$20 LCR ESR Transistor checker project

[MikeL]

Hi,

I recently received an AY_AT tester which was supposedly fully assembled and fully working, been trying to get it successfully thru the Self-Test,  but the thing won't read anything connected to TP1 and TP3. 

After doing the S-T a number of times with the same result of timing out of the test with the display still flashing '0pF', I discovered that if I held the cap to either 1 and 2 or 2 and 3 it would immediately give the approximate value;  I finally accepted that it was not going to read anything when hooked to TP1 and 3.     

Thanks to those lovely interconnect images posted by jake in that utube video, I've found a definitive symptom so I'm hoping to narrow it down to what the actual failure could be.  According to the schematic TP's 1, 2 and 3 hook directly to pins 23, 24 and 25, respectively speaking, on the Atmel chip:  TP1 to pin 23 measures less than an ohm, TP2 to pin24 measures less than an ohm, but TP3 to pin 25 measures about 2.5 Megohms.

Thinking about a jumper wire now... any ideas as to what's going on, what went wrong with the connection?  I ended up going over any dull-looking solder joints (which was  just about all of them).  Since the Atmel is socketed I reseated that, made no difference.   I tried to measure a few caps and it seems to be at least in the ballpark, but no testing of 3 lead devices kinda sux.

[JoeO]

Hi,

I recently received an AY_AT tester which was supposedly fully assembled and fully working, been trying to get it successfully thru the Self-Test,  but the thing won't read anything connected to TP1 and TP3. 

After doing the S-T a number of times with the same result of timing out of the test with the display still flashing '0pF', I discovered that if I held the cap to either 1 and 2 or 2 and 3 it would immediately give the approximate value;  I finally accepted that it was not going to read anything when hooked to TP1 and 3.     

Thanks to those lovely interconnect images posted by jake in that utube video, I've found a definitive symptom so I'm hoping to narrow it down to what the actual failure could be.  According to the schematic TP's 1, 2 and 3 hook directly to pins 23, 24 and 25, respectively speaking, on the Atmel chip:  TP1 to pin 23 measures less than an ohm, TP2 to pin24 measures less than an ohm, but TP3 to pin 25 measures about 2.5 Megohms.

Thinking about a jumper wire now... any ideas as to what's going on, what went wrong with the connection?  I ended up going over any dull-looking solder joints (which was  just about all of them).  Since the Atmel is socketed I reseated that, made no difference.   I tried to measure a few caps and it seems to be at least in the ballpark, but no testing of 3 lead devices kinda sux.

You have analysis paralysis. 
Just run the jumper wire and be done.

[MikeL]

I was hoping that someone familiar with the board's construction might have an idea of where the actual problem lies, and whether it's likely to progress or not, just asking for 'informed guesses'  &-)

Also, this tester was purchased as a fully assembled and working  tester, and, what with shipping costs to China, I guess I'm stuck with it,
and at the cost  (it was 12 bucks plus 6 for shipping) not getting hurt too bad, but I feel I'm just being played by a vendor who has defective wares to sell.

So, buyer beware, picture attached:

[madires]

Could be a bad PCB. Someone had such a clone with a short between one probe pin and Vcc. He managed to locate the short between two traces.

[MikeL]

Could be a bad PCB. Someone had such a clone with a short between one probe pin and Vcc. He managed to locate the short between two traces.

I've been telling the vendor I suspect the circuit board, I've sent her pictures, and she wants more pictures, doesn't understand what I write - I suppose it's possible it worked when it was shipped, but I think that's too much of a coincidence for me to accept.

So, I guess I'll add a jumper from the 'chip-clip' to pin 25 of the Atmel chip and see if that fixes it.

Thanks for you help, and for being so free with your knowledge.

[stj]

some AY-AT kits got shipped with blank microcontrollers.
you would know that if you searched this thread. 

[MikeL]

stj:  "some AY-AT kits got shipped with blank microcontrollers.
you would know that if you searched this thread."

Oops  8-).

I' m thinking I'm gonna try to leverage a spare Atmel chip for my troubles ; -).

Say stj, I think I read that the firmware is up to 1.28 now, this tester has 1.12 installed, any thoughts on wether to leave well enough alone, or do you think I should upgrade?  If so, any particular version?

Thanks

[madires]

There are two firmware versions:
- k-firmware: 1.13k
- m-firmware: 1.29m

[MikeL]

madires:  "There are two firmware versions:
- k-firmware: 1.13k
- m-firmware: 1.29m      "


Oh, okay, I see I need to read up on the firmwares - I've got the K version, so not really behind by much. 

This little tester is just so amazing, it'll be weeks before I know how to operate it...thanks

[MikeL]

Back again, another question about the AY-AT tester :  would it be possible for one of the the ADC inputs to be blown and the tester still work somewhat normal with the 2 remaining ADC inputs? 

Reason I ask is that when I went to put the missing connection to TP3 in it was no longer needed (there's less than an ohm between TP3 and pin 25 of the Atmel),  Something is still screwy with this thing and it still won't measure anything on TP1 to TP3 during the self-test, hopefully a new Atmel chip will straighten it out.  very hopefully.

[perieanuo]

Back again, another question about the AY-AT tester :  would it be possible for one of the the ADC inputs to be blown and the tester still work somewhat normal with the 2 remaining ADC inputs? 

Reason I ask is that when I went to put the missing connection to TP3 in it was no longer needed (there's less than an ohm between TP3 and pin 25 of the Atmel),  Something is still screwy with this thing and it still won't measure anything on TP1 to TP3 during the self-test, hopefully a new Atmel chip will straighten it out.  very hopefully.

You may have just a simple bad pin soldering on 328 pin.if you can resolder the 3 acquisition pins.regards,Pierre


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[innkeeper]

I'm looking for a AY_AT off ebay and preferably from a north american seller. but i've read where some are using components that are two high tolerance. can anyone tell me known good sellers?
assembled or kit is fine with me.

[MikeL]

You may have just a simple bad pin soldering on 328 pin.if you can resolder the 3 acquisition pins.regards,Pierre

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Thanks for the suggestion - I've now touched up all the solder joints on the bottom of the board. 

 This did result in a bit of an improvement as during the self test the 3 pF values AY-AT computes went from "42pF,46pF,12pF" to a more normal looking"44pF,46pF,43pF" - I have no idea what it means or how this affects it's calibration  8-{

The top of the board also has crappy looking solder where ever there's a through hole but my hands are a bit too shaky to attempt them (yet).

Seems odd to me but it seems to be capable of reading transistors, both fets and bjts, wish I had some known quantities I could try.  It does seem fairly accurate on capacitors, but still won't complete a self-test (unless I cheat).

[jakeisprobably]

All I have to say is - have you ever ordered cheap solder from the $0.99 sellers that offer these clones? In my opinion, it's not solder. It's string with shinny makeup applied. I assume this is what they use to put together the clone boards. By the looks of most of the kit soldering jobs I've seen, I believe they have some kind of drinking game that involves hanging upside down while soldering behind one's back. I would not trust a single spot.

  The AY-AT PCB has some really nice plated through-holes. Several have traces on both sides. I'd break out the flux pin and good solder for this kind of thing, especially for that ZIF socket that is guaranteed to receive a lot of mechanical stress.

  The AY-AT has been covered extensively here since page 83. The last 10 pages of this thread are mandatory reading on the subject. Several people have summarized problems and consolidated information. If you want even more references look through my images index 3 of 3. This will guide you to every time someone referenced the AY-AT with pictures. These include lithium batteries, Q charging, enclosures, unprogrammed chips, short circuit, bad capacitor, capacitor mods, programming options, schematics, etc.

[MikeL]

Hi Jake, and thanks for the links and info on the AY-AT, especially any info on how and where the board's vias and 'invisible' interconnections might be located? lol, I guess that's asking a bit too much.  I'm still reading this thread, up to 3700-somethingth
post so far, so maybe I'll get there...

This is my third tester, the first 2 I bought as DIY kits and had no trouble at all doing a self-test as soon as I turned them on.  The 1st one has the atmega168a-pu chip and is also socketed, which I think is a nice feature, since I can't imagine me replacing one of those smd atmega328's, which is what the 2nd kit I bought has in it. 

So, now I'm kinda wishing I'd just got another kit rather than get this one that pretty much needs a complete soldering redo, I'd have had it finished days ago now, rather than be still bickering with some clown 12K miles away who assumes (rightly) that there's nothing I can do about their crappy service/product.

There, I feel better now, sorry bout that. 

Anyway, as far as soldering and resoldering goes, I had mixed success  with the second tester - after using it for many moons, mainly checking capacitors, it got to where only 2 of the leads could be used (it would say "unknown or damaged part" if you tried using it), so I resoldered the chipholder, treating all pins w/good dose from a flux-pen, and It did go back to  normal for a few uses, but then after a few days started flaking out again;  so I resoldered again, with a little higher temp and when I was through the damn thing didn't work at all any more.   It seemed to me that maybe some connections inside the ckt bd. that need to wick in some solder for some reason don't wick in enough and some corrosion process starts up - I wonder if they get exposed to salt air at any time in their life.

Thanks for the ideas and the links, not to mention all the work that you put into assembling it.

[mauroh]

Hi Mike, welcome to the forum...
   do you mind take couple of pictures of your AY-AT board? Solder and component side closeup...
Also some pictures during self test could help to identify if there is some value completely off.
Instead of resolder everything, have you tryed to clean the board with isopropyl alcohol?
Ciao
Mauro

[jakeisprobably]

I will not keep making changes... I will not keep making changes...I will not keep making changes...

[MikeL]

Hi Mauro,thanks!
   
You said:  "do you mind take couple of pictures of your AY-AT board?..."

 Well, I wouldn't mind at all, but my SD Card reader quit working yesterday, so it may be a little while before I find an alternative.  How about a comparison of the stored data  ?

   Under 'show data' mine says:
R0  .51 .45 .47
Rint hi =22
Rint lo =19.9
C0  has 2 entries:  42,43,46 and 44 44 46
Ref C -5
Ref R -27
You also wrote:

 "...Solder and component side closeup...
Also some pictures during self test could help to identify if there is some value completely off.
Instead of resolder everything, have you tryed to clean the board with isopropyl alcohol?"

The board looks/is real clean, no residue of anything that can be seen, it's just the solder was all dull silvery-gray looking (either it's lead-free or they are all cold joints, or both), now it's only like that on the top. 

I guess I really need to do a video, but not up to speed on how to use youtube, maybe in a few days...but, simply put, It continually blinks '0pF' if you hold the cap leads to either the pads or if you clamp it in to the chip-clip's 1 and 3...damn, just went to check something and It finally completed self-test, Yay!  That seems to have changed the Ref values a bit, it's now -3 for C and -24 for R.

Regards,
Mike

[tablatronix]

If you have one terminal that refuses to work ,could it not be the TVS , sorry if it was mentioned yet, but tvs or micro pin seem the most obvious points of failure.

[MikeL]

I'm not familiar how a TVS protection ckt. works. 

No matter though because I think I've determined the actual problem - the pads are mis-numbered on the ckt. bd., The top pad is marked 3 and the outer lower pad is marked 2, if I switch the numbers it works right. 

[tablatronix]

ah you are right, the smd pads are 2-3 swapped

[innkeeper]

what is the appropriate replacement for the TL431A thats .1 % for the AY-AT?

[madires]

LM4040 for example.

[innkeeper]

sot-23?

[madires]

TO-92 and SOT-23 (check the datasheets for the pinout).