[time-nuts] Ebay Huawei Ublox M8T Modules Warning

[Didier Juges]

For reference, my original Thunderbolt Monitor had a 3.3V CPU (3.6V max)
and a "voltage regulator" from the 5V consisting of two silicon diodes in
series. That worked very well. The original kit still runs, 10 years later.
When Fluke.l (of eBay fame) copied the design, he saved the cost of the two
diodes (under $0.05 in his local money) by replacing them with two 0 Ohm
resistors (under $0.01).  He sold a truck load of them. I know because he
gave my email for customer service (!!!), even though I was not aware that
he was selling those and was certainly not making even $0.01 off the deal.

Well, they worked for a while, at least 20 minutes and a few ran for
several hours.

So, in the case of the M8T GPS module, you might get lucky and not fry the
kit instantly, but as always YMMV.

Didier KO4BB

NB: a few years later, another eBay seller also copied my design but he did
put the diodes, so I did not hear about it for a long while, that is until
someone asked me for the firmware upgrade to take care of the GPS Week
rollover. When I asked where he got the kit, he sent me a link. The vendor
had listed my website for manual and support...

On Sat, Jan 9, 2021 at 5:23 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> The “normal chips” that should be inside the module all have something
> like a 3.6V max
> supply rating on them. I would guess that 5V will melt a goodly number of
> them.
>
> Bob
>
> > On Jan 9, 2021, at 5:38 PM, Nigel gm8pzr via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >
> > During the December conversation re LEA-M8T modules on scraps of PCB
> from Ebay I commented that the same seller also had complete circuit boards
> available, and suggested this might be a worthwhile alternative.
> >
> > I've dealt with this seller before, always been very happy with the
> results, and agreed a price on three such modules which arrived just before
> Christmas, for reference this particular Ebay ID was 333619130232, and
> finally found time to start checking them today.
> > The modules themselves look very nice, but one of the auction photos is
> a connection diagram that shows Pin 2 of the 8 pin interface connector as
> "Power In 5V DC", and on this PCB that pin connects directly to the pin 6
> Vcc input on the Ublox module, which has an absolute maximum rating of 3.6V
> .......whoops!
> > This is not intended in any way to be a criticism of this seller, who I
> am more than happy to recommend, nor indeed of any other seller, but this
> is a generic diagram that several sellers are using for various
> Huawei/Ublox modules, some of which may have an onboard 3.3V regulator, as
> presumably did the one this diagram originally referenced, but some of
> which may not.
> >
> > So that's the warning folks, don't trust that diagram without checking!
> > Now a question, supposing someone did follow that diagram and applied 5
> Volts to Vcc on the M8T, what is the risk of damage and would it be
> immediately obvious?
> > And no, I didn't:-), but when modules are described as tested concern
> might arise as to the test conditions.
> > Nigel GM8PZR
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