Did this ever get solved Arnie?
I have a Whirlwind that is having a very similar issue and thought this would be a good post to resurrect.
I have it on the bench with only J17 hooked up for power. Just the 5V led is all that lights up. The reset lines are high but like Arnie, I have a stuck low blanking signal on U20. I also have a working game that I swapped U15,U26 and U27 out of. Those 3 from the dead board are working in the machine and the dead board is still the same so I can rule out the processor and ROMs. I have not done anything else so far and am looking to maybe send it to Chris Hibler but his website says he is 60 days out so thought I would try my luck a little longer.
The machine this came out of had a shorted BR1 on the power supply which I repaired but still would not boot so I pulled it out and put it on the bench. It looks clean with no acid damage and the only thing I can see is a previous repair where U17 and Q6 have been changed. Those are in the solenoid driver circuit so I don't think this is a problem. I am looking in the area of the 555 timer at U43. The blanking signal comes out of there at pin 3 and 7 and should be high. When I probe U43 pin2 trigger on my working board the signal is strobing but on the dead board it is showing high steady 3.3 volts. That line is tied to U51 pin 4 and U44 pin 21 and I am wondering if one of those could have failed or if there is something else in that trigger circuit like Q50 or C58 that I should focus on. Looking for some suggestions to try or maybe somewhere else reasonable to ship to with a shorter turnaround. Thanks.
(Topic ID: 222058)
