A500 trapdoor memory: free design

[katarakt]

Oh i forgot, is it better to use round pin header for connectiong gary adapter to mainboard ?

[Mathesar]

Originally Posted by katarakt

Oh i forgot, is it better to use round pin header for connectiong gary adapter to mainboard ?

Yes, otherwise you can damage the socket on the mainboard.
I use the one on the picture. The thin end of the header goes to the mainboard, the thicker pins are soldered to the gary adapter.

[PeteAU]

Originally Posted by Mathesar

BTW, I build up a complete rev B6 board and Gary adapter.
I am using Texas Instruments 70ns DRAM chips and only HCT logic.
So only 74HCT00, 74HCT74 and 74HCT139.

I am happy to report that b6 works like a charm. It passes all the memory tests and keeps the time perfectly.

QC passed

Some pictures of my nice restomodded rev 5 A500 from 1987 :

Nice! I bought all the parts for your IDE board too, one day I'll build it. What's this flat-flex cable you have there?

Originally Posted by Mathesar

I *think* you can only use the board as chipram on the A500+.
But maybe other can comment on this one.

I would agree. You'd have to modify a A500+ very heavily to get slow RAM. Just use the board as a chipram expander to 2.0 MB chip.

[alenppc]

Despite multiple attempts, I can't get the b5 board to work properly. Pete, do you think you could release the Gerber files for the board that used the other type of ram chips? I didn't have any troubles with that one.

[E-Penguin]

Originally Posted by PeteAU

I would agree. You'd have to modify a A500+ very heavily to get slow RAM. Just use the board as a chipram expander to 2.0 MB chip.

Yes, I'm coming to that conclusion too. It is apparently possible with RAM stacked on top of the 68000 directly and some muxes. I'm going to teach myself CPLD programming and get on it.

[katarakt]

Originally Posted by Mathesar

Yes, otherwise you can damage the socket on the mainboard.
I use the one on the picture. The thin end of the header goes to the mainboard, the thicker pins are soldered to the gary adapter.

Thanks Mathesar.

One more question:

Kinmami-Bom says C19 is 22µF ±10% 10V X7R 1206 Ceramic, can i use 22µF 1206 for C11 too (bom for C11 says 100nF) ? Because C11 is 1206 pad and it would fit better

[PeteAU]

Originally Posted by katarakt

Thanks Mathesar.

One more question:

Kinmami-Bom says C19 is 22µF ±10% 10V X7R 1206 Ceramic, can i use 22µF 1206 for C11 too (bom for C11 says 100nF) ? Because C11 is 1206 pad and it would fit better

This is what I would do:
C11: none
C12: 100nF 0805
C13: none
C19: 4.7uF tantalum (10 volts or better)

That's pretty much exactly Commodore's circuit in the A501.

Originally Posted by PeteAU

Dumb question: Did you close RAM enable jumper? It's needed for any slow RAM. Have you tried 0.5 CHIP + 1.0MB SLOW settings on gary adapter? You could also try swapping the two SEL wires.

Yes, i tried with open and closed ram enable jumper and probably every other combination of jumper I could imagine except swapping the SEL wires which I just tried 1 minute ago and got the same green screen as before. The only jumper that changes the green screen is the 512k-MORE on the gary adapter when moved to 512k give me a black screen instead.

I tested every pin on every ram chip with my multimeter in continuity, found a couple of bad soldered pins, fixed it but the result wouldn't change, at this point I must have a bad ram chip or my 74s are not working as they should. I will probably build another gary adapter for testing and another ram board, eventually I will succeed

Thanks for the help, sugestions are always welcome!

[Mq]

I propose to you to check carefully soldering on Gary adapter, because it's puzzling why You have black screen when You set jumper 512/more on 512 position.

And if You had couple of bad soldering on RAM chips, then check them once again. I know You already fix it, but I have another example from my experience. One time I was checking continuity on RAM chip pins and pads on the pcb. Multimeter shows good continuity, but it not works. Then it turned out that there was bad soldering, but when I touch pin by multimeter probe, then small presure of that touching connects little gap between pin and pad. There was bad soldering too, and I saw that by magnifying glass only.

[katarakt]

Originally Posted by PeteAU

This is what I would do:
C11: none
C12: 100nF 0805
C13: none
C19: 4.7uF tantalum (10 volts or better)

That's pretty much exactly Commodore's circuit in the A501.

Ok thanks PeteAU

Mathesar, have you built your b6 like PeteAU would do with these 4 positions ?

About the "512k - more" jumper on gary adapter ...if i jumper this to 512k, do i have to cut the trace to more with a knife ?

[Mathesar]

Originally Posted by PeteAU

Nice! I bought all the parts for your IDE board too, one day I'll build it. What's this flat-flex cable you have there?

I use one of these IDE to SD converters:
https://www.ebay.com/itm/SD-Micro-sd...item3d3be77cc8
Together with an extension cable to get a MicroSD slot at the back of the Amiga:
https://www.ebay.com/itm/TF-Micro-SD...oAAOSwGdhZnktp

This makes it very convenient to swap over the SD card to my PC and install software using WinUAE

Originally Posted by Mq666

I propose to you to check carefully soldering on Gary adapter, because it's puzzling why You have black screen when You set jumper 512/more on 512 position.

And if You had couple of bad soldering on RAM chips, then check them once again. I know You already fix it, but I have another example from my experience. One time I was checking continuity on RAM chip pins and pads on the pcb. Multimeter shows good continuity, but it not works. Then it turned out that there was bad soldering, but when I touch pin by multimeter probe, then small presure of that touching connects little gap between pin and pad. There was bad soldering too, and I saw that by magnifying glass only.

I will have to build a new gary adapter, it's impossible to try fixing/probing mine since I have soldered the sockets on top of the 74s. I'll have to order some round pin headers first though.

I think you are right, i must check those connections with a magnifying something. I will see to it right away.

Thanks again.

[Mq]

I'm sorry I'm talking about that magnifying glass again, and again many times. But years ago I heard the same from my friend, and I ignored that, then some day I finally takes a look to my "very good soldering" with magnifying glass, and I saw things I don't have seen before:-)

[appiah4]

A bit late to the party but yeah it works thanks PeteAU.

[Mathesar]

Originally Posted by appiah4

A bit late to the party but yeah it works thanks PeteAU.

Classic 512K+RTC

Next up a TF530 ?

[katarakt]

Originally Posted by PeteAU

This is what I would do:
C11: none
C12: 100nF 0805
C13: none
C19: 4.7uF tantalum (10 volts or better)

That's pretty much exactly Commodore's circuit in the A501.

Mathesaer, have you built yours like this?

[Mathesar]

Originally Posted by katarakt

Mathesaer, have you built yours like this?

I think I used a 10uF X7R cap for C19 I had lying around.

I wouldn't worry though, al the 100nF caps are the most important.
As long as C19 is in the 10's of micro-farads range you're set!

Originally Posted by Mq666

I'm sorry I'm talking about that magnifying glass again, and again many times. But years ago I heard the same from my friend, and I ignored that, then some day I finally takes a look to my "very good soldering" with magnifying glass, and I saw things I don't have seen before:-)

Mq, you were SOOOO right man! Really thanks for the help, i got a decent magnifying glass and found some things I would never have seen without it... Fixed it and voilà!!!

You guys are awsome, thank you all for this! Those kind of projects is what make retro computing so fun!

[hooverphonique]

Originally Posted by instorm

Attachment 55353

What's the deal with sysinfo there, saying it's 1.0MB, when it's 1.5MB?

[Mq]

I also think about it. Instorm, You are one step beyond, but I think You must run SysTest which we all used, and check out Your RAM extension. Workbench may show You right amount of RAM caused by Gary adapter signals, but RAM chips may not works properly, so check it. In SysTest You must to see proper amount of RAM in direct memory test, and that test must be passed for some rounds.