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Arcade King
14th April 2009, 04:04 PM
I bought this board via Supremicus on AA. Looking at the pics he put up of the game running it had some vertical lines running through the character graphics which 95% of the time is a common mask rom crapped out fault.

Problem: Vertical lines through the character graphics not evenly spaced.

Fix: Doing the usual mask rom test sure enough roms 7K (4 megabit) and 7L (8 megabit) came up BAD. I've fixed quite a number of Konami board with bad mask roms so I removed the roms and put sockets in ready to replace them. Burt some new roms popped them in and ....still ****ed...WTF? reading the original roms they both came up good. ****!
Pushing down on top of the custom at 3J the graphics came good. Found 2 lifted pins (see pic) board now works 100% and passes the mask rom test.
Ahh well live and learn. I'm so use to replacing bad mask roms on these things you start bypassing all the basic fault finding. No biggy the roms are bound to fail eventually.

On TMNT Turtles in Time, Burra sent me over another one to have a look at. I've attached a pic of the 2 boards. You can see the top one which is burra's is full of POS F(Fujitsu) IC's and the bottom one has good quality Hitachi which you dont see too often on Konami stuff.
Unfortunately I was unable to fix Burra's board because the Protection IC @ 7H is faulty. The thing was dead when I first got it but I found 5 bad F chips and a bad ram @ 1J. The thing boots up to the "RAM ROM TEST" then freezes. Some times it will get into the test but it constantly gives you random bad ram faults. It got as far as the cross hatch a few times.
A real shame too I think TMNT 2 is the only PCB to use this crappy protection chip.

AskJacob
14th April 2009, 04:07 PM
How the hell did you locate the lifted tracks?

Super-man vision?

Good work!

Cheers
Jacob

Arcade King
14th April 2009, 04:14 PM
I just go along with my logic probe and gently press each pin until i find the loose ones (with the power off of course)

It does help having one of those magnifying glass fluoro things on hand too.

nigelicious
14th April 2009, 04:43 PM
Interesting post, nice work

Supremicus
14th April 2009, 05:28 PM
Good to see you got it back to good as new trav.

Womble
14th April 2009, 05:52 PM
Nice one, valuable board too.

It just goes to show that the manufacturers tried to save every single cent they could, the only reason to wholesale swap between 74 series IC vendors would be price. Fujitsu were almost certainly the cheapest at the time Burras board was rolling off the production line, while Hitachi had the best deal when the other was made.

Every expense spared! Wonder what the failure rate for F chips was when they were brand new. Seeing as they were used for many years by many manufacturers I guess they were no worse than the others at the time, they just turned out to be a bit of a timebomb as the years passed. Funny that the TTL stuff is so flaky, have never met a faulty F brand RAM chip, even on a board which was full of knackered F TTLs.

Still, I actually like seeing F chips on boards that are faulty, means its likely to be a far easier fix than if it was Hitachi wall to wall, have a 3 tasty PCBs on the way to me at the moment, am hoping for Fs on 2 of them :)

Arcade King
14th April 2009, 06:49 PM
I agree with you mate boards with F chips are 99% of the time easy to work on and I always check the output on them first usually they are just dead pure and simple, you're also right about the rams they are usually pretty good. Depending on the value/rareness of a pcb if its full of F chips I just chuck it on the parts pile specially multi layered PCBs. Don't get me wrong its amazing that a lot of this stuff still works at all and it really shows which manufacturers made the quality stuff.

I'm forever patching up my TMNT boards full of F chips. Just pulled one out the other day which I knew was fine and the dips didnt work(I'm finding a lot of 253's are dying). I probably should replace the lot but it just takes a lot of time.

Hewitson
15th April 2009, 01:20 PM
It would be worth checking out the MAME source to see how they get around that protection chip.

li_gangyi
15th April 2009, 03:10 PM
That protection IC has to do with pulling data out of work ram and generating a display list to sprite ram, so the workaround is 'easily' coded in MAME (once you know how it works), but a little more difficult to 'clone' a drop in replacement chip.

It's also not an encryption thing, so you can't (like in CPS) burn a decrypted set of roms to make it work.

There are people working on making FPGA based drop-in replacement custom ICs, but I think this one is a custom with an MCU and code in it.

http://www.fpgaarcade.com/konami_customs.html

Arcade King
15th April 2009, 03:24 PM
yeah those are exactly the rams that in the boot up test randomly report BAD.