DRO Dead

[Smouser]

I purchased a Chinese LCD DRO from eBay in early 2023 for my milling machine and it worked great until now.

A few days ago when I turned the mill on, the DRO was dead. No beep, nothing on the screen.

It is a ToAuto DRO-3VA DRO.

To open it up, I only needed to remove 4 Philips screws.

The DRO side PCB.

The power supply PCB

I could not see anything obviously wrong.

The first test was to see if 220V reaches the power supply PCB once it has gone through the switch.
All good, 220V was reaching the power supply PCB.

The next step was to check the DC output of the power supply, it should be 5V.
This is where I was getting weird readings, the readings cycled through 0V, 2V, 5V, 0V, 3V, 6V, 0V, 4V etc.

I was hoping that the actual DRO part was still working and connected an external power supply (5V, 0.5A) to the DRO PCB.

Success!

Now I need to try and find a new 5V power supply PCB.
Unless somebody can tell me what component needs replacing on the power supply which will cause the output voltage to cycle.

*edit* 5V Chinese power supplies are so cheap, that it is probably not even worth trying to repair the existing one.
Amazon prime example

However, it might be worth buying a power supply from a 'reputable' company to avoid the same issue in the future.

 

[pawsnizzy]

eBay/Amazon - any 5v switch mode supply that will fit and has a suitable current output. You would probably get away with gutting a suitable rated USB charger wart (and leave the original I/P socket where it is)

 

[Smouser]

eBay/Amazon - any 5v switch mode supply that will fit and has a suitable current output. You would probably get away with gutting a suitable rated USB charger wart (and leave the original I/P socket where it is)

Very good idea.

I probably have a few USB chargers stashed away in a drawer......

 

[Guineafowl]

Sounds like the PSU is chirping - starting up, sensing a problem then shutting down. Often a short on the secondary - output diode main candidate.

What’s the voltage like when the DRO bit is unplugged?

 

[Smouser]

Sounds like the PSU is chirping - starting up, sensing a problem then shutting down. Often a short on the secondary - output diode main candidate.

What’s the voltage like when the DRO bit is unplugged?

That was with the DRO bit unplugged.
I didn't measure it with the DRO PCB plugged in.

While it would be interesting to see what failed, it is just not worth the time or effort to fix it
Another piece in the scrap. Throwaway society.

Why does the existing power supply have so many more components compared to a replacement on Amazon?

VS

 

[Red'n'Black]

However, it might be worth buying a power supply from a 'reputable' company to avoid the same issue in the future.

This, in spades.

Personally I wouldn't connect any no-name cheapy product to the mains. Low-voltage stuff that you can power with your own USB charger or whatever, sure, no problem.

A lot of the no-name stuff is probably fine. But I've taken apart far too many that were dangerous bodges and the safety certs were obviously faked. Having an identifiable manufacturer that people can sue if the product electrocutes them or burns down their house, keeps them honest.

 

[Guineafowl]

Why does the existing power supply have so many more components compared to a replacement on Amazon?

Quality - EMI filtering, fusing, electrical safety gaps, output stability… I wouldn’t risk the DRO (or yourself) with a crappy one. Note the original has an earth, but the Amazon ones don’t. There will be a reason for this.

Just have a test of the output diode D7 - meter in diode check mode. Probably a schottky so expect 0.2V drop one way, open circuit the other.

 

[Smouser]

Quality - EMI filtering, fusing, electrical safety gaps, output stability… I wouldn’t risk the DRO (or yourself) with a crappy one. Note the original has an earth, but the Amazon ones don’t. There will be a reason for this.

Just have a test of the output diode D7 - meter in diode check mode. Probably a schottky so expect 0.2V drop one way, open circuit the other.

I think you are correct about diode D7.
I have not tested it, but now that I have the board out, it looks like it is damaged.....

Great shout @Guineafowl

 

[Smouser]

Thank you to @pawsnizzy for his USB charger recommendation.

I found just the thing in a drawer!

The plug put up a strong fight but eventually, I got it open.

I also had a short surplus USB cable which could be used.

Out to the garage to get the new power supply installed.

I soldered the wires together, used heat-shrink over the joints and then used a glue gun to glue the new power supply in place.

 

[Barking Mat]

Nice work.

Looks like the diode was chewed by something.

I'm sure it wasn't.

 

[Smouser]

Nice work.

Looks like the diode was chewed by something.

I'm sure it wasn't.

Thank you.

Yes. It looks like physical damage.

I guess it got physically damaged when it 'popped' or it was a dodgy one from the factory.

It worked for just over a year though. That being said, I would estimate that the DRO has not been turned on for more than 200 hours total (that is including me leaving it on overnight by accident a couple of times).