Saturday, 23 March 2019

Outrun pcb repair

I did this repair a few days ago now and forgot to take certain pictures but I'll document what I can. This Outrun was watchdogging (resetting) and had a smeared red and blue image on screen which I forgot to photograph.

Firing it up with the extremely helpful test roms and a known working video board I could see a lot of bad rams on the CPU board, the watchdog was kicking in before the test would finish but I could see all I needed to for now. IC55 was failing every so often too so I replaced them all apart from IC114 and IC130 which are made by Fujitsu and hold up very well (unlike their TTL).


Swapping back to the original video board I could just about see that both palette rams (IC92 and IC95) were failing. With these replaced I got this image.


This was caused by two bad roms opr-10267 and opr-10268 if I remember correctly.

With these replaced the image was perfect apart from there being no road on the left side (again I forgot to photograph this).

The road issue was fixed by replacing a bad rom on the top board opr-10186 at location IC47.

This fixed everything graphically and the controls worked too.


Now the problem was the lack of sound, nothing completely quiet. The clock signal for the Z80 was stuck. Looking at the schematics I see the last thing I want to see.


That the clock is created by the 315-5218 surface mount custom chip. I tried a little experiment and created a 4mhz clock from the 16mhz clock using a 74LS74 and fed it into the Z80 to see if there was any life left in the custom but unfortunately there wasn't.

Here's the custom removed and pads cleaned up ready for the donor.


The new custom fitted, originally from a System X board.


Still no sound whatsoever but the clock was back and the Z80 was a lot more active. I decided to hook up the Fluke 9010a to the sound cpu (Z80) and see if the ram was good. First thing I do is a bus test and it reported A15 stuck high, this was caused by the main sound eprom epr-10187 which is interesting as the eprom programmer had no issue with it.

With the rom replaced there was still no sound, the fluke reported that the ram was fine so I moved onto the PCM eproms and rams. The two rams failed out of circuit testing and were replaced and the maskrom at IC70 failed and was replaced too.

This finally brought back the PCM sounds that were slightly too fast and getting cut off early but finally I could hear something.

I used a sound probe on the op-amp TL084 (IC125) and nothing was going in, this traced back to the YM2151 and sure enough nothing was coming out of it. I took a replacement from a System X donor board and all sounds were back and everything is working perfectly.

Repair complete.

Tuesday, 19 March 2019

Vectrex transformer repair

I've been after a Vectrex forever but the right deal never seemed to come along plus I didn't like the idea of having a vector tube sent through the post. A local one finally dropped in my lap and with a nice selection of games too.

The only problem was it was completely dead, checking the easy stuff first the fuse in the plug and the one inside were both fine. I could tell right away from the missing and mixture of screws that someone had already been inside before but luckily they seemed to give up when they saw the fuse was fine and they didn't damage anything.


Checking the output of the transformer and it was completely dead, a bit of research online and this is quite a common issue. I had a look for a replacement but the one maplin used to sell which is known to be an ideal replacement they no longer stock. I found another on ebay that was a good match but rated for 4amps where as the original is rated for 3amps (or possibly 2?) I was worried it would be too big and require some case modification that I'd prefer to avoid.

While continuing my search I found this very informative video here https://www.youtube.com/watch?v=zIqCVLveSys&t=1322s which shows how to repair the original transformer. It seemed that my transformer might be fine and the only issue is a bad thermal fuse hidden in the windings. You don't have to dig too far into the transformer to bypass or replace it either.

Here's my teardown, bypass of the fuse and rebuild.


 



The glue is all dried up so it was very easy to pry open, I dug into the insulation snipped the two wires for the fuse twisted them together and soldered them. Then a small bit of heat shrink sleeving (not necessary).

I sealed it all back up and fitted / soldered it back into the vectrex it fired up first time with no other issues.

Thinking about it afterwards I didn't have to tear into the transformer as far as I did, with the metal cover removed from the 18v side the two wires for the fuse are visible at the edge, I could have just soldered a wire or old capacitor leg across them or if I wanted to be fancy a new thermal fuse.

The thermal fuse really isn't needed though, there's already two fuses on the 240v side.

So there you have it, repair your old transformer don't replace it and a big thank you to Hugo B. on youtube. I don't think anyone knew about the hidden fuse until his video, I certainly didn't. :)

Tuesday, 26 February 2019

Block Block to Pang conversion

Block Block was Capcoms answer to Arkanoid and it's an okay version at best, a much better game on the same hardware is Pang / Buster Bros. This conversion is pretty straight forward but you will need to make a jamma adapter even if you have one of these.


This is the official Block Block jamma adaptor but it won't work with Pang as the controls are different.

Here's the pinout


This is how mine turned out, I left out 21,22,Z and a since eight +5v wires is a bit overkill.



Now on to the conversion itself, mine had been stripped of eproms and all markings on the board suggests non jedec type 27C301 eproms would be needed but actually four need to be the standard 27C010 type.

So 4x 27C301 4x 27C010 and 1x 27C256 you can obviously blank and reuse the original eproms if your board is still complete.

There's two options as far as which version of Pang to run you can either use the decrypted version from Arcadehacker posted here or you can use his method to reprogram the original Kabuki cpu that requires an Arduino Uno and a battery to be fitted to the board. I went for the easy first option but may try the other option at a later date to see how Super Pang handles on Block Block hardware (it should work fine).

With the no battery / decrypted roms option you still use the Kabuki cpu but you need to either have 28 sticking out of the socket or remove the resistor at R40 (which is what I did).

Decrypted roms
pang6.bin - 27C256 location 14F
pang7.bin - 27C301 location 15F

Now you need the mame rom pang.zip for the rest of the conversion. Mame usually has useful file names with locations but not in the case of pang.

pang09.bin  - 27C010 location 8H
bb3.bin        - 27C010 location 9H
pang11.bin   - 27C010 location 8J
bb5.bin         - 27C010 location 9J

bb10.bin       -27C301 location 2J
bb9.bin         -27C301 location 3J

bb1.bin         -27C301 location 2D





 Conversion complete.

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.