Porchy

Oct 152019
 

Got K1ngarth3r’s Mega-Tech PCB here.

On these boards there is a daughterboard present which houses the Z80 used for the menu.

This daughterboard is used for book keeping and isn’t really required so to save space I fitted the Z80 directly into the slot the daughterboard previously occupied.

The fault was the board didn’t see slots 4, 6 or 7 as shown in the picture he sent

Initial inspection showed the EPROM for the menu was fitted upside down but it wasn’t dead and the menu wouldn’t work at all if this were the actual fault.

Using the partial schematics I made a few years ago I could quickly pinpoint an area to start checking from.

Using my latest favorite tool, Slice, I could easily see that for some reason the 3 aforementioned cartridge slots were never being addressed.

This is a bit weird as on initial look at the disassembled code it seemed that it just counted through the slots.
A bit more code scrutinizing revealed that the CXD1095 chips are read back between slot addressing.
Using the Fluke 9010 I could now see that at certain output configuration on the CXD1095’s would lock up the chip and skip whatever it was doing.
I wasn’t really surprised at this because every single Mega-Tech PCB I’ve looked at has had issues with these chips.
I ordered a couple of these chips up and waited….. and waited……… and waited until I got hit with a lovely little letter from Royal Mail telling me I owed them money for customs fee’s.
I paid this and a couple of days later I received my items.
I removed the old and fitted the new

Pleased to say this board is now working again

 Posted by at 8:40 pm

Double Dragon repair log #10

 PCB Repair Logs  Comments Off on Double Dragon repair log #10
Sep 292019
 

Another PCB from Olly. Not sure if this is a bootleg or not but it is certainly of lesser quality than the other Double Dragon boards I’ve had.
Anyway, on boot up we get this mess but at least it boots

I pulled all the ROM’s on the video board to start with and found the 4 tile ROM’s dead.

I replaced these with 27C512 EEPROM’s which then gave me this

Much better but all the sprites are missing.
Looking at the schematics I could follow them through testing from the ROM’s onwards.

I ended up at a 7425 where all the inputs were active but the output on pin 8 was dead

I replaced this and tested again. All the sprites were back on the title screen but the in game sprites had coloured blocks around them.

Seeing as though I had 4 dead ROM’s I decided it wasn’t too ridiculous a thought to think that some of sprite ROM’s were dead too.
After confirming that the sprite ROM’s were being selected correctly I pulled them all and checked them.
I found 1 dead ROM here

Again I replaced it and tested

All graphics now fixed, the sound however was a different story.

The sound effects were all messed up but I could hear the music was fine in the background.
I pulled the two PCM ROM’s and tested them. Both failed.
Replaced these too and tested

All fixed.
7 dead ROM’s and 1 TTL. Not sure whether the ROM’s are just getting too old now or if they were taken out by a voltage problem.

 Posted by at 5:42 pm

Xexex repair log #3

 PCB Repair Logs  Comments Off on Xexex repair log #3
Sep 222019
 

Got this board from Olly.

Board looks very clean and plays but has graphical issues

Initial visual inspection showed nothing. All voltages seemed fine too.
Next I started gently pressing down on the custom chips which made a lot of changes when I pressed on 053250

Found a bunch of pins on that were lifted.
I reflowed these and checked the rest of the chip which all seemed fine.
Next boot up test gave me a lot better results but there were jailbars down the whole screen sometimes.

Continuing pressing the custom chips I could make everything change again by pressing on custom 054157.

Found most of this row lifted

and few a few here

Reflowed those little guys and all is fixed in Xexex land.
Its a really nice game that I’ve never played before.

 Posted by at 4:40 pm

Muter BMR 2005 repair log

 Equipment Repair Logs, Repair Logs  Comments Off on Muter BMR 2005 repair log
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

PLEASE READ

 General  Comments Off on PLEASE READ
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