I bought a BP Knee mill to replace the one that burned when m sop bred dow. It as Mitutoya DRO (Digital Read Out). It is damaged and the power supply was missing. I did some reasearch and found it uses a 120V/5V .5A regulated power supply. I've taken a USB charger and wired it to the display panel with the correct polarity to get to power up. The display is blank. I've pulled the display apart to look for damaged sections and really do not see any obvious damage to the printed circuit or components. Where do I start to troubleshoot this thing? I've have a limited knowledge of electronics, I understand the basics. I'm hoping there's a way to go through this without having to de-solder each component and test individually.

 

Unfortunately you may not get any help from Mitutoyo as the circuit is proprietary indicated also by the firmware/eprom.
Your best bet maybe to source a spare unit off ebay etc.
If the display does not light at all you could do some trouble shooting in this area taking voltage readings on the display pins?
Max.

 

Unfortunately you may not get any help from Mitutoyo as the circuit is proprietary indicated also by the firmware/eprom.
Your best bet maybe to source a spare unit off ebay etc.
If the display does not light at all you could do some trouble shooting in this area taking voltage readings on the display pins?
Max.

I'm waiting to hear back from Mitutoyo now. I'm also waiting for the Fluke 87V to arrive to do some basic testing. Is there a "normal" layout for a display as far as pin location? I'm wondering if I build a low voltage power supply that would not burn up the display, if I can pin it out the see if the display is good. I'm guessing a digital display is pretty much the same on most boards.

 

Stupid questions, but are you sure those switches are in the right positions, and that the batteries are good? How do you know the PCB in the pictures has any problems? In other words, maybe the problem is elsewhere.

All those resistors can be probed on-board. Most will read the nominal value, none should be open, and I wouldn't worry about values below nominal unless it's nearly a short.

Same for the diodes - your multimeter's diode test function should show ~650mV in the forward direction and nothing in the opposite polarity. None of the capacitors should show a short.

 

Stupid questions, but are you sure those switches are in the right positions, and that the batteries are good? How do you know the PCB in the pictures has any problems? In other words, maybe the problem is elsewhere.

All those resistors can be probed on-board. Most will read the nominal value, none should be open, and I wouldn't worry about values below nominal unless it's nearly a short.

Same for the diodes - your multimeter's diode test function should show ~650mV in the forward direction and nothing in the opposite polarity. None of the capacitors should show a short.

I'm guessing it's the PCB or something that sends the signals to the display from that PCB. I can't imagine the entire display circuit going out at one time. I guess I need to figure out how the display works and work backwards from there. If I can figure out how to power the display, then I might be able to trace out where it's NOT getting the proper signals from. I'm wondering if there's some type of driver chip that's bad. I did find another Power Supply with the mill, it was a 120V/6.5V supply. I'm wondering if they tried to use this one and "cooked" a driver chip circuit.
The switches are for making the DRO read from right to left or left to left direction of travel. The batteries are for the memory, they will allow it to save the last position the DRO was in if you cut the 120V power off and then restart. They are not critical from what I've found out.

 

Fair enough, but make sure those batteries are not shorted.

 

Fair enough, but make sure those batteries are not shorted.

Good point. I'll pick up some new ones, all I have here right now are Ni-Cads, and it says NOT to use them.

 

I think the concern is the self discharge rate of NiCds. They wouldn't be as reliable for this application. Just when you need them, they'd have run down. They also have a slightly lower voltage.

 

Does anyone have a link/tutorial on to how to power up or check the display itself? I'm always up for learning something new. Usually when I learn something new like this, a "light" comes on and I find a way to utilize my new found knowledge.