Re: Can't find info about addon card for HP-150 #VintageHPComputers


Sonno Ocea
 

On Mon, May 31, 2021 at 08:08 PM, Dave McGuire wrote:
On 5/31/21 2:00 PM, Sonno Ocea wrote:
I dismantled my HP-150 to check if there was anything wrong and while I
was at it I tried to take some decent quality pictures of some of the board.
(the crt driver, backplane, and psu required a total disassemble so I
didn't take picture of these)
Link to Google Drive folder.
<https://drive.google.com/drive/folders/1LazYapWf_gLPpIJhIRiVKVHhtFCokspS?usp=sharing>

One things that really bugs me is the board that I labeled as
"MISTERY-PCB", I have no clue on what it is, can someone please take a
look and direct me to some documentation?
Wow, that's an interface board for HP's "PC Instruments" series of
low-end test equipment. That's a fairly unusual board.

Also, all the light blue capacitor (22uF 25V) on the VIDEO and SERIAL
PCBs are leaking a green substance and I want to swap them for MLCC
equivalent so they last way more.
My question in this case is: should I do that? Or should I go for
another electrolytic cap that will leak again but is less out of place?
Replace it with an electrolytic capacitor. Sure, it may leak again,
but in 30-40 years.

The danger of replacing electrolytic capacitors with MLCCs is that the
latter tend to have issues with voltage coefficient of capacitance, i.e.
the capacitance goes down as the voltage across the capacitor increases.

You can lose as much as 50%, sometimes more, of your capacitance that
way...bad choice for a capacitor across a DC rail.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

 
The danger of replacing electrolytic capacitors with MLCCs is that the
latter tend to have issues with voltage coefficient of capacitance, i.e.
the capacitance goes down as the voltage across the capacitor increases.
I knew there were differences but I never had someone explain to me, too practical for formal lessons, too advanced for random tutorials on the internet. xD
I've seen some on lcsc and digikey: I wanted to use polymer ones so they don't leak corrosive stuff.
Sadly they seem to cost 10x more or they last 10x less than similarly priced Nichicon ones so I'm not really sure on what to use.

Also I did some reserch on my own and found out the AMD 8088-2 dissipates about 2W, so I think I'll stick a tiny heatsink on it.

Thanks a lot for the response!

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