I have been checking VRs and transistors in my old Yamaha RX V3000. I have a 7805 showing 6.5volts out and a 7812 showing over 14 volts out...I assume these should be tossed?
And you wouldindulge mewith another question...I have 4 2sc4512 power transistors that all seem to be bad...I'm using the diode function on the multimeter ...on two of them I get nothing...either some numbers flash then go to 000...or I get nothing at all...am I making a basic mistake??
And you wouldindulge mewith another question...I have 4 2sc4512 power transistors that all seem to be bad...I'm using the diode function on the multimeter ...on two of them I get nothing...either some numbers flash then go to 000...or I get nothing at all...am I making a basic mistake??
The 78xx regulators have a tolerance of +/- 5 % including variations over temperature, input voltage and output current, according to their datasheets.
Was the load current at least 5 mA? The spec does not apply without load.
Was the load current at least 5 mA? The spec does not apply without load.
Test some regular diodes like 1N400x series, both forward and reverse. Are these normal?
Obviously the transistors' PN junctions should not read a short in either direction.
At first sight I'd also say the vregs are stuffed, but.
Lets not forget 78 and 79 series regs can be 'tricked' into providing differing output voltages by the addition of a resistor.
So I would suggest you post the schematic before condemning them.
Lets not forget 78 and 79 series regs can be 'tricked' into providing differing output voltages by the addition of a resistor.
So I would suggest you post the schematic before condemning them.
I agree, the schematics is a common language for us all...
i use this type of tester to check parts... leaves out the guesswork....
https://shopee.ph/product/52451576/...MInYKJ1c6ogAMVFklgCh2fCQSnEAQYByABEgJMrvD_BwE
https://www.amazon.com/DiGiYes-Digi...=sr_1_6?keywords=lcr-t4&qid=1690245586&sr=8-6
I would check the accuracy/health of the meter as well. I have not encountered too many 78xx series regulators that were significantly out of tolerance. I haven't even run into a significant number that had stopped working.
I have had several inexpensive meters die due to ESD and mistakes on my part. I have good meters, but used to have some cheap disposables which is what they ultimately proved to be while the two Fluke bench meters and Keithley soldier on year after year.
I have had several inexpensive meters die due to ESD and mistakes on my part. I have good meters, but used to have some cheap disposables which is what they ultimately proved to be while the two Fluke bench meters and Keithley soldier on year after year.
Those regs may be floating , it's a common technique to get an arbitrary output from a set regulator.
As @UserAbuser said.
To check whether they are still OK be sure to measure Vout versus the common pin, which may be different from ground.
If Vout to common is OK, the reg is OK.
Jan
As @UserAbuser said.
To check whether they are still OK be sure to measure Vout versus the common pin, which may be different from ground.
If Vout to common is OK, the reg is OK.
Jan
Thanks to all for the help. I have solved the power supply issues and get proper voltage readings at all points. However, it seems I definitely have 2 bad
poweer transistors. What wouljd be an acceptable substitute for the sanken 2sc4512? Thanks again...
poweer transistors. What wouljd be an acceptable substitute for the sanken 2sc4512? Thanks again...