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TC1 lcr-meter transistor-tester fix

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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!

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