yorkshire_spam
Active member
- Credits
- 763CR
Starting point....
Game looks dead, but watchdog is "barking".
Replaced CPU socket so I can use the fluke on it.
Address error on rom test
A3-6 buffered through 7408@B2 - removed, tested faulty, replaced 74ls08
Rom tests now run, but error.
Next step, remove 6290-01 (first ROM) and test out of circuit.
So I built a 2600 rom reader with an Arduino.
The ROM reads 100% ok out of circuit, but still fails in the PCB
I desoldered the 6401 decoder prom - that tests 100% ok
7432@a2 used in adr7,8,9 looks faulty on logic comparator - replaced
At this stage the ROMS test as good in circuit, but ram test fails
No _WRITE signal.
74-174 @ A7 replaced - _WRITE now working.
I hooked up the logic analyser and found that although the RAMS were getting good write signals reading back the same address gave a semi-random value (at the chip according to the logic analyser)
So I socketed and replaced the RAMS.
At this point it passes RAM test, but the screen is still blank.
I found that the output on 74166@r3 was low - nothing.
I replaced a number of logic chips that feed various signals to the 166 and tested the 166 both in and out of circuit.
bad 74-10 @ r7 - replaced
bad 74-32 @ p3 - replaced
bad 74-175 @ n2 - replaced
bad 74-32@l2 - replaced
I replaced a couple of buffers and hooked some credit switches on the test loom and it's running!
Still to do:
It's been a fight to get it this far - first bronze age board I've fixed to I've learnt a lot.
Game looks dead, but watchdog is "barking".
Replaced CPU socket so I can use the fluke on it.
Address error on rom test
A3-6 buffered through 7408@B2 - removed, tested faulty, replaced 74ls08
Rom tests now run, but error.
Next step, remove 6290-01 (first ROM) and test out of circuit.
So I built a 2600 rom reader with an Arduino.
The ROM reads 100% ok out of circuit, but still fails in the PCB
I desoldered the 6401 decoder prom - that tests 100% ok
7432@a2 used in adr7,8,9 looks faulty on logic comparator - replaced
At this stage the ROMS test as good in circuit, but ram test fails
No _WRITE signal.
74-174 @ A7 replaced - _WRITE now working.
I hooked up the logic analyser and found that although the RAMS were getting good write signals reading back the same address gave a semi-random value (at the chip according to the logic analyser)
So I socketed and replaced the RAMS.
At this point it passes RAM test, but the screen is still blank.
I found that the output on 74166@r3 was low - nothing.
I replaced a number of logic chips that feed various signals to the 166 and tested the 166 both in and out of circuit.
bad 74-10 @ r7 - replaced
bad 74-32 @ p3 - replaced
bad 74-175 @ n2 - replaced
bad 74-32@l2 - replaced
I replaced a couple of buffers and hooked some credit switches on the test loom and it's running!
Still to do:
- LDV1B is stuck - so the back half of the white car is missing
- Check all the inputs
- Check the audio output
It's been a fight to get it this far - first bronze age board I've fixed to I've learnt a lot.
