Electronics > Repair

Sencore LC102 Capacitor Analyzer: Need Help With Incorrect Measurements

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EDIT: I replaced the microprocessor and that fixed the issue detailed below.  Now need help fixing the capacitance measurement ranges starting in reply 10.

Hello all,

This is a continuation of a previous thread below, starting a new one a year later in hope of repairing this poor LC102.  I would VERY much like to get this useful bit of kit running.  Note from previous thread I likely damaged something probing around the relays but the device was not functioning correctly even before this operator error damage.

Prior thread: https://www.eevblog.com/forum/repair/sencore-lc102-troubles/

Schematics are available here: https://bama.edebris.com/manuals/sencore/lc102/

Device Behaviors:

- Device will not read capacitance.  Relay will click, display remains 0000

- Device hangs/freezes when open lead zero is attempted.  It WILL zero (or acts like its zeroing) shorted leads.

- I get error 7 (component out of test range) when trying Dialectic Absorption and ESR tests.

- Device WILL present a reading for leakage 100uf/16v cap it reports 8.4ua leakage.

- Device WILL present a reading for coils/inductors both uh and rings.  220uh inductor it will present a reading of 190uh and 16 rings.


I have checked and verified power supplies, including (probably un necessary) electrolytic cap replacement. 

I have probed all diodes and transistors and all seem ok, at least none sort or open. 


- I have observed the 2000 board on thermal imaging, while nothing gets super hot I note that IC46, IC23, IC22, and IC27 are warm.  R84 seems warmish/hot.

- When I attempt the open lead zero, TR14 gets warm fairly quickly (a clue hopefully). The device hangs/freezes once the open lead zero is initiated.   

Things I have done so far:

- I replaced IC 27 just because it was in proximity to my clumsy probing.  No improvement. 

- Replaced PSU electrolytic caps.  No improvement.


-I assume the micro and ROM are fine, since the device will do certain readings and seems to operate at least some of the relays. 

-I think I damaged a logic device somewhere.  Unfortunately documentation is fairly light on this device, for instance I see NO mention of the lead zeroing process in the circuit description.  In fact, the previously mentioned TR14 is not mentioned in the circuit description at all. 

While I have come a long way reading schematics I am not quite up to the point where I can understand how to troubleshoot the circuit without more guidance, so I am at a dead end at this point.  I would greatly appreciate assistance getting this thing going. 

for the closed and opened zeroing, you have the big relay who could give some problems, like oxidized contacts, some members did have success with deoxit, when they made a small hole on it an shoot it inside

You must use for this sencore a specified coax wiring (capacitance) and a specified length, if theses specs are not correct  you will get zeroing problems too,  you have a special fuse socket

At k4obb  i did patch the service manual sheets into 3 majors ones


read the operation manual, it will give you some insight, you have firmwares dumps too


Sorry to say:  you did a few things wrong assuming this or that,  you don't change parts for fun or assume they are automatically bad, you have to properly diagnose stuff before changing a part

for the psu  you have many tests point to verify, and the main board too and be careful, as you know it,  it can output 1kv

There was known problems for the small black relays in it too

I did own this lcr meter in the past, it had a later revision of theses small relays, they were "metal" shielded, i did bought on ebay  an test lead made by a seller, it was working perfectly for open and close zeroing, before that i had errors too

https://www.ebay.com/itm/332712610011?   they are worth every penny

Thanks much for your reply.  I neglected to mention I did gain access to the large relays and cleaned the contacts.  They seem to be functioning correctly. 

I am certain the lead zeroing and failure to read capacitance are not related to the contacts or test leads, there is something else going wrong that I have yet to identify.  I did replace the IC27 and PSU caps out of frustration before putting it away for a year, though you are right to point out this was not wise. 

follow  some guides in the service manual / user manual, you will be able to check the psu / generator voltages / ranges,  if not  you may have logic problems ???

So far as I can tell all the PSU voltages are present and correct.   I am fairly certain it is logic issue, but I am not sure where to start with troubleshooting the various logic ICs on the 2000 board...short of de soldering them one by one...


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