Topic: Taito Cross Shooter Repair Log  (Read 3707 times)

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Offline Womble

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Taito Cross Shooter Repair Log
« on: October 26, 2009, 09:26:34 AM »
Ya can't beat a quick fix sometimes! This one was a 5 minute one from start to finish, the joys of oscilloscope ownership. Was over at another AussieArcade members place on the weekend and left with a metric shitload of boards, some loaners for troubleshooting boards I have on my to-fix pile, some I had bought and some he asked me to see if I could fix. One of the last sort was a Cross Shooter from Taito..



..probably an original due to the odd HUGE custom SIPs on it.



Simple fault was the board would boot and play but the sprites were corrupted.







Powered it up and went straight for the batch of TMM314APL SRAM chips (2114 type) on the upper board as a logical place to start, sprite RAM on boards of this vintage is often multiple small bit width chips like these.



The upper two in the set were being driven much harder than the others and seemed to be involved with sprite positioning as interrupting the address lines moved everything around the screen. The other 4 were the sprite data itself, and judging by the fault one of the data lines was putting out rubbish, 2114s are only 4 bit wide chips so they only have 4 data lines per chip, 3 of the 4 chips had healthy looking data lines...



...but one only had 3 good looking lines and one that had clearly lost its ability to drive the line, the data pulses are about 0.5v high - not good!



I happen to have a tube of 2114s floating around my stock, and even a few TMM314s, so I pulled the suspect chip, dropped in a good one and bingo - fault fixed.





The new chip is the bottom left one in the photo above, it has a different batch number to the rest and is somewhat cleaner.

Now it was possible that the fault was cured by my removing and reseating the chip, unlikely but possible, so I put the old chip back in to test, and the fault came back, so I binned it!

Board fixed! :)

Could use a bit of a clean tho!
Sic Transit Gloria Atari

Offline Panther

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Re: Taito Cross Shooter Repair Log
« Reply #1 on: October 26, 2009, 12:00:04 PM »
Quote from: Womble
Could use a bit of a clean tho!

Nothing a bit of fairy liquid couldn't fix  :P

Nice job again Womble  ;D

Offline resident paul

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Re: Taito Cross Shooter Repair Log
« Reply #2 on: October 26, 2009, 07:40:21 PM »
Agreed, another brill job & no soldering required :)

Offline Womble

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Re: Taito Cross Shooter Repair Log
« Reply #3 on: October 26, 2009, 10:12:41 PM »
Shame I cant play it, it uses inverse synch so the image is upside down in my cab, I could bodge it with an inverter chip but thats too hard. Tis a game I would like a quick blast on but norralot else. Hmmm, actually thinking I could fit an inverse switch into my cab permanent like, tho most games have a dip setting that does it.
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Offline woody.cool

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Re: Taito Cross Shooter Repair Log
« Reply #4 on: October 27, 2009, 06:52:57 AM »
Go on, you know you want stick that switch in your cab.
Then you can have that 'quick blast' on it, you know you're just urging to have a a quick go (or ten)

Offline Womble

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Re: Taito Cross Shooter Repair Log
« Reply #5 on: October 27, 2009, 10:09:27 AM »
Twould take me longer to wire in an inverter chip and power than it would to scratch that itch via MAME  :D
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Offline Elgen

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Re: Taito Cross Shooter Repair Log
« Reply #6 on: March 24, 2011, 03:19:50 PM »
Hmmmm, I have a bootleg LegendaryWings, where the sprites look exactly like these; a lot of vertical stripes cutting them...maby I should have a look at the srams on that one some time.
(I simply love these repair logs; I learn sooo much from reading them };-P)

Offline Womble

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Re: Taito Cross Shooter Repair Log
« Reply #7 on: March 26, 2011, 02:32:01 AM »
Lines through sprites usually mean bad ROM, RAM, or buffer logic that is leaving one of the data line undriven, it is then just held high by its pull-up resistor, giving the solid line.

I repaired a Legendary Wings a while back...

http://retrocomputermuseum.co.uk/forum/index.php?topic=1313.0

.. so I know the Sprite data lives in the ROMs U111 and U112 (assuming they are labelled the same on yours), I would start there looking for data lines doing nothing.

By the way - you can easily tell the difference between address bus faults and data line faults on graphics ROMs. Address line faults result in the entire data output of the ROM being totally wrong, giving results similar to the blocks of rubbish seen in the LW repairlog. Data bus faults result in most of the data being right, just certain pixels missing, resulting in a stripe through the sprite.
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