[xj] AC amp reverse engineering still progressing

XJ
1

I haven’t been ignoring my project to figure out the whole
climate control system… I’ve merely been waiting for the
vile brew to eat away at the epoxy surrounding the amp
circuit. After 10 days or so I finally got down to this:

A few caps disintegrated, but I think I know their values
since I was watching it as they were getting eaten. The
plastic covers on the relays vaporized pretty quickly.
Between the color codes and using an ohmmeter I think I can
figure out the values of the various damaged resistors. The
lump of epoxy left in the center is just covering jumper
wires so there was no need to go further.

From looking at the Jaguar supplied schematic I can tell
there were some drawing errors, and the circuit traces on
the back are completely clean so I can figure all that out.

What does Jaguar get for one of these, something like $800?
Have a good look at what you’re (over)paying for!

More reports as I make more progress…–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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2

In reply to a message from frobozz sent Tue 21 Jun 2005:

Wow…I wouldn’t pay more than $30 for that…what is the
stuff that does THAT to epoxy?

Regards, Andrew.–
84 Daimler Soverign 4.2 - daily driver / Dodge ute in bits!
Newcastle, Australia
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3

In reply to a message from typhoonpud sent Tue 21 Jun 2005:

Wow…I wouldn’t pay more than $30 for that…what
is the stuff that does THAT to epoxy?

Basically a really violent gel paint stripper… it just
doesn’t do it very quickly. Epoxy has pretty much no
porosity, so it has to dissolve it away tiny bit by tiny
bit. I discovered by careful application of a screwdriver I
could sometimes get chunks to come up, especially next to
components, where the stripper could seep between the epoxy
and the component… though of course I ended up damaging
some of the components in the process. I’d estimate that if
I had just let it sit without any help at sloughing pieces
off, it would have taken 3 or 4 weeks. If I get another bad
one to play with I’m going to try that. (Anyone else have a
bad one they’ll sell me cheap for the cause?)–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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4

In reply to a message from frobozz sent Tue 21 Jun 2005:

That is ridiculous !! I took a bit of electronics, and from what I
see, there is nothing particularly expensive looking there. I bet
someone with some good skills could build their own !!!–
1985 XJ6 Vanden Plas
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5

In reply to a message from 1985vdp sent Thu 23 Jun 2005:

That is ridiculous !! I took a bit of electronics, and
from what I see, there is nothing particularly expensive
looking there. I bet someone with some good skills could
build their own !!!

That’s certainly one of my goals in doing this… The
relays have to be far and away the most expensive parts on
there. Some of the resistors are higher precision than
normal but not exotic or expensive, and there is nothing
fancy about the transistors either.

Still looking for another sacrificial dead amp to subject to
the Evil Bath Of Dissolving Goop. With so many people out
there seemingly having had these problems, surely someone
has a dead one kicking around I can buy cheap? I need to do
it again to more positively verify some of the component
ratings (like resistor tolerance) by letting it stew longer
and not accidentally damaging components this time around.

If nothing else, I’ll sacrifice my own once I breadboard a
working new copy.–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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6

In reply to a message from frobozz sent Thu 23 Jun 2005:

If I find one Duncan, it’s yours but scarp SIIIs are getting harder
to find these days…–
The original message included these comments:

there seemingly having had these problems, surely someone
has a dead one kicking around I can buy cheap? I need to do

–
al mclean '93 XJS 4.0 79 SII XJ6 85 4.2 Daimler Sovereign
Telford, United Kingdom
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7

1985vdp wrote:

In reply to a message from frobozz sent Tue 21 Jun 2005:

That is ridiculous !! I took a bit of electronics, and from what I
see, there is nothing particularly expensive looking there. I bet
someone with some good skills could build their own !!!

Sure, Dave, but copying a design doesn’t take into account what went
into developing the thing, and producing it in rather small batches. And
I’m not too sure the parts were all that cheap at the time - though I
suspect they were…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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8

In reply to a message from Frank Andersen sent Fri 24 Jun 2005:

I’m not too sure the parts were all that cheap at the time

  • though I suspect they were…:slight_smile:

If anyone digs up a Bill Of Materials from the Delanair
files, I’d be willing to bet the transistors didn’t cost as
much as the epoxy used to hide them…–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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9

frobozz wrote:

In reply to a message from Frank Andersen sent Fri 24 Jun 2005:

I’m not too sure the parts were all that cheap at the time

  • though I suspect they were…:slight_smile:

If anyone digs up a Bill Of Materials from the Delanair
files, I’d be willing to bet the transistors didn’t cost as
much as the epoxy used to hide them…

…but it kept the cost and content safe from prying eyes - and
fingers, Duncan…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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10

In reply to a message from Frank Andersen sent Fri 24 Jun 2005:

Bah, you think Jag is gonna get mad at a 20+ year old design ??

Aren’trademarks only good for about 25 years ?–
1985 XJ6 Vanden Plas
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11

In reply to a message from 1985vdp sent Sat 25 Jun 2005:

Bah, you think Jag is gonna get mad at a 20+ year old
design ?? Aren’trademarks only good for about 25 years ?

It would be a patent, which was probably good for 17 years
back when this was designed, though it has changed more
recently and in any event I don’t know UK patent law. But I
am well within my rights to figure out why the (&(^^%
thing is broken, and fix it, with any means at my disposal
with one of the parts in my hand. If you build it, and I
own one, I can take it apart. And especially as concerns
repair procedures, I’m free to share my knowledge with the
world.

If I simply copied their design to produce new ones, and it
were still covered by patent, then I’ve stepped in it. Not
seeing any patent numbers on the amp, and given how
non-novel and non-patentable a design it is, my guess is
they simply relied on its obscurity and the epoxy to protect
their design and their profit margins.

I’ve drawn a first-pass schematic with a couple of question
marks, which I hope the next epoxy-dissolving will answer.
I’ve ordered all the parts to build one from scratch, which
will help me verify (or correct) my schematic. Being able
to watch and measure the amp internals while the system is
operational will also greatly help my mission to understand
every last piece of how the system works.

I’ve studied the faces of the relay contacts on the one I
took apart. One of them does have a pretty obvious divot
which could cause it to be intermittent, but it’s not quite
a smoking gun. I have to say I’m impressed with the design
of the relays: cross-wiping contacts, for instance. But
they definitely should have used a double-pole relay and
wired both sides in parallel for redundancy, instead of
relying on the single-pole style like they did.

I’ve ordered double-pole relays of two types to test out.
The cheaper ($2) one is only good for 100,000 electrical
operations, but that’s assuming a much higher current so it
should do many more operations at this low current.
Mechanically it’s good for 1 million operations. The more
expensive one ($8) is rated at a billion operations. Yeah,
that should be enough, no matter how much this thing flails
around in operation…–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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12

I very much doubt any patent is involved, Duncan…

After all the sole purpose of the amplifier is to make the servo turn
hither and thither based on sensor inputs. Not much patentable in that
as far as I can see. Much more Jaguar work likely went into working out
the interrelated positions of the cams to make the mechanical parts work
to best effect.

Thus I expect you to also clarify the interaction between the servo and
the amplifier, giving a run-down on the relevant in-car symptoms of the
amp failure - including sensor input faults. And I don’t envy your job!
But I’m cerainly looking forward to the results…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

frobozz wrote:>It would be a patent, which was probably good for 17 years

back when this was designed, though it has changed more
recently and in any event I don’t know UK patent law. But I
am well within my rights to figure out why the (&(^^%
thing is broken, and fix it, with any means at my disposal
with one of the parts in my hand. If you build it, and I
own one, I can take it apart. And especially as concerns
repair procedures, I’m free to share my knowledge with the
world.

If I simply copied their design to produce new ones, and it
were still covered by patent, then I’ve stepped in it. Not
seeing any patent numbers on the amp, and given how
non-novel and non-patentable a design it is, my guess is
they simply relied on its obscurity and the epoxy to protect
their design and their profit margins.

I’ve drawn a first-pass schematic with a couple of question
marks, which I hope the next epoxy-dissolving will answer.
I’ve ordered all the parts to build one from scratch, which
will help me verify (or correct) my schematic. Being able
to watch and measure the amp internals while the system is
operational will also greatly help my mission to understand
every last piece of how the system works.

I’ve studied the faces of the relay contacts on the one I
took apart. One of them does have a pretty obvious divot
which could cause it to be intermittent, but it’s not quite
a smoking gun. I have to say I’m impressed with the design
of the relays: cross-wiping contacts, for instance. But
they definitely should have used a double-pole relay and
wired both sides in parallel for redundancy, instead of
relying on the single-pole style like they did.

I’ve ordered double-pole relays of two types to test out.
The cheaper ($2) one is only good for 100,000 electrical
operations, but that’s assuming a much higher current so it
should do many more operations at this low current.
Mechanically it’s good for 1 million operations. The more
expensive one ($8) is rated at a billion operations. Yeah,
that should be enough, no matter how much this thing flails
around in operation…

===================================================
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13

In reply to a message from Frank Andersen sent Sat 25 Jun 2005:

Man, (slaps self upside head) I don’t know why I didn’t
think of patents earlier! Delanair got US Patent 3948312 in
1974 for their complete climate control system (not
specifically the servo amp, which is just described as an
existing known black box). Their patentable idea had to do
with the blending of the air temps in various ways, the
manipulation of fan speeds, the varying the reponse based on
outside temps, and using a cammed shaft to pull it all off.
I don’t know enough about the Delanair Mk I (assuming such
a thing existed) to know if this patent is describing that
or the MK II but it sure looks a lot like the MK II to me.

You can look up the patent yourself at uspto.gov If you
want the images you need to have a better than average TIFF
viewing plugin for your browser, which hardly anyone does,
so I have converted all the pages into a PDF for easier viewing:

http://www.backglass.org/duncan/jag/cc/delanair_3948312.pdf--
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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14

OK, Duncan…have you gotten a donor a/c amp? If not, let me know…I will
offer up my original, bad amp for your experimentations since I am totally
interested in your adventure and progress. I don’t know when I will get to
pulling it, but let me know and it’s yours, if needed.

Mike Vaughn
Oviedo, FL
87 xj6 SIII===================================================
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15

In reply to a message from Mike Vaughn sent Sat 25 Jun 2005:

OK, Duncan…have you gotten a donor a/c amp? If not,
let me know…I will offer up my original, bad amp for
your experimentations since I am totally interested in
your adventure and progress. I don’t know when I will
get to pulling it, but let me know and it’s yours, if
needed.

Thanks for the offer, but I have another one coming from a
generous lister. That should be the last dead one I need.
I just want to absolutely verify some of the component
values by waiting longer and damaging it less when
de-epoxifying it. In the meantime I’ve made educated
guesses at the mystery component values and will be building
up an amp on perfboard as soon as the parts get here
(Wednesday, according to the UPS website.) I’ll keep
everyone posted on the progress.–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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16

Great, thanks Duncan!–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

frobozz wrote:

In reply to a message from Frank Andersen sent Sat 25 Jun 2005:

Man, (slaps self upside head) I don’t know why I didn’t
think of patents earlier! Delanair got US Patent 3948312 in
1974 for their complete climate control system (not
specifically the servo amp, which is just described as an
existing known black box). Their patentable idea had to do
with the blending of the air temps in various ways, the
manipulation of fan speeds, the varying the reponse based on
outside temps, and using a cammed shaft to pull it all off.
I don’t know enough about the Delanair Mk I (assuming such
a thing existed) to know if this patent is describing that
or the MK II but it sure looks a lot like the MK II to me.

You can look up the patent yourself at uspto.gov If you
want the images you need to have a better than average TIFF
viewing plugin for your browser, which hardly anyone does,
so I have converted all the pages into a PDF for easier viewing:

http://www.backglass.org/duncan/jag/cc/delanair_3948312.pdf

–
Duncan Brown 1985 SIII XJ6

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17

In reply to a message from Cannara sent Sat 25 Jun 2005:

This may be of interest http://www.far-
out.demon.co.uk/cardiy/delanair.htm--
Keith Turner '79 XJ6 based Aristocat, , '81 3.4 XJ6
Swansea, United Kingdom
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18

In reply to a message from Keith Turner sent Mon 27 Jun 2005:

This may be of interest
http://www.far-out.demon.co.uk/cardiy/delanair.htm

Huh - looks like the Mark III was mostly the same system
concept, but with a lot more solid state circuitry driving
it. And two separate servo motors?–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
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19

In reply to a message from frobozz sent Tue 28 Jun 2005:

Yeah, just about right after I posted, I realized I meant to say
patent. I was waiting to hear that I was wrong.

Heh.–
1985 XJ6 Vanden Plas
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20

In reply to a message from 1985vdp sent Tue 28 Jun 2005:

Does anyone know what ever happened to Duncan Brown and his
efforts at understanding the Delanair system and his quest
at engineering a cost effective replacement AC amp?

John–
John
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