PCB Repair Logs – Page 10

Space Invaders DX double repair log

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Jul 262019

I received from Portugal a couple of Space Invades DX PCBs, a game released in 1994 by Taito (more or less a port of the original Space Invaders, with a few new features).

Both boards were in very good condition but completely dead.Here’s the first one:

All I got on power up was a steady black screen.Probing the 68000 main CPU revealed the address/data busses were active but the three interrupts inputs (IPL0-IPL1-IPL2) were all in fixed high logical state.I traced these inputs back to a PALCE20V8 marked ‘D72-07’ :

Then I disassembled the fusemap of the MAME dump of this PAL being able to identify its inputs and outputs:

/** Inputs **/
Pin 1 = i0;
Pin 2 = i1;
Pin 3 = i2;
Pin 4 = i3;
Pin 5 = i4;
Pin 6 = i5;
Pin 7 = i6;
Pin 8 = i7;
Pin 9 = i8;
Pin 10 = i9;
Pin 11 = i10;
Pin 13 = i12;
Pin 14 = i13;

/** Outputs **/
Pin 15 = o15; /**(Combinatorial, No output feedback, Active low) **/
Pin 16 = o16; /**(Combinatorial, Output feedback output, Active low) **/
Pin 18 = o18; /**(Combinatorial, Output feedback output, Active low) **/
Pin 19 = o19; /**(Combinatorial, Output feedback output, Active low) **/
Pin 20 = o20; /**(Combinatorial, Output feedback output, Active low) **/
Pin 21 = o21; /**(Combinatorial, Output feedback output, Active low) **/
Pin 22 = o22; /**(Combinatorial, No output feedback, Active high) **/

Pin 20-21-22 were outputs to 68000 interrupts lines and they were confirmed to be stuck high along with all other outputs :

Although PAL was secured I tried to read it in my programmer, this would have at least told me the state of ‘health’ of the chip.Reading failed hence the chip was faulty:

I burned a GAL20V8 (GAL and PALCE are most of time interchangeable) with MAME fusemap :

Board booted up with no further issue.First board repaired.

The second board:

As said, it was completely dead.Probing the 68000 main CPU revealed the clock input was stuch high:

I traced it back to a 74F161 @IC51 which acts as a clock divider of the 32Mhz signal generated by the near oscillator :

There was nothing coming from the oscillator into the clock input (pin 2) of this 74F161 counter:

At first glance I thought the oscillator was dead but before replacing it I made a visual inspection on solder side.I found a dry joint on its output pin :

I promptly reflowed it and then powered up the board again.It booted up with no further issues.Double repair accomplished.

Space Firebird repair log

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Jul 222019

One drunken day at the excellent Revival event I offered to look at a Nintendo Space Firebird PCB.
Initially I was given the eBay link which had a few pictures of the fault.

When I got the board I did my usual visual checks and found a few things I didn’t like the look of.
First up both main RAM chips are socketed. I removed these to check out of circuit and found this

I fixed that up by removing a leg from a donor chip and soldering it on

Next up was the 8212 Input/Output port. It too was socketed with a single wipe socket but what really got me suspicious was the state of the soldering

I wasn’t a fan of this so desoldered it. When I desoldered it I found this

A bit of trace has been lifted there. I can only assume this has been removed before.
I fitted a new socket and moved on.

Found a burnt looking resistor on the sound PCB

The resistor still reads 20 ohms but i will replace that once my parts order comes in.

Lastly there were a few areas with the solder mask removed and solder on it. Not a huge problem but it needs addressed.
I cleared the excess solder from these places and covered them using a Chemtronics pen.

Not pretty but it does the job.

Firing up the PCB for the first time confirmed the original fault was still present.
As the fault was with the video I looked there first.
I started by reseating the two socketed RAM chips

To my surprise this fixed up the graphics. Not sure what effects the previous fixes would have had but Im not removing them to find out.

New problem now. The game hangs at the title screen at the same point every time.
Whenever I get issues like this I always think RAM or ROM issues.
I had already confirmed the RAM so went on to dealing with the ROM’s.
All of them were a match for Space Firebird according to MAME’s ROMident but the ROM at location 5J was for a different version of the game.

It should have been this

I erased and reprogrammed the 2716 EPROM and now the game plays fine.

While comparing gameplay against MAME I realised some colours were missing

This should look more like this

I chased this round for quite a long time only to realise that the 74LS04 inverter I was using (as stated in the manual) to invert the colours was my problem. Switching to the proper Nintendo inverter PCB made everything look right again.

All that’s left now if to replace all those capacitors on the sound PCB and that burnt looking resistor and this board is done

Capcom Trojan PCB repair Log

Jul 212019

I got this board a few years ago when I got a Pac-Man cabaret cab that had been converted to Trojan.

The whole cab was sold to me as not working so I assumed the board wasn’t booting either I converted the cab back to pacman and put this board aside until this year

So I fired up the board and it booted up just fine. However there was absolutely no sound coming out.

One of the issues with this board is that there aren’t any schematics available for it.
Luckily the sound section is almost identical to Ghost n Goblins.
Since the traces are visible on the board, I drew them for help on the back of the board.
Crude but it helped figure out things a bit.

It’s got that same sound module (85H001) to drive two YM2203 (3 channel sound chip)
The signal is then fed to a YM3014 DAC, and LM324 Op-Amp and a final HA13001 power amplifier.

Probing the YM2203, YM3014 , LM324 I can see signal coming out of all these and into the input of the power amplifier .

However there’s nothing coming out of the HA13001 so I’m assuming this is the culprit here.
Removing it, half the legs broke off . No wonder it wasn’t working

I fitted a new one and the sound came back right away and I was able to enjoy a quick game of Trojan

A quick and easy one but you need these every now and then

And as usual, for those who prefer the video format:

Tatsujin Oh repair log #3

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Jul 122019

Got in the mail today this Tatsujin Oh PCB (japanese release of Truxton II), a great vertical shoot ’em up released by Toaplan in 1992 :

The board was bought on eBay and according to the seller it didn’t accept credits.But actually, when I powered it up, it booted to a ‘TILT’ message screen and then kept resetting in an endless loop:

I have experienced this issue many times and the culprit was always him, the “infamous” ‘HK-1000’ :

This custom IC handles all the inputs including SERVICE, TEST and TILT and it’s a very prone to failure part, especially the first ceramic revision (like the one present on this board) cracks very easily or goes internally bad.As you may know, I have done a reproduction of this custom IC so I installed a unit after removed the original part and put some round machine pin headers :

Board booted now into game and correctly played but audio was loud, especially explosions and other sound FXs :

As you can see in above video I could not even adjust the volume by acting on the 1K potentiometer :

So I removed it:

It was broken as it fell off in pieces :

I installed a good one:

Sound was fully restored, board 100% fixed.End of today job.

Out Zone repair log #8

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Jul 112019

Received some days ago an Out Zone PCB for repair :

Board was marked as faulty with player 2 stuck in down direction and so it was when I powered it up:

Probing the P2 DOWN pin (19 solder side) on the JAMMA connector revealed it was floating as if it was not pulled-up :

Checking the relevant pin of the 4.7KOhm resistor array (which acts as pull-up) gave me a value of 3.8KOhm, there was something pulling it low:

The signal from the resistor array goes then to pin 4 of a 74LS240 @15M whose resistance to GROUND was only 2.2KOhm:

I removed the IC :

Although the chip was tested good out-of-circuit I replaced it :

This fixed the issue with player 2 but the board suddenly died while I was testing it giving me a solid black screen on power up.From the top of my experience with this hardware I know that the audio circuit must be running otherwise the board will not boot.When I checked the Z80 audio CPU I found the clock input stuck low :