TC1 lcr-meter transistor-tester fix

[galaga1982]

Hello madires,
I also had an unfortunate incident where TC1 broke down while testing a charged capacitor. To be honest, I knew for the first time that measuring a charged capacitor could damage the device.

Anyway, trying to replace zd1 (6V8A) zener diode and dz2 (SRV05-4) diode.

dz2 (SRV05-4), SEMTECH is no problem to obtain, but ZD1 (6V8A) was difficult to know the exact PART NUMBER and MAKER
As you know, there's a lot of fake online. I would appreciate it if you could let me know the part information you know.

Thank you.

[madires]

Any 6.8V TVS should be fine.

[shved]

I've blown up another  TC1. Needed to replace and reflash AtMega and remove zeners. Now works as usual.

Backstory: I have several transistortester models, both store bought and DIY. Pin-outs are different on some of them. I took checked and discharged cap from an vintage amp I was repairing and mistakenly connected it to the zener (AK) terminals, then I've realized my screw-up(as this is the only model with zener mode) and reconnected the cap as it should be connected (123) terminals. Next thing i know - permanent resistors  between terminals no mater what....

The moral of the story: Discharge caps before testing! Do not connect anything but zeners and LEDs to KA terminals as this will charge the caps! If cap is big enough both internal and external zeners will not help. The repairs are simple enough, but annoying.

Have more than one tester for the job!
Hoard test equipment!

[elecdonia]

I also had an unfortunate incident where TC1 broke down while testing a charged capacitor.

I had similar accident with a Transistor Tester.

In the original Transistor Tester thread there are discussions about an upgrade with a small relay which totally disconnects the probes from the MCU until the power button is pressed. Additionally, while in the "off" state the relay connects resistors between all 3 probes to discharge capacitors. This is a very reliable protection system as long as one remembers to connect the probes to the capacitor under test while the Transistor Tester is in the "off" state.

I intend to add this relay protection mod to the Transistor Tester I use most often on my test bench.
(At this point I think I have at least 6 Transistor Testers )

[galaga1982]

I also had an unfortunate incident where TC1 broke down while testing a charged capacitor.

I had similar accident with a Transistor Tester.

In the original Transistor Tester thread there are discussions about an upgrade with a small relay which totally disconnects the probes from the MCU until the power button is pressed. Additionally, while in the "off" state the relay connects resistors between all 3 probes to discharge capacitors. This is a very reliable protection system as long as one remembers to connect the probes to the capacitor under test while the Transistor Tester is in the "off" state.

I intend to add this relay protection mod to the Transistor Tester I use most often on my test bench.
(At this point I think I have at least 6 Transistor Testers )

Hello?
Can you show me a real picture of the relay protection mod you made? I want to make this circuit, too.
In my case, even though there were ZD1 and DZ2 diodes, the VCC and GND of ATMEGA324P were damaged by SHORT.
I don't want to break the lovely $20 TESTER with CAPACITOR anymore.

[galaga1982]

Any 6.8V TVS should be fine.

Hi madires,

I've read this thread several times, removed zd1 and dz2, and hoped it would be no problem, but the sad prediction was never wrong.
I connected 3.7 voltage battery, but the screen became very dark, and after a while I had no choice but to look at cell voltage.

I think atmega324p is broken. When the resistance of vcc and gnd is measured, a low value of about 50ohm is obtained.
Maybe the I/O is damaged by the energized capacitor, but I don't know why the screen got dark.

Regarding atmega324p mcu programming,
I have Xgecu t48 (upper version of TL866 programmer). I'm trying to program it with 324p mcu using qfp44 to dip40 adapter and I'm wondering if I need an isp connection as well.

I'm not used to programming avr microcontrollers. There are many ways like USB-UART, 3V3, etc,
but rather than buying another programmer, I would appreciate it if you could tell me how to use the TL866-based programmer I have.

Sungmin

[madires]

Sorry, I can't help you with the TL866 based programmer. The universal programmer I have supports ISP and HV parallel programming of ATmegas. ISP is the standard method and the HV mode is used in case the fuses are screwed up and ISP doesn't work.

[indman]

Regarding atmega324p mcu programming,
I have Xgecu t48 (upper version of TL866 programmer). I'm trying to program it with 324p mcu using qfp44 to dip40 adapter and I'm wondering if I need an isp connection as well.

No, you don't need isp in this case. If the qfp44 to dip40 adapter is working properly, you should have no problem programming the ATMega324 and any other controller. ISP is necessary if you are going to program the controller without removing it from the PCB (in the schematic).

[galaga1982]

Thank you for answer. By the way, if the atmega324p breaks down, does the tc1 screen get dark? The zd1, dz2 diodes have already been removed.

[madires]

Could be a backlight issue. Does the 3.3V LDO for the display output 3.3V?

[galaga1982]

I think it's low drop out too, but I'm not sure if it's caused the mcu to fail. There was no back light problem before the disaster.

[digik]

I have this version:



after testing one charged cap is dead. I have dead short betweed D1 terminals.
I have removed D1, D2, C3, C25 and C30, same result.
I removed 78L05 and is still dead with a short between D1 terminal.

Is MCU bad?

[madires]

Yes, most likely. BTW, that MCU is an LGT8F328.

[digik]

is there a reliable way to test if is the MCU?

also seems that the LGT8F328 version is the highest specs one but also the only one without schematic available

[madires]

Power the tester by a lab PSU and look for hot components. Proper testers come with an genuine ATmega.

[digik]

everything stays cool. is there a schematic for this specific version? btw i have tested everything and no component seems shorted...except the MCU. I will desolder the MCU and see if the short goes away

[digik]

short is gone after removing the MCU. In the bin the thing goes.

[acerquax]

Hello all,

my name is Harry
I am  new here and I am impressed of all this  good ideas, repairing this "tiny" tester. Great stuff!!
I read this threat very thoughtful, but I am a bit unsure how to handle my killed tester?!
I did exact the same as many others:
Forgotten to discharge a condensator, tried to measure capacitance on my T7 and "PENG".
The result:
I switch it on, the display shows as usual Testing.... and after a while it shows some voltage sometimes between Pin 1 and 2 and sometimes between 2 an3 a.s.o.
I guess my ATmega324 has got some spike and is death.
So I have to replace it, but what do I have to flash, only the 324 or  the 15L104 as well?
I don't understand the function of the 15L104. 
Why do I have to flash it as well?

Can I get an idea here in this threat where to find an original firmware copy ?

Many thanks in advance
Harry

[madires]

If you got a copy of the T7's modified firmware (flash and EEPROM) you would only need to program the replacement ATmega since the STC15L104W still works. The STC15L104W is an additional MCU which controls power and the test button which makes that tester incompatibile with the standard design. The alternative is to go for an OSHW firmware and also reprogram the STC15L104W with an alternative firmware, or to replace it with a simple two-transistor circuit.

[acerquax]

Thx for your infos. great!
Where can I get a copy of the t7 firmware from?
I couldn't read out the firmware from my atmega 324, it was blocked..

[madires]

The Chinese clone manufacturers usually set the lock bits to prevent the firmware being read. I haven't seen any available copy of the T7's modified firmware so far.

[indman]

acerquax,madires, usually the circuit design of the T7 and TC1 clones with the ATmega324 and the STC controller is the same, so the original Chinese firmware can be found on my resource https://yadi.sk/d/yW8xa5NJgUo5z  in the folder LCR-TC1/Firmware/Original   
But since this firmware, apart from the presence of beautiful graphics, has no more advantages compared to m-firmware and k-firmware, and on the contrary, has many bugs and shortcomings, I recommend installing it only to check the functionality of the tester. Chinese firmware it is unsuitable for correct work with most parts.

[acerquax]

indman, madires, thanks a lot for your inputs

Ehmmm...
ATmega 324<-->Atmega644 1:1 replaceable?   Are there pincompatible for the T7-pcb or do I have to modity the T7 pcb?

[madires]

Yep, they are pin-compatible.

[acerquax]