Author Topic: Newall Digital Readout troubleshooting  (Read 9252 times)

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Offline R Lamparter

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Newall Digital Readout troubleshooting
« on: May 13, 2017, 09:08:39 pm »
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).
 

Offline Seekonk

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Re: Newall Digital Readout troubleshooting
« Reply #1 on: May 13, 2017, 09:56:18 pm »
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.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #2 on: May 14, 2017, 12:33:18 am »
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?
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #3 on: May 14, 2017, 09:51:58 pm »
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?
 

Offline Seekonk

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Re: Newall Digital Readout troubleshooting
« Reply #4 on: May 15, 2017, 01:06:28 am »
Pins 4 & 5 are common.  I'd start looking elsewhere.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #5 on: May 15, 2017, 01:22:44 am »
Pins 4 & 5 are common.  I'd start looking elsewhere.

Pins 2&3 have a common trace also.  I wondered if they were supposed to be -12v or -5v rather than -7.5v.  If looking for something other than replacing the electrolytic capacitors, where else would you look or what other tests should I do?
 

Offline Seekonk

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Re: Newall Digital Readout troubleshooting
« Reply #6 on: May 16, 2017, 10:48:48 am »
+5 & +12.   I'd look to see if the power actually made it to the other board.
 

Offline lowimpedance

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Re: Newall Digital Readout troubleshooting
« Reply #7 on: May 16, 2017, 11:22:02 am »
 One other thing are those resistors in the photo top left burnt ?.(cant tell well enough from the pic.). Near the power connector.
I have repaired two Newall readouts at work and it was the supply in both cases, (both completely dead though). Maybe excessive ripple with yours as you seem to have some life.
 Any away you should be able to get similar replacement types at the usual places like RS , Element 14, etc. Dont trust Ebay ones.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #8 on: May 16, 2017, 09:29:55 pm »
+5 & +12.   I'd look to see if the power actually made it to the other board.

Hmmm.  I need a little more instruction on taking voltages - a real newbie question.  I had the black lead on Pin #1 (wire from this had a black stripe), assuming that was ground and where the black lead should go.  How do you know whether to place the black or red lead on the pin with the black stripe?

I'll check to see if the power is getting to the end of the connecting cable and report back.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #9 on: May 16, 2017, 10:17:31 pm »
+5 & +12.   I'd look to see if the power actually made it to the other board.

I checked.  Directly from the pins at the mainboard end. 
Pins 2&3 -6.8v
Pins 4&5 -12.1v
Pin 6 -25.5v

 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #10 on: May 16, 2017, 10:20:46 pm »
One other thing are those resistors in the photo top left burnt ?.(cant tell well enough from the pic.). Near the power connector.
I have repaired two Newall readouts at work and it was the supply in both cases, (both completely dead though). Maybe excessive ripple with yours as you seem to have some life.
 Any away you should be able to get similar replacement types at the usual places like RS , Element 14, etc. Dont trust Ebay ones.

They looked odd to me when I first took the head apart, but I glossed over them because they weren't black.  I looked more closely today and they must have heated to the point where their values are no longer readable.  I didn't have time to take that board out and unsolder them to check resistance.  Closeup of the mainboard resistors in question below.  Any idea what their values should be?
 

Offline lowimpedance

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Re: Newall Digital Readout troubleshooting
« Reply #11 on: May 16, 2017, 11:15:31 pm »
Can you still measure them with your multimeter, at a guess they are 10  \$\Omega\$ 1 watt. As for the supply post a pic of both top (connector end with the ribbon con. removed) and the solder side.
I cannot remember exactly but the +5 and 12 volt supplies sound right. What you are getting is either wrong ref 0v (reason for more pics of the supply), or the supply is stuffed.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #12 on: May 18, 2017, 01:00:45 am »
Can you still measure them with your multimeter, at a guess they are 10  \$\Omega\$ 1 watt. As for the supply post a pic of both top (connector end with the ribbon con. removed) and the solder side.
I cannot remember exactly but the +5 and 12 volt supplies sound right. What you are getting is either wrong ref 0v (reason for more pics of the supply), or the supply is stuffed.

I unsoldered the two burned looking resistors.  They each measured 33 ohms.  That value fits with what remains of the color bands - orange, orange, black, gold for both of them.  I wasn't sure if they were red, red, black, but the 33 ohms suggests they were orange rather than red.  Photos of the power board in a second post.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #13 on: May 18, 2017, 01:06:40 am »
As for the supply post a pic of both top (connector end with the ribbon con. removed) and the solder side.
I cannot remember exactly but the +5 and 12 volt supplies sound right. What you are getting is either wrong ref 0v (reason for more pics of the supply), or the supply is stuffed.

Here are top and bottom photos of the power board.  I have closups of the triacs/scr's if needed.  Pin #1 was my reference and I connected the black wire of the multimeter to that.
 

Offline lowimpedance

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Re: Newall Digital Readout troubleshooting
« Reply #14 on: May 18, 2017, 03:02:08 am »
Okay , Measure again (being real careful here as mains is nearby!) using pins 4 and 5 as GND or common and see what pin 1, 2 and 3, and 6 have on them.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline Seekonk

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Re: Newall Digital Readout troubleshooting
« Reply #15 on: May 18, 2017, 02:14:39 pm »
Using pins 4 and 5 as GND or common and post what voltages are on each side of those burnt 33 ohm resistors.  I wouldn't concentrate on the external power supply.  Your problem is on the main board.

You should have mentioned those resistors first off.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #16 on: May 18, 2017, 10:17:09 pm »
Thanks lowimpedance & Seekonk.

Pins 4/5 (black=common) to 2/3 = +5.1V
Pins 4/5 Comm to 6 = -12.1v
Pins 4/5 Comm to 1 = +25.0 V

I hadn't carefully examined the two resistors on the main board because I was looking for something blackened, my inexperience. I just noted they looked a little funny.  It wasn't until I looked at them again when lowimpedance pointed them out that I noticed that they were cooked.   I had also jumped to the conclusion that I must have a power supply problem based on what the manual said about insufficient voltage.

I looked at the undersurface of the board to see what might make you guys say that 4/5 was the common/ground.  The only thing I note is that there's an almost continuous trail of solder on that trace.  Is that a hint that something is the ground?

I picked up a pack of 33 Ohm 2% tolerance, 1 Watt resistors at the local electronics supply today.  We're lucky to have a real electronics shop in in the area.
 

Offline lowimpedance

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Re: Newall Digital Readout troubleshooting
« Reply #17 on: May 19, 2017, 12:04:29 am »
Actually I would concentrate on the supply and if the +25v measured (under load??)was correct then its certainly stuffed. That rail should be +12V.
The 33 ohm resistors are in parallel and form a minimum loading on the +5V rail so one side will be 5 ish V and the other 0V.
Did you measure those voltages when the readout unit was plugged in?.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #18 on: May 19, 2017, 09:24:29 pm »
I checked the pins on the mainboard when under load.  Using 4/5 as the common/ground
4/5 to 2/3 = +5.3v
4/5 to 1 = +12.3v
4/5 to 6 = -13.6v
The two new 33 ohm resistors got hot and I unplugged it.  After I reread the posts from yesterday and went back to check the voltage on either side of the new resistors the main fuse to the power cord was blown.  I need to find another fuse.  I'll do that and report back - hopefully tomorrow.
 

Offline Seekonk

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Re: Newall Digital Readout troubleshooting
« Reply #19 on: May 19, 2017, 09:51:00 pm »
5V on 33 ohms is 3/4W.  5V is not turninig them into a charred mess. What are those heat sinked transistors doing?
 

Offline lowimpedance

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Re: Newall Digital Readout troubleshooting
« Reply #20 on: May 20, 2017, 06:12:11 am »
The resistors do get quite hot and the appearance is more long term baking leading to the paint peeling .
The two readouts at work that needed new supplies both had the BBQ d resistor's as well. After supply and resistor replacement they have been running years powered on 24/7. The resistor's were changed as a matter of course ,both had not gone open but still measured okay.
It appears you're supply is okay by your measurements thus if still no display then the problem is on the main board..
Check the output of each regulator with the heatsinks, close up pic to see what part no. They have will hell.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #21 on: May 20, 2017, 01:09:26 pm »
I'm providing closeup photos of the four heat sinked transistors.  I've identified them as best I can using the numbers.  What I don't know are details on how to check them.  Do I unsolder them from the board to test them or do I test them on the board?  I've done a little looking so I know that each will be tested like diodes if out of the board.  Or were you guys requesting voltage readings from their leads while under power?
 

Offline Seekonk

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Re: Newall Digital Readout troubleshooting
« Reply #22 on: May 20, 2017, 01:24:49 pm »
Close up heatsink area of the main board, not the power supply.  I'm curious about what those two heatsinked parts do on the main board and L1. Doesn't seem like there is any further need for regulation as it is too old for 3V3 parts.
« Last Edit: May 20, 2017, 01:30:17 pm by Seekonk »
 

Offline R Lamparter

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Re: Newall Digital Readout troubleshooting
« Reply #23 on: May 20, 2017, 05:53:46 pm »
Close up heatsink area of the main board, not the power supply.  I'm curious about what those two heatsinked parts do on the main board and L1. Doesn't seem like there is any further need for regulation as it is too old for 3V3 parts.

They are a 12v and 5v regulator.  Closeup of the chips and basic data attached.  Getting a shot of the opposite side will be problematic, but may have to be done eventually if they need to be removed for testing.  A display board is (*I think*) soldered in place over the area of  the back side of the regulator area.

Also.  I'm held up a little bit on the fuse.  The counter person at the electronics shop had a pack of the T1A 250V fuses in Buss brand for between $13 - $14.  He suggested that he could get the generic brand for $6 a pack for me by early to mid week, if one of the other stores had them in stock.  At half the price, I went with his suggestion.
 

Offline Seekonk

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Re: Newall Digital Readout troubleshooting
« Reply #24 on: May 20, 2017, 08:51:19 pm »
They may have decided to separate the power to the glass slides, having them powered by power supply and the board itself powered by the on board regulators.  Since the board is dead, likely one of those is bad.  Check what is going into them and if anything is coming out.  If the 5v is bad it could have been from a tantalum cap shorting.  Before just replacing the regulator, check resistance to ground. It should be at least a couple hundred ohms.

When I have a bad cap on a board, I generally power it with an external supply that is capable of a couple amps current limited. Regulators are supposed to get hot and go into current limiting. The bad cap often will heat up a little.  Measuring the voltage across each cap on the mv range can also get you close.  If you have lived a good life it won't be a chip. Start with low currents so the chips don't go up in smoke if bad.  Write down the part numbers to be safe. 
 


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