Electronics > Repair

Newall Digital Readout troubleshooting

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R Lamparter:
This is a DP7 digital readout for a milling machine and the reader shows no display.  The only indication of power is the green LED for in/mm glows when turned on.  The manual says that this is an indication that "the voltage of the power source is too low".  There is a corroded 3.6V battery on the mainboard, but the net says that this battery only affects memory, and the corrosion hasn't damaged any nearby traces.  The battery is not likely the cause.  I scanned the power supply and I don't spot any bulged capacitors or burned components.  It has a 6 wire output cable, but I have no idea how to even test the outputs from that.  The wire labeled #1 has a black stripe, so I assume that's the ground.  I have an email in to Newall, but from scanning around on the web, they have a reputation of not releasing their schematics and requesting that the devices be sent for service.  I am an electronic novice.  Where / how do I start troubleshooting this switch mode power supply?  I have available a multimeter and one of the multifunction transistor, diode, ESR, etc. testers.  I have an HP 54601 oscilloscope, but don't really know how to use it yet (it was too cheap not to buy it).

Seekonk:
I just might have a couple new 3 axis ones.  I was going to import them from China and then Newell found out.  I'm always suspicious of those connectors.  I just worked on another readout and I had to solder the wires directly to the pins to get it to work. I had done the same thing to the other end of the cable just about five years ago.  I'd look for familiar voltages to see if they were there.  The 5V can get low if the output caps dry out.

R Lamparter:
Is it safe to put one probe of the multimeter on pin #1 (wire with the black stripe) and touch each of the other pins in sequence to see what the voltages are, or will that cause problems?

R Lamparter:
I checked the voltages  on the output pins.  With Pin 1 as the ground, I got the following values
Pin 2: -7.5v
Pin 3: -7.5v
Pin 4: -12.7v
Pin 5: -12.7v
Pin 5: -24.8v

I assume the next step is to desolder all of the electrolytic capacitors on the secondary side and test them, right?

Seekonk:
Pins 4 & 5 are common.  I'd start looking elsewhere.

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