[chbot] Multi colour lamp

[Mark Atherton]

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.

-Mark



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: 
> https://photos.app.goo.gl/fTtxcjhyaSPKFSt97
> 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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