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Elevator Action x2 PCB Repair

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qjuk View Drop Down
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    Posted: 15 Feb 2021 at 10:09pm
PCB Repair - Taito Elevator Action x2

Board Set 1
Game: Original Taito 4-board pcb set (converted to Elevation Action).
Purchase Description: Complete and working.
Fault on Receipt: Game plays, but has red line graphic glitches and partial missing sounds.
Board Set 2
Game: Original Taito 4-board pcb set (converted to Elevation Action).
Purchase Description: Complete and working.
Fault on Receipt: Game plays, but has a minor graphic glitch and partial missing sounds.
 
I purchased both of these board sets as fully working to replace an already faulty original EA 5-board stack (which was also sold as working). Sadly both of these 4-board stacks arrived with issues so that means I’ve now received 3 faulty board sets, and not got a fully working game Cry
 
The aim here is to try and make at least one fully working game from these 2 sets, then hopefully repair the second set as a back-up spare.
 
Both these board sets have been converted from another Taito game, probably something like a Jungle King or Wild Western, but I genuinely have no idea what they were previously. All I know is that both stacks are using unencrypted/bootleg Elevator Action eproms so they can run on the original Taito pcbs, thus eliminating the need for the 5th security pcb.
 
The advantage of having two of the same board stacks is that I can swop boards between them and try to eliminate where the issues are. I know that sound issues are related to the larger top pcb, so both top boards on both sets will need looking at, however the graphic problems could be anywhere so my first job is to try and track down which board is causing what problem. Here is what I’ve discovered:-
 
Board Set 1
Eprom pcb – Fully Working.
Top pcb – Missing game sounds but background music fine, plus causing red line graphic glitches.
Middle pcb – Fully Working.
Bottom pcb – Fully Working.
 
Board Set 2
Eprom pcb – Fully Working.
Top pcb – Game sounds effects would disappear after a few minutes but background music fine.
Middle pcb – Fully Working.
Bottom pcb – Causing an extra “D” character above the word “CREDIT”.
 
I made up a new stack set using the 3 known good boards and the top (Game Board) pcb from the second set. The sound disappearing issue was caused by two of the four AY-3-8910 sound chips being faulty. I’ve not got any spare AY3’s but do have some YM2149F chips which are a drop in replacement. So I fitted 2 of these which fixed the sound issue. I now have one fully working EA board set!
 
Now onto repairing the second board set.
 
Missing sounds
Having already checked the four AY-3-8910 sound chips by swopping around with the first board set, I know these are good. The next likely suspect is probably a dead Op Amp. On the EA board there are three LM3900 Op Amps (at IC1, IC8 and IC17). The Amp at IC1 had already been previously replaced and soldered directly into the board. Since I had no idea which amp/s could be potentially faulty, I decided to remove all three. I fitted new sockets and three new LM3900’s. This fixed the missing sound issue. It turned out it was just the one Op Amp at IC1 that was dead (the one that was previously replaced). It’s a shame the previous repairer didn’t socket it, Op Amps are common parts to die so it’s worth socketing these.  It would have certainly saved me some time as I could have easily checked that first. Never-mind, time to move on…
 
Extra “D” character above the word “CREDIT”
This is a bit of a weird one. All I know is that this problem is definitely on the bottom (CPU) board.

 
I asked for some ideas on the UKVac Tech forum and one of the suggestions was to check for ram. Since my board set is part of the 5 board system  (but not using the 5th Security Board due to the unencrypted /bootleg version roms), there’s three 2016 rams at IC14, IC56, IC57. I borrowed the three rams from the first working board set stack (which happened to actually have 6116 rams) and tried them on this board, it cured the problem!  It was probably just one of the 2016 rams that was being funky, but since I didn’t want to mix 2016 and 6116 ram, I simply replaced all three 2016’s for three brand new 6116 rams.
 
Red line graphic glitch
After the pcb set has been powered on for a quite a few minutes, the following red lines start appearing onscreen…


The red line issue only seems to happen on a black background.
 
My initial thought was that maybe this is another ram issue. There’s a N82S09N bi-polar ram chip (labelled as 93419 at IC67 on the schematics) which is part of the colour circuit. The chip is socketed so I borrow the one from the first board set to test it and it makes no difference. I then put the original ram chip back in and move on.
 
Knowing this issue is definitely on the top (Game Board) pcb, I thought I would take a closer inspection of the board. I noticed a 270 ohm resistor at R164 is badly burnt…


The 470 ohm resistor at R162 also has some minor burn, so I replace them both. It made no difference.
 
I’m curious to see what part of the circuit this resistor is connected to. I get out the schematics and have a look around. I find something interesting, the burnt resistor is part of the red colour circuit and is the only resistor connected to a 7474 flip-flop at IC44.

 

This red line problem only happens after the board has warmed up and I wonder if this IC is the likely culprit which caused the resistor to burn out in the first place?  I removed the 7474 and put it in my tester…

 
It fails! I solder a brand new 7474 chip into IC44 and power up the board, it fixes the red line problem Smile. At this point I’m thinking the board is now fully repaired and everything seems to be running nicely Wink 

Then about 30 minutes into soak testing the board set I get this…


 
I have now got blue colour issues Ouch. I take a look at the schematics again, I’m now thinking maybe the 47273 flip-flop at IC67 has gone bad too. I pull the 74237 and check it in my tester, it passes fine so it looks like that’s not the issue. The only other thing I’m thinking is that maybe the N82S09N bi-polar ram has now decided to go bad on me. This time I rob a N82S09N chip from a non-working Wild Western stack, it fixes the blue issue! Just to make sure it’s not some sort of connection/socket issue, I put the old N82S09N chip in again and the blue comes back, put in the Wild Western N82S09N donor chip and the problem disappears.
 
These are the chips in the colour circuit that I replaced and checked…

 
The board set has been powered for several hours now (with a few obligatory game plays in-between Wink) and everything seems to be working great. I think I’m now at the point where I can call this repair done Thumbs Up
 
Parts needed for this repair:-
·         1x 270 ohm resistor
·         1x 470 ohm resistor
·         1x LM3900 Op Amp
·         1x 7474 Dual D Flip-Flop
·         1x N82S09N bi-polar ram
·         2x YM2149F sound IC (direct replacement for the AY-3-8910)
·         3x 6116 ram (direct replacement for the TMM2016P)
 
 
Wanted: Rainbow Islands original PCB.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Flinnster Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2021 at 1:49am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote r-type Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2021 at 9:24am
Clap Great game, definitely worth the effort.
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