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RetroNynjah / DELA-EPROMMER-II-27512-extension

Recreation of the DELA-EPROMMER II 27512 add-on
GNU General Public License v3.0
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a question related with the DELA eprommer #2

Open giobbino opened 1 year ago

giobbino commented 1 year ago

Hello, I've built your adapter. But I have an issue with the eprommer that prevent me to use both the eprommer and the eprommer with the 512k extension.

I know that you have nothing to do with the eprommer design, but you're the only one person I could ask some help...

I built the https://github.com/Commodore-Bench/DELA-EPROMMER-II project, but I'm getting corrupted / scrambled data when I try to read an EPROM. Unfortunately this project doesn't allow issues, so I have no way to contact the owner.

I got the following issue:

I read an EPROM (I tested it from 2716 to 27256.... I did a quick test with 2716 and 2732 and they seem to be ok, while I have the problem with 2764 to 27256) addressing it to $1000 as suggested in the original manual.

If I then compare the EPROM I've just read with the memory content at $1000, most time it seems to be the same (but sometimes it reported corrupted data);

I extracted the saved PRG from the disk, using DIRMASTER on my Windows PC; I opened it with an hex editor and I removed the two first bytes (loading address); I compared it with the original BIN: the content is scrambled: it is saved in blocks that are in different location respect the original BIN file (i.e. $0800-$0FFF is saved at $1800-$1FFF, etc.). Sometimes the content is different (corrupted).

I've built three different DELA eprommers (just to be sure it wasn't my issue in the assembling process);

I tried to replace all the ICs using another from other sellers (the only parts from the same seller are the zener diodes and the transistors);

I tested it with three different Commodore 64;

I tried to read a 27256 EPROM many times and saving it to disk, using both SD2IEC and real 1541 drive;

Honestly I ran out of ideas; I can only imagine there's a flaw in the project or some of the components I'm using are wrong/fail/fake/etc.

I know that you didn't design the above project, but have you any clue about what's going on and what could cause this kind of problem? I supposed the CD4040 would be the potential culprit, for that reason I bought new ICs from a totally different seller, but the behavior is exactly the same... also the other ICs come from different sellers / lots / brands;

Have you any way to know if the project I used (link above), is the same of the (no more available)https://github.com/DL2DW/DELA-EPROMMER-II project you cited in your page and / or if it's know to be a working project?

Any kind of help you can give me will be highly appreciated!

RetroNynjah commented 1 year ago

I have not used the redesign that Retrotinker did but I used his schematics for reparing two original Dela Eprommers. I started a build of his redesign but never finished it. I noticed a problem with his design and that was that the voltage rating on at least one of the big electrolytic caps was too low so it was cooking. The one on the original board was higher than in his design. Just checked my notes and it's CP3 that should be 63V. I had measured 49V over that capacitor on my boards. My testing of his board stopped there so I don't know if there's more errors in his design. Unfortunately his gone from Github and doesn't respond to email.

I've used my adapter with original boards from Dela and it works with them.

giobbino commented 1 year ago

Thank you for your prompt answer. I will check that cap (I used a 35v model; it didn't explode but it could be damaged).

Did you plan to finish the redesign of the DELA eprommer?

RetroNynjah commented 1 year ago

I hadn't planned too. I completely forgot about that build. Perhaps I can find some time to replace the cap and try to dump some ROMs and see if it works any different than the original hardware.

giobbino commented 1 year ago

I will try to replace the cap with one of the suggested voltage and see what happen. Can you confirm me that you can successfully save and load the EPROM images with the original DELA eprommer?

giobbino commented 1 year ago

...I replaced the CP3 capacitor with a 100v one. No changes. The board behavior is really weird:

-- compare the two eproms content with my MiniPro programmer: the content of the new eprom is scrambled!

I don't understand what's going on, I also wondered if my eng-translated version could have some issue, so I tried the original german version. No way.

So, here it comes my latest question: admitting just for a moment the hardware is ok (and assuming that probably it isn't), could it be a wrong software version? I mean, is there another software version suitable for that board? Because I don't understand how the software doesn't identify that the RAM content is different from the eprom...

RetroNynjah commented 1 year ago

I don't understand it either. I dug out my original DELA eprommers but I can't even get them to read a 27256 EPROM realiably using the original German version (non-512kbit). It somehow managed to read an AT27C256R OTP EPROM almost correct. There were a few sections of incorrect bytes though so I thought I should try an older UV-erasable AM27256 in case it was an compatibility issue but that one only returned a few correct blocks. It somehow managed to fry a few of my AM27256 EPROMs during my tests so I'm giving up on this. I don't have enough EPROMs that I can waste on troubleshooting it.

giobbino commented 1 year ago

Wow, it fried the EPROMs? Weird, indeed. At least mine didn't burn anything... Well, thank you very much for your help, I really appreciated your effort and support. Since I've built the eprommer for fun, I think it's time to give up. The MiniPro does its job quite well and I don't need the eprommer, actually LOL