Zaccaria Jackrabbit Maintenance 2021

20/03/2022 - Pre-show testing

Pre-show testing encountered intermittent issues with blue that I suspected was a monitor problem. The monitor chassis was removed for repair.

26/03/2022 - Hantarex MTC-900E/USA #PA20180628 repair, part 1

Starting with a static analysis of the neck board on the bench didn't find any anomalies across R,G,B transistors using the back-to-back diode check. Similarly testing on the main PCB colour drive circuits didn't find anything. Considering that possibly a neck pot was loose I measured all of the pots:

• RV8 - 6.7 Ohms
• RV6 - 1.7 Ohms
• RV4 - 213.3 Ohms

• RV9 - 298.5 Ohms
• RV7 - 332.3 Ohms
• RV5 - 335.6 Ohms

08/05/2022 - Hantarex MTC-900E/USA #PA20180628 repair, part 2

Back in the cabinet there were still intermittent blue issues and once again the chassis was removed for repair. Setting up on the bench and using a scope identified the blue instability as output from the main PCB. Using freezer spray confirmed the issue was in the blue pre-amp circuit. Targeting each transistor with a drop of freezer spray identified TR8 (BC547B) as susceptible. Switching a couple of times between freezer spray and heat from a soldering iron confirmed. Replacing TR8 (BC547B) fixed blue and eliminated any thermal response.

13/05/2022 - Jackrabbit game PCB #001/#002 repair

The spare game PCB was tested for a few hours on the bench and developed an intermnittant no boot & resetting issue. Checking the Z80 pin 26 RESET found it unstable & noisy. Checking IC 5C (LS02) pin 1 output was high with a lot of low noise. IC 5C pin 2 input watchdog was firing cleanly but IC 5C pin 3 input was low with high noise and borderline logic high. Working back to IC 5E (LS04), pin 3 input was idle at ~1.1V, borderline, and appeared to picking up pin 5, a clock. The output was also not inverted, and I suspected IC 5E was bad. Replacing IC 5E (LS04) fixed the noisy signal but now reset was stuck active. After a few minutes, the noisy signal returned. I suspected the reset circuit transistors Q1 or Q2 were bad. Q2/T2 (BC327) was removed and tested bad out of circuit. Both Q1/T1 and Q2/T2 were replaced with equivalents (BC327 === BC557 and BC548 === BC237). IC 5E inputs looked OK and the game ran without issue.

17/05/2022 - Jackrabbit game PCB #003 repair

During cabinet testing for the monitor fix, the game PCB developed lines in the picture and was removed for repair.

According to the schematic the final line mixing between the two alternating line circuits was done at IC 9E,9D (LS157). Checking the mixer outputs with a video probe found:

• IC 9E o/p pin 4 - A - clean
• IC 9E o/p pin 7 - B - clean
• IC 9E o/p pin 12 - C - clean
• IC 9E o/p pin 9 - D - lined
• IC 9D o/p pin 4 - A - lined
• IC 9D o/p pin 7 - B - lined

• IC 9E i/p pin 10 - COLOUT1 & i/p pin 11 - COLOUT4 - mismatched
• IC 9D i/p pin 2 - COLOUT5 & i/p pin 3 - COLOUT2 - mismatched
• IC 9D i/p pin 5 - COLOUT6 & i/p pin 5 - COLOUT3 - mismatched

• pin 6 - COL1` - active data
• pin 5 - COL2` - active data
• pin 4 - COL3` - active data
• pin 26 - COL4` - active data
• pin 25 - COL5` - active data
• pin 24 - COL6` - blank