Tuesday, 19 February 2019

Air Buster pcb repair

This repair has been going on for quite a while, first the custom for the I/O near the edge connector was missing (snapped off) when I got the board and the custom CALC1 chip was also bad. I bought a working Gals Panic off ebay for both these parts.

I also had to replace several missing and bad maskroms with eproms, this got the board running but it had a very annoying intermittent issue with the background flickering and disappearing.

Half the cloud is missing, it would also effect the buildings later in the level.

Probing around with my logic probe while the fault was visible I was eventually able to hear the issue. Thanks to my logic probe having a audio / beeper feature, I confirmed on the scope I was getting an invalid output from one of the 74LS352s.


The bad 352 removed and waiting for a new one. Any other TTL on this board I have plenty of spares but not a single 352 so I had to order some and wait.


 With the new 352 fitted the background is restored, repair complete.

Wednesday, 23 January 2019

Sunset Riders pcb repair

I got this pcb in a trade, it was described as not working. When It arrived it was confirmed not working, it just displayed a white flashing screen over and over again as it was constantly resetting (watch dogging). First thing I checked was the roms, they were in the wrong sockets but otherwise fine. Putting them in the correct sockets made no difference.

I then probed the main 68000 cpu and noticed a lot of stuck and floating address lines. I desoldered the 68000 (fun), this is the first time I've ever seen a 68k cpu go bad. Sunset Riders uses a 16mhz 68000 which I didn't have (the ones I have are only rated 8- 10 mhz) so I borrowed one from another konami board for now.

This got the board booting but it failed to get past self test, it complained about the eeprom and 2F / 3F. Powering off, holding down the test switch and powering on again fixed the eeprom issue but not 2F / 3F.



2F is the sound eprom which was corrupt but burning a new one with the correct data from mame made no difference. 3F is the 6116 ram for the sound section. I desoldered the ram but it tested fine, I started probing around the sound section and again found more stuck address lines on the cpu (Z80).

I replaced the Z80 and the board now passed self test everything looked good but the sound was just a constant noise with odd samples playing randomly. Interestingly the maskrom test wouldn't complete either, it just crashed after a few seconds. The only thing that made any sense to be causing this fault was the konami 053260 custom.


I removed the 053260 chip and then took a working donor from a Golfing Greats pcb, this fixed the sound completely.


Repair complete.

Wednesday, 12 December 2018

Gemini Wing pcb repair

I've had this original Gemini Wing pcb on the shelf for years, the main issue was the lack of schematics and that Tecmo covered all the traces much like Capcom did with some of their early games. I picked up a cheap bootleg from ebay to help with this repair.

The bootleg is such a close copy I was able to run the top board with a bootleg bottom board and vice versa. The main issue turned out to be a 'slightly' faulty Z80. I've never seen anything like this, it passes in my chip tester and works on most other boards, ZX Spectrum etc but putting it back in Gemini Wing it refused to run.

With a new cpu in place it ran but with missing player / enemy sprites and no sound. The sound issue was due to a missing M5205 (quite hard to find these days, also used on Double Dragon). With this replaced the sound returned and just left the sprite issue.

 
I found two LS257s on the bottom board with floating inputs, I traced this back using the bootleg board to a LS193. 193s aren't something I've ever needed before so didn't have any stocked but luckily I found one on a scrap board.


With the new 193 in place the missing sprites returned.




Repair complete.

Tuesday, 6 November 2018

Phoenix pcb repair

This board appeared to be completely dead at first but it turned out to be running blind. I narrowed this down to the 7407 near the edge of the board, the resistor network it is connected to was getting very hot.

After removing and replacing the 7407 with a good one I got a monochrome image.


I traced this back to the prom at ic41, the green pin was pulsing away but the blue and red pin were both stuck low. The bad 07 obviously took out the prom too.


 With a new prom burned and fitted...


The board is now fully working, repair complete.

Tuesday, 16 October 2018

TMS5110ANL sound chip adapter pcb

The TMS5110ANL sound chip was missing from one of my Bagman pcbs, I ordered a replacement from utsource but it didn't have a picture or any details. Once it arrived it turned out to be a shrink dip version which seems to be much easier to find than the standard dip version and cheaper too. It won't work in a Bagman pcb though, well not without a little help.

Instead of tracking down another one I made a very basic adapter in eagle and had oshpark make me some pcbs.


I ordered some 28 pin sdip sockets from China, not really necessary but makes it easier to swap the chip out if it fails.


Here it is installed in the Bagman pcb and now all speech is working.

Like I said the design is extremely basic but if anyone else wants to have some made up you can order them here.

Wednesday, 19 September 2018

Sega System X (After Burner) pcb repair

This board was completely dead I had sync but that was about it, after an inspection it soon became clear why.


Two nasty gauges on the back of the board taking out many traces, I removed the solder mask either side of the breaks with a fibreglass pen and repaired each trace using a single strand from some multi core wire, just like in a previous Sunset Riders Repair.


Liquid solder mask applied to protect the repair.

The board then booted right up and worked perfectly or so I thought. After I finished my harness to test it fully I could see that the analogue controls (joystick and throttle) weren't working. This turned out to be a bad ADC0804, I pulled a replacement from a scrap system x board and replaced it which fixed the issue.

This was actually a GP Rider to start with but after a rom / pal swap it's now an After Burner.


Up and running in its new home.

Tuesday, 21 August 2018

Bagman pcb repair notes.

 

I've labeled this one as notes rather than a repair log as it was three different boards I repaired at once and not everything is covered. A lot of TTL needed to be replaced to get these up and running.

Some issues I noticed across all three boards were that the Z80 cpus were bad and when removing them from their socket some of the pins broke off and stayed in the socket.

Missing player / enemy sprites on two of the boards was down to a bad 74LS163 @ M2
Can also be caused by a bad 74LS32 @ 2P

No speech (TMS5110A was ok) on one board it was a bad PROM @ R6 and on the other a bad 74LS151 @ S6

Bad PROMS in general, on one of the boards all three were bad. This causes colour issues and no speech.

An issue across all three boards was bad / missing video sync. This was a combination of bad 74LS161s @ A4, A5, B4 and B5.

Bad 74LS283s @D2 and D3 again on all three boards.

Certain controls not working 74LS245 @ 9A or 2B

The four sprite rams (27LS00) were fine on all three boards.

One final note, the PAL @ P6 is used for 'guards controlling' according to mame, which I guess is a cryptic way of saying controls the enemies. With the PAL removed the enemies seem to behave the same but I am guessing later in the game they behave differently and that it might make the game harder with it removed.

A similar security measure to what Bubble Bobble used maybe?


Download the full size image here

To help with my repairs I took the existing pdf scans of the schematics which are split up over several pages and combined them into a single page using photoshop. There's still quite a few areas that aren't legible unfortunately but I don't think the originals were that good to begin with.