Repair Logs – Page 31 – JAMMArcade.net

Battletoads repair log

PCB Repair Logs Comments Off

May 012018

Got from South Korea this Battletoads PCB for repair:

Board had a strange fault, it booted up but then always crashed after some time (going to a black screen) on title screen just before entering the attract mode :

But if you were quick enough coining up on title screen, you could start a game and play normally but sound was missing at all:

With these premises I started my troubleshoot.Since there was no sound during game I focused on the audio circuit.Hardware uses an audio DSP marked ‘BSMT2000’ , chip’s acronym stands for “Brian Schmidt’s Mouse Trap” from name of his designer:

This is a special masked-rom version of a Texas Instruments TMS320C15 digital signal processor, here’s pinout:

When I went to probe it I found that many data/address lines were either silent or stuck so chip was most likely bad.I removed it:

The BSMT2000 is not often used on arcade hardware (it can be found on many pinballs instead) but luckily I found a spare chip on a Police Trainer PCB :

With a good chip installed the game no longer crashed on title screen but sound was still missing.Probing again the BSMT2000 DSP revealed that pin 20 (data line D6) was stuck low, checking with multimeter it was almost shorted to GROUND :

I traced back this data line to pin 17 of two 74LS374 (used for data latching), these inputs were shorted to GROUND also after cuting their traces to the BSMT200.I desoldered the two TTLs and they failed the out-of circuit testing in same gate:

Replacing them restored sound.Repair accomplished.

Prehistoric Isle in 1930 repair log

PCB Repair Logs Comments Off

Apr 292018

Received from Germany some faulty boards to repair.There was this Prehistoric Isle in 1930 PCB, an horizontal shoot ’em up game developed by SNK and released in 1989.

Game boots up but some foreground graphics had vertical lines through them:

Relevant GFX data are stored in a 2Mbit MASK ROM located on video board:

I dumped the device and it was good.The data of the MASK ROM are read by the near custom silkscreened ‘SNKCG’.A visual inspection in this area reveleaed some corrosion on a trace :

Trace was connected to pin 17 of the custom, it was silent when I put on it my logic probe so either it was a dead output or an input not receiving any signal

I was not able to find where this pin was connected to so the trace was really broken due corrosion.Looking at the other near pins, they were all connected to data lines of the MASK ROM, I found corrispondance for all of them except pin 26 (D6).I run a jumper wire and foreground graphics were restored:

Happy with result I was about to close this repair when, during testing, I noticed that voice samples were missing, I could hear only some crackling noise instead of them:

Looking at sound section on CPU board I quickly found the culprit:

The 640MHz ceramic resonator (which provides clock the uPD7759C speech synthesizer IC) was missing, this a common issue on all boards that use it, it’s very easy that it comes off

I took the spare from a dead Sega System 16B motherboard:

Repair finally completed.

TumblePop repair log #1

Apr 242018

I got this game for a repair:

The game had some background problems ( unfortunately I forgot to take a pic ) and a sprite problem:

The background problem was fixed reflushing the custom chip 56.

As for the sprite problem, after some time checking the part of the circuit responsible for the sprites, I found a couple of 6116 sram @D5 and D6.

One of them had some weak signals on the data lines and tested out of circuit it was confirmed as bad

After replacing the sram the game was fixed

R-Type II (conversion on Major Title – Irem M82 hardware) repair log

PCB Repair Logs Comments Off

Apr 202018

I’ve been sent from Ireland this R-Type II PCB for repair, actually a conversion on Major Title (Irem M82 hardware)

Board played fine but sound was completely absent:

Here is an overview of the sound circuit:

Someone previoulsy tried to fix the lack of sound by replacing many components.The analog part of the circuit was doing his job as putting my fingers on solder side of the amp produced some noise.Probing the Z80 sound CPU revealed /INT line was stuck LOW.While testing components something strange happened, I got sound fully working :

The IC I was testing with a logic comparator is a 74LS244 @IC13 whose ouptuts are tied to the 8-bit data BUS of the Z80/RAM/ROM/YM2151.Signals didn’t look fine to me:

But when I put the clip of my logic comparator on the TTL they correctly toggled :

Data lines are tristate, this means they can be in high-impedance state (Hi-Z) in addition to the 0 and 1 logic levels.When outputs are tri-stated, their influence on the rest of the circuit is removed, and the circuit node will be “floating” if no other circuit element determines its state. Usually pull-up or pull-down resistors are used to influence the circuit when the output is tri-stated.This even more when a same line is shared among different devices like in my case.The 8-bit data BUS of the sound circuit is pulled-up by a 10K resistor array:

When I went to measure it I got high resistance on half of its pins :

I pushed the array a little and this happened :

It was actually cracked in a not visible way (this explains why the logic comparator fixed the issue, it acted like a pull-up).I replaced it:

This restored the sound, board 100% fixed

Teenage Mutant Hero Turtles repair log #6

PCB Repair Logs Comments Off

Apr 152018

Received a box of faulty PCBs to repair from USA.I started my work on them with this Teenage Mutant Hero Turtles by Konami:

PCB was in very good state and played fine with correct sound too but it had a color issue, the screen was yellowish simptom that the BLUE color was missing:

BLUE, as well as RED and GREEN, is generated by a custom SIL marked ‘052535’ (basically an R2R resistor ladder which acts as DAC , see my reproduction post here for more details)

Probing the custom revealed activity on all inputs (pin 2-3-4-5-6-7 ) but output pin 8 was stuck low:

So the component was internally faulty.I replaced it with same part taken from a spare board :

This restored the missing color.End of job.

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