HP 9915A failed 8048

[js at cimmeri.com]

On 2022-02-25 16:09, js--- via cctalk 
wrote:
>
> Hi, folks.
>
>    I've a HP 9915A computer with an 
> interesting problem.   The motherboard 
> utilizes a ceramic Intel D8048 chip.   
> The problem is that this 8048 has a 
> crack right across the top middle of 
> it, and half of the top of the chip 
> has begun to separate.
>
>   Powering up the machine as-is 
> unsurprisingly results in no 
> activity.   HOWEVER, if I push firmly 
> on the cracked area with my finger the 
> machine starts to operate normally.   
> All appearances are that clamping down 
> the separating piece of the chip 
> re-establishes any broken wire 
> connections within the chip.
>
>    I've obtained a replacement 
> P8048AH.   My question is: do these 
> chips simply swap like a CPU, or -- as 
> I fear -- is the 8048 a pre-programmed 
> piece?    More simply put, is this a 
> repairable problem?  Or am I SOL?
>
>    Any thoughts welcomed.
>
> - John Singleton
>


Hi, folks.   With the help of the 
extremely talented people here, the far 
less talented me was able to repair this 
seemingly impossible problem and get the 
9915 functional.

The process was to:

1) burn a new 8748 CPU with the 9915's 
8048 ROM code.
    I used a Data I/O 2900 for this purpose.

2) remove the remnants of the original 
8048 CPU

3) install a new milled 40 pin socket

4) install the 8748 into that socket and 
power-on test.


Thanks to Paul Berger, Will Cooke, and 
Wayne S for their useful suggestions.

A very special thanks to Tony Duell for 
offering to go to great lengths to help.

A very, very special thanks to Dave 
McGuire for having done all the hard 
work in retrieving the 8048's code to 
begin with (which he had done already 
for someone else), then providing the 
8048 ROM code to me in hex format, plus 
guidance on how to fix the problem all 
the way through.

- John S.