Maplin Clock flicker

[ChrisPDuck]

OK, i've had this clock a while, ( it has a LED matrix display) and it has a feature that between the hours of 9pm and 6am it dims the display.

Instead of just dimming the display, it has started to cause it to flicker ( noticeably)

i'm guessing its due to the PWM being messed up somehow, but i can't figure out how.

The Circuit has 3 IC's, two being "Octal D-type transparent latch" according to data sheets, and the third i can't identify.

I've taken some photos of the board, can provide more detailed shots if you think it would be useful

Clock board - a set on Flickr

I've already tried replacing the caps, but that didn't seem to help

If you have any ideas about how this can be fixed, that would be really usefull

If not, i want to try and "rebuild" the clock, so i would need to find a way of creating a circuit that could use the existing LED front, so i would need to control a 22 pin header, not sure how easy that would be.


Thanks in advance

Quack!

 

[blueroomelectronics]

Can't help without the schematic.

 

[Hero999]

Is that a kit?

Sorry but it looks like cheap Chinese crap and being from Maplin, you probably paid more than you aught to have.

The other unidentified IC might be a microcontroller which you'll need the software for.

EDIT:
Yes, you're right, it does use PWM, when dimmed the duty cycle is reduced but the frequency should be so high. you can't see the flicker but unfortunately you can.

 

[ChrisPDuck]

It probably is cheap chinese crap tbh, but with staff discount, and it being on clearance, i didn't pay more than £5 for it

I'll see if i can draw up the schematic, might be a challenge though! i was hoping someone would say something like, "with PWM its always component X that fails" oh well lol

 

[olly_k]

What is that horrible bridge looking bit of soldering below the upper ic? Also some other dodgy looking joints. If you describe the nature of the flicker it might give people a better idea?

 

[ChrisPDuck]

What is that horrible bridge looking bit of soldering below the upper ic? Also some other dodgy looking joints. If you describe the nature of the flicker it might give people a better idea?

That bridge is actually a reflection off some left over flux on the board,

The flicker its self is a very regular flicker that looks like the PWM has been offset somehow, I can replicate it by changing the time to some point where the clock is supposed to be dimmed.

Recreating the circuit in a design program seems like it'll take a long time ( due to the poor design work in the first place) and i'm not sure how much use it will actually be in resolving the problem.

I think the best option from here will be plan B) using the LED display, and completely remaking the electronics inside.

The connections to the LED display is a 22 pin header, which i have managed to reverse engineer the pinout.

Now my new question is what the easiest way to interface a 22 pin display, with a microprocessor? most of the chips i look at are only limited to 12 outputs.

by remaking it myself i can add some features < insert evil laugh>

Quack!

 

[Hero999]

I think remaking it would be good fun but it will probably cost you more than the original price of the clock.