Sep 082019
 

Please note that there are multiple contributors to this site and each has their own individual views and opinions and they are NOT necessarily the views and opinions of other contributors.
Each persons work shown on here is their own.

 Posted by at 11:10 am
Sep 142019
 

Not really much of a repair log but its just something I’ve been up to recently among other things.
Saw this recently on eBay for a cheap cheap price.

I didn’t necessarily want the unit itself but more the CRT adapters it came with but the price was right.

First pass on the visual inspection showed that something wasn’t quite right.

Removing the 4 screws on top lets you get into this thing and there is a spacer post and screw lying in the bottom which is clearly from the PCB housing all those buttons.

While fixing this in place I had a look over everything else and found something a little worrying.

The crispiness aside this is not standard. There are 2 diodes missing and replaced with a transistor with the middle leg cut off, a lot of the traces are gone due to the charring and the 10K resistors have been replaced for two in series and are also the complete wrong value.
I just opted to remove all of this and replace with what it should be.

There is a schematic for this in the back of the manual so could check the values and the connections but I also have the BMR 95 which I took a look at as well

Here is what I ended up with

Its by no means a neat job but short of reproducing that little PCB its pretty much the best I could do given the amount of damage.
I checked all the other components on this and they tested good.
I have now tested this on one of my monitors and compared the readings against my other unit and they are all good so Ill consider this one fixed.

 Posted by at 3:57 pm
Sep 102019
 

As someone may recall I’ve recently done a reproduction of the custom ‘CUS99’ used on Namco PCBs :

Namco ‘CUS99’ reproduction

After done it I thought it was good to take into account its “companion” too, the ‘CUS98’  which most times come along with the first.Package is pretty the same but with two further pins than ‘CUS99’

 

But functions are totally different and,  as Rolling Thunder schematics suggest,  the main one is to generate the master reset :

Secondary functions are coin counters and lockouts handling as well as lamps driving, it seems only few games (like Pac-Land and Gaplus) use this last feature :

I was obviously interested in reproducing at least the reset generation function which is essential for correct operation of the PCB  (but it seems Rolling Thunder can boot into game also with a missing ‘CUS98’).Therefore, as usual, I studied earlier Namco hardware where the custom had not yet been used and I came to a prototype developed on a breadboard:

The protoytpe worked pretty good :

Hence I developed a proper board :

Final testing on a Pac-Land PCB:

As said some functions have been intentionally omitted favoring the needed ones (watchdog circuit ad reset switch were implemented too).This will at least allow to save PCBs with a faulty/broken or missing ‘CUS98’.

 Posted by at 8:10 am
Aug 292019
 

Got for repair this original Rapid Hero PCB, an obscure vertical shoot ’em up released by NMK in 1994 and a very sought-after board :

The board booted up but some sprites were affected by jailbars :

Besides, an entire music track was missing or sometimes corrupted as well as some sound effects:

 

The board had some sign of previous repair on solder side :

This is the area of the ‘CN1’ and ‘CN2’ connectors where the ROM board, which contains all the game code and data, plugs into the mainboard:

The repairs let assume a weakness and subsequent failure of the headers connections probably due to repeated disconnections and insertions of the ROM board.So I checked with a multimeter in continuity mode all the traces from the ‘CN1’ header and found another broken one that I promptly patched :

This fixed the graphics, no more jailbars on sprites :

Now the sound issue.

The audio circuit was previousy reworked, one of the OKI MSM6295 was likely replaced and one trace was repaired but this was not the culprit :

I noticed that if I pressed the ROM board on the ‘CN2’ connector some of the missing sounds were restored.I checked traces from ‘CN2’ to mainboard and found two missing connections to the ‘NMK112’ custom ASIC (responsible of  bankswitching the sample ROMs of the two OKI6295 ADPCM chips)

I patched the traces with some AWG30 wire:

Sound was totally restored and board 100% fixed.Repair accomplished.

 

 

 Posted by at 10:57 am
Aug 262019
 

I recently received this Apple IIe PCB from the U.S to try my luck on salvaging the 60hz IOU and using it in my International NTSC board in the hopes of getting colour which I did successfully in my previous post. This board was advertised as untested, so that normally means “DEAD” and I assumed so.

 

 

Taking one look at the RAM suggests there were issues in the past and most likely still issues. We have some original mT ( Micron ) / Apple branded DRAMs mixed in with the various replacements. Micron don’t exactly have the best reputation in regards to reliability so this is definitely a red flag. These were used by Commodore, Atari and obviously Apple as well. I guess they were cheap!

 

 

Based on the excellent condition of the board I was happy and confident in firing it up. It displays some kind of RAM error but it’s not very helpful, definitely not as helpful as the reporting in the Enhanced IIes built in diagnostic. I don’t have a choice but to go through and check each DRAM individually.

 

 

My TopMax helps me find 4 bad DRAMs of the 8. Three of which were Micron ( expected! ).

 

Dead RAM chips on the left clearly marked  to remind me that these are dead and not to be mixed up with working. These will come in useful for refining my Atari 8bit diagnostic tool.

I temporarily replaced the dead RAM chips with known good Micron pulls from my friends Atari 800xl. But I do have some NOS TMS 150ns chips that will be going in shortly.

 

Replacing the RAM confirms the fix.

 

It’s nice to have a second board ready to go if I need it, and the fact that it’s a non enhanced board with everything socketed is a plus.  I’ll be looking at converting this over to enhanced at some point via a enhancement kit which involves a 65C02 and newer roms for Apple IIc compatibility.