A500 trapdoor memory: free design

[Nbdy]

Originally Posted by Turrican_3

Not possible apparently unless you further mod your machine:

https://eab.abime.net/showthread.php?t=97077

It's a fairly common mod with plenty of tutorials online, here's one:

https://lyonsden.net/upgrade-amiga-a500-1mb-chip-ram/

Hi, had some problems with my A500, and now waiting for parts, but in meantime ordered the 2mb expansion with garry adapter ... also waiting to come ....

The question is now : can I add the missing ram chips on board, and to use the ram expansion with garry adapter to have 1mb chip and 2mb of extended ram ????

I mean will the added ram be recognized with the ram expansion and garry adapter ????

Te ram expansion is from PeteAU

Amiga 500 memory expansion designed by PeteAU.

[Turrican_3]

Sorry, I don't think I know the answer to your question.

[Nbdy]

I have read all this again, and dind't find/understand will it or will it not work if the additional ram chips are soldered to borad ...

The board is 6a wich has 4 empty slots for RAM ...

As I have read for that ram to work it has to be cut the JP2 1-2 and add a short on 2-3 ...
With this adapter is only the JP2 point 2 used to be soldered to gary adapter ...

So could this be done that the amiga has 1MB chip onboard and the rest on this expansion 2mb as additional RAM ???

THX

[cmorley]

Originally Posted by Nbdy

So could this be done that the amiga has 1MB chip onboard and the rest on this expansion 2mb as additional RAM ???
THX

No. The extra 4 sockets on the motherboard share control signals with the trapdoor connector. You can fit one or the other.

[Nbdy]

Hi, bought this expansion and faound some days ago a manual, but was lazy to download ...

And now I can't find it any more, does someone have the assembling manual for this or a link where to download ???

thx

Found it :

https://www.dropbox.com/sh/vnhm8br4i...G8Oj8xrLa?dl=0

[Nbdy]

Guys HELP !!!!

Soldered all together, and have a Green screen .... Red screen ....

Grey screen .... and the amiga seems like rebooting ...

Rev. 6a A500, soldered all chips, RTC, all Caps (even 2 where missng,but found them in my drawer) ....

All jumpers on garry down ....

Ext,clk,ras1 (all) jumpered ...

[Nbdy]

Here are the pics ...

[Nbdy]

OK, removed the gary adapter, resoldered pin 1-2 on JP2 and put the expansion in ...

Workbench showing 512kb chip and 512 slow (somthing less) ...

So the problem is in gary adapter ...

Any advices ???

[Nbdy]

Some conclusion ...

Soldered the JP2 on the mainboard and got 512kb chip and 1.5MB slow RAM

But when I desolder the JP2 and solder the wire from gary adapter ...

Don't have boot screen on all jumper settings on gary adapter ...

Even the diag rom will not start is shows red and violet colors ...

[shaf]

I think I see a solder bridge between pins 13 and 14 on the Chip at U1 also check pins 18 to 20.

[Nbdy]

Originally Posted by shaf

I think I see a solder bridge between pins 13 and 14 on the Chip at U1 also check pins 18 to 20.

Nope ... this are a little flux leftovers, cleaned them after taking pictures be cause also thought that they are soldered together ...


Can some tell me what chip is for the extra 512 chip, be cause that is what I'm missing ...


But don't have a green screen that the ram should be wrong ...


Could it be to do with gary adapter ???

[Mathesar]

Ok, got your message. Few things to check:
Did you cut the XCAS jumper traces? Otherwise the gary adapter won't work.
Also, remember Gary messes with the A19 address line into Agnus to make the computer think it has 1.5mb chip. Even when the RAM expansion itself is not even populated with enough ram. So, the fact you got Workbench to report 1,5mb slow means the adapter is doing something.

[esel]

Do you habe the right Agnus ? Some early rev 6a got a 8371 Agnus which Can only adress 512 kb Chip as Maximum.
You nee a 8372A for 1 MB Chip.

[Nbdy]

Originally Posted by Mathesar

Ok, got your message. Few things to check:
Did you cut the XCAS jumper traces? Otherwise the gary adapter won't work.
Also, remember Gary messes with the A19 address line into Agnus to make the computer think it has 1.5mb chip. Even when the RAM expansion itself is not even populated with enough ram. So, the fact you got Workbench to report 1,5mb slow means the adapter is doing something.

Have the board with no XCAS shorted ... even desoldered the pins to recheck ... :-)

Rechecked all rams for connections to the board and all have a god connection ...

Sorry for the DM, but have rechecked all 5-10 times for connections, resoldered the gary, found out that pin 14 on gary adapter was not connected to board, and then shorted the pin ... Just all is holding my amiga for 10-15 days since I made the board, and would like to finish it and put together ...

Originally Posted by esel

Do you habe the right Agnus ? Some early rev 6a got a 8371 Agnus which Can only adress 512 kb Chip as Maximum.
You nee a 8372A for 1 MB Chip.

Yes the 8732A agnus is in ... so it should accept 1MB of chip ram ...

THX both for reply :-)

[Nbdy]

Found some PC ram with HY5118164B chips ...

Could I use them to test the ram chips ???

I have a stupid question .... Do all pins from gary adapter have to be connected from gary to round pin strips or must the "REGEN" and "RAMEN" not been shorted ???



I mean do all this "red dot's" have to be short with multimeter ??? (all 42 pins)

[Mathesar]

Originally Posted by Nbdy

Found some PC ram with HY5118164B chips ...

Could I use them to test the ram chips ???

I have a stupid question .... Do all pins from gary adapter have to be connected from gary to round pin strips or must the "REGEN" and "RAMEN" not been shorted ???

I mean do all this "red dot's" have to be short with multimeter ??? (all 42 pins)

No, REGEN and RAMEN are controlled by the logic on the gary adapter and must not be shorted.

BUT.... you have the wrong Gary adapter! It is the old version which does not work properly. The proper Gary adapter has 4 logic chips instead of 2!

[Nbdy]

Originally Posted by Mathesar

No, REGEN and RAMEN are controlled by the logic on the gary adapter and must not be shorted.

BUT.... you have the wrong Gary adapter! It is the old version which does not work properly. The proper Gary adapter has 4 logic chips instead of 2!

I found the picture here, this is not my adapter ...





This is my adapter, it has 3 00 and one 74 chip ... and the pin 14 that was not shorted ... with pin 14 i got 1.5MB of slow ram with JP2 in original state (2-3) ...

[Mathesar]

Originally Posted by Nbdy

I found the picture here, this is not my adapter ...



This is my adapter, it has 3 00 and one 74 chip ... and the pin 14 that was not shorted ... with pin 14 i got 1.5MB of slow ram with JP2 in original state (2-3) ...

Do it get it right now that you fixed the missing pin14 on the gary adapter.
And that

• the system boots!
• Workbench reports 1.5mb slow and 512kb chip?

Can you confirm that?

[Nbdy]

Originally Posted by Mathesar

Do it get it right now that you fixed the missing pin14 on the gary adapter.
And that

• the system boots!
• Workbench reports 1.5mb slow and 512kb chip?

Can you confirm that?

NOpe with fixing pin 14 I only have the 1.5MB slow with JP2 shorted ...


With JP2 on (pin 2) on gary I don't have a boot screen ...


I got light grey screen ...

[Mathesar]

Originally Posted by Nbdy

NOpe with fixing pin 14 I only have the 1.5MB slow with JP2 shorted ...


With JP2 on (pin 2) on gary I don't have a boot screen ...


I got light grey screen ...

Got it, so the Gary adapter is succesfully fooling the Amiga into thinking there is 1.5MB slow ram installed. That part is thus working. However, somehow the adapter is not selecting the right ram chips OR the ram chips are faulty.

The circuitry for selecting the right ram chips is built mainly around U2, U3 and U4 (the '74 chip) on the Gary adapter. Check all the solder joints on these chips especially.

Also, on the trapdoor ram card there is the '139 chip that decodes the 2 wire signal from Gary and then selects one of the four RAM chips. Check all the solder joints there as well.

You could also try swapping the two wires going from the gary adapter to the trapdoor board to change the ram bank order just to see it makes a difference.