way to desolder a chip without damaging track is to(using good quality fine side cutters) cut each leg of the chip then remove each leg using a solder iron and pull the leg with cutters,then use a solder iron and sucker to remove the remaining solder,this method means less heat and pressure on the track,i have used this method on williams dot matrix displays and they have about 50 pins

[Q*Bert_OP]

IMHO, the easiest way to remove a chip is to get that desoldering iron($10) from Radio Shack with the solder bulb built in, but cutting it off also works.

[Luigi]

Thanks a lot for your hints.

I once removed a chip from my old C64. But I knew, it was dead, so I could cut the legs and remove it easily.

But since I don't know exactly if the two 2114 are dead I'd like to leave them in one piece

I ordered two rolls of desoldering wick. One roll will go for practice befor I try the Zaxxon PCB

[Luigi]

Back again.

Both RAMs have been replaced.....error remains     



Any suggestions on how to continue?

[RayB]

Are there capacitors near those chips? If they aren't being powered correctly they will appear to fail. Check that the capacitors dont have broken legs or other damage.

[Luigi]

Are there capacitors near those chips? If they aren't being powered correctly they will appear to fail. Check that the capacitors dont have broken legs or other damage.

I'll take a look this evening but as far as I remember there are no caps around.