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Title: S+ cpu - Q22? Post by: FOXSSLOTS1 on February 05, 2012, 03:11:39 PM I have way to much time on my hands so I decided to look at some cpu boards - I have an early (may 30 1997 tag) on a 7550570 board - (75505704 rev a tag) - was missing the Q22 and has a jumper for R61 - all my other boards all have the Q22 and R61 - my schematic/parts list does not list the R61. The schmatic shows R61 to U29 as 1K res. What would this jumper do?
Title: Re: S+ cpu - Q22? Post by: CommTech on February 05, 2012, 03:41:34 PM Without Q22, R61 is not needed. R61 would be a bias resistor for Q22. The jumper would simply complete the "GND PRINT" circuit to pin 8 of the opto-isolator U29.
Title: Re: S+ cpu - Q22? Post by: FOXSSLOTS1 on February 05, 2012, 04:08:18 PM okay - so that circuit is not needed? q22/r61 have no purpose? if I add them both ?
Title: Re: S+ cpu - Q22? Post by: CommTech on February 05, 2012, 04:21:33 PM I am not sure what the purpose of that entire "PRINT" circuit is for to begin with. I know there is no Printer in the S+. :103-
Perhaps Q22 is some kind of a De-bounce circuit? If there is no "PRINT" device, then this circuit is useless anyway. Title: Re: S+ cpu - Q22? Post by: FOXSSLOTS1 on February 06, 2012, 10:47:45 AM thank you for the info - I like to look at boards and fix the obvious - since the board in ? was missing the Q22 seemed like an obvious fix? will add the circuit and watch for smoke or a printout!!!
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