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TC1 lcr-meter transistor-tester fix

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zappenduster:
Hello eevblog forum,
here is my TC1 (TC-V2.12k) experience. If your tc1 doesn't switch on anymore check capacitor C11 and C12.

I got the meter two weeks ago (18 Euro ebay purchase, shipped from china to germany).
I tested about 20 components successfully and then: screen black. I no longer could turn it on.
It was not my fault - i surely did not connect a charged capacitor or external voltage to input terminals.
Only usb-charging function seemed still be OK: red LED for some time, then turned green.
 
U5 boost-IC of my flawed meter was getting hot; voltage at Cathode of D2 about 15V.
With some web-hints i figured out a faulty component: a short circuited C (C11 or C12 - not sure anymore which one; they are connected in parallel).
One of them got a 'short' of 120 Ohm. The other's value is 5uF. I replaced both with 100nF and 4,7uF electrolytic 100V-rating. Now the meter works again.
Cathode of D2 is now at 37V (47V during usb-charging). This voltage is generated for zener-diode testing.

While pcb-inspection i measured some capacitors: C8 = C9 = C14 = C15 = 9 uF. C10 = 118 nF
D1 = D2 = D3 = 'SL' marked diodes (schottky-type because U_f ~ 250mV).
U1 = 44-pin uC Atmega 324PA ; Y = 16MHz crystal
U4 = 8-pin uC STC15L104W for wake-up from sleep / measurement cycle / subsequent automatic power-off
U5 = 6-pin boost/step-up IC. Marking AL718 (another forum-post states AL605)
U6 = 6-pin charge-IC
ZD1 = zener-diode 6V8 ; DZ2 6-pin marked V05. Some pcb miss those two elements - maybe earlier layouts...
battery = li-ion 3.7V 450mAh ; some tc1 got a much larger battery (2x base area)

At this position there would be a picture of my handmade pcb-to-schematic translation together with the actual pcb - but i can't insert them here... You can find them attached at the end of this post.

Current consumption is 300..400 mA (On-state) and 0,2mA in Standby/power-off). That means 150mAh per month (0,2mA * 24h * 31 days). So a fully charged battery would be drained after three months of non-use.
While measuring the circuit sometimes this happened: Standby current 0,2mA switched to 10mA for 25 seconds. Then it sank to 15 uA and remained there till next (On-)Button pressing.
After some trial and error i ended up adding a 33k resistor to the 5V-regulator output (soldered piggyback onto C15). This seems to do the job of triggering the 10mA_for_25s period immediately after shutdown. By that sleep-mode is reached safely.

Operational states (duration/current): 25s -> 25s -> sleep
25 seconds: On-button was pressed, screen is lit, meter tries to identify connected component. I = 300..400 mA
25 seconds: 10 mA current draw after automatic shotdown, screen black
xx seconds: 15 uA sleep-mode till next button pressing / measurement cycle
If i keep my tc1 busy (pressing button repeatedly) sometimes the sequence is 170s-170s-sleep. I don't know what goes on here...

IR remot control detection:
The ir-indicator (red dot in upper-right corner of screen) is flickering sometimes although input-area is covered up. I added a 100nF capacitor between Ground and Vcc of ir-receiver. But no change, this intermittend behavior is still there...

My guess about U4 port-configuration: Pin_1 is configured as interrupt: pressing button wakes device from sleep. Pin_3 switches on U5 boost-ic. Pin 5+6 used as common input to determine desired automatic power-off time (10s/15s/20s/25s - depending on connections P1/P2 <-> Ground/U4_Vcc).
About U4 functionality see also https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg1553608/#msg1553608

TC1 manual: www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/?action=dlattach;attach=310740
TC1 high-resolution pictures: https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/2225/
TC1 review + hr-pics: https://lygte-info.dk/review/ComponentTester%20Multifunction%20Tester%20T1%20UK.html
uC STC15L104W is described/listed here: http://www.stcmcu.com/datasheet/stc/STC-AD-PDF/STC15-English.pdf

Some web search brings up T6 labeled models (monochrome display, ir-receiver is placed on screen's right side). T7 looks the same as tc1. At startup it shows a brand/firmware name for a second.

Indicated data of tc1-testet components:
As lygte-info.dk review states, scr/triacs are partly recognised as resistor or BJT; h_FE values of darlington-transistors with BE-resistors are much too low. 
To me also capacitor ESR-values seem low: My Peaktech 2063 LCR-meter shows much higher values (it's presumably identical to Extech 380193 meter; component test-frequency can be switched from 120Hz to 1kHz)
What do you think of those misrepresentations/discrepancies? Can i just add a fixed offset to displayed capacitor ESR-values?

Thank you to eevblog and previous contributors to that matter...
zappenduster

hydroksyde:
Thanks, mine just arrived with the same issue. Replacing C12 with a 100nF ceramic fixed the problem..

zmaxpayne:
Hi to all.
I damaged mine (tc1).
I was so stupid to hook on a charged capacitor :-(.
So when i press to measure it stays black. Black screen.
The loading led is still working.
Do you guys think i can fix it?
What component could i damaged?
Thx.
Stefan from Belgium.

indman:
Remove DZ1 = with zener-diode 6V8; DZ2 6-pin marked V05. To give power on a tester without remote elements. If the problem remains, then YOU have damaged the ATMega324 processor. His replacement and a new firmware is necessary. :(

cataboier:
Thanks so much !

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