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Tracking END BLANK down to its origin at 74157 U3C shows no pulsing on pin 7. It reads high. Grounding pin 7 suddenly shows a screen full of random characters!!!! I'm close I can tell. EDIT: The screen jumps to life when connecting pin 7 to GND. The screen however is doubled. Left side is repeating ...

Ok...had a few spare moments to look at this. U4E - both inputs are not pulsing. U4F - Pin 4 & 8 are connected in the schematic and are not pulsing. Pin 13 is END BLANK, and we already know this is not pulsing and I confirmed it. Pin 9 is pulsing, and Pin 10 is Pulsing too. Checking IC's around this...

That was the exact direction I was going to take for testing. It's so nice to have a confirmation that I'm doing things right...for a change. I have no training in electronics, and although I've managed to fix a lot of computers and old arcade boards, it often comes down to three things. A general u...

My only thought about a pad is that because the board is in a very tight space then it may be very difficult to get a probe in for testing, a couple of VIA's would be great. As for the A15 board, I think it could be hand drawn in Illustrator and using some software converters to convert it to DXF (h...

Been chasing the ghost in the machine for some time now. Luckily I've got a working board that I can compare signals with. I'm at the point where I see that END BLANK is not pulsing and that seems to have a ripple effect through lots of components, and I'm now chasing down where that originates from...

Good point. Very optimistic of you. Anyway, I've been probing around for the last hour and I think I may have found something. I've been focussing on the signal coming out of the composite color line on J1 pin 5. Basically this is continually low when probed. There is a 2N5225 NPN transistor that is...

I recently ordered some insulation-displacement 40-pin DIP headers from Digikey, part# HDP40H-ND. I just did a search, and foundthat Jameco has a similar connector, PN# 8200-40-R, at a better price. Good luck! Best regards, Dave Great! If I can't find anything in Akihabara, I may just take you up o...

Thanks for the advice in the Xtal. I went to replace the Xtal today and realized that I had left the machine on for the past 10 hours or so. Unfortunately there is nothing to indicate wether it's on or off except for the position of the switch. Anyway, the video bored now displays nothing, were as p...

I upgraded to Eagle 6.0 so that I could view your files too. I have to admit that I can only really look at your schematic on a very superficial level as I'm not really good at circuits! So I'm just going to have to have faith in your superior skills and assume the logic is all good ;-) However, It ...

Dropped by Akihabara on the way to a meeting today. No 11.79Mhz or 12.08Mhz Xtals available at a all. Closest is 12Mhz.
Will 12Mhz work?

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