‘Arcade sync stabilizer’ by Martin Jones

 General  2 Responses »
Jan 152015
 

Sync troubles, i.e. rolling/flickering picture,curved sides, etc.., on your beloved arcade PCBs?

Now the “sync stabilizer”, copyright by ‘MARTINJONESTECHNOLOGY’, beats ’em all !

Today I assembled on a stripboard this little circuit and installed it in my supergun.It really fixed all my sync issues with my troublesome boards (mostly bootlegs) which I never been able to solve in other way (trying, for example, the LM1881 sync stripper/cleaner)

Circuit is simple to do (but very effective),it requires only few common components.Technically speaking, it doesn’t modify the sync signal frequency but only the horizontal pulses lenght bringing them back in the broadcast standards.

sync_stabilizer

For bill of materials and other technical explanations, I refer you to the official page of the creator:

https://martin-jones.com/2014/09/16/that-syncing-feeling-classic-arcade-games-that-wont-stay-still/

I highly recommend you to give it a try, you won’t be disappointed.

 Posted by at 9:23 pm

G.I. Joe repair log #2

 PCB Repair Logs, Repair Logs  Comments Off on G.I. Joe repair log #2
Jan 142015
 

Yes, yet another G.I. Joe PCB on the bench (this is the third I repair).Let’s start with the log.

PCB was in a clean state:

G.I. Joe_PCB

But, as often happens with this Konami hardware, board had the watchdog active sign that there was a problem in main code execution or in the CPU itself.As usually I started my troubleshooting analyzing the main 68000 CPU and I found that, though the RESET signal was correctly generated by the custom ‘051550’ and reached the CPU, PIN17 (/HALT) and PIN18 (/RESET) of 68000 were stuck LOW so it was not never inizialized (all control lines were obviously silent ,too).So, judging from this,I started to suspect that 68000 was really faulty.I decided to do an “extreme” piggybacking with a good know CPU and sometimes I got it booting showing a bad color RAM:

G.I.Joe_color_RAM_error

This was enough to desolder the main 68000 CPU (a 16MHz one manifactured by ST) fitting a proper 64PIN socket:

68000_rework

Trying it in another board I obtained a solid black screen sign that it was realy bad (it’s the first time I came across a faulty 68000 CPU, never happened before).With a new 16MHz 68000 fitted in the socket board succesfully booted always showing the color RAM error above but I quickly fixed this by replacing both 2018 SRAM (also the one @14C was bad)

As I expected in this kind of Konami hardware which use ‘054986A’ hybrid custom sound module there was absolute lack of sound ,only some popping noises sign that the LA4707 amplifier was still alive at least.So was time to replace all the SMT electrolytic capacitors with new tantalum ones as they were leaking and having ESR value out of specs:

bad_ESR_054986A

and install proper 1.778mm pitch sockets for the module to finish the job:

054986A_recapped_socketed

 

 Posted by at 4:12 pm

Son Son repair log

 PCB Repair Logs, Repair Logs  1 Response »
Jan 122015
 

Welcome to my first repair log!

I bought this (very) expensive pcb from ebay in October 2014.

I played the game a couple of times and then after about one week, all the sprites disappeared while I was playing. Only background and text were present:

Foto 22-10-14 20 52 25

I couldn’t believe, at first I began to press everywhere hoping it was a loose or oxydized connector but soon I realized something got faulty.

This game hasn’t any schematics available so I knew from the beginning it would have been very tough to fix it.

I connected my trusty logic probe and began to short some pins on the pcb to see what changed on the screen so that I could focus on the right part of the circuit.

 

Foto 29-10-14 23 30 26

After about 30 mins turned on, the sprites started to reapper but missing some lines:

Foto 29-10-14 23 07 33

I then remembered that 1942 hardware is very similar to Son Son and the schematics are available.

I was right, the way that TTL chips are connected on 1942 is equal on Son Son. Only the positions of the ICs are different but the logic is really similar.

I probed the 2148 rams @F2 and @F4 on Son Son pcb which on 1942 schematics are described as OBJ rams and I found a stuck /WR signal @F4 on Son Son (J4 on 1942):

 

son2

I followed back the signal always taking a look on 1942 schematics, and I found finally the source of the problems on the missing signal on pin 11 of an 74LS00 @F11 (on 1942 I circled the equivalent IC @K11).

On  1942 schematics available on internet, someone circled the 74LS00@N8 writing “no plane”, probably he had the same fault. 😉

son1

 

Foto 29-10-14 23 27 24

Replacing the 74LS00@F11 gave me back all the sprites

 

Foto 29-10-14 23 29 25

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