Heathkit Troubleshooting
Dec. 6th, 2021 04:41 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
stormdogMy multimeter showed up today! I paid about $18 Canadian including shipping, and you definitely get what you pay for. But it works, basically. The rotary switch is a little...special. So I dug into troubleshooting the Heathkit!
It has 700 microamps across the meter when turned on with no probe connections. The meter reads full scale at 20, so of course it pegs. I'm pretty sure the problem is a bad transistor, either Q1 or Q2. Q1's source is connected with Q2's base and they read more than 8 volts to ground. The schematic suggests that measurement there should be about 5 volts. So either Q2 is bad, or it's running full on all the time because Q1 is bad. I think? I guess I'll order some transistors and find out!
Also the resistor measurements are all way low of spec! Not sure if it's a flaky multimeter, or measurements in-circuit are off, or if the resistors have just drifted after 60 years or so. Once I get a power supply for the soldering iron that Mark gave me as a birthday present (*so awesome!*), I'll take one off the board and check it out.
It has 700 microamps across the meter when turned on with no probe connections. The meter reads full scale at 20, so of course it pegs. I'm pretty sure the problem is a bad transistor, either Q1 or Q2. Q1's source is connected with Q2's base and they read more than 8 volts to ground. The schematic suggests that measurement there should be about 5 volts. So either Q2 is bad, or it's running full on all the time because Q1 is bad. I think? I guess I'll order some transistors and find out!
Also the resistor measurements are all way low of spec! Not sure if it's a flaky multimeter, or measurements in-circuit are off, or if the resistors have just drifted after 60 years or so. Once I get a power supply for the soldering iron that Mark gave me as a birthday present (*so awesome!*), I'll take one off the board and check it out.
