eBay Chinese Electronic Clock Kit

[Rulycat]

Ok so I bought one of these kits from eBay, which eventually arrived:

https://www.ebay.co.uk/itm/DIY-Green...72.m2749.l2648

Now I soldered everything how I thought was a-ok with my knockoff of a Hakko 936D iron.

However when powering nothing happened at all. Even using a 3V coin cell nothing also happened.

I tried rotating the switch (see centre right) and the cap in the images blew its guts out.

The polarity seems ok as I think that the solid line on the PSU (little 9V 100ma switcher) is the negative which would go to ground?

How do I know which way round the switch goes?

Am I a dummy?

[petehall347]

Re: eBay Chinese Electronic Clock Kit

did you test polarity of power supply ?

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

did you test polarity of power supply ?

Ok - another stupid question - the black lead is going V(Omega cymbol)mA and the red is going to COM - let me guess... this is the wrong way around??

Btw I have no formal background in electronics!!

[vinceroger69]

Re: eBay Chinese Electronic Clock Kit

if you have a multimeter test the power supply voltage just incase its been wired up wrong inside the adapter part. Can you post a picture of the back of the clock pcb so we can look at the traces etc.

[petehall347]

Re: eBay Chinese Electronic Clock Kit

cap is correct way round and is rated at 25v .
the switch is easy to work out with your multi-meter .
mostly capacitors blow up from reverse voltage or too high voltage .

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

This is how my multimeter is wired... the black connector (negative) I am putting against the wire with the white strip down it on the PSU... it reads 8.88V which seems about right.

[petehall347]

Re: eBay Chinese Electronic Clock Kit

Ok - another stupid question - the black lead is going V(Omega cymbol)mA and the red is going to COM - let me guess... this is the wrong way around??

Btw I have no formal background in electronics!!

if this is your multi-meter black goes to com . red to VΩ
if wiring is backwards meter will read in negative .. example -9

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

if this is your multi-meter black goes to com . red to VΩ
if wiring is backwards meter will read in negative .. example -9

Looks like I am reading the PSU backwards then... which means white line is +VE!!! That will be why cap has blown!!

D'oh!!!

[petehall347]

Re: eBay Chinese Electronic Clock Kit

the transistor next to it might be blown too plus other things .

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

For the cost of it I should just order another and chalk it up to stupidity.

[petehall347]

Re: eBay Chinese Electronic Clock Kit

try a new cap and see how it is then . best to get quality ones anyway .

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

Got some crap caps at my dads house so for the sake of £2 lets see if anything else is goosed and if not then I'll put proper caps on it.

[Harvey]

Re: eBay Chinese Electronic Clock Kit

the transistor next to it might be blown too plus other things .

Underneath the cap is a 5V 78L05 regulator. They generally withstand reverse voltage on them for a while. It might be worth trying the circuit without the exploded capacitor, it should work given 8V.


http://hipcatcoolcap.blogspot.com/20...879-clock.html

[stj]

Re: eBay Chinese Electronic Clock Kit

£3 - inc post.
still an amazing price for 3 displays, a microcontroller that costs more than that at RS probably, and a pcb!!

[petehall347]

Re: eBay Chinese Electronic Clock Kit

Underneath the cap is a 5V 78L05 regulator. They generally withstand reverse voltage on them for a while. It might be worth trying the circuit without the exploded capacitor, it should work given 8V.


http://hipcatcoolcap.blogspot.com/20...879-clock.html

i did wonder where the regulator was .i did guess it had something to do with it but never thought it was the actual regulator .
if dc is smooth i agree it shouldn't need the cap to test it . old 9v block battery might be a better choice as supply

[Harvey]

Re: eBay Chinese Electronic Clock Kit

Actually, having looked at the circuit diagram, the clock should work just off the 3V battery...

[petehall347]

Re: eBay Chinese Electronic Clock Kit

i assumed 3v was a backup supply . will check schematic now .

[petehall347]

Re: eBay Chinese Electronic Clock Kit

it is a soldering project .. am wondering if anyone has a working one ...

[Harvey]

Re: eBay Chinese Electronic Clock Kit

i assumed 3v was a backup supply . will check schematic now .

I assumed that too, but its to be connected through a diode to the vcc supply... unless the MCU has voltage sensing and goes into backup (no display) mode below a certain voltage.

I also notice there is a resistor bypassing this diode (I can't make out the numbers on the circuit diagram) that CHARGES the 3V battery when connected to a supply! So DON'T use a standard 3V coin cell in there or you'll have another exploding component!.



*EDIT * What goes on with R12 on your PCB? Trick of the light or has that only got one band?

[Harvey]

Re: eBay Chinese Electronic Clock Kit

gah, I do wish people would scan circuit diagrams in with enough clarity that its possible to read them. I'm wrong, it DOES need more than the 3V supply, there's 2 VCC rails, one for the MCU, one for the LEDs.