• Please review our updated Terms and Rules here

Another Project, help me diagnose.....

T

tblake05

Experienced Member
Joined
Aug 21, 2017
Messages
295
Location
Minnesota
This is a telemeter from a vending machine. It is what communicated over cellular for credit card payment. This is now the third one I've had quit working the exact same way. Just dies. No indication, nothing. Blank screen as if it lost power. All 3 had the same failure. And as a matter of fact all three were just shortly out of warranty. The first two failed and I was able to buy a remanufactured exchange units. This time I contacted them and they no longer offer remanufactured units. Some chip shortage or something blah blah blah. They wont even take mine to rebuild. Only option is to buy the newest version which is not cheap. (of course there are plenty of chips for them). Through the grapevine I found the parent company who manufactures these units. I have a call in with them to see if they can rebuild it or even just provide a schematic. So far have not heard back. And I'm not hopeful.

Anyway, can any trained professionals look at the pics and maybe point me towards any common failure points?

I poked around briefly with my ohmmeter. 34V DC enters, goes through F2 which I assume is a SMD fuse? Then goes to D24 (left side) I have not connected it to my bench supply just yet to see if I'm getting voltage out of D24. I cannot seem to find the correct datasheet for D24. markings on chip show 909k, psc, D1156s (I think). Question though. The fuse F2(LF050?), Should that show 3.2ohm across it? Do SMD fuses go bad? Tonight if I have a chance I'll hook it up to my bench and try and trace the voltage. As to me it seems like an open in the voltage circuit.

Thanks for any help!

~Tim

IMG_5754.jpgIMG_5755.jpg
 
Are you positive 34v DC goes in? D24 is a bridge rectifier.
It's easy to identify from the markings that on one side indicate an AC source and the output has plus/minus polarity.

DF08S.jpg
 
odd. I see that now. I'll double check tonight before I connect it up. It connects to the machine through standard MDB. I could have swore I read that its 34V dc supplied through it.
 
Ok so I set up a vending control board and measured the voltage that is being supplied over MDB to the telemeter. 24v DC

So. Is F2 a fuse for sure? What I read is that it could be sort of a self resetting fuse (circuit breaker).

Here’s what I got....

0 volts out of rectifier D24. 0 volts on the input side either.

There is 24v to one side of the fuse but not the other.

The side which has 0 volts is directly connected to the input side of regulator D24.

Fuse blown? But it’s apparently self resetting.

Jumpering across the fuse briefly puts my power supply in over current and protect.

Shorted regulator? Causing the fuse to go open and not self reset?

Should I replace the rectifier and fuse? Can anyone find a data sheet for D24? And would there be any better options available? I feel these things are made as cheaply as possible.

Plus if the regulator is bad... MDB can supply anywhere from 24-34v which I assume it was running over voltage and over heated since it’s only rated at 24v

Thoughts? Thanks guys!
 
You must log in or register to reply here.
Back
Top