Author Topic: $20 LCR ESR Transistor checker project  (Read 4229108 times)

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Offline madires

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Re: $20 LCR ESR Transistor checker project
« Reply #9750 on: November 25, 2024, 10:04:44 am »
but one of them if i put the negative lead on the collector (its pin 3 right ? the rightmost one when the flat part is towards you) and the positive on the emiter it will show continuity or it was the other way around (positive on collector and negative on emiter) this was T1

The BJT driven by PD6 should be an NPN (S9014) and the one driven by the encoder's push button too. The BJT switching the battery power is a PNP (S9012). The designators in the schematic posted by snapper are T1 (driven by PD6), T2 (driven by push button), and T3 (battery power). The NPNs can be replaced with any jellybean small signal NPN. And the PNP also, but its hFE needs to be about 300 or higher.
 
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Offline indman

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Re: $20 LCR ESR Transistor checker project
« Reply #9751 on: November 25, 2024, 01:42:46 pm »
No, it's ATMega328P, this is indicated by the 1000pF capacitor between pins 21 and 22.
In the future, you will need to look for a 16 MHz quartz crystal as a replacement - this will significantly expand the possibilities.
You are mistaken - this is a Chinese clone of the LGT8F328, which is now mainly sold in Chinese stores. And 16 MHz quartz is already installed on the board.
These copies are easy to convert to ATMega328, you just need to add a few jumpers after installing the new classic ATMEL chip.
 

Offline madires

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Re: $20 LCR ESR Transistor checker project
« Reply #9752 on: November 25, 2024, 02:42:58 pm »
Yes, the MCU is most likely an LGT8F328.

No, it's ATMega328P, this is indicated by the 1000pF capacitor between pins 21 and 22.

ATmega328 32-TQFP pin 21: Gnd
LGT8F328 QFP32L pin 21: PE2/SWD

The board has a 5-pin header for programming (P2) and there's a thin trace from P2 to MCU pin 21. That's SWD, not ATmega's ICSP. Another hint is a thin trace from P2 to MCU pin 18 (LGT8F328 QFP32L: PE0/SWC/APN4, ATmega328 32-TQFP: AVcc).
« Last Edit: November 25, 2024, 02:54:10 pm by madires »
 

Offline indman

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Re: $20 LCR ESR Transistor checker project
« Reply #9753 on: November 25, 2024, 02:47:16 pm »
The board has a 5-pin header for programming (P2) and there's a thin trace from P2 to MCU pin 21. That's SWD, not ATmega's ICSP.
Absolutely right, this can be clearly seen in the photo of the board from banane!!!
Here is a schematic diagram in which connector J2 is clearly visible
« Last Edit: November 25, 2024, 02:58:24 pm by indman »
 

Offline Kim Christensen

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Re: $20 LCR ESR Transistor checker project
« Reply #9754 on: November 26, 2024, 05:19:37 am »
Here is a schematic diagram in which connector J2 is clearly visible

Gee, they didn't even bother to put a resistor between the gate and source of Q1.  :palm:
 

Offline Per Hansson

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Re: $20 LCR ESR Transistor checker project
« Reply #9755 on: November 27, 2024, 08:24:07 am »
Cosmic_Starlight: the picture of your board still shows one tantalum capacitor for the crystal oscillator, replace it with a ceramic 22pF (picofarad) capacitor, exactly same one as you bought at the store and is installed in the other spot for the crystal.
« Last Edit: November 27, 2024, 08:26:01 am by Per Hansson »
 
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Offline Fuzzy Star

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Re: $20 LCR ESR Transistor checker project
« Reply #9756 on: November 27, 2024, 03:02:34 pm »
the picture of your board still shows one tantalum capacitor for the crystal oscillator...
Those yellow caps look like multi layer ceramics.
« Last Edit: November 27, 2024, 07:12:35 pm by Fuzzy Star »
 

Offline hapless

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Re: $20 LCR ESR Transistor checker project
« Reply #9757 on: November 28, 2024, 08:58:33 pm »
These kits don't come with any tantalum capacitors. They are all multi-layer ceramics, so they should work without issue. The boards have a serious issue with the way it's laid out though: There is very little space between traces under some components, making it very trivial to just short out a transistor and not even notice. My advice would be to just go from trace to trace with a multimeter in continuity mode... you may not see it with the naked eye, but there may be a short somewhere!
 
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Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9758 on: November 28, 2024, 09:42:52 pm »
Cosmic_Starlight: the picture of your board still shows one tantalum capacitor for the crystal oscillator, replace it with a ceramic 22pF (picofarad) capacitor, exactly same one as you bought at the store and is installed in the other spot for the crystal.
thats what they guy at the store i bought the replacements told me but at the same time you can see yt videos of ppl buying this exact same with with the same capacitors and theirs work fine

These kits don't come with any tantalum capacitors. They are all multi-layer ceramics, so they should work without issue. The boards have a serious issue with the way it's laid out though: There is very little space between traces under some components, making it very trivial to just short out a transistor and not even notice. My advice would be to just go from trace to trace with a multimeter in continuity mode... you may not see it with the naked eye, but there may be a short somewhere!
thats whats most perplexing for me, i had just bought these very thin and sharp like a needle dmm test leads and i made doubly sure that there were no continuity between any two contiguous transistor or ic leads and there were none, and even the point of the leads could pass trough the sodler pads of the transistors no problem but it seems two s9012 are shorted or were defective from factory

but one of them if i put the negative lead on the collector (its pin 3 right ? the rightmost one when the flat part is towards you) and the positive on the emiter it will show continuity or it was the other way around (positive on collector and negative on emiter) this was T1

The BJT driven by PD6 should be an NPN (S9014) and the one driven by the encoder's push button too. The BJT switching the battery power is a PNP (S9012). The designators in the schematic posted by snapper are T1 (driven by PD6), T2 (driven by push button), and T3 (battery power). The NPNs can be replaced with any jellybean small signal NPN. And the PNP also, but its hFE needs to be about 300 or higher.
i dont know what to do, at the present time am fighting the AE seller for a refund or a partial refund at least.

i could try and go downtown again and just buy replacements for all the transistors and ICs but:

A. i dont know if i could get those exact same ones
B. if i cant get the exact replacements what should i replace them with ? like what specs should the ICs and transistors meet ? same pinout i guess should be one

i could maybe try and replace all the transistors and caps but if i add the ICs and maybe another atmega (thats not even adding the cost of a programmer for it) and if am really unlucky the screen too it could get expensive FAST and i just might aswell buy another fully built working one and and just repair this one just slow so that the economical impact isnt felt too much

if i do end up buying another one am eyeing the one one known as "GM328A" that has a black pcb and the atmega in a dip package and the caps and resistors are smd some sellers call it "old english version"

like am sure my AY/AT can be repaired and made to work its just am not sure its financially viable at the present moment

sorry for the delays in replying, i since am a beginner i usually try and take things slow and make sure i dont break anything (and so far the only electronics device that ive had issues working in is this one, i managed to partially revive my fathers early 70s sony hifi amp to at least get sound on the right channel only in the mean time) so am not an entire foreign to soldering on pcbs like the seller tries to claim it being my fault

(not to mention other ppl o yt videos have the exact same problem as me)

anyways sorry for the wall of text any help or guidance is greatly appreciated

oh and BTW how do i know if the screen i got sent is a color one or a black and white one ?
« Last Edit: November 28, 2024, 10:56:27 pm by Cosmic_Starlight »
 

Offline snapper

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Re: $20 LCR ESR Transistor checker project
« Reply #9759 on: November 29, 2024, 12:11:08 am »
If you have reported the problem correctly, the complaint will be resolved by AE and not directly with the dealer. If you paid with PP, you also have the option of submitting a complaint here. In most cases, you will get the purchase price refunded without any problems because returns are not possible due to the high return shipping costs.
The AY-AT version of the GM328 tester with the socketed Mega328 in the 28-pin PDIP housing has the advantage that it can be upgraded with an adapter board to the ATMEGA644 with more memory so that the newer, larger firmware versions can be loaded for a larger range of functions!

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4890983/#msg4890983  :clap:
« Last Edit: November 29, 2024, 12:44:16 am by snapper »
 
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Offline hapless

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Re: $20 LCR ESR Transistor checker project
« Reply #9760 on: November 29, 2024, 12:31:29 am »
If you just want to see if the main components work, you can connect the MCU and the screen and carefully connect 5V between VCC and any ground connector. The tester should come to life and this will also answer your question about whether the screen is color (most likely is). This should help:
https://youtu.be/mRMRtrzh6rI?feature=shared&t=88

As madires said, you can use just about any transistor to replace the dead ones as long you don't get the PNP and NPN ones mixed up when putting them in. The TL431 doesn't need to be soldered. And the voltage regulator is something you may want to have an extra few of just in case anyway; these either give the right voltage or they don't.

but one of them if i put the negative lead on the collector (its pin 3 right ? the rightmost one when the flat part is towards you) and the positive on the emiter it will show continuity or it was the other way around (positive on collector and negative on emiter) this was T1

The BJT driven by PD6 should be an NPN (S9014) and the one driven by the encoder's push button too. The BJT switching the battery power is a PNP (S9012). The designators in the schematic posted by snapper are T1 (driven by PD6), T2 (driven by push button), and T3 (battery power). The NPNs can be replaced with any jellybean small signal NPN. And the PNP also, but its hFE needs to be about 300 or higher.
 
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Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9761 on: November 29, 2024, 04:20:49 am »
If you have reported the problem correctly, the complaint will be resolved by AE and not directly with the dealer. If you paid with PP, you also have the option of submitting a complaint here. In most cases, you will get the purchase price refunded without any problems because returns are not possible due to the high return shipping costs.
The AY-AT version of the GM328 tester with the socketed Mega328 in the 28-pin PDIP housing has the advantage that it can be upgraded with an adapter board to the ATMEGA644 with more memory so that the newer, larger firmware versions can be loaded for a larger range of functions!

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4890983/#msg4890983  :clap:


i think ive been as clear as i could with the seller showing pictures and vidoes and also evidence that other people online have had the exact same issue ive had with mine ive even went as far as using deepl and message them in chinese

and yeah the upgradeability and what seems extensive documentation of the AY/AT clone is the exact reason i chose that specific version, since i dont have much experience with electronics i cuold just follow their tutorials or just replicate their mods

If you just want to see if the main components work, you can connect the MCU and the screen and carefully connect 5V between VCC and any ground connector. The tester should come to life and this will also answer your question about whether the screen is color (most likely is). This should help:
https://youtu.be/mRMRtrzh6rI?feature=shared&t=88

As madires said, you can use just about any transistor to replace the dead ones as long you don't get the PNP and NPN ones mixed up when putting them in. The TL431 doesn't need to be soldered. And the voltage regulator is something you may want to have an extra few of just in case anyway; these either give the right voltage or they don't.

but one of them if i put the negative lead on the collector (its pin 3 right ? the rightmost one when the flat part is towards you) and the positive on the emiter it will show continuity or it was the other way around (positive on collector and negative on emiter) this was T1

The BJT driven by PD6 should be an NPN (S9014) and the one driven by the encoder's push button too. The BJT switching the battery power is a PNP (S9012). The designators in the schematic posted by snapper are T1 (driven by PD6), T2 (driven by push button), and T3 (battery power). The NPNs can be replaced with any jellybean small signal NPN. And the PNP also, but its hFE needs to be about 300 or higher.

wait what do you mean about the tl431 not needed to be soldered ? means i can remove it from the pcb and do without it ? and about the 7550 i can replace it with whatever has the same pinout and matches or exceed its specs ?

and about the test you mean i should put the positive lead of a 5v dc power supply directly to the vcc of the atmega and any ground ? ? like what would work as ground here ? any negative pin on say the electronic caps ? the metallic part of the encoder ? literally any piece of conductive metal even if isnt part of the gm328 ?

i dont think i have an specific 5v power supply i can get 5v out of, closest i have is a variable psu that i remade from years ago using a lm317 on a protoboard

forgive me for my ignorance id rather ask and look stupid than risk it and possibly break it even more

ill maybe post photos of screen tomorrow
 

Offline Feliciano

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Re: $20 LCR ESR Transistor checker project
« Reply #9762 on: November 29, 2024, 11:08:40 am »
As madires told you days ago, you don't need to buy the exact transistors replacements, any PNP and NPN with high hFE would be enough for switching the unit on and off.
But before buying parts, check the ones you have. On a transistor you should have diode continuity on only two ways (b-c, b-e, no others). And sometimes the pinout of a transistor is not the one on the PCB, sometimes you are suposed to have a BCE, but the one in your hand is CBE or ECB, or viceversa, so you would have to arrange the pins the right way.

As for the TL431, is used as voltage reference for measurements. Therefore for testing whether the unit turns on and works, it's not mandatory.

And the MCU works with 5V (some units works from directly from an USB charger, some use a 78L05, some use a 7550), so you should make sure it's receiving that when you press the button, and another pin on the MCU should latch a transistor to keep that power on when you release the button.

And have you read the project documentation? there are FAQs, and long manuals with many details that allow you to understand how this OSHW works, and hence, to troubleshoot it.
« Last Edit: November 29, 2024, 11:57:08 am by Feliciano »
 
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Offline Per Hansson

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Re: $20 LCR ESR Transistor checker project
« Reply #9763 on: November 29, 2024, 03:11:13 pm »
Cosmic_Starlight: the picture of your board still shows one tantalum capacitor for the crystal oscillator, replace it with a ceramic 22pF (picofarad) capacitor, exactly same one as you bought at the store and is installed in the other spot for the crystal.
thats what they guy at the store i bought the replacements told me but at the same time you can see yt videos of ppl buying this exact same with with the same capacitors and theirs work fine
Sorry if I wasn't really clear but the reason I wrote this is I would not mix and match capacitors for the crystal oscillator circuit:
They should both be from the same construction otherwise you might have startup problems for the oscillator, and you wrote that once it did start up and stay on that tells me it might be a oscillator startup problem...
(You also have not shown a picture of the value of the original capacitor that you installed and since the seller sent you the unit with missing components I can't know if you even have the correct one installed here...)
 
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Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9764 on: November 29, 2024, 08:50:10 pm »
Cosmic_Starlight: the picture of your board still shows one tantalum capacitor for the crystal oscillator, replace it with a ceramic 22pF (picofarad) capacitor, exactly same one as you bought at the store and is installed in the other spot for the crystal.
thats what they guy at the store i bought the replacements told me but at the same time you can see yt videos of ppl buying this exact same with with the same capacitors and theirs work fine
Sorry if I wasn't really clear but the reason I wrote this is I would not mix and match capacitors for the crystal oscillator circuit:
They should both be from the same construction otherwise you might have startup problems for the oscillator, and you wrote that once it did start up and stay on that tells me it might be a oscillator startup problem...
(You also have not shown a picture of the value of the original capacitor that you installed and since the seller sent you the unit with missing components I can't know if you even have the correct one installed here...)

I've attached a photo of the caps of the crystal and also the screen

As madires told you days ago, you don't need to buy the exact transistors replacements, any PNP and NPN with high hFE would be enough for switching the unit on and off.
But before buying parts, check the ones you have. On a transistor you should have diode continuity on only two ways (b-c, b-e, no others). And sometimes the pinout of a transistor is not the one on the PCB, sometimes you are suposed to have a BCE, but the one in your hand is CBE or ECB, or viceversa, so you would have to arrange the pins the right way.

As for the TL431, is used as voltage reference for measurements. Therefore for testing whether the unit turns on and works, it's not mandatory.

And the MCU works with 5V (some units works from directly from an USB charger, some use a 78L05, some use a 7550), so you should make sure it's receiving that when you press the button, and another pin on the MCU should latch a transistor to keep that power on when you release the button.

And have you read the project documentation? there are FAQs, and long manuals with many details that allow you to understand how this OSHW works, and hence, to troubleshoot it.

I will give the FAQ and troubleshooting questions a read and will maybe try feeding 5v to the MCU vcc with the screen attached and see what it does
 

Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9765 on: November 29, 2024, 09:46:42 pm »
If you just want to see if the main components work, you can connect the MCU and the screen and carefully connect 5V between VCC and any ground connector. The tester should come to life and this will also answer your question about whether the screen is color (most likely is). This should help:
https://youtu.be/mRMRtrzh6rI?feature=shared&t=88

As madires said, you can use just about any transistor to replace the dead ones as long you don't get the PNP and NPN ones mixed up when putting them in. The TL431 doesn't need to be soldered. And the voltage regulator is something you may want to have an extra few of just in case anyway; these either give the right voltage or they don't.



Well I just did the test of feeding 5v directly to the atmega328p vcc pin (pin 7) and for ground I used pin 22 and for the PSU I used an android phone charger that was outputting 5.1v (I made sure to use the USB voltage pins not the data ones)

And what happened was the screen lit up solid white again and that's it removing power and adding it again didn't change anything, so idk if that'd a good thing or a bad thing
 

Offline Feliciano

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Re: $20 LCR ESR Transistor checker project
« Reply #9766 on: November 29, 2024, 10:29:59 pm »
A different approach would it be to connect an ISP (ICSP) cable (provided you have or can easily find or build one). This kind of cables power-up the ATmega in programming mode, so you could check whether your MCU is still good, or it's damaged. I attach an example of such cable and connection.
 

Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9767 on: November 29, 2024, 10:47:02 pm »
A different approach would it be to connect an ISP (ICSP) cable (provided you have or can easily find or build one). This kind of cables power-up the ATmega in programming mode, so you could check whether your MCU is still good, or it's damaged. I attach an example of such cable and connection.

Unfortunately I have no such hardware of that kind, no programmer no ports no USB programmer thing, nothing, like I know I would've had to buy them down the line anyway bit since in its current state the gm328 is not working I don't even know how much of a money pit this can become

Like I would love to know if the screen is good or not since I saw a video or two on yt of ppl with my same issue and they said the problem was fixed by replacing the screen

And from what I've seen locally a screen that sort of looks like this one is the cost of a new atmega+programmer

Also I don't even know what those 3 smd components below the zif socket are, how to test them worst of all I have no tools to work on smd stuff
 

Offline Feliciano

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Re: $20 LCR ESR Transistor checker project
« Reply #9768 on: November 29, 2024, 10:50:52 pm »
Unfortunally, the cost of replacing parts like the MCU or screen usually is higher than the cost of replacing the whole thing. That without considering the man-hours invested/wasted (deppending on your viewpoint), and binging it from abroad. In that case the original one maybe can be left behind as parts supply.

Still, in my particular case I have opted for repairing/improving a few, just because the difficulty of finding an original ATmega nowadays, and the units in hand fill/can_fulfil my requirements.
« Last Edit: November 29, 2024, 11:05:47 pm by Feliciano »
 

Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9769 on: November 29, 2024, 11:33:00 pm »
Unfortunally, the cost of replacing parts like the MCU or screen usually is higher than the cost of replacing the whole thing. That without considering the man-hours invested/wasted (deppending on your viewpoint), and binging it from abroad. In that case the original one maybe can be left behind as parts supply.

Still, in my particular case I have opted for repairing/improving a few, just because the difficulty of finding an original ATmega nowadays, and the units in hand fill/can_fulfil my requirements.

Ok so given that the behaviour of solid white screen with 5v direct to atmega vcc could one say the fault is either in the atmega or screen ? And thats impossible to know without either a programmer or a replacement screen ?

It seems the wisest desition given that i have no working gm328 unit would be to buy another one but the question is which version ?
Another AY/AT ? DIY kit or soldered already ?

The black one known as gm328a with atmega on dip package ? Aka old english version

Or the other black one thats only smd components known as new english version ?

Also where do i buy it from ? AE again ? Ebay or where

I guess cheapest way would be to buy all caps again with all new transistors and ics and hope it works but with the test i did earlier am not so sure

Maybe the mcu is un programmed or is corrupt or has wrong software for screen but also could not be, cant really know for sure without spending money lol
 

Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9770 on: November 29, 2024, 11:42:18 pm »
Unfortunally, the cost of replacing parts like the MCU or screen usually is higher than the cost of replacing the whole thing. That without considering the man-hours invested/wasted (deppending on your viewpoint), and binging it from abroad. In that case the original one maybe can be left behind as parts supply.

Still, in my particular case I have opted for repairing/improving a few, just because the difficulty of finding an original ATmega nowadays, and the units in hand fill/can_fulfil my requirements.

Ok so given that the behaviour of solid white screen with 5v direct to atmega vcc could one say the fault is either in the atmega or screen ? And thats impossible to know without either a programmer or a replacement screen ?

It seems the wisest desition given that i have no working gm328 unit would be to buy another one but the question is which version ?
Another AY/AT ? DIY kit or soldered already ?

The black one known as gm328a with atmega on dip package ? Aka old english version

Or the other black one thats only smd components known as new english version ?

Also where do i buy it from ? AE again ? Ebay or where

I guess cheapest way would be to buy all caps again with all new transistors and ics and hope it works but with the test i did earlier am not so sure

Maybe the mcu is un programmed or is corrupt or has wrong software for screen but also could not be, cant really know for sure without spending money lol

Huh... Come think of it could i just buy the gm328a old english version and just swap over the mcu and screen to my current ay/at (provided this one actually works and isnt dead too)
 

Offline snapper

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Re: $20 LCR ESR Transistor checker project
« Reply #9771 on: November 30, 2024, 02:31:14 am »
« Last Edit: November 30, 2024, 02:39:10 am by snapper »
 

Offline Cosmic_Starlight

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Re: $20 LCR ESR Transistor checker project
« Reply #9772 on: November 30, 2024, 05:35:14 am »
now come think of it doing some calculations here, it seems for the price of another new unit+shipping i could locally get:

another atmega328p (dunno if original or not, nor do i know if that makes a difference)
a cheap programmer for it
and a ST7735B (which is the cheapest one i could find that sort of looks like the original)
in half the time the new one would take to arrive, (that is if the new one isnt dead too)

but now ive just seen that one has 11 pins and the current one and socket only has 8 so idk what to do there, looking online it seems the firmware is capable of using that screen but the ones ive found locally are the B ones

also idk if flashing what seems the M firmware which i think its the latest development series would require any hardware modifications to work with a device that i assume was supposed to have a modified chinese k firmware
 

Offline Yuriy_K

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Re: $20 LCR ESR Transistor checker project
« Reply #9773 on: November 30, 2024, 06:24:52 am »
also idk if flashing what seems the M firmware which i think its the latest development series would require any hardware modifications to work with a device that i assume was supposed to have a modified chinese k firmware
Before thinking about new m-firmware, you need to make the ttester itself with k-firmware work. What current does your tester consume when powered by a 9 V battery? By pressing and holding the button. Show a photo of your display from the side of the chips.
« Last Edit: November 30, 2024, 06:27:23 am by Yuriy_K »
 

Offline snapper

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Re: $20 LCR ESR Transistor checker project
« Reply #9774 on: November 30, 2024, 06:31:40 am »
@Yuriy_K "Show a photo of your display from the side of the chips"

he already posted it yesterday !

« Last Edit: November 30, 2024, 06:42:07 am by snapper »
 


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