[chbot] Multi colour lamp
markaren1 at xtra.co.nz
Sun Feb 7 04:57:38 GMT 2021
Odd that the CPU stopped in a potentially moist environment. Could there
be a weak pull-up on the reset line which is being pulled down by
moisture ? How difficult to add an external 1k pull up to /MCLR (between
pin 1 and pin 4 ?).
Doubt if it has a crystal, but if so they are high-impedance networks
which are sometimes conformally coated (even in dry applications) to
keep moisture from buggering things.
I would also be tempted to clean the whole assembly, re-solder
everything, then conformally coat again; there isn't very much of it.
Anyway, just a thought or two.
On 7/02/2021 5:19 PM, Richard Jones wrote:
> The Multi colour lamp module in our spa stopped working, it looks like
> quite an interesting design. Link to photos:
> I thought I would share the issue, just in case anyone has some good
> advice for fixing, otherwise I can try to buy a new one as a last
> resort. The module looks like a drop in replacement for a 12V 6W halogen
> bulb, and it displays different sequences of colours which may gently
> fade from one colour to another. Different sequences are selected by
> turning the lamp supply on and off. A casual examination reveals an
> input bridge rectifier and reservoir capacitor. The 8 leg device is a
> PIC 12F629 which has 5V applied between pins 1 and 8. There are 3 driver
> transistors (bipolar or FET?) which drive 3 of 9 LEDs red, green or
> blue. When I connect 5V via a 1k resistor to each driver transistor 3
> LEDs of one colour will light. There is no apparent water damage. So it
> looks as though the PIC is not running. The assembly has a thin
> conformal coating that is easily pierced for measurements.
> There is a 5 pin connector that looks as though it takes the standard
> PIC programming signals. But I have never got around to designing and
> programming with PICs. The construction is a mix of through hole and
> surface mount devices and looks easy enough to rework. This PIC needs a
> 12V flash programmer, and is generally programmed in assembly language.
> So it looks to me as though the learn in and tools required for
> replacing this ~$2 SMD are just not worth the time. Shame.
> Thoughts anyone?
> Richard Jones
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