Repair Logs – Page 117 – JAMMArcade.net

Super Chase repair log

Mar 022012

So I saw this Taito board on eBay. The seller says its broken and unknown but was most likely a Super Chase and supplied a System 16/24 adapter with it, which in its self is very nicely made and they can cost quite a bit.

Only thing is, Super Chase is not a System 16 or 24 pinout.

*pinout supplied by Stefan Lindberg

I made a quick and dirty adapter up with and tested the board, dead.
Now I made a very stupid mistake at about this point. I moved the board down from the test bench and into one of my cabs just to rule out any voltage issues that ive seen before BUT for some unknown reason I left the pinout adapter in the test rig.

After the smoke dispersed I checked the damage.

Power supply is fried. Turns out, without the adapter I tied the +12v line to the +5v line and destroyed the PSU.
At this point I didn’t hold out much hope for the board anymore but tested it anyway.

The board was unsurprisingly still dead.

I check the RESET and HALT lines on the CPU, the watchdog was doing its thing.
Pulled and checked the program ROM’s and 2 didn’t match.
A strange thing here. One has only 1 byte difference right at the end and the other was clearly trashed with random read outs at every read.
I copied the first dump over to MAME and ran it. Turns out this is probably a different region to the one in MAME and that byte difference either displays the country warning screen or not. Mine does not.

I got nothing but a bit of garbage on screen

I fired up MAME and checked what the game should be doing and it does perform RAM checks. I also saw in the code that it has RAM fail messages on screen should it encounter a problem.
Probing around the board in this state didn’t help at all as the watchdog reset everything before I could really see what was going on.
After a quick look at the CPU code I see I can bypass the shared and screen RAM checks very by changing only 1 byte. I did this and replaced the relevant EPROM and watched the game boot

So the screen RAM is at fault. The screen RAMs are the 2 Sony 58257 chips in the center of the board.
I pulled both of these and both failed. Replaced them and the game boots once more.

A narrow escape I think. This will hopefully teach me to slow down a bit, but I doubt it

Commodore 128 repair log #3

Feb 252012

Motherboard clearly had a dodgy ON/OFF switch.
Removed it and replaced it with one from a C64.

On power up I had a blank screen.
Did a few quick checks with the scope and all data/address lines were pulsing properly.
Checked the voltages with a multimeter, the 5v was present but the 9VAC was not. Traced this right the way back to the switch I had fitted.
When I soldered the new switch in, one of the legs musnt have made a connection as they were a little shorter than the original. I resoldered the legs on top of the motherboard as well as the underside and it now boots up.

One of the CIA chips was missing, fitted a new one and C64 mode now works too.

Virtual Boy repair log #1

Console Repair Logs, Repair Logs Comments Off

Jan 212012

Got a Virtual Boy the other day with the Flash Boy Plus cartridge.
The unit worked fine with the Red Alarm game that was already on the cart but when I changed the game to Bound High I was greeted with a solid red screen. The music played and I could run the game blind but that was no use.

I reflashed with Red Alarm and after a couple of screen artifacts in the left screen the game played fine.
After a quick Google around it turns out that this can and will happen to every Virtual Boy made and occurs when the glue holding the FCC ribbon deteriorates so that connections become unreliable.
There are a couple of different fixes for this. One is to strip the plastic back and solder the very fine connections directly onto the board which is a permanent fix, the other is to but the little module into the oven at about 80 degrees C for a couple of minutes then apply pressure to the cable afterwards in the hope that the glue will reset making a nicer connection. This is not a permanent fix but will get you away. The later method is what i opted to do as I’m pretty lazy and dont have the chemicals needed to dissolve the plastic.

The first hurdle is actually getting into the unit as Nintendo kept with the same gamebit screws they used for other devices but they also stuck them down a deep hole so standard gamebit drivers cannot normally reach as they are too fat.
The solution is to make your own from a flat blade driver. I used my milling machine to cut it down and cut a groove in the end. Its certainly not pretty but worked perfectly.

On opening the ribbon cables are on either side of the unit and is held in at the board by 2 little crosshead screws. DO NOT try removing the 2 bigger screws near by, they control alignment.

The top of the cable just pulls out (carefully!).

Get a bit of tin foil, sit the offending article onto said foil, preheat the oven to around 80 degrees C and bake for around 1.5 – 2 minutes.
After its done remove it (its not hot) and rub or apply pressure onto the connection side until its sufficiently cooled and the glue will have reset.
After this, take some sticky tape and apply it to the area wrapping it round so that it applies a little pressure onto the connection.
Refit and test.
This worked perfect for me and many other people have said the same thing.

Time to waste my weekend playing some headache inducing goodness

VIC20 repair log

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Jan 072012

Got Stiggys other VIC20 the other day, it wont load anything via the serial port and just reports back “DEVICE NOT PRESENT”.
According to Ray Carlsen this can be caused by a dodgy 7406 IC and he wasn’t wrong.

I checked all the states of this chip with a logic probe and all seemed to be as it should be so I went through each gate with a logic pulser and checked for its output. The outputs on pins 4 and 6 were stuck.

Removed the chip and eventually found one on a C64c motherboard that was scrap.
Replaced and tested with a demo and a couple of games.

I also took this opportunity to try out the VIC20 JiffyDOS (PAL).
My original test with JiffyDOS on this failed, nothing would load up. Turns out there is an NTSC and a PAL version, the later being significantly harder to find but we got there in the end.

Jumping repair log #1

PCB Repair Logs, Repair Logs Comments Off

Jan 042012

Got this Rainbow Islands bootleg yesterday.
The game worked when I tested but was told about a dodgy ribbon connector before buying it so decided to take a look. Not sure what happened after that but the board refused to boot.
After finding a few stuck address lines I decided to check the program ROM’s. Found 3 that would not read properly so I replaced them.
In MAME it lists 2 of the program ROMs as being from the genuine Rainbow Islands set but these are double the size so needed to be split into 2 files and burned to 27512 EPROMs.

Probably worth mentioning that if you use the older 2005 ROMIdent program then the dumps from Jumping actually show up as 2 separate ROMs. Must have been like this at one time.
Booting up now gives me a screen of garbage

Every now and then I could make out a “SCREEN RAM ERROR” message. The screen RAM is located on the second board and suspected this is what happens when the ribbon connector got a bit wrong but couldnt get the game to boot again no matter what I did so I decided to socket the 68000 cpu and see what was going on, kinda wish I hadnt now as I got this

Accepting the error just kept flagging more “tied bits” errors. Turns out this was a red herring as these lines are controlled by a PAL20L8 chip and everything passes if this is removed. Wasted a little bit of time on this.

After taking a careful look at the connector it turns out the plastic housing that holds the ribbon cable in place was damaged and this allowed the ribbon cable to come away from the pins. I properly reseated the cable and tested, the board now fires up in all its crazy bootleg glory

The game plays pretty much like Rainbow Islands does but some of the sprites and names are different and I think the secret rooms don’t work too well.

This game has 3 PAL chips on it, unfortunately all are security locked and I am only able to read 1 of them (might be able to read the one on the video board but never tried).

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