Gemini Wings repair log

 PCB Repair Logs, Repair Logs  3 Responses »
Feb 042017
 

I bought this game for my collection as fully working but unfortunately it had sound problem.

The FM part was very distorted and the drums (which are samples) were missing.

I noticed that someone attempted already to repair the sound section.

There was an LM324 and a potentiometer changed and a flying wire underneath which looked offcourse not done in factory (not pictured)

The game has no schematics and unfortunately, as a protection, Tecmo covered all the traces with a special paint, so it is really difficult to trace the connections.

The game runs on the exactly the same board as Silkworm even if the pcb code code is different.

On Silkworm they put a Z80 with some logic inside an epoxy block just to prevent a romswap

With Silkworm board in hand I could confirm the flying wire was not original, so I proceeded to disconnect it.

The game now had no FM music and only samples!

With my sound probe I proceeded to “listen” to the music which offcourse was being clearly produced from the OP amps but disappeared at one point between the resistors.

The cicruit was very complex and I couldn’t follow up very well without seeing the traces.

A bootleg , which is an exact reproduction of the pcb , could be very useful but I hadn’t any.

After some hours, I noticed that one of the resistor ( R26) was moving a little bit and with a screw driver I could confirm it wasn’t soldered well on the pcb!

 

Actually there were three of them that weren’t soldered correctly and this was a factory fault because they didn’t fill completely the pad (you can see on the pic the gap without solder ).

After soldering the three resistors the music and samples were restored but still I had this ugly distorted sound!

I was about to desolder the amplifier to change it when I saw something casually that catched my eye.

In comparison to Silkworm pcb, on my Gemini Wings there was an additional capacitor in pos. C18  and it was a different model than the others.

It was added by the previous repairer for unknown reasons.

Often the manufacturers prepare the pcbs to add different models of amplifiers therefore they design additional circuits which are not used.

After desoldering the cap at C18 I fully restored the music output

 

Final Star Force repair log

 PCB Repair Logs, Repair Logs  2 Responses »
Jan 062016
 

Recently got this Final Star Force PCB with graphical glitches on the sprites.

fstarforce1

This game uses a motherboard (pictured above) and has a romboard on the other side fitted with no other chips than the game’s ROMs.

All the ROMs were tested ok on my programmer and cleaning the connectors and looking at the signals, everything seemed fine with that romboard.
The motherboard has a rather simple layout with a lot of RAMs, some ASICs and a few TTLs. After a few hours looking for suspicious signals, I finally found the faulty ones.

There is a row of 12 Sanyo LM33464G RAMs (64k-word x 4-bit). Two of them were bad (the ones at IC22 and IC33). Piggybacking them with new ones partially brought back clean sprites, even if there were a few glitches remaining. These glitches totally disappeared after replacing the RAMs.
As these models of RAMs are a bit uncommon, I took compatible TMS4464 as replacement (highlighted in red):

fstarforce2

Here are before and after pictures:

fstarforce3 fstarforce4

Tecmo Knight repair log #1

 PCB Repair Logs, Repair Logs  Comments Off on Tecmo Knight repair log #1
Aug 252010
 




Game looked fine initially but when starting the game and on one of the intro scenes, the sprites had jailbars in them.

After a couple of frustrating hours figuring out what to read the maskroms as and if they were in the right places I settled on reading them as 27C040.
Three of the masks on the B board dumped fine but one of them gave random junk out at every read so it looked ok on the logic probe but the eprom reader told a different story.
Hunted out an 27c040 eproms and burned a new chip from the MAME set, the game now runs and plays 100%.