Saturday, 2 June 2018

Sunset Riders pcb repair

This was just sold as faulty so I wasn't sure what to expect with this one. First of all a visual inspection, I noticed right away a deep scratch on the bottom of the board that had taken out several traces. Someone had taken off some soldermask and figured out which were the bad traces but not made any attempt to repair them.

I was going to use kynar wire but this was too big, the traces are extremely small and close together. So I ended up taking some multi core wire and using a single strand about the size of a hair.

With the micro surgery complete and no other visible issues I powered the board up. At first all I got was a black screen so didn't think it was running but then the music kicked in and part of the title screen appeared.

I fixed another Sunset Riders pcb recently that didn't end up getting logged but it gave me a good idea where the issue was. The other board wasn't as bad but had colour and background issues caused by a bad 053251 konami custom.

By touching certain pins on the custom chip I was able to get it to display slightly more of the background.

I took a donor 053251 from a Golfing Greats pcb.

Not quite there yet but better.

Time to check the maskroms as these are another common failure on this era konami board. I went into test mode but wasn't able to read which was the maskrom test, I used mame to see what I should be seeing. Then I could see the bottom two turned red which again in mame I could see was 16K and 1D, 16K maskrom contains graphics data and D1 contains the audio. This explained the lack of shooting and certain other sounds.

I then replaced the two maskroms with eproms (27C400 and 27C800). Luckily they were all in sockets from the factory, usually they're soldered directly into the board.

A blob of liquid soldermask to protect the repaired traces on the bottom and the repair is complete.

Tuesday, 29 May 2018

Popeye pcb (bootleg) repair

I bought this Popeye bootleg pcb in a lot of faulty boards, it included the worse jamma adapter I've ever seen. It's made from another cut up pcb, anyone know what game it was?

The board was working apart from the character layer of the graphics, making the text scrambled and blue blocks appear over the background and other sprites.

I didn't notice at first but blue and green were also switched, this was an issue with the adapter though and not the board.

The first thing I did was dump all the eproms and make sure they matched the ones in mame. Eprom 5 failed but this was a red herring as it was fine even though it's not in mame. :)

This did lead me in the right direction though as the data causing the issue is stored on this rom, it looked much better with it removed from the board. So I started looking around this area, I piggybacked a 2114 ram @ F8 and things looked much better, leaving the ram in place and power cycling the board completely fixed the issue.

I replaced the bad ram and made a new jamma adapter.

The colours are now correct, repair complete.

Saturday, 26 May 2018

Aliens pcb repair

I bought this Aliens pcb as faulty with the error bad i3.

Someone had already replaced and socketed i3 (a 6116 type ram) and this made no difference to the error.

Checking the very nice schematics there was pretty much only one thing that could be the issue.

The 051960 konami custom chip. I had one left in my little box of customs, in unknown working condition. It came from a Main Event board that I'll be harvesting for more parts later in the repair.

Anyway back to the 051960

Replacement custom in place.

Yay the ASIC is good.

This just left the sound section, four capacitors were broken off the board.

The electrolytics I have plenty of but I didn't have the correct value for the mylars so I dug out the scrap Main Events board and pulled two from that.

Sound fully restored, repair complete.

Saturday, 21 April 2018

Thunder Force AC repair

After a long break from board repair I finally got the ball rolling again with this Thunder Force AC conversion pcb I just picked up. It was sold as having issues with the background graphics and that was exactly how it behaved for me too. The background would constantly flicker, everything else seemed fine.

On close inspection of the pcb I found a few issues, there were a couple of small patches of corrosion. Most of it just needed cleaning but one spot it had gotten as far as eating through one of the traces.

I tinned all the traces in the area where there was corrosion and added a tiny bit of wire to the broken trace.

Then finished it off with a small amount of liquid solder mask. This fixed the background issue, all that was left to do was replace a broken resistor.

Repair complete.

Sunday, 8 October 2017

Spy Hunter pcb repair

I wasn't planning to log this one but as the fault turned out to be something I haven't come across before I thought it was worth mentioning. That's also why the screen shots are from mame.

This playtronic Spy Hunter pcb would either start with no background graphics or run fine for an hour or two and then the background would vanish.

Intermittent faults are always time consuming and a lot of guess work, it looked like a failing chip that was failing as it heated up but often from cold there was no background and spraying chips in the background circuit with freeze spray made no difference.

The midway schematics came in very handy, the playtronic board doesn't have screened chip locations but the schematics include a picture of the pcb with locations. After ruling out all the single wipe sockets for the ram (2b) and eproms (3a - 6a) used in the background I was left scratching my head.

I had previously replaced all the ribbon cables and also reflowed the connectors with no change to the fault.

I took a short break and when I came back to the board the background had returned, this makes finding the fault impossible so I had to leave it on for around an hour for it to vanish again.

Once the background vanished I checked all the outputs of the TTL connected to eproms (3a - 6a).

The outputs on the 74LS174 @ 13e were all low, the truth table for the 174 and schematics confirmed that pin 1 should be high as it's connected to +5v through a 1K resistor but it was reading low.

Checking the resistor and 5v was going in one side but nothing coming out the other, I changed the resistor and sure enough 5v back at pin 1. The resistor was obviously going open but not just from heat as from cold it was often open too. The resistor has no signs of damage or corrosion.

Best of all out of circuit the multi meter says that the resistor is fine and exactly 1K.

Saturday, 9 September 2017

ZX Interface 2 repair

The Sinclair Inferface 2 adaptor plugs into a ZX Spectrum computer and adds rom cartridge support and two joystick ports. Unfortunately this one had issues with the player one port, left and right were moving very slow and erratically. I opened it up and reflowed the joystick port and connector that goes to the spectrum and also cleaned everything as there was a lot of flux left over from when it was manufactured.

This didn't fix it, meaning the only possible cause could be the custom MT62001 chip. It doesn't look like this chip has a gal or any other type of replacement available or was used in anything else so I thought that was that.

After a little more research though it turns out that Amstrad continued to use this chip in later computers but renamed it to 40057. As luck would have it I have a scrap +2 (grey) motherboard that's been mostly stripped but still had this chip intact. After installing it into the interface 2 it now works perfectly.

Repair complete.

Tuesday, 1 August 2017

Kung Fu Master pcb repair

I've had this Kung Fu Master pcb sat in the to do pile for a year or two now as the custom KN6034201 chip on the top pcb was bad and I wasn't able to find a replacement.

It caused the background graphics to just show up as solid colour blocks.

A big thank you goes out to Caius for not only making a modern day replacement for the custom but also for selling me one of his spare pcbs.

 The KN6034201 reproduction pcb populated and ready to be fitted.

All graphics are now 100%, the only issue remaining is that there is no sound. This turned out to be a bad 6803 cpu, I confirmed this by swapping it into my other Kung Fu Master board. The 6803 cpu seems to be pretty rare at least when it comes to video games, they were more common in pinball machines so I didn't have any on hand.

I ended up ordering some from utsource (who I don't recommend) but they were very cheap so I ordered a few, this was lucky as the first one I tried was DOA. The next one I tried worked and the sound was fully restored.

Repair complete, thanks again Caius for making this repair possible.