Naomi repairs - Stuck inputs and Error 4

I had a lot of six Naomi motherboards in for repair recently, mostly just replacing rams so nothing worth logging but one of them was interesting. It would boot but would not enter test and the dip settings were stuck on, I traced the dip switch traces to the other side of the board. To a Sega custom chip 315-6146, I decided to replace the ram connected to it first as that is was much easier to swap and thankfully it was just the ram, a common 62256 type.

While playing with Naomi stuff I found that the Net Dimm board that I have owned and used for a good 15+ years was slightly faulty. It wouldn't return a serial number, this isn't usually a problem apparently because I haven't noticed an issue before, not until I tried to load Ikaruga and got error 4 that is.

A google search brought up the exact issue, serial number not returned by Dimm board but not many people with the issue, I only found one forum post with someone else with the error. It doesn't look like they ever fixed it either.

The serial number is stored on a tiny EEPROM on the bottom of the Dimm board at IC6S

 

I took a replacement from a scrap board but a new 93C46A EEPROM programmed with the dump from mame would have also worked.

That got her going.

Sega Mega-Tech motherboard repair

Another Mega-Tech on the bench for repair, this must be about the sixth one I've worked on. They are always filthy so the first thing I had to do was clean it. The sockets also all needed to be replaced too like in previous Mega-Tech repairs.

When powered on I got nothing on screen and one of the Sony CXD1095Q chips was getting super hot. Replacing the Sony CXD1095Q with a nice new old stock one it powered up and worked on first power up displaying the cartridge list but on the second power up it was having trouble seeing the cartridges and only loading games from certain slots. The other CXD1095Q failed so I replaced that one too, this fixed the slots and loading issues.

 

Now to plug in the main screen and see what's happening, I could see colours but no sync. Tracing out the sync signal it goes through a 74LS125 and to the Sega custom 315-5313. The 74LS125 input pin was shorted.

 

With the 74LS125 socketed and replaced there was still no sync output. Sadly the 125 killed the sync pin on the custom 5313 chip when it failed. Fortunately I have a Mega Drive console that I've used for parts already as it had a broken case and the 5313A chip is still on there. The A version is a later version but is pin compatible.

Replacement 315-5313A fitted and I get a sync signal and a good image, the only remaining issue is I noticed on the all white Sega logo screen in Sonic the white was a little green looking. This again is a common issue with these boards where the transistors on the video output aren't equal, they all test fine but the only way to get a really balanced image (without adjusting the monitor) is to replace all three transistors with new ones, so that's what I did.

 

 

The camera makes it look a little blue but it's perfect now. Repair complete.

Eprom programmer power supply upgrade

I have owned a lot of different programmers but the Dataman 48Pro (Beeprog) is by far my favorite as it's fast, reliable and usb!. I'd even argue it's better than the new version as this one allows the use of standard adapters for non dip stuff. The newest one is far more locked down and forces you to buy expensive adapters.

It's great for the arcade hobby as it'll do oddball proms, pls153s etc, the only problem is it will some times come up with a warning about the power supply not being powerful enough and fail to burn some of these chips. That's because Elnec (Dataman) cheaped out and only included a 1amp power supply, a 4amp is what is needed to cover everything.

Why include a 4amp power supply when you can charge the customer another £100 for a 4amp one later. Well I'm not going to be paying that.

Thanks to Purity for sending me a picture of his original power supply from a Labprog+ which is the same as used on the 48pro. I also confirmed it with a meter but the pinout shown is correct.

So I needed a 15v 4amp power supply and a 6 pin mini din plug. A quick ebay search and I bought this old Laptop power supply for £5 and a plug for £2.50.

 

 Soldered them together and I can now burn any prom without issue for the total cost of £7.50. 😀

Space Firebird (Bootleg) Repair - Part 2

I couldn't wait until tomorrow to finish this repair. 😆 Being a Nintendo board the first place to start with a sound issue of this era board is the 8035 MPU . I don't have one... and they're getting quite hard to come by now but I remembered I bought a bunch of 8039s for Donkey Kong repairs. The 8039 has more internal ram than the 8035 but that's not a problem.

The 8039 brought the majority of the sounds back but no shooting sound. Using the audio probe on the op amps I could hear the shooting sound on one of the inputs but nothing on the output. Replacing the LM324 op amp and everything is now working.

Space Firebird (Bootleg) Repair - Part 1

Another Nintendo board for repair and the collection, I got this in a trade a good while back but have only just gotten around to making a jamma adapter and testing it. When doing a google search for a pinout a ukvac thread comes up where someone says that it's the same pinout as Phoenix, that isn't quite the case but more on that later.

When powered on I got an explosion sound and a starfield and not much else. There were a few dots and lines that were meant to be sprites. This turned out to be a bunch of bad 2101A rams on the video board, thankfully they're all socketed and I am able to test each one out of circuit in the Boardmaster. All but two failed, AMD branded.

I've had issues with AMD branded logic in the past too, maybe they should have just stuck to CPUs.😄

New RAMs fitted. This brought the sprites back and showed a new issue. All the bullets were on the very bottom of the screen under the player ship.

I went looking for counters on the video board, there's some very nice quality schematics for this board online which is a nice change from the usual no schematics or unreadable schematics.

Piggybacking didn't work but using a logic probe I could see the outputs on 74161 @ 4G were all shorted to ground, which also explains why piggbacking a good 161 on top didn't work.

 

Unusual brand of TTL on this board that I don't recognise which is usually a bad sigh but they work for now.

That fixed the bullets issue, a very hard game to photograph as it turns out.

 

 I took 40 pictures and that was the best of them.

 

That's all for now, I'll have to return to it at some point to see why I only get explosion sounds and the rest of the time it's completely silent.

Here's the pinout.

 

This is not at all the same as Phoenix pinout, the controls and video are on opposite sides, you also need -5v for Space Firebird as it has its sound data stored on a 2708 eprom.

Nintendo Vs Super Mario Bros pcb repair

I got this Nintendo Vs board in a trade, someone had taken a heatgun to it at some point and done some damage to the board along with taking off a bunch of TTL, '104' capacitors and the eproms.

Once repopulated and fixing a blow out via caused by the heatgun damage I powered it on but the game did not run, just a solid green screen.

It's not shown in the picture but the top part of the board had a standard cpu installed, with Vs Super Mario Bros you need a dummy cpu in this socket for the game to be run.

Thankfully you can get away without having a dummy cpu and just bridge two pins on the cpu socket instead.

 

This got the game running but with some strange issues such as bad graphics, messed up scores, phantom coin inputs and other times it would run fine for 10-15 minutes.

I was worried it was going to be an issue with trace(s) caused by the heatgun damage and I was going to have to check every connection in the area with a multi meter. Before all that I went through and checked all the ram and TTL chips first as I already knew the cpu / ppu were fine from trying them on another board.

The trusty boardmaster 4000 flagged a 74LS157 @ 5J as having a stuck low output on pin 7.

 

 

This was confirmed out of circuit, a new 157 fitted and it is now fully working.