Received from Germany this faulty DonPachi PCB for repair:

Board played almost ‘blind’, most of graphics was missing, only some corrupted text was visible:

According to MAME source there are three layers of graphics:

ROM_REGION( 0x100000, “layer0”, 0 ) /* Layer 0 */
ROM_LOAD( “atdp.u54”, 0x000000, 0x100000, CRC(6bda6b66) SHA1(6472e6706505bac17484fb8bf4e8922ced4adf63) )

ROM_REGION( 0x100000, “layer1”, 0 ) /* Layer 1 */
ROM_LOAD( “atdp.u57”, 0x000000, 0x100000, CRC(0a0e72b9) SHA1(997e8253777e7acca5a1c0c4026e78eecc122d5d) )

ROM_REGION( 0x040000, “layer2”, 0 ) /* Text / Character Layer */
ROM_LOAD( “text.u58”, 0x000000, 0x040000, CRC(5dba06e7) SHA1(f9dab7f6c732a683fddb4cae090a875b3962332b) )

I translated this info on hardware and figured out the relevant circuit of each layer:

Each circuit consists in a QFP custom ASIC (maked ’38’) which addresses an 8Mbit MASK ROM (or a 2Mbit EPROM for the text layer) reading back data that then are written to two 8K x 8-bit static RAMs.After succesfully  checked connection between ASIC, ROM and RAMs my suspicions fell on the 8k x 8-bit SRAMs, they were all manufactured by Sanyo so in my experience not a great guarantee of reliability.Probing the ones @U50 and U51 (which lie in the ‘layer 0’ circuit) revealed weak or stuck signals on many data lines:

I removed both:

Actually only the one @U51 failed the out-of-circuit testing:

Now all graphics were visibile.Backgrounds and sprites were fine but text was corrupted throwing garbage over the screen :

The ‘layer 2’ identified in MAME source as ‘ Text / Character Layer’ was obvioulsy the involved one.Checking the two Sanyo 8K x 8-bit SRAMs @U55 and U56 revealed again weak signals on data lines:

I removed them and installed machine sockets:

Actually both RAM chips successfully passed the out-of-circuit testing of my different programmers.Anyway, replacing them fixed completely the graphics:

But sound was horribly scratchy and corrupted as you can hear in the above video.Here it comes again to help my audio probe for checking the relevant circutit:

“Listening” to various points revealed the sound was clear on the analog output of the two OKI MSM6295 and still good on outputs of the LM324 OP-AMP and input of the LA4460 amplifer.It was fine too on one output (pin 7) of the LA4460 amplifier:

 

But corrupted on the other output (pin 9)

I ruled out all electrolytic capacitors checking them in-circuit with my ESR meter (bad ones can affect sound in this way) so I decided to remove the LA4460 amplifer:

Put back a good one and some thermal compound for a better heat dissipation:

This restored a crystal-clear sound.Mission DonPachi accomplished!

I’ve been sent from Germany some faulty PCBs for repair.There were among them two PCBs manufactured by Toaplan :

• Knuckle Bash

 

• Fixeight:

The first was throwing a “A VRAM ERR” message on boot:

The video RAMs (VRAM stands for this) are two 8k x 8-bit static RAM located @42 and U51:

They are accessed by the QFP ASIC marked ‘GP9001’ which is the graphics controller of the system:

For first I did a visual inspection of it and found some pins not really firm (common issue on QFP with this fine pitch)

I reflowed them but this didn’t led to any improvement so I moved to check the VIDEO RAM ICs and found weak signal on data lines:

I pulled both RAMs, only the one @U42 failed the out-of-circuit testing:

The board successfully booted into game now but the colors were wrong, they were “bleeding”:

This is another common issue on this board so I knew where to look exactly.The data bits from the two 6116 (2K x 8-bit) palette SRAMs are latched by two 74HC273:

Probing with a scope the 74HC273 @U9 revealed weak signal on outputs (inputs on the left of the below snapshot, outputs on the right)

I pulled the IC:

It actually passed the out-of-circuit testing on all my programmers so I think IC was not really bad but it had altered voltage thresholds.Anyway, I replaced it and this fixed the board completely.

 

 

Now the FixEight troubleshooting.

Board gave me a steady black screen.This board uses the GP9001 graphic controller too:

Found some lifted pins on it:

I reflowed them as well as replaced the main program code 4Mbit EPROM since it had some rebuilt pins that gave me trouble when dumping it:

But still no boot.But I noticed that pressing  the PAL16V8 @U51 :

produced a couple of different RAM error messages on screen:

Solderside of the PAL socket had some dry joints:

So I replaced it and finally the board initialized but it quickly went straight into SERVICE mode and then reset in an endless loop :

 

From a still image I noticed that some inputs were stuck in I/O check:

The inputs are handled by the custom ‘HK-1000’, you can find more info about it in a past article from mine:

Toaplan ‘HK-1000’ reproduction

On my PCB a replacement board had been used in place of the original part:

Some inputs of a 74LS240 on this replacement board were shorted to ground.Instead of repairing it, I opted for a reproduction of mine (the blue jumper wire was already there to patch a trace previoulsy broken during the removal of the original ‘HK-1000’)

Finally the board booted into game with no further issues.Toplan double repair log accomplished.

I got this Data East Robocop pcb from a friend that was totally dead.

I had more Data East pcb’s around so I could test the bottom ROM board with one of those CPU boards and it was also not working. So I started pushing the EPROMs in their sockets and after that the game booted up.

So now I tested the ROM board with it’s original CPU board and game booted but the screen was almost completely black apart from some graphical elements like the energy bar.

After visually going over the CPU board I found that one of the custom ASIC L7B0072 had a crack in the center of it.

I had a broken Midnight Resistance board (not the previous repair) that had this ASIC, so I opted to transplant it over to the Robocop board.

I noticed that the top of the ASIC had a brownish discoloration, but I didn’t know if it was toast or not, so I desoldered it with my hot air station and soldered it onto the Robocop board.

Confirmed that there were no shorted pins on the ASIC and booted the game, but unfortunately the transplant did not help. Some graphics appeared, but mostly scrambled characters and when coining up and pushing start, the game reset. (forgot to take a picture)

After having a conversation with caius (thanks again for all your advice) we opted to do another transplant but with a better looking ASIC.

Redid the procedure, hot air station to remove the ASICs and then soldering again and lo and behold, the game has good looking graphics once again 🙂

But I quickly noticed that there were no audio at all. Using my audioprobe I found that there were music been generated by the YM3014 at 4M and FX from the YM3014 at 3M and then going to the OP-AMP 3403 at 4N

Nothing came out of the 3403, so I eventually found that there were no +12V input on pin 4 of the 3403. Checked the JAMMA edge and found a broken track. I guess that the operator had some form of voltage measuring device and somehow broke the track at some point. I soldered a little metal wire to bridge the gap and booted the game again.

Now audio could be heard for a short second and then silence again.

I eventually found a shorted capacitor at 

After replacing the capacitor the audio was loud and clear again. Job done 🙂