Playing with HP2640B

[David Collins]

Marc, in addition to Mattis’ forthcoming reply, my recent experience with a moldy 2624A was that the hot wire method was very poor. Too hard to get the wire in, didn’t melt the ‘glue’ very well, smelly. Gave up when the wire broke. 

What worked best for me was a flat blade screwdriver that was small enough to sit sideways in the gap between the front glass and the tube. I sliced sections of the glue and picked them out with a hook. I also squirted in a combination of RP7 and household cleaner but not sure either did anything other than lubricate the surfaces - they may have helped lift the glue a bit. 

My ‘glue’ was like a layer of silicon rubber which hung on for as long as possible but I got it all off without any damage. 

I replaced the front glass and held it on with a bead of black silicon rubber used for shower glass. I spaced it from the tube with pieces of wire around the edges and pulled them out when the silicon dried. 

Worked well for me but keen to hear how Mattis went. 

I didn’t try the hot water soak but it would probably help. 

David Collins


> On 17 Nov 2017, at 6:12 pm, CuriousMarc via cctalk <cctalk at classiccmp.org> wrote:
> 
> What did you do for the screen mold? Hot wire method to separate CRT from implosion window? Put the CRT in a hot water bath? Chip at the glue?
> Marc
> 
> 
> 
> On Nov 15, 2017, at 11:48 AM, Mattis Lind via cctalk <cctalk at classiccmp.org> wrote:
> 
> I have been working on a HP 2640B terminal. It was mostly about fixing the
> "screen mold" problem and cleaning up the liquids that had been seeping out
> from the screen down into the bottom.
> 
> The small coaxial wire that connects the 4.9152 MHz clock signal form the
> power supply (never seen a crystal controlled SMPSU before!) to the
> backplane was broken off, but after fixing that the terminal worked fine.
> Just needed some adjustment to the brightness.
> 
> With the correct terminfo installed it worked quite well as a serial
> terminal to a Linux box.
> 
> Then I tried the short 8008 programs that Christian Corti pointed to
> 
> http://computermuseum.informatik.uni-stuttgart.de/dev_en/hp2644/diag.html
> 
> and
> 
> ftp://computermuseum.informatik.uni-stuttgart.de/hp/hp2644
> 
> I tried both a couple of times. The terminal enter the LOADER mode but just
> hangs completely at the end. I tried different baudrates but no difference.
> 
> The selftest STATUS line tell me 40<802 which should indicate that there
> are 4k memory in the terminal. However there should be 5k since there is
> one 4k board and one combined control store and 1 k RAM board. Maybe there
> is a fault in the 1k SRAM? The terminal doesn't complain though.
> 
> Regardless, the programs listed either starts at adress 30000 or 36000
> which should then be within the available space.
> 
> The question is, should these program work for the HP2640B as well? It has
> a 8008 but my guess is that the firmware is different from the 2644. What
> is the joint experience regarding this? Has anyone ran these small programs
> above on a HP2640B?
> 
> The HP 2640B firmware consists of four EA 4900 ROM chips which annoyingly
> are not  anything like normal EPROMs. So dumping will need special
> considerations.
> 
> Has anyone dumped the HP 2640B firmware already? I didn't find it on
> bitsavers.
> 
> /Mattis