About the HP E3611A Power Supply

After messing around some time with homemade power supplies and some of them in kit form I decided to bite the bullet and acquire a "real" lab power supply: the HP E3611A.

This power supply works like a charm. It is precise, robust, excellent stability... a real pleasure to work with. But as soon as I started to use it I noticed a small annoyance. Some times at power on, and almost all times at power off it produced a big "plop" in any speaker I had in the room. The "plop" was also heard in RF with a receiver. It was only an small annoyance so I didn't pay too much attention to the "plop".

About bulged electrolytic capacitors

In the last 20 or so years, in about 95% of my repairs the problem were always bad electrolytic capacitors. There are people who claim the capacitor plague ended in 2007, but it is 2020 and I still routinely find bulged and/or leaking electrolytic capacitors in equipment build well beyond 2007.

A bulged or a leaking electrolytic capacitor is the best thing that can happen to you. Just look around, see the damaged capacitor and replace it. Easy. But... how to find a bad capacitor still not bulged? Use a capacitor tester and measure its ESR. This is the most logical response I should obtain. It was also my first idea. And I did it.

Cleaning a Power Bank

One common option to supply the small TTGO LoRa boards is to use a small power bank. For supply small devices like these boards I use one really cheap power bank, so cheap it can be obtained for 0.80 euros from China (with no 18650 li-ion cell included, of course).

The 0.80 euros power bank

It seemed to work just fine but powering a 433 MHz TTGO board I noticed the power bank itself radiates a lot of noise in this frequencies.  UHF noise from a switching mode power supply is a new record for me!

But... Can it be cleaned?

Fuses in TTGO LoRa V1.6

Today, probably the most common ESP32 LoRa board is the TTGO V2-1.6. In a very small factor it offers OLED screen, WiFi, Bluetooth, micro SD slot, li-ion charger... and a lot of problems.

The problems seem to come from the polyfuses installed in the board. There are two of them, and each one offers a different set of problems.

The Screaming TTGO T-Beam

If you are playing with LoRa devices it is pretty sure you have some ESP32 LoRa boards, and probably a ESP32 based TTGO T-Beam. This board is quite interesting because it includes a GPS, making very easy to compute distances of messages sent and received through LoRa chips.

TTGO T-Beam ESP32 based LoRa Board

Icom IC-R7100 and its clicking noise

Some time ago an Icom IC-R7100 arrived to my shack. It's a nice receiver and works surprisingly well but almost the very first time I powered it up an annoying feature came up: every time the squelch opens or closes, It produces a clicking noise.

It is ok for the first five minutes but it can be irritating after that.

Repairing an Anritsu MS2711A handheld spectrum analyzer

One night, I was searching eBay with no especial interest when I found something interesting, a cheap non working Anritsu MS2711A spectrum analyzer. The photos shown a turned on analyzer, and some signals (noise) appeared in the LCD. The LCD had some dead lines at the bottom, but nothing serious.

A small size spectrum analyzer is very tempting. I have another two full-size spectrum analyzers but they are so big and my space so limited I rarely use them. These small units are somewhat very limited compared to a real spectrum analyzer, but I was pretty sure I would use it much more often than the two units I already have.

After a few minutes, I decided to buy it.