- 2026
- Jan
- 21
A Simpson 715 AC VTVM Part 3: Continuing capacitor replacements.
In the last part, we started to replace some of the parts that are known problems in older devices. While most of these probably won’t do anything to fix the non-zero issue (and that is probably some other parts out of tolerance) - they will need to be replaced if this meter is going to go into service with any reasonable expectation of working.
This part sees some of the components in the meter circuit replaced, and takes care of most of the (current) work on the bottom of the device. There’s a capacitor-resistor pair that we’re going to replace, and this is a component directly in the meter circuit. There’s also another resistor on the topside that’s part of this circuit, but that isn’t going to get replaced until later.
Here’s the components we’re working with:
In particular, the capacitor and the 2W 680Ω power resistor are being replaced. The 30Ω resistor is for later. The capacitor and resistor mentioned are soldered across one another, so removing the capacitor means the resistor gets removed as well.
I didn’t need to use a 2W part here, but that’s what I had on hand. It’s pretty much the same size as the old 1/2W carbon comp, so why not.
Here’s what we’re going to replace:
This part attaches to a terminal strip that carries a wire up to the meter board, and snakes down to a tube socket on the other side. They unsoldered fairly easily, and I was able to bend leads and remove the parts intact for later testing.
The new parts don’t need to go in the same way, they are small enough that they can simply run directly to the connection points with a little bit of ‘lectric sketti.
That was much easier than I expected, and I took the time to remove the filter capacitors as well. That’s next.
The old part was pretty much +100% at 1.4Ω ESR, so it’s getting tired.
Next up is the filters, then the meter board goes back on with some parts attached to it. Stay tuned!
Next part of this series: Coming soon.
Previous part of this series: https://wereboar.com … x-the-no-zero-issue/