On Thu, 2 Dec 2021 18:47:47 -0000 (UTC), bob prohaska
<
bp@www.zefox.net> wrote:
Jeff Liebermann <jeffl@cruzio.com> wrote:
On Wed, 1 Dec 2021 17:44:36 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:
After some years the pump became erratic in action and I replaced
the original diode with a 1n5407G, which worked well for many years.
Was the original diode a 1N5407 or something else?
This was back in the late 1990's and I don't remember.
I thought that I was the only one who tears something apart, let's it
age for 10 to 20 years, and only then tries to fix it.
It's
possible the diode was physically damaged to the point the
markings weren't readable. I do remember the pump coil potting
cracked and I replaced the pump at some point, though maybe
not at the same time.
Sigh. That's not very helpful. For all I know, the original "diode"
could have been a thermal fuse that somewhat resembles a diode.
Do you have the manufacturer and model number so I can do some
Googling for info? Taking a shot in the dark, I found this hint
suggesting that the diode might be a zener. <
https://www.fixya.com/support/t782403-breville_800e5xl_didoe>
Here's the service manual and schematic: <
https://siber-sonic.com/appliance/breville800sm.html>
Hmmm... See schematic on printed Page 19. Looks like the motor has a
1N4007 diode across the winding and an SCR for power switching. That
suggests that it's running on DC, not AC.
What got me suspecting the diode was a strong but not perfect
correlation between how long the espresso machine had been heating
and the onset of low pump output. First cup in the morning was
fast, subsequent (~20 min later) much slower. Next morning the
cycle repeated.
Yep. Something is getting hot. The cracked epoxy(?) potting compound
suggests an overheated pump coil. The zener for the Breville depresso
machine drops the peak line voltage 24V. An ordinary diode in place
of the zener drops it only 0.6V. Kinda sounds like it might be a hot
pump coil. Got a gun type Infrared thermometer? Measure how hot the
pump coil gets.
Occasionally the first cup from a cold start was slow also, but
that was relatively infrequent, maybe once a week.
Overheating the pump coil might make the pump parts move around. My
guess(tm) is you'll find some correlation between the number of
minutes (or hours) you ran the expresso machine the previous night.
The longer it ran, the greater the likely hood that something in the
pump became mis-aligned or moved out of place. Just a guess(tm).
Right now the machine is set up with three parallel 1n4007's of
unknown quality plus two connected as crowbars. The crowbars do
seem to make a difference in slowing down the water flow, which
is undesirable. That they do make some difference is slightly
encouraging, as crowbarring the coil would slow field decay.
And, so far the pump behavior has remained consistent.
I probably should pull the pump apart and look inside, but I really
can't imagine a mechanical explanation on something so simple.
After 26 years, I would expect some corrosion and lime deposits.
Thanks for reading and replying!
Y'er welcome. Good luck.
bob prohaska
--
Jeff Liebermann
jeffl@cruzio.com
PO Box 272
http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
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