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Tech help - WPC CPU Board - No Lamps (at all)

By JamesH007

10 years ago

Topic Stats

8 posts
4 Pinsiders participating
Latest reply 10 years ago by terryb
Topic is favorited by 1 Pinsider

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#1 10 years ago

JBH

Need help diagnosing a WPC CPU board that works well other than no lamps will light at all (GI or lamp matrix) I did not think that the cpu controlled GI, but any way I have swapped boards between machines and it is definitly on the cpu board as the lamps work when I put the test cpu board in the problem machine and the lamps dont work when I put the problem board in the good machine. It looks like u13 and u14 had been replaced on the problem board (not sure what they control), but the work looks good and clean. Any suggestions where to look/test or what the problem might be?

#2 10 years ago

JBH

JamesH007

Pinside+ Frequent

11y 46,400 150 24

Anyone ? What on the CPU Board would prevent the GI from lighting ?

#3 10 years ago

LTG

Pinside member

Hopkins, MN

12y 191K 56,974 24 7

OP
Quoted from JamesH007:
What on the CPU Board would prevent the GI from lighting ?

Not sure what, but something on there probably triggers the triacs on the power driver board.

LTG : )

#4 10 years ago

TAB

terryb

Inactive member

Banning, CA

11y 90,150 4,795 14

As LTG said the control for the GI comes from the CPU board. Try reversing both ends of each ribbon cable that goes from the CPU to the PDB, and see if the problem changes.

If someone's worked on the switch matrix circuit, 9/10 times they've hacked the board. Test every trace and through-hole on that circuit for conductivity.

Do you have a logic probe?

U14 column drivers. U13 row drivers.

#5 10 years ago

JBH

JamesH007

Pinside+ Frequent

11y 46,400 150 24

Ok, I checked all the through holes and traces and everything tests good and the work is really clean. The chips they replaced say "ST T474LS240B1 99029" compared with "(Texas Instruments symbol) 324274K SN74LS240N" on the good board that had not had the chips changed. Is it possible they use the wrong chips ?Are these chips direct replacements for each other ? No I do not have a logic probe

#6 10 years ago

FLE

flecom

Pinside member

Miami, FL

12y 53,650 852 44 36

they are both 74LS240 chips so unless one is bad you should be ok...

if you are only losing lamps I would check what the select line for the GI and controlled lamps goes through on the CPU board

#7 10 years ago

JBH

JamesH007

Pinside+ Frequent

11y 46,400 150 24

Do you know what connector and pin that is and where it goes to? I have the schematics but still not sure I can figure it out ?

#8 10 years ago

TAB

terryb

Inactive member

Banning, CA

11y 90,150 4,795 14

J211 goes to the PDB (the pins are labeled), but not sure there's much more you can do without a logic probe, or better yet an oscilloscope, and the soldering skills required to do board work.

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