400 ROM chips

[xrbrevin]

rooting through my bits looking for a 16k RAM board, i found this:

 

i thought i'd try and power it up but i need ROM chip A105. i know an EPROM can be used for the XL/XE models but can i use one for this?

also, can anyone identify the modded RAM board?

 

crikey, im getting a crash-course in 400s at the moment - its great fun!

thanks in advance 🙂

[xrbrevin]

further research suggests the missing chip is the "math pack" used on both the 400 and 800.

could this be it?

floatpnt.rom

[jamm]

That poor thing needs some deoxidizing spray!

[+Nezgar]

The computer should actually work for a lot of things with the floating point math ROM missing if you want to test it out as-is. Ie. you should still be able to load DOS and most games. Notable exception would be BASIC, which makes heavy use of it.

 

If you easily can't find a replacement original, you could adapt a 2764-512 type eprom to 2316 configuration with an adapter such as this:

http://store.go4retro.com/23xx-adapter/

 

[xrbrevin]

found the RAM board details here:

 

its tough to do continuity testing due to the oxidisation, can anyone recommend a cleaner/technique?

[xrbrevin]

4 minutes ago, Nezgar said:

The computer should actually work for a lot of things with the floating point math ROM missing if you want to test it out as-is. Ie. you should still be able to load DOS and most games. Notable exception would be BASIC, which makes heavy use of it.

 

If you easily can't find a replacement original, you could adapt a 2764-512 type eprom to 2316 configuration with an adapter such as this:

http://store.go4retro.com/23xx-adapter/

 

thanks - your knowledge of EPROMs & their workarounds is enviable!

[xrbrevin]

i did some work on the RAM board

the DRAMs have been removed and every one suffered broken pin(s). 2x chips have pins snapped right at the body so ive got some dremeling to do to expose a contact..!

the board itself has cleaned up reasonably well, i will further mint the edge connector up today.

of all the glue logic chips, only 1 pin broke - i needed a bit of luck.

the 2x 680ohm resistor desoldered nicely with a bit of flux. ive had to order new ones as i dont have any in stock.

i heard that sodium bicarbonate/water paste will do the job

note the chip sockets are not notched for orientation, instead there is a little blob of white!

thanks to the above link, i have identified which way round the red and orange wires go

[+Nezgar]

Wow that's a lot of busted pins... yeah not much you can do for the ones broken off right to the plastic...

 

For the ones that still have the top part remaining, you could graft/solder replacement pins over top... It would only be worth the effort if you enjoy that sort of thing. (I've only done a couple one-offs... )

[BillC]

23 hours ago, xrbrevin said:

the DRAMs have been removed and every one suffered broken pin(s). 2x chips have pins snapped right at the body so ive got some dremeling to do to expose a contact..!

That's a lot of work to repair some 4164 DRAM chips that are still available.

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=4164+dram&_sacat=0

[xrbrevin]

yeah, i tried to shave back the plastic casing but inevitably i also shaved the remaining stub of metal contact so they all got binned

i have a set of 256k DRAMs to test with (when the resistors arrive) but ive also ordered some 64k ones

the fact that the glue logic chips survived demonstrates that the mostek DRAMs are built to a lower standard so i wasnt particularly disappointed to condemn them to the bin