AwkwardPotato Posted May 19, 2022 Share Posted May 19, 2022 Hi all, Thought I'd share this in case anybody with a PEB 32K card (PHP1260) runs into a similar issue, since this was a bit confusing at first. It would appear that this also applies to the original PHP2200 32K sidecar, but I haven't verified that past a quick glance at the schematics. The symptoms of my card's failure: XB or EA5 programs loaded from disk either error out or crash the system, respectively Doing a rudimentary RAM test with the Minimem cart (as described by Willsy here) reports seemingly random failures Listing of an XB program looks like below, where e.g. "DSK1.SPEAK" becomes "DSK1, @EAK", and where incorrect characters change with each successive program listing In my case, the culprit was one of the two 74LS257 (U15, U16), although I accidentally removed the wrong one at first and ended up replacing both at the same time. While the 32K card is now functional, moving forward I'll look into possibly picking up a SAMS card. Been a while since I got new 4A goodies... 3 Quote Link to comment Share on other sites More sharing options...
GDMike Posted May 19, 2022 Share Posted May 19, 2022 (edited) I've heard from others that the buffers go bad bad once in awhile. Great fix!! Edited May 19, 2022 by GDMike 1 Quote Link to comment Share on other sites More sharing options...
AwkwardPotato Posted May 19, 2022 Author Share Posted May 19, 2022 For sure! This PEB's disk controller was afflicted with a bad LS245 buffer several years ago. 1 Quote Link to comment Share on other sites More sharing options...
+videofx Posted May 19, 2022 Share Posted May 19, 2022 Thanks for the tip. I have card that when I power up with my Card I just get a blank screen. When I replace my 32k PEB card (PHP1260) with another, it works. So I need to figure out which chip(s) are causing the issue. I will start with the 2, 74LS257 (U15, U16). I will test those with my retro chip tester. Hopefully that will fix my 32k board! Thanks! 2 Quote Link to comment Share on other sites More sharing options...
+videofx Posted May 19, 2022 Share Posted May 19, 2022 (edited) 8 hours ago, videofx said: Thanks for the tip. I have card that when I power up with my PCard I just get a blank screen. When I replace my 32k PEB card (PHP1260) with another, it works. So I need to figure out which chip(s) are causing the issue. I will start with the 2, 74LS257 (U15, U16). I will test those with my retro chip tester. Hopefully that will fix my 32k board! Thanks! just an edit. my 32k PEB card fails with my Card Enabled. I will check the 74LS257s tomorrow Edited May 19, 2022 by videofx 1 Quote Link to comment Share on other sites More sharing options...
AwkwardPotato Posted May 21, 2022 Author Share Posted May 21, 2022 On 5/19/2022 at 9:28 AM, videofx said: Thanks for the tip. I have card that when I power up with my Card I just get a blank screen. When I replace my 32k PEB card (PHP1260) with another, it works. So I need to figure out which chip(s) are causing the issue. I will start with the 2, 74LS257 (U15, U16). I will test those with my retro chip tester. Hopefully that will fix my 32k board! Thanks! The LS257s on the 32K card are used to multiplex the row and column addresses onto the 4116 DRAMs. If any of the LS257s' outputs fails (hi-Z/floating in my case), reads and writes to certain parts of the 32K expansion will also fail. For a card like yours that locks up the TI at startup, I'd suspect one of the parts closer to the edge connector. The 74LS245 buffer comes to mind, and the voltage regulators are also worth checking just to rule out the obvious. The schematics for the 32K card can be found on Mainbyte. 1 Quote Link to comment Share on other sites More sharing options...
+videofx Posted May 21, 2022 Share Posted May 21, 2022 2 minutes ago, AwkwardPotato said: The LS257s on the 32K card are used to multiplex the row and column addresses onto the 4116 DRAMs. If any of the LS257s' outputs fails (hi-Z/floating in my case), reads and writes to certain parts of the 32K expansion will also fail. For a card like yours that locks up the TI at startup, I'd suspect one of the parts closer to the edge connector. The 74LS245 buffer comes to mind, and the voltage regulators are also worth checking just to rule out the obvious. The schematics for the 32K card can be found on Mainbyte. It only happens at power up when my P-Code card is turned on in the PEB. If I switch the P-Code card off then everything works fine until something accesses the 32K card. Quote Link to comment Share on other sites More sharing options...
AwkwardPotato Posted May 21, 2022 Author Share Posted May 21, 2022 Do other programs accessing the 32K cause the system to lock up too? If not, it might be worthwhile to try one of the memory test programs out there. 1 Quote Link to comment Share on other sites More sharing options...
+videofx Posted May 23, 2022 Share Posted May 23, 2022 I am working with @Fritz442. He gave me a program to use to test. I am upgrading my Tipi now then I will test with MEMWRITE 2 2 Quote Link to comment Share on other sites More sharing options...
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