Tehkan Games

[channelmaniac]

Model: Pinball Action
Tip: Wiring a JAMMA adapter

When wiring a JAMMA adapter for this game, be aware that the edge connector is pinned out different than the manual.

The edge connector on top of the board is labeled from B1 through B18 and on the bottom of the board is labeled from A1 through A18.

The manual shows pinouts from pin 1 through pin 36.

When trying to wire the board be aware that pin 1 is A1 and is on the BOTTOM of the board, not the top. Pin 2 is B1, Pin 3 is A2, Pin 4 is B2, and so on.

[channelmaniac]

Model: Mega Force
Symptom: Graphic corruption and motion sprites in wrong places on screen.

Replaced bad 74LS244 at D7 to fix graphic issues. Replaced bad 74LS161 at Q4 to fix motion sprite placement issues. The 161 had outputs but they were incorrect. A logic probe missed this but a logic comparator spotted it immediately.

Edit: Motion sprite issue reappeared after a last minute check before shipping. Replaced bad 50 pin board interconnect and restested. The interconnect had corroded pins and was making poor contact.

[channelmaniac]

Model: Mega Force
Symptom: Dead. Missing ROMs

Replaced missing ROM 2 and 4 and replaced bad ROM at ROM 3. Tested board and found the background stars were all streaks like a warp drive and the enemy bases were flashing streaks of random colors. Replaced bad Fujitsu 74LS32 at N10 and tested.

[channelmaniac]

Model: Super Dodge Ball
Symptom: Dead, random music at times

Replaced a 74LS08 with dead outputs. The 74LS08 was missing 2 inputs. Traced those back and replaced a dead 74LS175. Board booted but sprites were corrupt and shifted to the top of the screen. Replaced a bad 2018 SRAM and tested.

[channelmaniac]

Model: Pleiads
Symptom: No audio and missing blue

Replaced 2 incorrect and 2 missing resistor packs. Replaced 7407 and R66 (150 ohm) to fix the blue color issue. Recapped the PCB and installed a missing cap to restore audio, but the sounds were incorrect. Replaced bad 7414 in the sound circuit to fix the sound issues.

[channelmaniac]

Model: Pleads
Symptom: Dead. Missing chip.

Cleaned the CPU PCB and cleaned the edge connector. Replaced the CPU socket, music chip socket, and a socket for a missing color PROM. Installed the missing color PROM, reconnected a loose bodge wire, installed a missing bodge wire, and replaced 10 broken .1uf poly film caps. Installed 5 replacement 47uf caps, a replacement 470uf axial cap, installed a missing 6.8uf tantalum cap, and tested. Only colored blocks showed on the screen where graphics were supposed to be.

On to the Video PCB, replaced 2 backwards EPROMs, reprogrammed 2 EPROMs with bit ROT, and replaced an EPROM that would not reprogram. Installed 2 poly caps and tested. Some graphics elements were still missing and music levels were barely audible. Replaced a bad ribbon cable to fix the missing graphics elements. Modded the audio circuit to fix the audio levels for the music and retested.

This game should've been factory modded to improve audio levels on the music circuit, but for some reason was not. Luckily I had a freshly repaired Pleiads PCB next to the bench to compare it to.

[channelmaniac]

Model: Pleiads
Symptom: Jittery screen every other level.

Board had horizontal sync issues on the bird and landing levels but was perfect on the initial level and the mothership level.

Had to dig out the oscilloscope on this one. The clock frequency for the horizontal sync was changing drastically. Replaced 2 74LS163 chips in the clock divider circuit to fix the issue.