On Sat, Nov 08, 2003 at 03:09:21AM -0800, Uwe Zimmermann enlightened us
thusly
> DM> I have a 3 channel chart recorder for repair. The problem is an
> error DM> '9999.9 - ADFAIL' comes up on all three channels. At the
> heart of each DM> is a 28 pin plcc chip. It says DM> <logo>
> TIP DM> 9924NCC DM> C17619 DM> 120S1355 DM>
> REV 01
>
> DM> The logo is a smallish 'M' in a circle, but it's a very plain 'M',
> not DM> reminiscent of Motorola or Maxim, who use slightly fancy 'M'
> in their DM> logos. There is three of the above chips. The cpu is
> separate.
>
> DM> Google returns rubbish, of course.
>
> DM> It's about 5 years old, and I suspected a power supply, but all
> seems DM> good. It's a bit difficult to tell, because the circuit has
> loads of DM> little 78Lxx and low power lm317s in strange places and
> is inclined to DM> dissappear up it's own backside when you try and
> follow it ;-). All the DM> other stuff is Common enough (National/ST
> parts) and the transistors are DM> pro electron, so we appear safe
> from inscrutable Far Eastern devices.
>
> DM> The other bits on each channel (taking a variety of temp probes)
> are a DM> 93LC66 (serial eprom) LM324, LM393, & some optocouplers.
> There isn't a DM> databus going off either. Serial?
>
> DM> Nothing that looks like an a/d on the main board. A Mostek(!)48Z02
> and a DM> Goldstar(That's an Irish meat company!) GM76C88AL-12 are the
> only things DM> beside logic, and the cpu, which is a 68HC11.
>
> If I'm not completely mistaken MOSTEK also used a circled M as logo
> during some time! From the other description I would guess that the
> 28pin plcc is a microcontroller with built-in A/D. In the EEPROM there
> might be calibration data and/or configuration data for each channel.
They died in the eighties.... didn't they? I was working with an ex-
Mostek guy then and he reacted as if he had lost both his parents :-/.
I started thinking cpu & a/d, but it's all funny. There are not 8 pins
going off from the 28 pin plcc chip.. There is one channel onboard,
and 2 on add-in cards. The 93LC66 has nearly all pins going off board,
but no databus from the 28 pin chip does.
>
> Are there separate analog and digital ground lines? Are both
> terminating in the central 28pin plcc? Of course one could also build
> a discrete dual-slope A/D just with 324/393 which could be controlled
> by a purely digital controller...
Yes there are 2 separate grounds at least. From the transformer, I have
2 separate 35V lines, and 21V,11V 9V, and a 17VAC which I haven't traced
yet. I found a 24V dc which I can't connect to any of them. It's obvious
that..... actually nothing is obvious ;-)
There's 2 voltage references(?) and two regulators in each add-on card
and another glued down (which is probably for heat sinking) in TO-92
packages. I'm normally good at this but...I'm losing this one.
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
INET: [EMAIL PROTECTED]
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