PCB Repair Logs Tiger Heli Bootleg
Tiger Heli (Bootleg)
Problem: Character graphics missing, some times it flickers very quickly and you can see some. Background is fine, colours fine.
Fix: Theres no markings on this PCB so I've taken a pic of the effected area.
Using a logic probe I found the outputs of the 4 74ls166's A,B,C,D (pin14) were all sitting low(closed) but when the graphics flickered on you would get a erratic pulse.
Checking all the other pins I noticed pin 15 (Shitft/Load) was behaving the same which is a good indication of a problem. Tracing that pin back to a 74ls32 @ E output pin 8. The inputs pins 9 and 10 were pulsing normally. Removing the IC I found that pin 8 was sitting high. There are no resistors pulling up that track so we have a short somewhere in one or more of the 166's.
Good trick here is to cut the effected pins, in this case its pin 15. A was already in a socket so I'll just leave that chip out. Looks like chip C is the problem.
Put a socket in replaced the chip and reconnected the pins i cut with a bit of solder, now graphics are 100%
Notes: Top board does Sound and character graphics, Bottom pcb does background, colour and main program.
PCB is missing the Sound AMP if anybody has one of these can you please let me know what type of amp is on yours so i can continue testing.
Ok Bootlegs use a NEC C1181 or 1182 (reversed pinout) Went to put a MB3712 and noticed there was a extra leg. The hole was there but has never been desoldered. Going by the cap configuration I worked out they use the 1181/2, I've made plenty of external amps before using these for Atari stuff.
Very common amp on bootlegs (so is the mb3712/13 for that matter)
Fired her up sound works great, just need to wire up the controls on the harness now.