68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.
Apple II+ pure white screen?
Posted by: zezba9000 on 2020-09-01 15:32:19 So I'm having a problem still after adding a disk-drive interface card. It stops reading drive and spits garbage data similar to @bibilit issue he shared here. FYI: Frogger I loaded above was done via tape input. Many times loading from tapes will have the same/similar issue. What I do: * Power on computer with drive and Mario Bros disk mounted with FloppyEmu * Computer beeps * Computer beeps AGAIN but spits out junk similar to @bibilit issue he shared. * Drive stops being read and game never loads What I've tested: * Drive works perfect in known fully working Apple II+ motherboard and Apple IIe computer. * I tested ever single chip with known good ones from Apple II+ motherboard. RAM etc is all good. * The 74LS283 was not the issue as I hoped like bibilit had. * If I turn on the computer with no disk mounted THEN mount a disk it SOMETIMES will load BUT text is messed up in some apps I'm currently deep cleaning the motherboard to see if anything changed. I'll take a picture of what it displays after its cleaned but if anyone has any ideas what could cause this when all chips are confirmed working.
Posted by: bibilit on 2020-09-01 21:36:16 If you can, try a copy of MECC inspector or similar, to test ram an Rom. A single bad ram chip can do that, I know that you are confident ram is ok, but I have seen ram becoming bad pretty quickly.
Posted by: zezba9000 on 2020-09-02 08:41:59 If you can, try a copy of MECC inspector or similar, to test ram an Rom. A single bad ram chip can do that, I know that you are confident ram is ok, but I have seen ram becoming bad pretty quickly. You're right I had 3 bad ram chips. Guess I tested wrong last time. Now its 100% stable and working! Ran it for an hour with no issues. I also added some heat-sinks on chips that got hot. Hopefully it keeps them from overheating and lasting longer. Also modified my FloppyEmu cable so I can easily attach "DISK ][" drive cables
Posted by: techknight on 2020-09-03 09:24:15 What was the chip type/number of the chip you replaced out of curiosity? (I am taking a tally mentally from all the different repair experiences, and so far Ive found the LS138 to be less than reliable)
Posted by: zezba9000 on 2020-09-04 06:56:02 What was the chip type/number of the chip you replaced out of curiosity? (I am taking a tally mentally from all the different repair experiences, and so far Ive found the LS138 to be less than reliable) Besides the bad ram the bad logic chip was: SN74LS153 to the right of the last upper row of ram as you can see in the picture.
Posted by: techknight on 2020-09-04 06:59:24 ok yea the 153s are dropping like flies too, especially in Arcade boards.
Posted by: zezba9000 on 2020-09-04 07:10:41 ok yea the 153s are dropping like flies too, especially in Arcade boards. You also keep track of how many people had these go bad while using original PSU? The Apple ][+ I got had a bad PSU making a clicking sound with voltages not good. Now that I replaced it with a custom PICO based one my guess is there will be less issues down the line. I have original PSUs for Apple IIe & III and if the there are parts on the legacy PSUs that are the root of the problem I wan't to replace those at some point. All these PSUs have a mechanical part that makes some noise that to me feels like could be a possible longer term issue for these computers.
Posted by: techknight on 2020-09-04 07:12:46 You also keep track of how many people had these go bad while using original PSU? The Apple ][+ I got had a bad PSU making a clicking sound with voltages not good. Now that I replaced it with a custom PICO based one my guess is there will be less issues down the line. I have original PSUs for Apple IIe & III and if the there are parts on the legacy PSUs that are the root of the problem I wan't to replace those at some point. All these PSUs have a mechanical part that makes some noise that to me feels like could be a possible longer term issue for these computers. Nope, im only keeping a tally of failed electronics "in general" when it comes to logic ICs. nothing product-specific.
< 2