Commodore A3640 Rev. 3.1 watchdog mod

Hi, I’ve bought a A3640 recently which I intend to use in an A3000.


The A3640 has REV 3.1 printed on the circuit board. I had to switch all the caps on it for new ones (Panasonic SMD elec. polymer hybrids EEHZC-series) as the old ones had some signs of leakage and at the same time I did the polarity mod (http://amiga.serveftp.net/A3640_capacitor.html) for C105, C106 and C107. Also I’ve cleaned the card from resin residue and the acid from the old caps.


One thing I did notice in the cleaning process was that the U209 had some extra resin residue around it and the version number 01 had been over painted by black inc. That made me suspect that a previous owner of the card had the PAL/GAL reprogrammed. According to a lot of pages on the net (http://www.amigawiki.org/doku.php?id...s:a3640_rework) the Rev. 3.1 cards should have rev 02 of U209. Also a rev. 3.1 cards should have the C400 removed and a “U490” - RH5VA43A (http://www.amigawiki.org/lib/exe/fet...arts:rh5vt.pdf ) reset generator installed. This card does not have this watchdog circuit and still has the cap C400 in place. The U204 has version 01 printed on it.


Now, I tried this card in my A3000 which has KS 3.1, SCSI 08, Ramsey 04 and DMAC 02 and it seem to work flawlessly!? I tried it with different apps/games a couple of hours but it showed no signs of weird behavior. The 68040 does run quite hot (70+ deg. Cel) and the heat sink is not the original one so I need to get an extra fan fitted near it somehow though.
Does anyone know why the reset generator U490 needs to be installed at all? I could not locate a SOT-89 RH5VA43A anywhere but found a TO-92 DS1233-10+ that to my limited knowledge in this area seem to do the same job. RICOH documents (http://www.ricoh.com/LSI/info/discon.pdf) says that it has been succeeded by R3111H but I could not find this locally either.


I am planning on selling this A3000 along with the A3640 and do not want to sell it if it is not 100% OK in this combination.
Please anyone help me shed some light over these questions.

Thanks!

[alenppc]

I think that as long as the card works reliably according to your tests, you're good to go. I have looked at my A3640 cards, and there isn't one that is the same. They all use a various mix of chip revisions, some have the reset fix, some don't, some have the U200 fix, some don't.

Neither one uses the full set of chips belonging to the same revision, but they all seem to work ok regardless.

[hooverphonique]

the semiconductor reset generator replaces the simple RC reset generator which is there now. the RC one is not as reliable and component tolerances may cause them to go out of reset early. if your card works, I would not worry. My 3640 has the RC version as well, and has worked reliably for 20 years..