Amiga 500 Plus 1MB Memory Expansion Board

Hello, thank you for the quick response! All chips are TMS44C256-80N and all 20 that I have are confirmed as working. They also test fine when in U1-U4 position. Only when populated all 8 troubles start. Any ideas?

Also, no add on cards, vanilla Amiga 500+ no mods nothing added. All original factory!

Hello, This design is based on CBM's original A501+ RAM Expansion card design. I have tested many times with different RAM chips on two different A500+ Rev.8 boards. (see screenshot photos) PCB works fine. But these RAM chips sometimes come across as defective because they are very old chips and some are used. Please try different RAM chips. I recommend TMS44C256 (Texas Instruments) RAM chips. I tested RAM expansion cards with bare A500+ motherboards. I have not tested it with any accelerator add-on cards, I cannot guarantee the compatibility of all add-on cards produced by third parties.

Could be a soldering error, Can you make another RAM Card? If you really need to believe it works, I can record a video for you tomorrow.

I do have an additional card that I can assemble. Been building circuits for 40 years plus this is pretty much full proof with heavy silk screen and cover. Could not make a short even if I wanted. I believe you if you say it has been tested. I'm just stating what is happening. No schematic either to troubleshoot.

There was no schematic. I tested for hours with different RAM chips. Can you please replace all 8 chips with differet ones and test again?

Just assembled second board. Same exact issue. First 512K works fine as soon as full 1Mb is inserted memory test error. Tried 20 different chips always the same results regardless of what chips used. With U1-U4 all good when U1-U8 inserted no good! 1.5Mb total works no issues, 2Mb is not working. Again 2 separate boards and multiple chip combinations.

Do you have another A500+ motherboard to test ? Maybe the problem is with the motherboard. Which software are you using for testing?

I have only one A500+. Using same software as you did what is posted above in the pictures.

Can you please tell me if your motherboard is a REV.8 a500 (normal) motherboard or REV8 A500 PLUS motherboard, what is its ROM version? Can you send your motherboard photos and ram-card photos to c64istanbul@gmail.com

Will do!

Pictures and info sent to your email. Thank you again for taking the time to help!

https://youtu.be/muo5Eawe04A

I can say i built about 5 of the 512K ram version of this. They all worked fine using workbench and Amiga Test Kit. On the fifth one however it did not work. Turned out it was a bad ram chip. 1 out of 4 bad. So i replaced it till i worked out which one it was. Would be good if i knew how to test ram chips before i put them on rather than playing a "puzzle"

Agnus version and Denise chips on A500 must be revised. To reach 2MB Ram Chip, only some versions of them can work. If I'm not wrong That could explain your issue.

Thank you Peter Dimitriovski, you are very kind. :)

https://www.tsb.space/bl0g/upgrade-amiga-500-rev-8a-board-to-amiga-500/ I followed the ram portion, and ignored the clock portion.

Thank you RECEP UNAL :)