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  #1  
Old 10-30-2016, 05:08 PM
Bill R Bill R is offline
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Sencore LC53 question

I have a Sencore LC53 that I have a couple of questions about. First I know I do not have the correct low capacitance probe, but shouldn't it give a reading even if the value is off? Would the probe make a difference for capacitor leakage measurements? Currently I can connect the clips together and it will zero on inductance, but no change with probe clips disconnected when trying to zero for capacitance. The display comes up with 000 and does not change even with a known good capacitor. Leakage test shows 0000, even on known leaky caps. When checking value the correct led comes on for uf, and on leakage the indicator comes on for higher voltages.
Any ideas?
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Old 10-30-2016, 05:47 PM
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Quote:
Originally Posted by Bill R View Post
I have a Sencore LC53 that I have a couple of questions about. First I know I do not have the correct low capacitance probe, but shouldn't it give a reading even if the value is off? Would the probe make a difference for capacitor leakage measurements? Currently I can connect the clips together and it will zero on inductance, but no change with probe clips disconnected when trying to zero for capacitance. The display comes up with 000 and does not change even with a known good capacitor. Leakage test shows 0000, even on known leaky caps. When checking value the correct led comes on for uf, and on leakage the indicator comes on for higher voltages.
Any ideas?
Do you ever get any reading other than 000? If the clock oscillator wasn't running, you'd get no reading other than 000 or other, fixed, nonsense display. Are all the power supplies up and running at the right voltage? Don't buy a manual - there are free ones on the web..

Has anyone "worked" on it before?

The low capacity cable (same as used with most LCXXX Sencore testers) is just a known length of RG58, RG59 or RG213 - nothing special beyond the known length, and thus, the total capacitance of the cable...

I have an LC53 that had a bad power tranny - I can dig it i out and see how complete it is, perhaps to offer troubleshooting assistance.

My main LC meter is the Sencore LC102, but for quick checks, I use one of those $15 Chinese Transistor tester/capacitance meter/ESR meter/freq counters like this:

http://www.banggood.com/DIY-M12864-G...l?rmmds=search

Best 15 bux I've spent in a while - 9 days shipping from China, and about an hour to pur together and calibrate.
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Old 10-30-2016, 06:47 PM
Bill R Bill R is offline
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I will have to dig up the schematic and check voltages and such. I bought this one not working for $25 at an antique mall. I really do not know any of the history. I have opened it up and there is evidence of past repairs to the connection headers, but the connections seem fine. the only time I have seen other than 000 is when I connect the clips and zero for inductance. readings then go from - to + values and I can zero it. But I still do not get and inductance value. Just like I see no capacitor value, even though the correct range led lights. I have other ESR meters and an old school leakage tester that works fine so this is not critical. I did notice one of the connectors to the display board seemed flakey. I will check the schematic in a bit. Since it is selecting the correct range there may be a problem with the BCD drivers.
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Old 10-30-2016, 11:11 PM
rogerstv rogerstv is offline
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My LC-53 fix

I have had an LC-53 on my bench for years, I recently had a hard failure and could not read inductance at all. I ended up replacing a bad chip and resoldered the entire main PC, all good now I also just use a regular 50 ohm coax 3 ft long and I am able to zero normally.
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Old 10-31-2016, 06:17 AM
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All the documentation for the LC53:

http://www.ko4bb.com/getsimple/index...e_LC53_Z-Meter
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Old 10-31-2016, 01:54 PM
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Here are some troubleshooting tips that helped me repair 2 units. Some I got from Sencore and others I found myself.

Faulty cap values and no response when trying to zero leads:

Check for pulse entering digital (bottom) board at pin 11 and leaving at pin 7
Pulse should change when Caps Value button is pressed
Check for shorted or open transistors TR20 and TR21 (2N5771) on digital board
If TR20 is shorted the pulse will be only partial level

Follow pulse through system to look for bad gates

Check IC12 pin 12 for 200hz square wave


Inductor test problems:

Check for 20 volts DC at pin 20 of board interconnect
Check for open series pass transistor TR11 (2N4401) on analog (top) board
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Old 10-31-2016, 02:02 PM
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I also have the calibration procedure.
Attached Files
File Type: pdf Sencore LC53-Cal-01.pdf (199.3 KB, 8 views)
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  #8  
Old 10-31-2016, 07:28 PM
Bill R Bill R is offline
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Thanks for the documentation. I will check it later this week. Some of the soldering does not look great.
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  #9  
Old 01-01-2017, 06:24 PM
Bill R Bill R is offline
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Well it has been awhile, but I thought I would get back to this project. I checked the voltages and the 5,7, and 20 volt supplies are there. I found a problem on the analog board with a broken trace and repaired that and one transistor in the ringing circuit. It now appears to work on the inductance side. I can zero the leads, it will give a value, and the ringing test seems to work. But capacitance test still does not work. The oscillator is working, and I do have the 200 hz sort of square wave on IC12 pin 12. I do not have any pulses on pin 11 of the digital board. I have traced back to IC14 which is just a D flip flop with set and reset. I have pulses at the clock input, but none on the Q output pin 13. The D input is 7 volts, and as long as the set input pin 8 is high I will not have any output. However pressing the cap value button pulls the set input low through TR05 an with no set or reset I should have pulses on pin 13 the Q output, BUT I do not. There is no pulses on the output even with no set or reset. That would explain why no pulses on pin 11 feeding the analog board. My question is would this not have to work for the inductance side of the tester to work, or would it only effect the capacitance test?
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  #10  
Old 01-02-2017, 04:09 PM
Bill R Bill R is offline
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I replaced IC14 with no change. At this point the only thing not working is the cap value test. Inductance value, ringing, and Cap Leakage test all are working now. I hate to give up on things, but this is getting frustrating.
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