Backup RAM & Video RAM errors

channelmaniac · Dec 26, 2007

When diagnosing the Backup RAM problems on a NEO-MVH MV2 2-slot board:

Upper Backup RAM location: H3
Lower Backup RAM location: H4

Enjoy!

RJ

Dingo69869 · Mar 8, 2008

4-slot Video RAM error

Guys,

I'm also having a video RAM error on my big red - the message I'm getting is:

ADDRESS: 00000E04 WRITE: AAAA READ: AAA2

Can anyone help me ID exactly which chip needs replacing on my board?

Thanks,
-Steve

channelmaniac · Mar 8, 2008

Surface mount RAM chip at location K9

Dingo69869 · Mar 8, 2008

Thanks a million!

I've ordered a couple chips from your link mentioned above.

Thanks again for the help.

-Steve

Hewitson · Mar 8, 2008

channelmaniac said:
There is a way to do it without having the surface mount gear but it's a little risky.

Take a very sharp disposable razor knife - the kind with the break off blades - and put just barely enough tip out to cut and cut the pins off at the chip body.

It takes a sharp knife so you don't rip the pins and pads off the board. You want just a tiny tiny amount if blade sticking out and rest the body of the knife on the body of the chip to help prevent the blade from cutting traces on the board under the chip.

Once the body of the chip is cut away, take a bit of liquid resin flux (not acid flux!!!!!!) and put it on the pins/pads. Then you can take the soldering iron and 'wipe' the pins right off the board. It takes very little pressure to do this as you don't want to pull the pads off the board.

Next is cleaning up the pads. Use a vaccum desoldering pump or solder braid. Just be careful to not use too much heat as again, that could lift the pad off the board.

Now that the solder pads are clean lay the chip down. Be SURE it is oriented correctly! You don't want to solder down the new chip just to notice it's in backwards! Be sure to have the legs of the chip centered on the pads then tack the 4 corners down with solder.

Take the liquid flux and put some down the pins on both sides of the chip. This will help the solder flow and stick to the legs and pads better. Put a small ball of solder on the tip of the iron and hold the board up at about a 60 degree angle, put the soldering iron on the pins at the highter end slowly pull the iron down towards the lower end, soldering all the pins down the side at once.

If there are pins bridged then wipe the soldering iron tip clean, add a little flux to the bridged pins, and wipe the soldering iron across them to remove the extra solder. It takes practice but it's easy to learn to solder them down with the hot iron method.

RJ

For others that may be attempting to do this I thought itd be worth mentioning that a small "hoof" tip is the best to use for this purpose.

To be honest I've never thought of cutting the chip away and "wiping" the pins off the board. Thanks for the tip

channelmaniac · Mar 9, 2008

It takes liquid rosin flux to be able to wipe them away the easiest.

Without it you may smear the solder around between the traces and you'll be more likely to lift a trace.

RJ

jub · Dec 2, 2008

ncflagg said:
Video RAM Error:

Address Write Read
00008000 5555 FF55

I got this error and installed a RAM chip at L9. After hooking up this MVS 4 Slot again and power it on I get the same error!? I thought at least I would get a different error. I saw in another thread to try shorting pins 13 and 14 to narrow down the bad chip. When I shorted the newly installed L9 I get

Video RAM Error:

Address Write Read
00000000 5555 FF51 (or was it 5155?)

When
I short K9 I get some garbled text with lots of AA's and 11's

Hepl?

i got 00008000 5555 0000 Video Ram Error.

After checking traces and changing the rams (with the one from another board that is not working) i really dont know what to do efficiently next.

Can anybody give me a hint to go further?

Nightmare Tony · Dec 2, 2008

The high RAM is bad, period. One of the two CXK5814 RAMs. The high is the two left output numbers and the right is the two input numbers.

It is because the read is FF instead of something else, it is a pure bad chip. No broken lines or such, unless it is a bad control line (rare).

To find out which one, on each chip, short pins 10 and 11, (D2 and ground).

If the FF55 changes to FF53 or sometyhing like that, then that is the good chip and replace the other one.

If you did that to the bad chip, it will still read FF55 or may read F855 or some.

but you get the idea.

mainman · Dec 2, 2008

Nightmare Tony said:
The high RAM is bad, period. One of the two CXK5814 RAMs. The high is the two left output numbers and the right is the two input numbers.

It is because the read is FF instead of something else, it is a pure bad chip. No broken lines or such, unless it is a bad control line (rare).

To find out which one, on each chip, short pins 10 and 11, (D2 and ground).

If the FF55 changes to FF53 or sometyhing like that, then that is the good chip and replace the other one.

If you did that to the bad chip, it will still read FF55 or may read F855 or some.

but you get the idea.

yet another extremely rare appearance, how you been doing guy

Nightmare Tony · Dec 2, 2008

Job hunting right now. Still glad I got the side job with Eldorado on game repairs. Been working out on Spy Hunters lately. Working on the pinball program as well. Working on releasing 2 more CDs of music. doing what it takes to keep the farm

too many projects at times!

But yup, feel free to email me or get me in here with any questions, the forums definitely let me know. For email, my name at yahoo.

jub · Dec 2, 2008

Thanx for your fast answer. Hmmm i checked that, but the bytes stay on 0000.

I will take care of it tomorrow and will take a closer look on the board - here in germany it is really late...

So thanks a lot! Keep up the good work.

I hope to find your mail address.

Nightmare Tony · Dec 2, 2008

The 000000 will stay the same as that is the address sent out by A0.

The write of 5555 is the data being put into the 2 RAMS as a 16 bit wide word.

The reason for 5555 and AAAA is alternating bits. 5555 is 0101010101010101 while AAAA is 1010101010101010

So the read is what actually tells you what the RAM is outputting.

As a hint, if the address of 000000 is a higher number, it is an internal number to the RAM itself or a snapped address trace, though it cannot really catch the duplicate addressing error (I fixed that mistake in the pinball program I am doing)

jub · Dec 2, 2008

so 5555 is written and 0000 is read out...

that means all is wrong... So there is maybe a prob somewhere else. I will check all the connections of boths chips.

Nightmare Tony · Dec 2, 2008

Nonono.

if I remember:

Address 000000
Write: 5555
Read: FF55

The address being the first place tried in sequence
The write is what is being put into the RAMs
the Read is what comes back out.

the upper FF comes from the high RAM which is defective.
the lower 55 is the correct response from the lower RAM

If it was reading correctly, it would read a 5555 and then write an AAAA and step upwards to the next address sequentially.

jub · Dec 2, 2008

just to make it clear. i get 0000 not ff55 back... that means both are making trouble or something deeper is the prob.

but thank you... maybe i will get a working board, that will help me to fix the problem. But now i will get some sleep.

Nightmare Tony · Dec 2, 2008

yup, if the output read is 0000 then both rams are bad or the control lines are zonked, the chip select or read/write line though though would usually lead to random garbage numbers that change each time you poiwer off and on.

usually, a burned out RAM chip on the 5814s will give an FFFF instead of an 0000 reading. Curious.

Can you screen capture and post it?

channelmaniac · Dec 2, 2008

If you have a logic probe it's easy to check pin 18 and 20 to see if the control lines are working.

Pin 18 is stuck low (grounded) and pin 20 is pulsing low to read the chip.

RJ

PS: Hi Tony! Next time I'm out in SoCal, I'm going to have to buy you a beer just to meet you.

Nightmare Tony · Dec 2, 2008

hey RJ, thanks but I don't drink alcohol. I may use beer in cooking rice but only super rarely. Would go for a cream soda or coke though...

heck, drop by out here, would show you the latest design projects.

TheBakachan · Dec 3, 2008

channelmaniac, great info as always!

How about the RAM chip locations for MV1C and MV1B boards?

I'm finally ponying up the cash for an SMD rework station, and am looking forward to fixing the cheap 'non-working' boards I've acquired in my travels

Nightmare Tony · Dec 3, 2008

http://www.hakkousa.com/detail.asp?CID=51,167&PID=778&Page=1

weapon of choice back at SNK and ended up purchasing my own, it ran me about 700 bucks. Still my main axe today.

channelmaniac · Dec 3, 2008

Hey, thanks for the pr0pz!

I have a Pace MBT250 station I paid $700 used for back in '99. Got it for about a quarter of retail with all the tips and irons to do everything but BGA.

I bought it from the place I used to work for. It was my station when working there and they sent me to Pace school to learn how to use it.

As for the RAM locations? They aren't hard to deduce. The high speed Sony CXK5814/6116 SRAMs in a pair are the $8000 Video RAMs. The one by itself is the Sound RAM. The 256K SRAM tied to the video chip is the other Video RAM. The 256K SRAM tied to the CPU AND powered by the backup battery circuit is the Backup RAM which leaves the other pair of 256K SRAM to be the Work RAM.

I thought I had the 1C documented on my repair log site. If I don't, I'll get that done since I have a 1C in the shop.

Raymond

Nightmare Tony · Dec 3, 2008

The final ram you forgot was integrated into outputs on later chipsets is the duial 6264 which served as a final pallete RAM.

The basic color set is 16 colors, 4 bits wide. The 256 RAM at the A0 selects basic palletes giving 256 colors. The final RAM takes the 2456 colors to 16,384 by selecting the color resistors directly.

doggydodomi · Dec 3, 2008

Not kidding dude, that is a very good deal, paid about $2.9k for mine, new thou. Come with a whole lot of tips...recently the heater of the Xtractor burn out..cost me $135 to replace...should have gone with a Hakko...lol

channelmaniac said:
Hey, thanks for the pr0pz!

I have a Pace MBT250 station I paid $700 used for back in '99. Got it for about a quarter of retail with all the tips and irons to do everything but BGA.

Raymond

TheBakachan · Dec 3, 2008

channelmaniac said:
As for the RAM locations? They aren't hard to deduce. The high speed Sony CXK5814/6116 SRAMs in a pair are the $8000 Video RAMs. The one by itself is the Sound RAM. The 256K SRAM tied to the video chip is the other Video RAM. The 256K SRAM tied to the CPU AND powered by the backup battery circuit is the Backup RAM which leaves the other pair of 256K SRAM to be the Work RAM.

I thought I had the 1C documented on my repair log site. If I don't, I'll get that done since I have a 1C in the shop.

Raymond

Awesome, thanks! And no, I don't remember seeing info on the 1C in your repair logs, though I could have missed it.

As for me... I find no shame in saying I'm going for a cheap Chinese knock-off hot air and vacuum pickup workstation from AOYUE. :P The PCB can't tell the difference, but my wallet sure as hell can!

doggydodomi · Dec 3, 2008

TheBakachan said:
As for me... I find no shame in saying I'm going for a cheap Chinese knock-off hot air and vacuum pickup workstation from AOYUE. :P The PCB can't tell the difference, but my wallet sure as hell can!

No shame at all, Aoyue work just as well and thousands of asian pirates and cellphone technician can't be wrong. :make_fac:

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