[xj] AB14 Amplifier Zener Diode

Hi all,
After all sorts of amplifier trouble recently had me
trawling the archives of this site, I couldn’t find any
reference to the actual specs of the Zener diode in
discussions.

Going through my stash of dead amplifiers, I managed to find
one with the diode complete with part number on it.

It is a Lucas part #83628A. When punched into google, the
only reference is an equivalent asian-made LD3520 diode. It
is an 16V, 35A avalanche diode which sounds plausible for
protecting the module. Same 10mm press-fit package as the
original Lucas part.

Unfortunately, I can’t find them for sale anywhere, so is
there anyone out there who could recommend an equivalent?

Many thanks,
Dylan of Melbourne.–
XJ-Valdez
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Hi all,
After all sorts of amplifier trouble recently had me
trawling the archives of this site, I couldn’t find any
reference to the actual specs of the Zener diode in
discussions.

Going through my stash of dead amplifiers, I managed to find
one with the diode complete with part number on it.

It is a Lucas part #83628A. When punched into google, the
only reference is an equivalent asian-made LD3520 diode. It
is an 16V, 35A avalanche diode which sounds plausible for
protecting the module. Same 10mm press-fit package as the
original Lucas part.

We had a lot of discussions on the list about this, Dylan - but not entirely
conclusive as nobody could locate the specs…

…particularly at the voltage and current rating, as some implied a very
much higher voltage rating would be called for. To me, your ‘find’ sounds
right - and if so; an alternative is to find a diode with a comparable
rating. Which is very unlikely to be a straight fit, but selected with some
attention to the space available, may serve the purpose…

To me it seems like the AB14 connections implies that the diode is meant to
pass excessive voltage harmlessly to ground - ie, it is normally in
‘blocking’ mode. But there is no actual description of the overall AB14
internal functions. I talked with an american ‘hot rodder’ and he mentioned
that they commonly just disconnected the diode when it was suspected of
causing ignition problems…:slight_smile:

Incidentally, my problem was an engine that quit as soon as the idle dropped
below some 500 rpms - but otherwise worked perfectly. I went through a a
veeery thorough engine check-up, with no anomalies found. Then pursued the
AB14 for faults, including trying several amp modules on the same AB14, with
no change - finally ‘solving’ the problem with a replacement AB14 compete.

Never actually found the specific fault as I could not locate a replacement
diode either - to test the theory. So I still have the suspected AB14 - and
would indeed appreciate your solution…:slight_smile:

Happy New Year…

Frank
xj6 85 Sov Europe (UK/NZ)

Unfortunately, I can’t find them for sale anywhere, so is
there anyone out there who could recommend an equivalent?-----Original Message-----
From: XJ-Valdez
Sent: Saturday, January 02, 2016 4:35 PM
To: xj@jag-lovers.org
Subject: [xj] AB14 Amplifier Zener Diode

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In reply to a message from Frank sent Fri 1 Jan 2016:

Happy new year to all!!!

when I was fighting the ‘‘Starter Wars’’,
I became aware that my conversion kit
called for diodes on two of the legs of the
starter relay. I never got an answer that
I could understand as to why they were there.

Seemingly used in blocking mode.

I went shopping and found that ‘‘Radio Shack’’
had a nice supply. cheap, too!!

Soldered in and the relay kicks just fine.

Carl–
The original message included these comments:

Never actually found the specific fault as I could not locate a replacement
diode either - to test the theory. So I still have the suspected AB14 - and
would indeed appreciate your solution…:slight_smile:


Carl Hutchins 1983 Jaguar XJ6 with LT1 and 1994 Jeep Grand
Walnut Creek, California, United States
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In reply to a message from XJ-Valdez sent Fri 1 Jan 2016:

The diode is for protection of the AB14 output transistor
and is not absolutely necessary. Ringing of the coil primary
circuit when its current flow is broken (either by points
or by the AB14) is typically around 300V, which the output
transistor can handle. If the coil fires into an open
circuit (one or more plugs disconnected, for example) the
ringing voltage can be higher. The zener voltage is in the
range of 300-350V. Here’s one of the recent threads on the
AB14; the zener is discussed starting about half–way through.

[Jag-lovers Forums - Jag-lovers]–
The original message included these comments:

After all sorts of amplifier trouble recently had me
trawling the archives of this site, I couldn’t find any
reference to the actual specs of the Zener diode in
discussions.


Bob Wilkinson, 73 XJ6
Saint Louis, MO, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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In reply to a message from Frank sent Fri 1 Jan 2016:

Interesting that you mention this, Frank. I went through all
sorts of problems which turned out to be the coil, after a
new AB14 did not solve the problem. When I instelled a new
coil , problem persisted. When I took out the new AB14 and
replaced it with the old one, problem went away. I sent the
new AB14 to the supplier who shipped it back to England for
‘testing’ and said it was fine, including a ‘lab report.’ As
far as I’m concerned it’s complete nonsens. If the old AB14
now works & the new ‘tested’ one does not, I’d say the new
one is a pile of rubbish & the supplier refused to replace
it or refund the wasted money spent. BTW…these days car
is running great, still with the’old’ AB14…go figure…–
The original message included these comments:

Incidentally, my problem was an engine that quit as soon as the idle dropped
below some 500 rpms - but otherwise worked perfectly. I went through a a
veeery thorough engine check-up, with no anomalies found. Then pursued the
AB14 for faults, including trying several amp modules on the same AB14, with
no change - finally ‘solving’ the problem with a replacement AB14 compete.


Mel R.
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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In reply to a message from Mel R. sent Sat 16 Jan 2016:

Maybe you didn’t earth the new one as well because the
coated finish was better and hindered the connection?–
The original message included these comments:

new AB14 to the supplier who shipped it back to England for
‘testing’ and said it was fine, including a ‘lab report.’ As
far as I’m concerned it’s complete nonsens. If the old AB14
now works & the new ‘tested’ one does not, I’d say the new
one is a pile of rubbish & the supplier refused to replace


66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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