$20 LCR ESR Transistor checker project

[Feliciano]

I bought an AY-AT clone and bought the resistor and IC needed for the upgrade. But when I wanted to burn the M firmware, I found that I could not find the pre-compiled firmware that could be burned in the Windows system... It seems that it needs to be compiled and burned on the Linux system...

If you prefer the m-firmware, you won't find it pre-compiled online, as there are many features one person may want to enable and other person don't. It's not so difficult to compile it yourself, you may want to read the "Clones" file for instructions on what to modify for your particular unit.
Regarding your other question, it's not mandatory to use linux, there are Windows tools for the task, let's say AVRdudess and others. You will also need the cable for programing it, and the toolchains.
For more infiormation, you can search old posts of this thread.

[Fuzzy Star]

<offtopic>

...I have some diodes I need to test - should I be really careful in which way around they go?

What do you want to measure? Zener voltage? Forward voltage? There are simple ways to measure diodes (Google it). You don't need to risk your tester.
</offtopic>

[elecdonia]

Assuming you have that particular version of the tester, my advice is DO NOT test anything on the zener test pins (K - A) until you have made the mods. You might get away with it if it is a higher voltage zener and you are fast but there is a good chance you will burn D2 and possibly damage the DC-DC boost IC.

There is one item which can be safely tested across the zener test pins (K-A) on every version of the Transistor Tester, modified or not:

        This item is a 1k ohm resistor

No matter what condition the Transistor Tester is in, the absolute maximum current which will flow through this 1k ohm resistor will be safe. It will be no higher than 30mA.

In fact the “zener voltage” displayed by the Transistor Tester (for the 1k resistor) represents the mA flowing from K to A.

     This is just Ohms Law: The voltage drop across a 1k ohm resistor is exactly 1V per mA.

Transistor Testers with the original OSHW zener test circuit will display 2-3V for “zener voltage” with 1k resistor connected to K-A. The original OSHW zener test circuit is a 30V DC source feeding the “K” pin through an internal 10k ohm series resistor. The “A” pin is grounded. This internal 10k series resistor therefore limits the absolute maximum zener test current to 30V/10k = 3mA.

In contrast, unmodified (but working) LCR- units with APT32F172K8T6 MCU and the poorly designed U7 circuit will display 5-8V “zener voltage” with the 1k resistor connected to K-A. This is because DC-DC converter U7 actually does function as a constant current source (until it gets damaged).

An LCR-TC1 where the current-limiting portion of U7 has been damaged, but where the rest of the circuit still works, will apply about 30V across the 1k resistor. In this case the tester may display “unknown or faulty component”. However, a multimeter connected in parallel with the 1k resistor will read 25-30V.

Finally, if D2 and/or U7 failed catastrophically, then the tester may report a zener voltage of either 0V or 4V.

[elecdonia]

Hi there, I've ordered 2 replacements as unfortunately being without this bit of tat sucks. Before I do the mods any recommendations? I have some diodes I need to test - should I be really careful in which way around they go?

I have a Transistor Tester just like yours where the current limiting feature of U7 failed, but fortunately I avoided roasting D2. Therefore my unit is still generates 30V, but without any current limiting. I went ahead and installed the 2k2 series resistor between the junction of D2/C14 and the K test socket pin. This limits maximum short-circuit current to about 15mA.

IMHO putting in the 2k2 series resistor alone is good enough to prevent anything from smoking.

I continue to recommend replacing U7 too. The 2k2 series resistor protects U7. Even if a direct short is placed from K to A, the 2k2 series resistor keeps U7 safe and happy. After installing a new U7, testing with the 1k resistor should display a “zener voltage” of 5-6V. This indicates U7 is properly limiting the zener test current.

[MrSqueaky]

I've discovered a problem with the reference voltage on pin PA3 for my stock LCR-TC2. I was looking at the config.h file of the m-firmware and saw an option for defining the reference voltage so I decided to measure it on my tester but found it was only 45mV.

The TL431 works fine out of circuit so I cut the trace going to PA3 and now the reference voltage is 2.495V. So something is wrong with PA3 pin or it is not being configured properly by the firmware. The resistance between PA3 and ground is ~26 ohms when powered and open circuit when not powered. The voltage drop between 5V and PA3 is 5V so it must be being pulled low.

I'll try to compile and upload the m-firmware and see if the problem still persists.

[madires]

Have you enabled HW_DISCHARGE_RELAY by chance? That would ground the TP_REF pin (in your case PA3) between probing cycles.

[MrSqueaky]

Have you enabled HW_DISCHARGE_RELAY by chance? That would ground the TP_REF pin (in your case PA3) between probing cycles.

The reference voltage problem was with the original Chinese firmware (3.1E). I compiled the 1.48m firmware and uploaded it. Now when I press the test button I get a white screen that turns off after 30s.

The LCD is a 14 pin Z180SN009 (same as TC1 I think). I used the display configuration for the TC1 (ST7735). According to my multimeter LCD_RES stays low the whole time which might explain the white screen.

[madires]

The 'original Chinese' firmware is a modified k-firmware. And apparently they didn't disable the support for the discharging relay. When LCD_RES stays low then there could be something wrong with the configuration, e.g. same pin also used for some other function.

[indman]

I've discovered a problem with the reference voltage on pin PA3 for my stock LCR-TC2. I was looking at the config.h file of the m-firmware and saw an option for defining the reference voltage so I decided to measure it on my tester but found it was only 45mV.

This is not a problem, but a feature of the tester that you need to know and take into account. In this circuit, the PA3 pin of the MCU is periodically connected to ground (by software), so the reference voltage of 2.495V appears only when the measurement cycle starts for a very short time.

[MrSqueaky]

I've discovered a problem with the reference voltage on pin PA3 for my stock LCR-TC2. I was looking at the config.h file of the m-firmware and saw an option for defining the reference voltage so I decided to measure it on my tester but found it was only 45mV.

This is not a problem, but a feature of the tester that you need to know and take into account. In this circuit, the PA3 pin of the MCU is periodically connected to ground (by software), so the reference voltage of 2.495V appears only when the measurement cycle starts for a very short time.

I also have a round GM328A(BGR)2 tester and the reference voltage stays on for a couple of seconds after pressing the test button. I'm pretty sure it wasn't with the LCR-TC2. I overwrote the Chinese firmware so I can't test it anymore to double check

[indman]

I also have a round GM328A(BGR)2 tester and the reference voltage stays on for a couple of seconds after pressing the test button. I'm pretty sure it wasn't with the LCR-TC2. I overwrote the Chinese firmware so I can't test it anymore to double check

If you have a copy of k-firmware installed on your GM328A, then I'm sure the same behavior with Vref was also on your LCR-TC2 with Chinese firmware,which, as madires rightly pointed out, is a modified k-firmware.

[MrSqueaky]

I finally got the v1.48m firmware working on my LCR-TC2 with hardware SPI.  The pin assignment for the LCD conflicts with the hardware SPI. Tracks need to be rearranged to make a permanent solution. Bit banging works without any need for hardware modification but the output seemed a bit slow. Also, I had to half the hardware SPI speed otherwise I just got a white screen (possibly due to the jumper wires)

Code: [Select]

/* hardware SPI in config_644.h: */
#define SPI_HARDWARE
#define SPI_PORT         PORTB     /* port data register */
#define SPI_DDR          DDRB      /* port data direction register */
#define SPI_PIN          PINB      /* port input pins register */
#define SPI_SCK          PB7       /* pin for SCK */
#define SPI_MOSI         PB5       /* pin for MOSI */
#define SPI_MISO         PB6       /* pin for MISO */
#define SPI_SS           PB4       /* pin for /SS */

/* ST7735 using hardware SPI  in config_644.h: */
#define LCD_PORT         SPI_PORT       /* port data register */
#define LCD_DDR          SPI_DDR        /* port data direction register */
#define LCD_RES          PB0            /* port pin used for /RESX (optional) */
#define LCD_CS           SPI_SS         /* port pin used for /CSX (optional) */
#define LCD_DC           PB1            /* port pin used for D/CX */
#define LCD_SCL          SPI_SCK        /* port pin used for SCL */
#define LCD_SDA          SPI_MOSI       /* port pin used for SDA */

/* set SPI clock rate for hardware SPI display in ST7735.c: */
// SPI.ClockRate = SPI_CLOCK_2X;    /* set clock rate flags */
SPI.ClockRate = 0;    /* set clock rate flags - SPI2X = 0, SPR1 = 0, SPR0 = 0, SCK = fosc/4 */

/* set power management pins in config_644.h: */
#define POWER_PORT       PORTD     /* port data register */
#define POWER_DDR        DDRD      /* port data direction register */
#define POWER_CTRL       PD1       /* controls power (1: on / 0: off) */

#define BUTTON_PORT      PORTD     /* port data register */
#define BUTTON_DDR       DDRD      /* port data direction register */
#define BUTTON_PIN       PIND      /* port input pins register */
#define TEST_BUTTON      PD2       /* test/start push button (low active) */

/* set probe colors to match decal in color.h */
#define COLOR_PROBE_1         COLOR_RED
#define COLOR_PROBE_2         COLOR_YELLOW
#define COLOR_PROBE_3         COLOR_GREEN




[indman]

I finally got the v1.48m firmware working on my LCR-TC2 with hardware SPI. 

In my experience, for a 1.8" color display at 16-20MHz, there is no particular need for a hardware SPI.
The difference in speed compared to software SPI is not noticeable. For displays with a diagonal of 2.2 inches and above, hardware SPI really gives an increase in the speed of updating the picture, but still not as big as we would like.

[alex_D]

Got this AY-AT kit and it works really well, mounted the ZIF socket in a standard 14 pin DIL socket so I can easily swap it out if need be, the 16Mhz upgrade
was easy-peasy, thanks to all involved with the open source firmware.

Thinking about getting another AY-AT kit, wondering what it would take to make it work with a 3 color e-paper display, i'm guessing it would help a
bit with battery life. https://uk.banggood.com/Waveshare-1_54-Inch-ink-Screen-Module-152x152-Electronic-Paper-SPI-Interface-Yellow-Black-and-White-Three-color-Display-p-1750623.html?imageAb=1&cur_warehouse=CN&rmmds=CategoryElectronicsPop&a=1676811431.4374&DCC=GB&currency=GBP&akmClientCountry=GB

[madires]

Recently we've tried an SSD1681 based EPD. It's so slow that it's infeasible. A b/w full display refresh takes several seconds, a three color update even longer. A b/w partial refresh is a bit faster (and blurry), but requires a full refresh after every few partial ones.

[py-bb]

Hi there, I've ordered 2 replacements as unfortunately being without this bit of tat sucks. Before I do the mods any recommendations? I have some diodes I need to test - should I be really careful in which way around they go?

I have a Transistor Tester just like yours where the current limiting feature of U7 failed, but fortunately I avoided roasting D2. Therefore my unit is still generates 30V, but without any current limiting. I went ahead and installed the 2k2 series resistor between the junction of D2/C14 and the K test socket pin. This limits maximum short-circuit current to about 15mA.

IMHO putting in the 2k2 series resistor alone is good enough to prevent anything from smoking.

I continue to recommend replacing U7 too. The 2k2 series resistor protects U7. Even if a direct short is placed from K to A, the 2k2 series resistor keeps U7 safe and happy. After installing a new U7, testing with the 1k resistor should display a “zener voltage” of 5-6V. This indicates U7 is properly limiting the zener test current.

Replacing U7 is out of the question, the boards on mine are not very clean and I've barely used a heatgun before, but I can do the other one.

I think you have made a mistake though, the junction  between D2 and C14 is the K test point so you'd be putting it in parallel with a wire. Do you mean I should knife the trace? That doesn't seem reliable.

Thanks.

Ed in an earlier post you explain this'll require cutting the trace

I can't find that manual link and I'd like to see a picture of your modifications please - I noticed the replacements but not the cut trace in a post you made 3 pages back

[py-bb]

<offtopic>

...I have some diodes I need to test - should I be really careful in which way around they go?

What do you want to measure? Zener voltage? Forward voltage? There are simple ways to measure diodes (Google it). You don't need to risk your tester.
</offtopic>

This is a non-answer but it'd be nice to measure the breakdown voltage (or "the voltage" when using them as voltage regulators) - but mostly I just want a tool I can't break if some wires touch somewhere.

This is why I like hand-held (or differential) voltmeters, you can stick those probes anywhere and it'll be fine (except in weird contrived circumstances which if you bring up I'll point out that if I end up in those conditions something has already gone very wrong - like lack of job equipment & training a person in that situation would actually have)

[GraemeG]

I think you have made a mistake though, the junction  between D2 and C14 is the K test point so you'd be putting it in parallel with a wire. Do you mean I should knife the trace? That doesn't seem reliable.

Thanks.

Ed in an earlier post you explain this'll require cutting the trace

I can't find that manual link and I'd like to see a picture of your modifications please - I noticed the replacements but not the cut trace in a post you made 3 pages back

I don't have a photo to show you but you are correct in your first comment and in your edit. The track from the junction of D2/C14 and the K test point must be cut and the 2K2 resistor soldered in to bridge the cut in the track. This is definitely reliable and it fixes a flaw in this version of the tester.

Almost the first use of my tester was to measure the forward voltage drop of some schottky power diodes. I used the zener test terminals for a slightly higher current than the normal test terminals. In theory U7 is supposed to limit the test current but after just a few tests my unit failed and I discovered D2 totally burned. I don't know what current was flowing during the test but D2 was well past its specs! By inserting the 2K2 resistor the short circuit current is limited to a maximum of about 14mA into a short circuit on the K-A pins. ie. approximately 31V supply divided by 2200 ohms = 14.1mA

[Fuzzy Star]

<offtopic>

...I have some diodes I need to test - should I be really careful in which way around they go?

What do you want to measure? Zener voltage? Forward voltage? There are simple ways to measure diodes (Google it). You don't need to risk your tester.
</offtopic>

This is a non-answer but it'd be nice to measure the breakdown voltage (or "the voltage" when using them as voltage regulators)

As I said, Google it. Like Google 'measuring zener voltage' or 'testing zener diodes'

[mastershake]

so out of the insane amount of various clones out there can so done simply suggest one that works and will allow firmware upgrades if need be? I've been trying to get through this thread but with one eye down reading for me is a lot slower than it used to be. I'm about 1/4 way into the thread but think maybe I should have started on 330 and went backwards. I'm looking for really the best of the clones I guess but one I can upgrade or will that require changing the chip regardless. thank you in advance and I def appreciate any help or info. I'm heading back in for two weeks to the hospital for more cancer stuff and I'd love to get one ordered before going in. hopefully lots of boxes waiting for me when I get out.

[madires]

Which clone to get is a common question and you'll find the answer quite often on the last 10 pages. Be aware that some clones currently come with an alternative MCU not supported by the OSHW firmwares.

[mastershake]

Thats why I was asking does anyone have a recc seller or one you have recently bought that was legit? I just don't want to go through a bunch trying to get a good one. any AliExpress or Amazon etc link anyone could share if you know you got a legit one recently?

[indman]

mastershake,so this is the problem that no one will give you a 100% guarantee that the seller will send you the LEGIT device.Because in most cases, the seller has no idea about the contents of the goods.Today one person received a legitimate product, and tomorrow another person will receive an "illegal" product from the same seller.

[mastershake]

is there a certain board layout that one would want vs the rest of them at least? that sucks about not being able to get a legit one from any one seller.

[alex_D]

Right now from my experience, it seems the best option is to get the self build kit, that way you can be sure of getting a component tester you can easily self repair, mod and upgrade the firmware.