Re: SEGA G80 - Star Trek Draw Problem..

   Well, first of all ' Thank you ' I appreciate any and all reaponse regarding this ' odd ' problem....  Ok here is what I did (including my results)... Verified Continuity between Pin 8 (2114 RAM) U27 and U31 Pin 8 and U46 Pin 4 - Continuity is ' Good '. Replaced LS244's at U48 and U49 - no change, problem still the same. Replaced LS374 at U13 - no change, problem still the same.  Replaced LS245 at U14 - no change, problem still the same. Replaced all 6 Diodes (with new ones) - no change - problem still the same. Replaced LS139 at U46 - no change, problem still the same. Replaced U1 to U5 - again (since I had socketed these) - with no change.  Nothing looks correct anywhere on the screen - random lines being drawn / blanked / drawn all over the place. (I call it repeated ' misdraw ' ) So here is what I tried - out of curiousity - . Pulled Each Ram (2114) one at a time - then initiated CPU - Self Test (Red Button) -  (As one would figure - CPU Always comes up (initially - OK - since it has its own RAM)... however.... The end Result of Removing Each and Every Ram (2114) chip is that no matter what or which one is removed (including U27) the Test Always (even with All Ram chips removed) will begin to Fail and get Stuck at U27. It's as if this Control Card was ' stuck ' on U27 and ignores All other Faults, including its own Ram  (that is unless the System is designed to Read - Ram - starting at U27? - first?) I also say the above, since even after pulling (for Test purposes).... 2114 (Ram) between U24 - U31 <--- with Memory removed there is no picture, but U27  still indicates Fault. LS244's at U48 and U49, LS245 at U14, LS283 at U33,   At this point I am open to try just about anything, in order to try to get this thing going.    Only thing I did not do yet is hook up to a Scope.... but if anyone thinks that's a good idea I will do this. Thanks, Regards, _Arcadius  From: Douglas Gauck <douglas@gauck.com> To: vectorlist@vectorlist.org Sent: Monday, April 9, 2012 7:59 PM Subject: Re: VECTOR: SEGA G80 - Star Trek Draw Problem.. You know all this from the schematics, but chip select is pin 8 for 2114 RAM, and that's selected by the LS139 at U46. Should have continuity between U27 pin 8, U31 pin 8 and U46 pin 4. Of course it could be the LS244s at U48 and U49 that interface video RAM with the address bus, or the LS245 to the data bus, or maybe the LS374 you put into U13 is bad? Then you'd have more bad RAM (which it sounds like you do) that the self test may not have indicated because I bet it stops at the first error it encounters. But the faults you're getting now are with the diodes in place? Getting anything on screen that looks right? Difference between screen and scope? -DrG  On Apr 9, 2012, at 11:04 AM, Arcadius Stempak wrote: All, >  > Apologize for the slooooowww response, been busy .... >  >Ok things have gotten a bit worse since my last update.....please read ..Thanks.. >  > So I went on to replace U13 - unfortunately still no change.... >Ok so I said why not pull D2 and D4 - (associated with Green Output - connecting to Pin 6 and Pin 8 of U1. >And in fact in doing so I found one bad Diode (I forget which one - but one of then indicated a Reading in both directions). >However  this is where I made (my fault)  a * Big * mistake (well from my perspective) >  >Even though I was going to proceed with Replacing the 1N4148 - Diode - (which I should have just done) >In my infinite wisdom (or lack of) I lifted one of the Diodes (Iegs) of D2 and D4 and plugged in / powered on Control Board. >Since that time, I now have the following Fault(s).... >  >- Unit Powers up - OK - but Screen is now filled with Random / all over the place - Vectors being Drawn - >- Control Card - continues to Fail - U27 Memory Chip >  >If I press the ' SELF TEST ' Switch on the CPU - I get the following Results - >- (CPU Led indicates One Long Flash - 2 short flahses- One long pause - 7 short flashes - Repeat) - >- I Replaced U27 - with no change - >- I Replaced All Memory Chips - with no change - >- I replaced U27 socket (which was not required - but I was desperate) - with no change - >  >If I swap the Timing Card with a Known Good set of Timing/Control Cards (I have two sets) it works OK. >If I swap the Control Card with a Known Good Set of Timing/Control Cards - same (U27) problem - (as listed above) - >  >So the problem is isolated to the ' Control Card ' but I am not sure what could be causing a ' Mis-read ' of U27 ? >Does anyone happen to know what (on the Control Card) controls Memory Access / Self Test / Verification? >  >Thanks.... appreciate any and all input..... >  >Regards, >_Arcadius
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Received on Mon Apr 9 22:57:39 2012