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+--- Thread: HP 48 ram card from Ebay: why would self-test be required? (/thread-16959.html)
HP 48 ram card from Ebay: why would self-test be required? - arborist - 05-17-2021 05:57 PM
This (unofficial) HP 48 card is sold with surprising instructions and there are two things I don't understand:
1. Why do they ask to go through the port ram test (On + D, then "up")? Does this test do something useful to reset the card? Given the instructions, it seems like one can expect this to fail at first but then eventually succeed. Why would that be?
2. They say the card only works in slot 2. After step (1), wouldn't it work also in slot 1, with only 128kB visible?
RE: HP 48 ram card from Ebay: why would self-test be required? - Dave Britten - 05-18-2021 01:37 PM
I don't see anything saying you have to run the test, I think they're just explaining it for the benefit of the buyer that wants to confirm the card is working.
I don't know how the 48SX behaves with cards larger than 128 KB installed, but I think the warning is there to indicate that you're not going to see 1 MB if you don't put it in slot 2 of a 48GX (though they neglect to mention that it's only fully supported on the GX model).
Also, I would be very cautious about using any cards that don't explicitly say they are for a 48. There are some cards (Epson maybe?) that are functionally compatible, but there are allegedly electrical differences that could damage the calculator.
RE: HP 48 ram card from Ebay: why would self-test be required? - mfleming - 05-18-2021 02:23 PM
I bought a visually similar card from a different seller a few years back and it worked fine in a 48GX. Mine is marked "Grid" as the manufacturer rather tha "VALID" but otherwise looks the same. The instructions for testing the card beats downloading a test program to do the same verification. Don't try the card in a 48SX, I locked mine up so badly I thought I had permanently damaged the processor. I don't know the provenance of these cards, but the price certainly beats that of the HP branded cards.
RE: HP 48 ram card from Ebay: why would self-test be required? - trojdor - 05-19-2021 04:51 AM
I've bought the same cards from the same vendor, and first one was a bad one...
But the guy was good/fast about replacing it and the second one was perfect.
I've seen no difference between these and several actual HP cards in the GX's I've got.
(But like mfleming said, don't try them in an SX....I had to pull the foot and use the paperclip reset to get mine to come back to life, lol.)
mike
RE: HP 48 ram card from Ebay: why would self-test be required? - arborist - 05-20-2021 09:15 PM
Thanks for the replies.
I imagine that the "Grid" one you got is similar to this one?
I'm a little worried because of the well known issue of carefully choosing the voltage level before grounding the RAMCARD pins for ESD protection (c.f. FAQ).
"Standard Epson cards have a significant chance of seeing this voltage as to low and shutting down. We have seen cards do this in the lab. When it occurs the calculator locks up with VDD pulled down to about 2.5V and 250mA being drawn from the batteries. This current drain greatly exceeds the ratings for the power supply and can damage your calc. The least that will happen is a loss of memory."
There are even specific reports of issues with the grid cards here. Linked from this post, which gives the following context:
"
"Grid" brand computers also adopted the same Epson typewriter cards as storage,
but did not modify the original specs -- consequently,
there were various sources of original, unmodified Epson cards,
which were bought anyway by some HP48 calculator users,
either not knowing or disregarding the risk.
"
I wish it wasn't all so complicated to get a card
RE: HP 48 ram card from Ebay: why would self-test be required? - rprosperi - 05-20-2021 09:50 PM
It's not complicated at all, it's simple to just purchase one of these:
https://www.ebay.com/itm/224291967059, $269.00
https://www.ebay.com/itm/224302800251, $269.00
Less than 1/3 of that price is where you get into complicated.
p.s. But please don't buy one of those, I'd hate to be part of giving business to someone that prices like that...
p.p.s. It's probably also worth adding I've used a Grid (previously wrote Epson by mistake) 1MB card for many years with no issues at all.
RE: HP 48 ram card from Ebay: why would self-test be required? - mfleming - 05-21-2021 12:26 AM
(05-20-2021 09:50 PM)rprosperi Wrote: p.p.s. It's probably also worth adding I've used an Epson 1MB card for many years with no issues at all.
Same here wrt the Grid card. Thankfully I was ignorant of the stated risk!
RE: HP 48 ram card from Ebay: why would self-test be required? - Allen - 05-21-2021 02:35 AM
(05-17-2021 05:57 PM)arborist Wrote: 1. Why do they ask to go through the port ram test
IIRC, this is the same ram test in appendix A of the user manual to verify the RAM card is working.
Running this test with a known good card also tests all the pins on your HP48GX as some kinds of surveying dirt can block ram contacts.