HP82915 Modem

[Tony Duell]

> 
> At 10:18 PM 9/5/05 +0100, you wrote:
> >I recently won an HP82915 Modem on E-bay (my first, and so far, only 
> >purchase there).
> 
>   Tony? E-bay??  Now I know the end of the world is coming! :-)

Ineed...

> 
> 
>  I was suprised to get it for the opening bid, I though 
> >I'd have at least one other HP collector to contend with. It is, you see, 
> >the internal modem for the HP Integral.
> 
>    Darn you! I keep a constant watch on E-bay for Integral stuff but I
> didn't see it!

Lucky me :-)

It wasn't listed as an Integral part, only as an HP82915 Modem. I was 
pretty sure that was the Integral modem, one of my manuals mentions it in 
passing.  When it came, I was certain. Right size board, right connector 
(a DIN 41612 socket), plastic cover over the solder side, etc.

> 
> >
> >Anyway, it's a single PCB that fits into one of the Integral's expansion 
> >slots. Cotnains about 20 ICs, most of which I recognise. One odd thing is 
> >that the serial chip used is an 8250, a somewhat odd choice for a 
> >68000-based machine.
> >
> >Does anyone here know anything about using it?
> 
>    Not much. It's a 300/1200 Baud modem. ONE sales brochure list it in ONE
> place but give NO details or pictures and never mentions it again. The

it's not that interesting to look at. It looks like any other Integral 
PCB. As I said, about 17 chips, a crystel, a crystal oscillator, a 3 
terminal regualtro, a transformer, a reed relay, a transistor, and some 
passives. 2 US-style phone sockets on the bracket, both unmarked (may 
just be wired pin-pin, with the appropirate pair of pins also going to 
the modem circuitry).

> service manuals don't give ANY details about it. (It's one of those "If it
> fails, replace the CCA. If it still fails, replace the whole thing."

Repairing it would probably violate the FCC approval (it would certainly 
violate BT appoval for a UK modem). Since I don't intend to connect this 
to a public phone line, that doesn't bother me.

That said, the HP Portable Plus service manual (I have it) does give some 
repair procedures and a scheamtic for its internal modem (totally 
different ot the IPC one, BTW). I does say that certain components 
(mostly resistors) must not be replaced in the field, since this could 
affect the FCC approval (incorrect transmitter level, etc).

> procedures.)  To test it they have you install two modems in the IPC and
> plug them into separate phone lines and call one from the other while
> running the diagnostics program. The diagnostics program will report No
> Carrier, No Dialtone and the like but that's all. There no mention of a
> null-modem type cable. 

Well, there won't be any form of null modem cable. There are only 2 wires 
to the telephone line, and polarity shouldn't matter. However, we had a 
brief discussion here a few weeks ago about linking 2 modems without the 
use of a public telephone system, e.g. by buying a small telephone 
exchange. I am wondering how much is actually needed for _this_ modem.

-tony