(Topic ID: 229485)

Big Guns switch column out...so close to remedy..,maybe


By lpnsocal

12 months ago



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  • 8 posts
  • 2 Pinsiders participating
  • Latest reply 11 months ago by wayout440
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InkedInkedbg 1J8 schematic_LI 2 (resized).jpg
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Williams_1987_Big_Guns_ pg 51.pdf (PDF preview)
Inkedbg 1J8 schematic_LI (resized).jpg

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#1 12 months ago

Ok, I made it pretty far(so I think) without having to call on the experts, but alas here I am. It's column 5(grn-blk) and initially I found two disconnected diodes, repaired them and tested the rest, all good. Still no column switches so I check continuity from switches to connector 1J8 and then to first component past it, all good. There is a small inter connect board but the 1J8 wires go straight to pf. Then I check continuity between all components up to leg 5 on u40, all good. R77 tested good, so Then I check Q48 w/ diode test, red lead middle leg/blk outside legs and got the same results as surrounding transistors, 670 +/-. With options running out/along with my skill set, I wip out my latest lil tool, logic probe! Ok, now I'm testing the connector attached and the U40 legs while in game play mode, with my 3 and 4 player displays out this way seems easiest.. Connector results w strobe all Lo, cept for pin 5 which is Hi. All the corresponding output legs strobed Lo.

This is where the big dumb blank stare happens upon my face..., I figure I'm close but, I don't know.

Thoughts?

Williams_1987_Big_Guns_ pg 51.pdfInkedbg 1J8 schematic_LI (resized).jpg
#3 12 months ago

Well, this is interesting. I checked the resistance on the SR15 and what I thought was pin#5 was a 4.65k similar to the rest except for the 4th from the end(#7?) and it was 1.65K. ( BTW, There is a dot at one end of SR15 and it seems to be tied into a larger trace so I call that #1.) Normally a small celebration would have ensued but that wasn't where I expected to find the low reading!

So now what? I can change U40 and this component but would have prefered to see the fault for a lesson to be learned.
Thanks for the help/lesson.

#5 12 months ago

I tested SR15 w board in so pin#1 is to the far rt. But and it's a big butt..., I now understand how I ended up down the blind alley. When I first looked at schematic and subsequently circled in green what I thought was for 1J8-5(column 5) but I actually circled pin #4 and tested as if. The odd reading is where it's supposed to be! and maybe as important, when Q43 was tested a short was found on the rt leg! So at the very least Q43 is bad and maybe the SR15(?) Still not sure why leg 5 on U40 strobed Hi, but considering my poor vision and schematic following skills...,who knows?

InkedInkedbg 1J8 schematic_LI 2 (resized).jpg
#7 11 months ago

I replaced the Q43 and SR15, tested components and continuity, fired it up and column works like a champ. I'm sorry I can't follow a simple(?) schematic, but your help kept me asking questions until I found my screw up. I hope there comes a day when I feel confident enough to assist others, beyond my "check fuses and continuity" skill set.

Again, Big Thanks!

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