Products > Test Equipment

TC1 lcr-meter transistor-tester fix

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indman:

--- Quote from: belzrebuth on December 18, 2020, 05:12:00 pm ---I noticed that if I connect my bench PSU to the battery terminals providing 3.7V if I press the button I get about 0.35A current draw and then after a short period of time almost no current draw(0.9mA) or so.
Forgot to mention that I get about 3.4V at the 5V regulator input and 1.7V at it's output.

--- End quote ---

It is very likely that your MCU is damaged. Take a multimeter and check the resistance of the PA0-PA3 test ports against + 5V and the ground. You can also check the resistance of pin 4 (VCC) to ground.
AL619 (AL715, AL718) this is the marking of the SD6271 chip  :)

belzrebuth:
Vcc to Ground is around 25ohms.
I mentioned it before and it seems weird that it's too low but when I power the thing directly with 5V its current consumption is within spec at around 350mA.
 PA0 to Vcc 560k
 PA1 to Vcc around 20οhms
 PA2 to Vcc around 112ohms
 PA3 to Vcc 2.2k

I wonder why they used a 644 in my revision instead of a 324 which is almost triple the price. PCB version is 2.0.

indman:
belzrebuth From + 5V, the serviceable tester consumes from 24.6mA to 44mA. You have a defective processor, you need to replace it. It is not difficult if you have the skills to solder such things. Better to buy the same ATMega644. Chinese friends very often install those parts that are currently in stock. In terms of cost, the difference between chinese 324 and 644 is very small. They earn more due to the large number of devices sold.  :)

belzrebuth:
Ah okay..thanks:)
I thought the current draw was normal all this time :palm:
I'll replace the MCU and post back.

shved:
belzrebuth, I've also had excessive power draw. Double check the caps, esp. C6 & C7. Also check for corrosive flux. Give a quick read to the rest of the thread.

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