exxos's Atari, Amiga & retro forum

rubber_jonnie wrote: 30 Jan 2025 21:31 [Yeah, I'm going to very likely do the onboard RAM expansion, looks like 4 RAM ICs, 4 decoupling caps and a couple of SIL resistors for pull ups, but I'll go and get the full SP from the interweb.

You also need to change a solder jumper, which is located just to the West of the Fat Agnus. The on-line stuff also tells you to change one by the trap door abut seeing as this is purely an RTC input the instructions are bogus and will stop any trap door clock modules from working.

I think it's a B52 Rock Lobster (from memory, sorry about the pun) - the same as another of the A500s I have...and possibly the A500+ too (less sure about that one though)

If I get a minute or two I will test a 512k expansion in my A500 to see if that is working, just to try and rule out something obvious.

stephen_usher wrote: 30 Jan 2025 21:54

rubber_jonnie wrote: 30 Jan 2025 21:31 [Yeah, I'm going to very likely do the onboard RAM expansion, looks like 4 RAM ICs, 4 decoupling caps and a couple of SIL resistors for pull ups, but I'll go and get the full SP from the interweb.

You also need to change a solder jumper, which is located just to the West of the Fat Agnus. The on-line stuff also tells you to change one by the trap door abut seeing as this is purely an RTC input the instructions are bogus and will stop any trap door clock modules from working.

Actually I don't think the SIL resistors are required after looking at the schematic, but I haven't found a guide on how to do it yet., also I think the Agnus jumper is only required to make the trapdoor ram work as fastram (Though I could have this wrong.)

I may well yet get the Lotharek upgrade and have done with it as it'll give me 8MB of RAM plus IDE.

JezC wrote: 30 Jan 2025 21:55 I think it's a B52 Rock Lobster (from memory, sorry about the pun) - the same as another of the A500s I have...and possibly the A500+ too (less sure about that one though)

If I get a minute or two I will test a 512k expansion in my A500 to see if that is working, just to try and rule out something obvious.

'We were at the beach, everyone had matching towels...'

I did find a jumper next to Agnus that has clearly been cut, however it looks like this is done to select PAL after looking at the schematic, so I don't think it's related.

rubber_jonnie wrote: 30 Jan 2025 22:37 [Actually I don't think the SIL resistors are required after looking at the schematic, but I haven't found a guide on how to do it yet., also I think the Agnus jumper is only required to make the trapdoor ram work as fastram (Though I could have this wrong.)

I did experiment.. the solder jumper is needed otherwise the on-board RAM never gets mapped in. If you have the jumper, no on-board RAM but trap door RAM that doesn't work either. It's JP2. Have a look at this: https://lyonsden.net/upgrade-amiga-a500-1mb-chip-ram/

As for the SIL pull-ups, they're not needed. I think Commodore added the holes just in case there was a stability issue as it's cheaper to design them in and not use them than find out that your PCB production run is useless.

Please do not put the ram on the board, it would be a shame.

There are some expansions for the trapdoor that expect the ram to be on that board.
KCS power PC boards
1.8MB ram boards (you can go for 1mb chip and 2mb slow ram total)
( https://amigastore.eu/710-amiga-500-tra ... n-rtc.html )
And one or two extra....

The PSU's on the amiga are pretty good, they seldom fail and I have only seen them fail with a lot of noise on the line or just dead.
That why I told you to check it.

The c64 psu's are the ones that are crap.

Maximilian wrote: 30 Jan 2025 23:53 Please do not put the ram on the board, it would be a shame.

I've not decided yet, but it will depend on the viability of the trapdoor. I cant say if it's the RAM board or the Amiga yet so I'm weighing up my options but this is looking like what I'll do: Lotharek Amiga 8MB/IDE upgrade EDIT - Lotharek no longer sells direct to the UK, looks to be that RetroLemon is the official UK supplier.

Maximilian wrote: 30 Jan 2025 23:53 There are some expansions for the trapdoor that expect the ram to be on that board.
KCS power PC boards
1.8MB ram boards (you can go for 1mb chip and 2mb slow ram total)
( https://amigastore.eu/710-amiga-500-tra ... n-rtc.html )
And one or two extra....

As I suggested, I'm not sure how viable the trapdoor is, I need to do some more testing before I decide. I may rework the connector over the weekend on account of the corrosion it had, though luckily it didn't get onto the mainboard.

Maximilian wrote: 30 Jan 2025 23:53 The PSU's on the amiga are pretty good, they seldom fail and I have only seen them fail with a lot of noise on the line or just dead.
That why I told you to check it.

And I did check it :) I am giving it a recap though once I get the parts I'm missing.

Maximilian wrote: 30 Jan 2025 23:53 The c64 psu's are the ones that are crap.

Oddly my C64 PSU's have given me no trouble, though I had to replace the one for my C128.

stephen_usher wrote: 30 Jan 2025 22:47
I did experiment.. the solder jumper is needed otherwise the on-board RAM never gets mapped in. If you have the jumper, no on-board RAM but trap door RAM that doesn't work either. It's JP2. Have a look at this: https://lyonsden.net/upgrade-amiga-a500-1mb-chip-ram/

I think we had a mix up...

I thought you were saying the jumper had to be set for trapdoor RAM, but you meant the on board RAM. I have seen that site, looks perfectly simple to do.

stephen_usher wrote: 30 Jan 2025 22:47 As for the SIL pull-ups, they're not needed. I think Commodore added the holes just in case there was a stability issue as it's cheaper to design them in and not use them than find out that your PCB production run is useless.

Yes, I found the schematic and it did say that, so that makes it easier if I decide to do that upgrade.

So it seems RetroLemon doesn't sell this: Lotharek Amiga 8MB/IDE upgrade

Unless I'm going mad

It's new, only finished production in December.