Testing S+ 10mhz Boards - Code 21

[CVslots]

So, been testing a few S+ boards (10mhz) in a known working machine. Ran into one board with a 21 code. Using same SP731 and SS chip all along. Have tested and repaired a few other boards using this same machine and chips. 


Since I know the optics are good (tested with known good board), I am looking to find what component/diode/resistor/thingamajig on the MPU board may be causing this on this particular board? 


Any insight is appreciated.

Thanks in advance!!! 

[Jim]

well since the +vb appears to be good coming from the board, I would start by looking at RP4 and RP5 ,these are yellow resistor packs, look for hair line cracks, broken, etc.  those inputs go into U-5,  U-12, U-21 ,U-14.

Jim 

[CVslots]

Excellent Jim!!!  thank you, thank you 

I will check it out and report back!!

-Roslyn

[CVslots]

All right, checked out RP4 & RP5. They look good (this is an old board, so they are the light green instead of the yellow). No cracks, breaks, or visible damage. U5, U12, U14, & U21, no obvious signs of problems.  Not sure what the next step would be...

What is proper way to test the RPs? If i tested them correctly, they all read 1.00-1.01 ohms (on the working and the non-working boards). And would anyone know if I end up needing to replace one of these little guys (whew, 14 lil legs!) are they a "Radio Shack" find? I could always harvest one off another board...While digging through some boards this morning, I found one board that had multiple burns, in multiple places, so I can use it as a "donor" board.

Thanks for your help (and patience) in my new-found hobby/adventure...it was actually very rewarding to revive the last few boards that would have otherwise been tossed. I do not have full schematics, so every tidbit of info offered available is being logged for future use. 

-Roslyn

[Buzz]

Roslyn  Jim in Cincinaiti ask me to help you out.   

[CVslots]

WooooHoooo!!!!!



Thank you guys!!!