What's new

ekorz

Multi Boyz 4 Pi
Legendary
Multi Boyz
Joined
Aug 21, 2016
Messages
5,187
Reaction score
7,770
Location
Boston, MA
Lucky Moron PCB Repair
Episode 2: Strikers 1999
(or: Sold "Tested Working 100%")

Symptom: eBay seller willfully ignored the boot-up screen where it CLEARLY SHOWS "WORK RAM NG!" and sold the board as working anyway. Game also freezes several seconds into game-play. Why do I even eBay anymore?

jY6EDnc.png


Other Guy's repair log: Boot screen shows Work RAM NG. Replaced Work Ram. Game fixed.

My repair log: RAM? Damn it. OK well RAM are usually the chips that are moderately sized, but not the ROM chips I know and love, and also not the little logic chips. These guys have at least 20 pins minimum. They're also not the CPU or custom chips. Whatever is left, that's RAM. You'd think I'd have this Psikyo SH2 MAME driver memorized by now, but let's take yet one more look at what is up. Sourcey source.
Code:
PS5
|-------------------------------------------------|
|HA13118      M514260      PROG_L.U16    DATA.U1  |
| VOL    3771 M514260      PROG_H.U17             |
|                                    *PROG_DATA.U2|
|                          PAL                    |
|                                                 |
|   JRC4741                          0H.10   0L.3 |
|J          |-----|                               |
|A          | SH2 |      57.2727MHz  1H.11   1L.4 |
|M  YAC513  |     |                               |
|M          |-----|       |-------|  2H.12   2L.5 |
|A                        |PSIKYO |               |
|                         |PS6406B|  3H.13   3L.6 |
|                         |       |               |
|                         |-------| *4H.14  *4L.7 |
|                                                 |
|                           62256   *5H.15  *5L.8 |
|                           62256                 |
|                   93C56                         |
|            JP4             YMF278B    SOUND.9   |
|-------------------------------------------------|
MAME diagrams do show the RAM usually. From my vast and enviable experience I do recall that '62256' is RAM. A google search tells me M514260 is also RAM. The good news is I also have a working version of this board, so I have two boardsets. The bad news is that neither board has either of those ICs and I'm not smart about describing RAM in the abstract. I need actual part numbers to search for... so let's take a look.

cliNSla.jpg
RtTZXI6.jpg

Working Board U20/U21 - EliteMT LP61256GS-12 (pair)
Working Board U33/U34 - Silicon MAGIC SM81C256K16CJ-35 (pair)

DocYJkp.jpg
V26ZJkq.jpg

Busted Board U34 - NEC 42S4260-70
Busted Board U33 - HM514260DJ7
Busted Board U20 - KM68257CJ-20
Busted Board U20 - GLT725608-12J3

But which ones are the Work RAM? Time to phone a friend.

Me: hey @Hammy
Hammy: stop
Me: I googled 'Work Ram' but it just told me how RAM works but I didn't understand that either. Which RAM is "Work RAM" on this Strikers 1945iii [pic]?
Hammy: It's the ones near the silkscreen "RESET", by the program ROMs
Me: humor me, how do you know that so immediately?
Hammy: beep it out yourself you clot, Work RAM will connect to the program ROMs
Me: hahaha wow that sounds like work I'm just gonna shotgun it. Cheers!
Hammy: no just send me the board, it deserves to live again

Ok so we know which are the Work RAM now, but how can we tell which one is bad?
This comes up a lot, so here's the balls-on accurate way of handling diagnosis on any pair of RAM.

Step 1: Set your multi-meter to continuity
Step 2: Connect your logic probe to 5v power and ground
Step 3: Google the pinout/datasheet for the RAM you're probing
Step 4: Initialize your oscilloscope to the appropriate speed
Step 5: Start MAME using -debug and select the Debug menu to view memory
Step 6: I forget where I was going with this, but my probe is stuck in the debugger
Step 7: Replace both entirely; if one went bad the other one was surely at death's door anyway

So I gotta order me some RAM. First try is always at digikey and/or mouser, so I know I'm getting good fresh parts that work. The downside is they require a painstaking level of detail about the chip I'm after, which I typically fail miserably to elucidate. I don't see any options for SOJ-40 packages, and I don't feel confident that I did it right, so I try start from ALL MEMORY and whittle down the options with filters like "DRAM" (not sure about EDO, FP, or regular cola flavor), "Surface Mount", "5v", and am left staring bleakly at only TSOP packages. So much for getting new ram.

So I gotta order me some RAM.
So I gotta order me some OBSOLETE RAM from CHINA.
AliExpress? Savory.
eBay? Isn't that where I started this whole mess!??
Sigh. eBay. Of all the options I could search, I at least got a hit on used HM514260DJ7, and order two.

But I'm impatient as hell, so let's check out the scrap pile!!! Where'd I put that busted Psikyo PS4 mahjong thing, eh Taisen Hot Gimmick 72 grand-master challenge?

MAME tells me it's got some Fujitsu 814260-70 256k x16 (4MBit) DRAM (SOJ40) and that is good enough for me!
I nuke my bad ram off my Strikers, and the Fujitsus off the Taisen, and get ready for install.

But we already said this was SOJ40 package chip, and I'm not ready for this:

FkrReCA.jpg

Surface mount, but no legs... NO LEGS!!! I feel a little queasy. Show me how this is done, oh master!

Drag soldering like that looks do-able, but I've been looking for an excuse to try solder paste so I go that route instead. I didn't take any photos, but it worked out quite well. My application was pretty even, so I only had a few solder bridges that were easy to touch up. Despite all pins connecting and none being bridged, the board didn't boot at all, reminding the world that I'm bad at this. Why? Wrong type of RAM? Also dead? I suck at solder paste? Got killed when I removed them? Fujitsus just never work? Whatever it was, my used eBay RAM showed up shortly thereafter, so I removed the Fujitsus to eliminate variables.

HM514260DJ-7 install time.
More solder paste.
Slightly fewer solder bridges.
Exact same amount of abject failure; it still doesn't boot.

Nothing daunted, I attempt one final (?) eBay search, and turn up some juicy "MT4C16270DJ-5 MICRON 4MEG 256Kx16 40 PIN 50NS SOJ EDO DRAM DYNAMIC RAM NEW". See at the end there? "NEW". As good as it's gonna get, I expect, and at this point I just outright enjoy heating up SOJ-40 packages and installing them with solder paste and heat.

I'm reminded that the surest sign of insanity is doing the same thing over and over and expecting different results.
So I swap the Work RAM, for the third time.

9qc4Lvw.png
tKP21zF.gif


Game. Fixed.
 
Last edited:
Wow

My Dragon Blaze Just Died on Me ;( ;( ;(

With the Dark red display
 
Wow

My Dragon Blaze Just Died on Me ;( ;( ;(

With the Dark red display
Sorry to hear that! That’s a good one, certainly worth repairing. It just boots to red screen? Checked the program roms? Getting clock to the cpu? Reset signal doing whatever a reset signal is supposed to do? I’m pretty OK if the game starts up, but I don’t have a lot of weapons for something that doesn’t boot at all. I’ll write some logs for dead pcbs.... if I ever get them working.
 
Reset ic or the program roms, been a noob in repairing things, just end up watching the board in the Glassed Closet
 
Keep going while you are on a roll, momentum is everything and there's no shortage of shit boards!!!
 
Keep going while you are on a roll, momentum is everything and there's no shortage of shit boards!!!
I just got a few finishing touches on the next log, it’ll be up soon. One or two more fixes are on deck after that. repairs are done, just need to write up the narrative.

But I’m gonna hit my brick wall soon after that... I’m calling that stage my “Boot Camp” episodes as they’ll cover a bunch of pcbs that don’t boot. But none of them boot yet!!
 
@ekorz I love reading your logs. It shows with some willingness to learn and put some effort you can achieve success.

Want to learn Chinese? 2 attitudes:
1) Nah, too difficult for me, it's going to take me years. Result: in 5 years you'll still be sitting on your ass not speaking a word of Chinese.
2) Ok, I know it's difficult but let's start today. In 5 years you'll probably speak a decent level of Chinese!
:D
 
I feel like I'm reading myself trying to fix boards...

funny as hell. Thanks.
 
Back
Top