"JW" wrote in message
...
On Mon, 27 Aug 2012 11:32:16 +0100 "Gareth Magennis"
wrote in Message id:
:



"JW" wrote in message
. ..
On Sat, 25 Aug 2012 19:30:12 +0100 "Gareth Magennis"
wrote in Message id:
:



"Gareth Magennis" wrote in message
.. .

"JW" wrote in message
...
On Wed, 22 Aug 2012 09:57:52 +0100 "Gareth Magennis"
wrote in Message id:
:

Hi,

can't seem to even find a printable datasheet for this well obsolete
device.

Its an 8080A controller/bus driver, just wondering if anyone knows
where
I
might find a replacement - perhaps someone knows of a common old
piece
of
equipment that might have one I can salvage.


This is in an AMS DMX 1580, a digital delay from the last century.

Ebay?
http://www.ebay.com/sch/i.html?_from...&_nkw=uPB8228C

Datasheet:
http://www.datasheetarchive.com/UPB8228C-datasheet.html

Intel also made the 8228. Very likely that Intel designed it, and NEC
copied.


Oops, must have made a typo when I searched Ebay yesterday.
There's one on Ebay UK too which I've just bought.


Cheers,


Gareth.




Damn, replacement didn't work.

Reason for suspecting this device was that the systems _WR line was held
at
around 1 volt, other Address/Data lines look normal.
Isolating this device from that line produced a solid zero, so worth a
punt,
I thought.

Just a thought... If you can isolate it again, try putting a 2.2K resistor
pullup on the signal to see if the CPU can drive that lower than .8V

No I don't have a schematic, but it is a small PCB. The _WR line also
goes
to 2 DRAM chips, but nowhere else as far as I can tell.

Normally I'd suspect the DRAM chips as well, but not so much if isolating
the _WR signal to the 8228 seemed to correct the voltage level.

Also, the 8080A had three power supplies (+12V, +5V and -5V), but you
probably already checked/knew that.

[snip]



Oops, sory about that double post, finger slipped.

Its a public holiday in the UK today but just popped into my workshop cos
I'm curious, and this actually belongs to a friend of mine.

I did try a pullup resistor on the _WR line which gave a good zero, as did
simply removing the 8228. Only when the 8228 was connected did the line
hang at around 2v. A bit weird, but that's what lead me to replace it.

But I think I may be closer now. I'd checked the 3 power supplies, but
scoping all the 8080A lines just now reveals one other dodgy looking one,
D6. The pulse train is only 3v pk to pk instead of 5v.
This line connects only to D6 on the 8228, and on removing the 8228 it
remains at 3v.
So it looks to be the 8080A processor then, with a faulty D6 (and possibly
_WR).



Thanks,


Gareth.