Re: HP 9135A, compatible hard disk drives

Paul Berger


There is this manual that covers all models that covers all models of the 913x.  It does have information about jumper settings.


On 2020-06-05 11:29 p.m., HP75_8687 wrote:
Unfortunately my HP 9135A (large form factor first desktop 5MB HDD/ 5.25" FDD combo drive) has a broken hard disk. (head crash, definitively no chance to recover).
The HDD is a Seagate ST-506, 5MB; that is the first ever 5 1/4 inch desktop hard disk drive. ST-506 is also the name of the corresponding interface.
These HDDs are difficult to find today (has anyone got one? I'd love to buy it.)

Now the question is whether it could be replaced by another HDD that is fully downward compatible.

Seagate's second HDD was the ST 412 , 10 MB (built into the 9134B, for example).
Unfortunately (from my perspective :-) ) Seagate introduced a new interface for the new HDD, not surprisingly called "ST-412 interface".
HDDs that are designed for ST-412 interface are more common and easier to get, like the ST 225 (20 MB).

What are the differences between the ST-506 and the ST-412 interfaces? It seems they are tiny, but is is there some compatibility?
More concrete: Should an ST 412 or ST 225 work at an ST-506 controller, only slower? (ST-412 introduced kind of a burst mode).
If it should turn out to be impossible to get an ST-412-type HDD to work at the ST-506 inside my 9135A, I'd like to know if there are pure ST-506 drives other than the ST-506 itself, and would be happy if someone had a tip where to find.
I have to admit that I am not totally sure that a ST 412 won't work in a 9135A (then reduced to 5 MB capacity, of course). I have a spare drive that I tested in my 9134B a few weeks ago, it worked fine. Now it doesn't work in my 9135A (throws "DISC" errors, when I try to INITIALIZE). But theoretically something could have happened to the drive meanwhile ... unlikely, but possible.
Paul suggested that there might be next to no difference between the controller boards of a 9134B and a 9135A. There has never been a 9135B, B versions (featuring the 10 MB ST-412) exist only as 9134 (HDD only) and 9133 (HDD/3.5" FDD). A 9135A probably is too old to know about the newer standard ... but who knows ... there are a few jumpers on the board.
Has anybody got a copy of the service manual for the 9135A? I could not even find it mentioned anywhere.

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