TC1 lcr-meter transistor-tester fix

[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 !

[ahmad_hodrob]

dear Sir,

kindly note that I have  T7 transistor tester that suddenly stopped working upon checking i found that C11 is shorted I replaced it with a 10uf capacitor, know the device is working but it doesn't go to calibration mode when I connect a short wires to it, instead it reads the short wires as a resistors with a value of about 11 Mohm.

please I need an advice and if anybody can help me with the software of the unit.   

[flodo]

I made a new firmware for U4 and the standard-firmware

how to flash it is explained here and here

the current version is v0.2, you can find it here


Unfortunately my tc1 is still drawing 0.11mA at sleep mode - seems to be a bit high.
I am not yet sure what the problem is.

[flodo]

@zappenduster: how have you measured the drawn current? I wasn't able to do that properly since every resitance in series is preventing power on somehow.

[Bighouse]

My TC-1 suddenly only measures a weird cell voltage all the time. Whatever I put in the the thing. Shorting the 3 probe pins also doesn't trigger the autocalibration anymore . Kind of a noob in this diagnosing. I don't read anyone having this specific problem.



The value varies somewhat, but it's between those pins all the time.

Any thoughts?

[flodo]

Maybe this helps (thanks to indman for the schematic).
I would start by measuring all those components within the yellow marking (especially DZ2).

[flodo]

DZ2 is probably the most promising part since you seem to have a positive voltage at socket ② - is the diode still working correctly?
You can find a datasheet here: https://www.semtech.com/uploads/documents/srv05-4.pdf

You can get a new one here (at least in Germany): https://www.conrad.de/de/tvs-diode-bourns-cdsot23-srv05-4-sot-23-6-6-v-500-w-1055462.html

[Bighouse]

I remember having the device plugged in with an (empty) Capacitor for a maybe a few weeks. Could it be that the capacitor got charged up by having it plugged in, and then releasing it's charge damaging my device in the process? I only hear about 'real' dead devices, with black screens when people plug in a charged capacitor. My issue looks somewhat more subtle.

Will try to measure. All those tiny spots, hope it'll work.

[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.

Bighouse,already I wrote earlier how quickly to define malfunction.

[flodo]

Good idea indman! Yes Bighouse, instead of measuring you can simply remove DZ2 and see if the Tester still shows an voltage.

[flodo]

does someone have already dumped the original fw?

[eliocor]

Quote from: flodo on Today at 21:44:26

does someone have already dumped the original fw?

it seems to me that you have dumped a protected device, hence read data is not valid...

[indman]

The Chinese original firmware ATMega324 for clones of LCR-TC1,TC6,TC7 are protected from reading of Lock by bits! Don't suffer, it won't turn out to remove them. If only who has available an electronic scalpel and the corresponding equipment for reading of the opened crystal.

[zappenduster]

@flodo I put a multimeter (Aneng AN8008) in line. I bridged the multimeter while tc1 is in on-state. When tc1 shot down i removed the short and measured about 15uA sleep current.
Your 0.11mA Standby seem to be the 0.2mA i measured (range about 0.13 - 0.19 mA). By adding a 33k resistor to the 7805-output i got it to 15uA sleep, see my first post. But i don't know how reliable this is...


Here are some notes (which were new to me) for tc1-repairer , gathered by others:
DZ2 = TVS Diode Array  = SRV05-4 (on some pcb its silk-screened ZD2)
U5   = DC-DC controller = SD6271 Step-Up Current Mode PWM Converter. Marking ALxxx (xxx = three digit lot-number)

tc1 schematic from azure:    https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/?action=dlattach;attach=521336
tc1 schematic from indman:  https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/?action=dlattach;attach=521411

That makes it a lot easier to get a broken tc1 back on track.

[Mechatrommer]

i bought this TC1 unit with expectation it is the same as M328 variant that i bought and worked charmingly earlier, but now my brother is using it now so i have to buy for myself. it turn out this is different atMega324 with STC15W104 chip, this turn out to be nightmare. and then i found this thread. after back and forth reading this thread i managed to get something from STC-ISP...

Checking target MCU ...
  MCU type: STC15W104
  F/W version: 7.2.5T

Current H/W Option:
  . Current system clock source is internal IRC oscillator
  . IRC frequency: 32.975MHz
  . Wakeup Timer frequency: 36.825KHz
  . Do not detect the level of P3.2 and P3.3 next download
  . Power-on reset, use the extra power-on delay
  . RESET pin behaves as I/O pin
  . Reset while detect a Low-Voltage
  . Thresh voltage level of the built-in LVD : 2.66 V
  . Inhibit EEPROM operation under Low-Voltage
  . CPU-Core supply level : 3.74 V
  . Hardware do not enable Watch-Dog-Timer
  . Watch-Dog-Timer pre-scalar : 256
  . Watch-Dog-Timer stop count in idle mode
  . Program can modify the Watch-Dog-Timer scalar
  . Do not erase user EEPROM area at next download
  . Do not control 485 at next download
  . Do not check user password next download
  . TXD is independent IO
  . TXD pin as quasi-bidirectional mode after reset
  . P3.3 output HIGH level after reset
  . Testing time: 2017-9-22

  . MCU type: STC15W104
  F/W version: 7.2.5T


  Complete !(2018-10-08 01:17:05)

if i choose STC15L104W as demonstrated by earlier experimenters, i wont get any report from the chip.

the problem when i got this unit is the shorted C11, so i changed with 100nF, no more short, but when battery is applied, lcd turn on white for half a second or so and then random garbage before turned off immediately. pressing start button do nothing. sometime the tester did turned on and firmware on mega324 did start, but its just luck. after reprogramming STC15W104 with frodo's tc1_u4_v0.3.1.hex, now its totally blank. removing and applying battery, there is no more white screen, no start button respond nothing. ah F the STC chip what was that? support us people of China guaranteed powerful home grown business FU so much so for anti disturbance super strong chip.

earlier i removed the STC chip and connect Vbat pin to the next pin controlling the boost dcdc chip (AL673 marking), the atmega did start but halted at welcome screen its like waiting for signal on either P3.3/PD2 or P3.2/PD1 i suspect to start measurement. i have to experiment later. i think i will remove the STC chip and glue it to blank space on the pcb so it can wave dick all day long all its like. i need to find a way to start the atmega chip the hard way. or anybody else can help me make program for the STC15W104 chip? i will be gratefull, for now i dont have time to play/install with Keil or whatever. i just want it to work and then move on.

btw,
1st picture: thermal imaging superimposed when shorted C11 is installed. the SD6271 got hot 73degC as registered by my camera.
2nd picture: how i connect the STC15W104 to USB-UART converter. need few experiment though since warning from people to use 3.3V rail, 5V may damage the fucked up super strong STC. it turned out i just use 5V UART and it just worked fine.
3rd picture: the fucked up super strong anti disturbance STC15W104 chip made home grown in China, please support it people of China. i really pissed off can you imagine by now?

thanks to people directly or indirectly contributed to this thread esp OP zappenduster, frodo and others, but your FW doesnt work with mine and schematics providers indman and azure.
edit: added 4th picture with its IO state to PD1/PD2 from my crude test.. and the mega fw wont start by simply toggling PD1 pin, so there must be the right sequence to turn it on

[prakash_kadri]

  @zappenduster, I had same issue with my T7. Replaced  C11 and C12 with 100nF 100V and 4.7uF 100V. Now it is working. Thank you very much for sharing the fix. 

[funkervoigt]

Hi !
I also have an defective TC1 Tester and followed your fabulous troubleshooting tips here.
The unit didn´t startup, i checked the capacitors C11 and C12, and the zener-diode DZ1. They seem to be OK.
After that i removed the TVS Array DZ2. Now the Device boots up (display flickers a few times when starting) but shows a cell voltage like in the picture from "bighouse".

For my understanding: Is it correct, that after removing DZ1 and DZ2, the ATMega should work normally, otherwise it is damaged (by overvoltage) and needs to be replaced ?

Thank You !

[Attilator]

Hi,
I am lucky and got a fully functioning TC-1 unit. My question is about setting the shutdown time to 25sec.

I see in the manual that both P1 and P2 need to have ZEROs. Could you please suggest where this ZERO PIN is located? Just want to be safe before soldering.

Thanks.

[amunro]

I know this is an old thread, but it seems a good thread to append my experiences to! I recently bought two TC1 LCR testers. One was fine, while the other was difficult to turn on, and then it just would not turn on. So just spent the evening removing components and testing them. What I found was similar to others; U5 gets hot. However my issue was a short on the 5v rail, rather than the 35v rail. I was seeing a short of about 9 ohms. Thought it would be a shorted capacitor; not just from this thread, but its a common issue on lots of smt circuits. I could not find anything else hot, which was strange (mind you my room is quite warm where I was working, which does not help). The caps are really small and time consuming to remove and put back so wasted lots of time on that. Anyhow turns out it was the SRV05-4; when removed from the board it had 9 ohms between vcc and ground, and on the pcb, the short had gone. Furthermore, as soon as plugging in the battery the display fires up with the normal startup. Anyhow not wishing to experience failures because of the removal of the V05, I quickly disconnected the battery. V05 (as printed on the chip) are dirt cheap from China in a SOT23-6 package; got 10 of them ordered for £1.80, and they should turn up in 2 or 3 weeks to the UK. I don't mind waiting as it will be handy to have some spares incase of a repeat or incase I destroy one with a charged capacitor!

Which brings me back to why was it faulty straight from ebay? I suspect it was a return where someone might have damaged it, and requested a return. Then the seller just stuck it back in stock without checking it. Alternatively the SV05 was just bad?

[amunro]

Also some of my capacitor parts were different to zappenduster. What I wrote down as I was testing:
c8 = c11 = c12 = 5uF
c9 = 16nF
c10 = 9 uF (slight out 10uF?)
c14 = c15 = 10 uF

Looking at what spec of 4.7/5uF 0805 capacitors are available, they seem to only go up to 16v. 0805 is 2mm x 1.25mm so that quite an achievement for such a small device. However for c11/c12 I measured 32v (and circuit diagrams above say 35v), so thats way under specified. Thus ordered some 50v 10uF, similar to what zappenduster mentioned, and will swap them out for 1 x 10uF, and add a decoupler of 100nF with 50V spec.

I know I am rambling here, but this thread was really useful to fix my unit, and hopefully my experiences will help others.

[amunro]

My saga continues. The SV05s turned up from the slow boat from China (£1 for 10 of them). Soldered it in and still have an issue. Seems there is still a short on the 5V rail to ground (tested with an ohm meter), but not a sufficient short to pull the 5v down and to cause U5 to get hot. After some fault finding, I lifted pin 27 (avcc) of the atmega off the board and the short went away. So looks like the atmega324 is at fault. Ordered some more and will wait for them to turn up from China ($1.40 each).

In the meantime decided to learn about atmega flashing as I am going to need to flash the new atmega when it arrives. Soldered some pins onto the LCR-TC1 for the ISP port. Bought a USBASP programmer off ebay for not much money, installed avrdude (I use ubuntu so just install it via apt). Disconnect the LCR-TC1 battery and connect up the USBASP; it finds the atmega fine; tried to read the eeprom and flash; avrdude reads it and then reports the file is zero bytes (don't remember the exact message). Seems the lock bits are set. Did some reading up on lock and fuse bits (or bytes); understand these now. Decided to erase the atmega via avrdude; can't read the eeprom/flash anyway, so might as well. Then try and flash some new firmware. Discovered indman's LCR archives on yadi.sk and downloaded some firmware, which works (but the chip is broke so can't fully test); both the Markus Reschke firmware and the original firmware he posted (9/16/2019) flash and boot fine. Many thanks to indman for collating and making available these firmwares.

This unit I got off ebay, but was faulty on arrival so I got a refund on it. Thus its sitting round doing nothing so figured its worth fixing and experimenting with. Even trying different firmware on it. I bought another to replace this faulty one so its not as if I am desperate to get it fixed.

Again another ramble, but hopefully my hard earned time learning all this will be useful to someone!