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 Post subject: Sencore LC53 flashes 8s when testing capacitor update 5/12
PostPosted: Apr Wed 01, 2020 2:17 am 
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Location: Omak,wa,usa
Hello Guys,
well I decided to try to fix my sencore LC53 capacitor and inductor tester this sat at my other home and had stopped working some years ago before brought to my new place this last summer .
since I have lots time it would be nice to fix it .
Anyway it flashes 8s when try reading cap values any idea my first thought bad electrolytic capacitor since this is 1980s unit and has seen 1000s of hours of use .

Sincerely Rich


Last edited by radiorich on May Wed 13, 2020 4:43 am, edited 2 times in total.

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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Wed 01, 2020 2:56 am 
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Joined: Aug Fri 12, 2016 1:49 am
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Location: Houston, TX
Does it do it with all caps or just lytics?
Does it show overrange when you depress the value button with leads open?


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Wed 01, 2020 5:35 am 
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Hello Vin,
here is a photo of what it does when check the value of a brand new coupling cap
Sincerely rich
P.S. the other photo shows when zero it .


Attachments:
cap value test2.jpg
cap value test2.jpg [ 324.68 KiB | Viewed 916 times ]
sencorezero.jpg
sencorezero.jpg [ 151.97 KiB | Viewed 916 times ]
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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Wed 01, 2020 4:08 pm 
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Location: Houston, TX
With leads open, it should read 00.0 with the negative sign appearing occasionally, and the pF LED should be lit.

Your pics suggest it isn't as simple as miscalibration. For confirmation, try a large value, known-good cap. If it still shows overrange, and especially if it illuminates the pF LED instead of the μF LED, you've got more serious troubles.

Could be a number of things in that case, but I'd go with your gut and start by looking at the lytics.

Do you have the schemo & parts list?


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Wed 01, 2020 9:55 pm 
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Location: Omak,wa,usa
Hello Vin,
yes I have the factory Schematic
little 10 years ago I installed all new electrolytic caps I installed 105 degree Nichicon and one Sprague Atom .

Sincerely Rich


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Thu 02, 2020 2:40 am 
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Location: 07450, New Jersey
Here are some tips I got from Sencore Tech Support years ago when I had troubles with mine.

Check for pulse entering analog 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 analog 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 on digital board for 200hz square wave

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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Thu 02, 2020 3:55 am 
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hello Tim,
thanks


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 5:24 am 
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Hello Guys,
I ordered some of those transistors from Digikey NTE (2N5771) replacements the originals are no longer made .

Sincerely Rich
P.S. hopefuly this fixes it


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 5:33 am 
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Joined: Jan Tue 10, 2012 8:39 am
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https://www.electronicsurplus.com/natio ... 2n5771-cut


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 5:40 am 
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Hello Bob,
thanks


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 5:29 pm 
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Joined: Mar Thu 15, 2018 2:23 pm
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Just wondering.. did those 2N5771's actually test bad in your unit?


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 5:47 pm 
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Hello Mr fabe,
I am going to double check them today


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 6:00 pm 
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If this unit was working fine before you stored it away, I would assume some oxidation issues which are known to affect these Sencore units. Clean out the BNC connectors on both the leads and the unit. Remove the fuse and clean those contact points and the inter board connections. A little Deoxit or contact cleaner on the cap value switch and work it several times. After this, try your testing again.


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 6:14 pm 
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Location: Omak,wa,usa
Hello MR fabe,
yes I am going to do that I think it might be in the switch since when rebuilt this unit 10 years ago I replaced all electrolytic capacitors with good nichicon caps this unit in it's day has seen a lot use in my repair shop it was used like 6 days a week like 3 or 4 hours a day for years .
I wonder what easiest way to get into the switch I hope don't need to pull the board .


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 6:26 pm 
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Joined: Mar Thu 15, 2018 2:23 pm
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You don't need to pull the board unless your going to clean out the interboard connects or for testing/ replacing the 2n5771. You can take a dropper and lube the switch from the exposed side.


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Mon 13, 2020 6:42 pm 
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Location: Omak,wa,usa
Hello Mr. Fabe,
well first thing I just tried was replacing the fuse and cleaning the fuse holder and BNC jack my cable is almost new and it's a factory original replacement from Sencore
what I like using far as contact cleaner sold by MG Chemicals Super Contact Cleaner with PPE A slow drying contact cleaner that cleans, lubricates, protects, and removes stubborn residues. It also bonds onto the surface of metals and is particularly effective on gold, protecting gold contacts for life. A must have for audio systems.
Sincerely rich


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Tue 14, 2020 7:02 am 
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Hello Mr. Fabe,
Anyway I tried cleaning it but one thing I noticed is when am testing the value of the capacitor it flashes it's value and same with the inductance too
Sincerely Rich


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Tue 14, 2020 2:10 pm 
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Joined: Aug Fri 12, 2016 1:49 am
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Location: Houston, TX
So it now flashes an actual value instead of all 8's like it was doing before?

If so, I would suggest checking the reported value against a known-good meter (even a cheap Chinee one off eBay will do). If it's showing an accurate value, that will be a good starting point for further troubleshooting.


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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Tue 14, 2020 5:32 pm 
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Location: Ohio 45177
Some of those LED Sencore bridges came from the factory with a "standards" box containing several caps and coils, that where individually checked and hand marked. TO confirm operation and reasonably the accuracy. I don't know if any of them are floating around out there for sale. If you had a pal with a cal lab, you could have them test two or four little caps that are of a stable material and same with chokes or inductors. Or someone with a really high accuracy calibrated bridge. Sort of a go/no go confirmation. Plastic project box with loops to clip the test leads onto.

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 Post subject: Re: Sencore LC53 flashes 8s when testing capacitors
PostPosted: Apr Tue 14, 2020 5:51 pm 
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Location: Houston, TX
wazz wrote:
Some of those LED Sencore bridges came from the factory with a "standards" box

The FC221 (FC stands for Field Calibrator) also had to be sent back to Sencore (or a metrology lab) for recalibration to NIST. The coils aren't [presumably] going to change over time, but the caps definitely can.
I wouldn't trust a used FC221 with an expired cal date (often by many years) to help accurately calibrate a meter.

An alternative might be brand new precision components, but then you have to trust the manufacturer/seller to send you parts that aren't off stated value.


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