$20 LCR ESR Transistor checker project

[jakeisprobably]

So first peak at my incomplete rough draft of all LCD options. I'm trying to go between KH's PDF, Markus's readme and controller datasheets to create this. I am worried I may be making some dumb fundamental errors with topology. Hopefully someone can help me catch them early.
    This is the first time I've plotted the file and it has some odd text sizing issues with the way I labeled stuff with text. I'm not worried about that. I'm mostly interested in the basic stuff like how I set up the buffer/pull up resistors. If anyone can just have a quick glance I'd appreciate it
Feel free to PM me as well if that's more appropriate,... doesn't matter to me.

[penmarker]

bad chip socket contact?

What's a safe way to test it? Would it be ok if I stick continuity probes to the chip leg in top and the solder point at the bottom?

I had the same problem and was open the 27K resistor that goes between collector of transistor S9014 and pin7 of Mega 328

Thank you very much, I'll try and see if that could be the case too.

[stj]

no problem with checking continuity with a meter, the chip is 5v tolerant and i'v never seen a meter use more than 3.5v

[perieanuo]

bad chip socket contact?

What's a safe way to test it? Would it be ok if I stick continuity probes to the chip leg in top and the solder point at the bottom?

yes and no.you have to do somme shitty work like test with ohmeter endpoint to endpoint ALL traces and EVERY trace with his neighbor
hoping you find this way some imperfection on pcb trace (uncoroded copper);but this will not always work (you tension the board a little,the
unwanted remaining copper may do or not do an unwanted electrical contact between 2 separated traces.
Solution:microscope or magnifier, like an detective.there are posts here telling bad experiences like that,happens all the time with easy-peasy board
manufacturers with zero testing board procedure (hope you got it,you may have uncoroded copper remaining between different traces/nodes)

I had the same problem and was open the 27K resistor that goes between collector of transistor S9014 and pin7 of Mega 328

Thank you very much, I'll try and see if that could be the case too.
[/quote]
more rare but can happen very easy/quick to see with your ohmeter

[mauroh]

If the tester works fine for a bit and than stops, I don't think it is a permanent damage like a short or an open component/trace.
How are you powering the board? I have to go back to your posts, but are you using a fresh 9V battery or a power supply?
Have you measured the 5V across the Atmega power pins (pushing the button) when it is not working?

I know I'm boring and I ask this every time, but can you provide pictures of the board with and without the display? (component side and bottom side)
Mauro

[penmarker]

I'm using a new battery and tested the pin 7-22, there is 5V on the board. I've tried checking the 27k resistors too with same voltage.

Emailed the seller and he asked his engineer. The engineer said it could be faulty 9014 transistors. Here's my board photos. The capacitors look different because I ordered them from Element14.

 

[mauroh]

Ok, remove all transistors and check it with your transistor tester....
If you can, check the placement of the transistors and replace it one by one verifying if something changes.
Do the same with the 2 electrolitic capacitors, I can't tell the polatity from the picture..

The capacitors look different because I ordered them from Element14

?? Why, there was something missing in your kit? It was a preassembled board?
As quick test, remove the SVR5-04 ad D3 (P6KE...) if nothing changes, when you will fix the unit you can place it back.

Wait for the tester to fail and measure the voltage on this pins of the microcontroller:
13 = 5V if the tester is on
12 = 5V if the tester is on

How is Ubat when the tester fails? (refer to the schematic, i mean Vbat after T1)

Mauro

[penmarker]

Ok, remove all transistors and check it with your transistor tester....

*ba dum tishhh*
Oh you..

If you can, check the placement of the transistors and replace it one by one verifying if something changes.
Do the same with the 2 electrolitic capacitors, I can't tell the polatity from the picture..

?? Why, there was something missing in your kit? It was a preassembled board?
As quick test, remove the SVR5-04 ad D3 (P6KE...) if nothing changes, when you will fix the unit you can place it back.

Wait for the tester to fail and measure the voltage on this pins of the microcontroller:
13 = 5V if the tester is on
12 = 5V if the tester is on

How is Ubat when the tester fails? (refer to the schematic, i mean Vbat after T1)

Mauro

The capacitor polarity is correct, I've referred to the silkscreen.

I ordered some of the components separate from E14 because from past experiences I've received some dubious components (mainly amplifier and PSU kits), and this being a reference tester I figured I should confirm myself with original components from a trusted shop. I bought; all ceramic and electrolytic capacitors, HT7550, and TL431. 9012 and 9014 aren't available at the time. I didn't get resistors because they're always within 1-5%.
The problem had started the first time I turned it on, so thinking it was the transistors I bought being a different spec, I swapped them out with the ones that came with the kit.

Is this what you meant with SVR5-04 ad D3?


And testing the 12 and 13 pins with reference to ground?

[innkeeper]

LOL ... gotta love it.

when we all know its cheaper just to buy another one .,.. but. you cant just let it go
that is what makes EEVBLOG forum great!

never say die!

[penmarker]

Imagine replacing everything onboard only to realize the firmware in the atmega was corrupted.

[stj]

well they have been sold with BLANK chips before!!
 

[innkeeper]

that thought had crossed my mind, corrupt firmware, but, it seems he says works for a bit at times after he re flows, like its aggravated with heat.
still could be a bad at mega .. worth swapping out.

ya know eventually this is going to become like Abe Lincolns ax, all original, but the handle and the ax head have been replaced.

[penmarker]

1) As quick test, remove the SVR5-04 ad D3 (P6KE...) if nothing changes, when you will fix the unit you can place it back.
Wait for the tester to fail and measure the voltage on this pins of the microcontroller:
2) 13 = 5V if the tester is on
3) 12 = 5V if the tester is on
4) How is Ubat when the tester fails? (refer to the schematic, i mean Vbat after T1)

1) I did not do this yet, I ran out of solder wick to desolder it.
2) Pin 13 to ground is 5V
3) Pin 12 to ground is 0.63V
4) Vbat to ground is 8.7V

[madires]

Pin 12 (PD6) drives a NPN transistor which keeps the tester alive. The voltage of 0.6V looks suspiciously like the NPN's V_BE.

[penmarker]

1) As quick test, remove the SVR5-04 ad D3 (P6KE...) if nothing changes, when you will fix the unit you can place it back.
Wait for the tester to fail and measure the voltage on this pins of the microcontroller:
2) 13 = 5V if the tester is on
3) 12 = 5V if the tester is on
4) How is Ubat when the tester fails? (refer to the schematic, i mean Vbat after T1)

1) I did not do this yet, I ran out of solder wick to desolder it.
2) Pin 13 to ground is 5V
3) Pin 12 to ground is 0.63V
[/b]4) Vbat to ground is 8.7V

Pin 12 (PD6) drives a NPN transistor which keeps the tester alive. The voltage of 0.6V looks suspiciously like the NPN's V_BE.

I'm very sorry, the 12 and 13 are reversed.
Pin 12 is 5V
Pin 13 is 0.67V

[madires]

Have you measured the voltage at pin 13 while pressing the rotary encoder?

[penmarker]

Have you measured the voltage at pin 13 while pressing the rotary encoder?

When pressing the encoder, pin 13 has 7.1mV.

[madires]

Pin 13 should have 5V when the tester is running and the rotary encoder isn't pressed. When pressed the voltage should be V_CE of the driver transistor. If my circuit diagram is correct it's T2 (or Q2). Since the power/test push button is low active the firmware thinks the rotary encoder's push button is pressed all the time, because 0.67V is much too low for a logic high level. I'd check the parts between the rotary encoder's push button and pin 13.

[all_repair]

 Just found this and ordered one from Taobao.  Looks like an interesting variant, by Mastech this time.

[bitseeker]

Kind of a cool enclosure. Bummer there's no rotary encoder.

[stj]

interesting, it has a discharge resistor on the left, 2 buttons??

[all_repair]

interesting, it has a discharge resistor on the left, 2 buttons??

Guess so, 1k resistor, slots fot capacitor to be put in for 2 sec to discharge.

If possible, I am thinking to put in an encoder later but the interations on taobao are much faster than mine.

[madires]

If possible, I am thinking to put in an encoder later but the interations on taobao are much faster than mine.

And please don't forget to take some pictures of the PCB

[penmarker]

Pin 13 should have 5V when the tester is running and the rotary encoder isn't pressed. When pressed the voltage should be V_CE of the driver transistor. If my circuit diagram is correct it's T2 (or Q2). Since the power/test push button is low active the firmware thinks the rotary encoder's push button is pressed all the time, because 0.67V is much too low for a logic high level. I'd check the parts between the rotary encoder's push button and pin 13.

I went to my local electronics shop and got myself two 9014 and a 9012. Replaced them and it works somewhat.
When there's no components plugged in, it kept showing there's a capacitor something in the range of 300uf-400mf. sometimes it'll work well and shows no or faulty component.
I kept buggering with it some more and doing the self test a few times and it works ok now.

But for some reason the rotary encoder doesn't work anymore. It works as a pushbutton now. To navigate the menu you click once to move next, press and hold to select, and press and hold to exit the selection.
Also I think I buggered one of the transistors now because with the battery plugged in, the LED and screen lits up without pressing the encoder.

I'm like the opposite of having the Midas touch.

I bought a latching button and just turn it off when the battery is plugged in. It turns on whenever its plugged in now.

[all_repair]

If possible, I am thinking to put in an encoder later but the interations on taobao are much faster than mine.

And please don't forget to take some pictures of the PCB

Yes, shall do so when it arrives.  For the time being, more screenshots: