Well, this time it was more luck than anything else. Let me explain.
I promised a while back that I would tell you about me enjoying the newly repaired TS-440S. I do enjoy it, that’s not the problem, but the amount of enjoyment is short. How come? My power supply consist of two 7 Ah SLA batteries, which I charge with a wall-wart. With a 100 Watts output I can operate for an hour and that’s it. Even in listening mode it’s not more than a few hours longer as the set draws quite a current. When the batteries go flat it takes some 18 hours to charge them again, so I have to plan my activity very well.
So meet Mr. Jack Huang, a.k.a. BU2BA.
He is living down the street from my mother-in-law, on the edge of Banqiao. He is quite an active ham and so it was obvious that I paid him a visit when I first arrived here a year ago. He has a room full of transceivers and a small dipole on the roof of his 15 storey apartment building, so he is limited to daytime operation due to noise. It’s always nice to chat with him and he is much more technical than I ever will be.
I had to sell off all my 220 Volt power supplies before we moved here, because Taiwan has 110 Volt coming out of the wall sockets. Jack had an old 30 ampere PSU lying around which he sold me together with a Yaesu FT-690mkII for a good price. It is a locally made PSU, so no circuit description, modded with a fan and – to be honest – some shoddy soldering. It worked fine until I started to have problems with RF feedback. Over the course of a few months it became worse and worse until I couldn’t even draw 1 Amp of current out of it. With my modest test equipment and knowledge I measured everything I could: all normal. I put in some new transistors and an IC in the voltage regulating circuit, just in case. Learned a lot about PSU’s in the process, but I still couldn’t find the cause. I even made a video of it.
Back to Jack with the 10 pounds of heavy metal. With his sophisticated equipment he tested the whole thing: couldn’t find anything wrong, either. Then he hooked up a 50000 uF capacitor instead of the 2×10000 uF which were in the PSU and waddayaknow? It worked! Out with the old, in with the new. You guessed it: still the same problem.
I am not a technician by nature. I approach everything with logic, curiosity, trial-and-error and by eliminating the impossible. And then there is my gut feeling which said: “it’s the voltage regulator, sonny!” So with the PSU gutted on my bench I noticed this trimming potentiometer on the voltage regulator controlling pin 2 of the CA723CE IC. Time for a dose of curiosity: what does it do if I turn it? Well, it creaked and squeaked a bit and all of a sudden the PSU came back to life. I hooked up a halogen lamp and no problem drawing 2 amps. I hooked up my TS-130v and no problem drawing 4 amps. I would have hooked up my TS-440S, but the kids called for dinner and Sinterklaas was also scheduled to pay us a visit that night (he never forgets Dutch ex-pats, because he is a really nice Saint), so I left it there.
I later took out the potentiometer and couldn’t measure a steady resistance at any point. I guess it is a 20 MOhm one, but I only had a 1 MOhm at hand. That one did the job too, so I was right in time for the ARRL 10 meter contest. All’s well that ends well. So, am I great or am I just lucky?