Feb 212017
 

Some days ago I had on the bench for a repair this pretty rare Air Raid PCB (manufactured by Seibu Kaihatsu) :

As you can see from picture above hardware use some big SIL modules which contains all tiles/sprites data (currently undumped but MAME team is working on).My board was faulty, it has sever graphics issues :

Tiles was filled with garbage :

And sprites had blank lines through:

PCB was in almost mint state, only two 2k x 8-bit static RAMs replaced.Besides, it was fully populated with Hitachi TTLs which  are very reliable.So, my suspicions fell on the remaining RAMs (more than on SIL modules) since they were all TMM2015 (like the already replaced ones, all 6116 pin to pin compatible) which means high chance of failure

Probing the two @6D and 14D revelaed unhealthy signals on data lines:

They failed when tested out-of-circuit:

Replacing them restored graphics completely.End of job.

 Posted by at 11:36 pm
Feb 202017
 

Received for repair this original Track & Field (manufactured by Konami but actually it mounted the Centuri ROM set)

On power up it showed almost nothing on screen, most of graphics were missing, only some sprites were barely visible:

On a closer ispection board was corroded especially in the backgrounds generation circuitry, both sockets and inserted ICs ( the ‘082’ custom and the three EPROMS) were affected:

I replaced the sockets, rebuilt the ‘eaten’ legs and cleaned the oxidized ones but this didn’t improve anything.All the graphics is generated on bottom VIDEO board and most of the logics were from Fujitsu (which means an almost certain failure) so I went to probe TTLs with my logic comparator and found a bad 74LS157 @9H (its outputs generate some address lines for the two 2018 tiles RAMs)

This improved a lot, more graphics were displayed :

Always probing in-circuit the Fujitsu TTLs, I found a 74LS139 @14D with all floating outputs:

It obviously failed when tested out-of-circuit:

Now graphics were mostly present but gameplay was accelerated and sound missing too:

This is issue must have caused by some problem with main CPU,  all the circuitry was on top board and also here Fujitsu TTLs were massively used.Probing around I found a 74LS244 @1C just near the Konami-1 CPU with some stuck outputs:

Replacing it restored completely graphics, speed and sound:

But I couldn’t coin up and start a game with both players, inputs were unresponsive.Tracing them back from edge connector they are tied to some 74LS253, from Fujitsu of course:

Without thinking twice I removed the two ones @3E-3F involved in P1 and P2 controls (the other two are for P3 and P4)

They both failed when tested out-of-circuit:

Now board played perfectly, the last issue I had to solve was that highscores and records were not saved, I got only some random characters instead:

This obviously had to do with the +3Volt CR2032 battery installed on CPU board , it was really low (only few millivolts measured)

I installed a fresh battery with its holder to finish the job :

A great classic preserved!

 Posted by at 10:29 pm
Feb 182017
 

Recently I got hold of this favourite game of mine after a long searching. Apparently it is not so common nowadays, so when I saw a sales thread of this pcb  in faulty conditions from an italian arcade forum I took immediately the opportunity and bought it.

The seller posted a video in which the sprites where wrong and the red and blue components were inverted (this latter problem was caused by wrong wiring of jamma adapter)

When the pcb arrived it was in very good conditions with all rams socketed in factory, therefore I immediately tested them out of circuit which unfortunately  were all good (so no easy repair 🙂 )

It had also an horrible hack on the sound amplifier, more on that later.

Therefore I started the troubleshooting without having any schematics and no similar hardware to look for.

Game had this main fault:

and even if it was not seen in the video of the seller, sometimes I got also the logo and some other images messed up

 

The sprite problem I was sure was caused by some wrong addressing of the sprite graphics, therefore I shorted some address line of the eproms on the video board to see which ones contained the sprite graphics and found the four responsible.

Addr 7 and 8 of the eproms 10 to 13 were fixed low. I traced back to a 74ls153@IC38  which had both outputs fixed .

Piggybacking it with a good one restored the sprites, therefore I proceeded with replacing it and fixed the sprite problem

The TTL was from Fairchild (not Fujitsu part!) and it was the oldest one on the pcb, dated 1979!

Now the logo problem, it was strange because sometimes it was shown right, sometimes bad.

After some hours of playing, the logo was not shown right anymore, therefore I asked David Haywood (Haze of Mame fame) where it was contained and it pointed me in the eproms A14 and A15 (different bitplanes which were combined to form the final pic). Both eproms had to be addressed in the same time.

Also he told me that the graphic was bank switched, therefore some logic had to select a particular part of the memory area to show the correct gfx.

I probed their address lines and found the upper one A12, was always fixed low. I forced it high during gameplay and the backdround got corrupted but when the title was shown , the logo was there clear.

So the logo was contained on the upped half of the eproms and the logic was not selecting the A12 bit high or low depending on the situation.

I traced back to the only Fujitsu ttl present on the board, a 74LS259@IC72,  8 bit addressable latch.

Before desoldering it, I tried to understand the datasheet of the part, which is not very common to see on arcade boards , and probes 3 select inputs which were oscillating and the enable line was pulsing everytime it changed from title logo to gameplay.

All his outputs were stuck low, and the HP logic comparator confirmed some outputs were at the wrong logic. Only few are used by the hardware, but I expect in later levels I could get other wrong graphics…

I desoldered it and tested out of circuit:

Turned out Fujitsu was again the source of problems!

I had a hard time to find a replacement, because as said the 74259 is very seldom used by arcade hardware.

At least I found one in the following junk pcbs I had: Rock and Rope boot, Equites and Dig Dug.

I took the one from the bootleg (it is always a pity to cannibalize an original board 🙂 ) and problem was fixed!

 

Since the pcb would go directly in my collection,  the last thing I wanted to fix, was the ugly hack they did by replacing the original amplifier with an LM380 (same used on 1978 space invaders….)

 

This thing worked but it was really ugly!

After spending one hour to clean the disaster with soldering irom and soldering wick, I installed back in place the 2x missing caps and I looked to find the original MB3731 amp among some of mine junk pcbs.

Besides being used on Taito hardware of the era, it was often used on Konami hardware from late 80s/early 90s.

I took it from a junk Main Events pcb and now it looks much better:

 

Feb 092017
 

My Alien Syndrome pcb one day decided to stop working and it showed a black screen.

I changed the battery 9 years ago and I thought it was suicided.

Just to be sure I tested it romboard and FD1094 module on another motherboard and it worked without problems.

I took a Tetris romboard then and tested on Alien Syndrome motherboard and this time the game showed a stuck reddish diagnostic screen which unfortunately I didn’t take a picture of.

Tested the inputs to see if there was a shorted one but there were all OK.

The program was running otherwise I wouldn’t get a stuck diagnostic screen therefore looking at the schematics I started to probe the 74LS253 (all Fujitsu parts) to see if the comunication with the cpu good.

The logic probe didn’t show stuck signals but I didn’t trust it and proceeded with piggybacking all of them with a good 253.

The game booted when I piggybacked the 74ls253@C15 but with wrong colours.

I desoldered it and tested it on my programmer and it was confirmed bad

After changing it I was welcomed with a running game but as said wrong colours

I ran the diagnostic memory test and the ram @J10 was given as bad.

Unluckily the ram was under the romboard therefore difficult to test in circuit

I decided to have another look at the schematics:

As you can see we have 2x 74ls244 which address both rams. The RAM given as bad was only J10 therefore it couldn’t be the 244.

After the 16 bits data lines we have 2x 74ls245 , and the first 8 bits from ram J10 are connected to the 74ls245 @H10.

Without even probing anything it was clear for me which chip to change blind

We had a Toshiba 2015 ram and a Fujitsu 74ls245.

Obiviously I decided to change the fujistu part

The guess was right because the game was fixed 100%

 

Feb 092017
 

This pcb from my collection developed lately a sound problem only with the jump sound which is a sample

 

This particular sample was distorted, the others were all OK

The clock and the 7759 sound chip which is responsible for the samples I was sure they were OK otherwise

all the samples would have the issues

I dumped the sound program rom 11372 and the samples roms 11288 and 11289 expecting that one of them could be corrupted

but surprisingly everything was fine.

If you have noticed, I still the original NEC module with a suicide battery from 1987. The battery is still working after all these years but unfortunately cannot be changed since the module is one piece injected with epoxy.

I started to think that the module could have the decryption key stored in ram somewhat corrupted after all these years and this could affect of course the sounds

Therefore I proceeded to use a z80 with the decrypted program rom taken from a mame set which use the same 5358 rom board (it is currently set 5)

The jump sound was correct with decrypted rom, confirming my theory that the key in the module is corrupted.