ICL7611 op-amp (was: Motorola MC14081B)

[Adrian Graham]

On 24/12/2016 19:04, "Brent Hilpert" <hilpert at cs.ubc.ca> wrote:

> On 2016-Dec-24, at 4:07 AM, Adrian Graham wrote:
>> On 24/12/2016 03:48, "Brent Hilpert" <hilpert at cs.ubc.ca> wrote:
>> 
>>> The ICL7611 is, I expect, a very-low-power (Intersil's niche) op amp.
>>> Together
>>> with the CMOS 4081 the circuit appears tailored for low-power operation.
>>> Is it supplied by the battery?
>>> It may require the battery presence for stable supply at time of power-up to
>>> get reliable reset operation from this power-on-reset circuit.
>> 
>> That's a very good point so now I'm going to have to scrabble around to find
>> the battery to find out what voltage it was since I removed it ages ago and
>> may have recycled it. I don't recall any markings on it though, it looked
>> like a 'normal' 3 terminal NiCAD wrapped in blue plastic. I did take hi-res
>> pictures of it however.
>> 
>> The 5V input at R395 does head off towards the battery location before it
>> hits the resistor so I'll trace that out too.
> 
> 
> The circuit makes sense if the battery is connected to the Vcc line of the
> ICL7611, 4081, etc.,
> D1 would be backflow prevention into the +12V line .
> R416 would be current limiting providing ~ 8mA trickle charge of the NiCds.

Looking at the back of the board the battery WAS originally connected to the
7611 and 4081 at manufacturing but then that connection was physically cut
out and a jumper wire added to the line that supplies the MM58174AN RTC
that's next to them, which is derived from the 12V DRAM supply.

Pity, I was kind of hoping that if I added the/a battery back in then the
7611 would be happy at power up but it looks like it's not involved at all.
Could I add a bit of adjustability by replacing R397 with a 100K pot?

*embarrassed face* The resistor formerly known as R416 is actually R424,
seen here top right in a hybrid front/back mix of the board around the
battery which includes the CMOS chips:

http://www.binarydinosaurs.co.uk/STCExecutelBatterySectionHybrid.jpg

You can see the cutout under the upper left hand battery terminal and the
blue jumper wire running to the 4081. The two green resistors upper left in
the cluster of 5 are R398 and R406. All the red caps are decouplers.

> Speaking of such equipment, our museum has one of these buried somewhere, a
> Nortel Displayphone:
> http://classiccmp.org/dunfield/disphone/index.htm
> I don't think it has all the apps of the Executel,
> it's phone + on-screen phone directory & phone apps + RS232 terminal with
> 300bps modem.
> I hope to work on it and document it sometime.

Nice!

Hope you have a great xmas :D

-- 
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?