Star Force log...

channelmanic

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OK,

Have a Tehkan Star Force here for repair and thought I'd just document where it is so far. It has been a royal bitch!

Symptom: Dead. Stuck in watchdog. Audio amplifier heatsink gets red hot.

The audio issue is interesting because this particular board has 2 audio amps and double the audio circuitry compared to most of the board pics I've found online. I'm sure it's going to be a wiring issue with the JAMMA adapter I have so for now I've disconnected the +12v from the adapter to keep from burning up the audio amp chip.

Quick inspection showed 5 x Fujitsu logic on the CPU board and 6 x on the middle board. The 2 74LS27 chips on the CPU board had no outputs and were replaced. One of the 74LS138 on the CPU board had no outputs and was replaced. A second LS138 had chirping on all 8 outputs and was replaced.

One of the LS27 chips had a dead input. Traced that back through the PCB to the 2nd board and found a bad plated thru hole under a 74LS86 IC. Soldered some Kynar wire to the top and bottom sides of the thru hole to patch it.

Board would still not boot. Replaced a bad 74LS74 IC on the CPU board and now the board would boot if powered off/on a couple of times, but had graphics corruption. Reinstalled the 2 ceramic caps onto the new 74LS74 to fix some of the graphics corruption.

Replaced a dead 74LS27 on the middle board and 2 of the 4 Fujitsu 74LS175 chips with dead outputs to fix the rest of the graphic corruption. I went ahead and replaced the last Fujitsu LS138 chip to see if that had an effect on the boot issue, but it did not. That chip was fine and the board will still boot/play if power cycled a few times. Replaced the 10uf cap on the reset line to no effect on the issue.

Next I'll try tracking down one last missing gate input tonight, but I think that is relegated to the sound section. After that is replacing the EPROMs one at a time to see if that's the issue with the boot.

WHEW. Just wanted to write it all down and think about why it's not booting properly. The next step after the EPROMs will be looking through the logic gates on the CPU board with an oscilloscope to see if one or more has some malformed signals.
 
Thanks Raymond, it is great that you are logging this.

You should see the pile of Fujitsu failed ICs on the Tehkan Pinball Action I am currently repairing (99% working)... I cannot believe there could be so many failed ICs on a single PCB.

Good luck!

paris
 
Oh, I can believe it! I had a failed Track & Field boardset that had about 30 bad Fujitsu 74xx logic chips.
 
Try 40 on a Wonderboy.

Every single TTL was Fujitsu and was either dead or half working they tend to fail in patchs so when one goes the next one goes ect ect

If it wasnt a original PCB i wouldn't of bothered going to all that effort
 
And I thought 15 was bad.

The worst thing about them is when they decide to fail one after the other as you're working on the board.
 
Symptom: Dead. Stuck in watchdog. Audio amplifier heatsink gets red hot.

The audio issue is interesting because this particular board has 2 audio amps and double the audio circuitry compared to most of the board pics I've found online. I'm sure it's going to be a wiring issue with the JAMMA adapter I have so for now I've disconnected the +12v from the adapter to keep from burning up the audio amp chip.
Hi Raymond.
After fixing this board did you ever circle back to the red hot audio amps?

I have the exact same board with double audio circuitry also and the same exact problem on jamma.

These things got to be space shuttle reentry hot. I found 3 bad caps in the area, recapped the section around the amps and audio is super shit on its best day but sounds perfect all around audio circuit using audio probe.

Any notes from the past would be helpful.
 
OK,

Have a Tehkan Star Force here for repair and thought I'd just document where it is so far. It has been a royal bitch!

Symptom: Dead. Stuck in watchdog. Audio amplifier heatsink gets red hot.

The audio issue is interesting because this particular board has 2 audio amps and double the audio circuitry compared to most of the board pics I've found online. I'm sure it's going to be a wiring issue with the JAMMA adapter I have so for now I've disconnected the +12v from the adapter to keep from burning up the audio amp chip.
For future reference, yes it was most likely your jamma adapter.

Many people use a Tekhan adpater for Rygar (info thx to @Jamesv833 ) that shows 5v on Pins 16/T

On the Star Force DUAL AMP version of the board, the second amp feeds pins 7/8 from the second 51516 to 16/T.
The manuals I have found for Star Force show 16/T as blank, but they are supposed to go to speaker on Dual Amp version.
Which checks out, so I am assuming it is stereo L/R in original game, with separate outputs for each speaker, or one is for sound effect and one is for music and they can be combined on jamma.

I have found a bunch of pics online showing single amp, I even found one with double wide heatsink bolted on, but still only single amp and sound circuit populated, mine has dual amps and double wide heatsink.

My guess is earlier versions had dual amp and sink, then they decided to cut cost or make a conversion board and went down to single amp, and had to use up the dual amp sinks, then eventually got down to single amp, single sink config.

note to future repairs - if you have dual amps check 16/T on your adapter to make sure its going to speaker and not 5v.
 

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After fixing this board did you ever circle back to the red hot audio amps?
Don't remember. That was long ago.

This board will also have problems with game switcher boards as well since those extra pins won't be switched by any relays.

Just now seeing your post. Went to ABQ and back over the weekend to pick up a truck/trailer load of fairly rare vintage Unix systems: AT&T 3B1, Be Box, and Amiga 3000UX.
 
The manuals I have found for Star Force show 16/T as blank, but they are supposed to go to speaker on Dual Amp version.
Which checks out, so I am assuming it is stereo L/R in original game, with separate outputs for each speaker, or one is for sound effect and one is for music and they can be combined on jamma.

Turns out I have the same dual amp version of the Star Force board set. Using the pcbjunkie Tehkan JAMMA adapter (which I know understand to be a bad idea based on your info), I still hear both music and sound effects during gameplay. So I suppose it must be stereo L/R rather than one amp/output for music and the other for sound FX?
 
Turns out I have the same dual amp version of the Star Force board set. Using the pcbjunkie Tehkan JAMMA adapter (which I know understand to be a bad idea based on your info), I still hear both music and sound effects during gameplay. So I suppose it must be stereo L/R rather than one amp/output for music and the other for sound FX?
I haven't figured it out yet. I blew up 3 amps trying to see wtf was going on. Once I get new amps I'll test some more. If you plug yours in I'm going to guess the volume pot closes to the edge of the board will do nothing.

I've listened to the board using audio probe and then on mame and feel like there is a difference but I think I may have been for a stereo cab not one for fx and one for music. When I get new amps in, now that I have figured out the problem, I'll report back.
 
I always learn new things ;)
I have 2 Senjyo boards ( Tehkan and Taito) and 2 Start Force pcbs ( dedicated and the official conversion from Senjyo) and the second amp circuit is not populated.
So actually Tehkan made some boards with the second amp circuit populated....
I wonder if it's actually stereo or it is just same sound sent to different amps....
 
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