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st2

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Everything posted by st2

  1. Yes I realized that 😀 Well, I've got a populated board and I'd like to try getting it to work to avoid contributing to electronic waste 😁. The board is small and limits modding and upgrade opportunities. I'll try rigging up 4 AA batteries for -6V negative supply and see what happens. I tried simulating a 7905 but, for this option too, voltage swing is missing for that current. But building a dedicated aux power supply for 40 mA -5V would go beyond any common sense...
  2. I had some time to analyse the simulation, it appears there's a problem of current, the negative rail needs 40 mA but the charge pump can provide no more than 9-10 mA before collapsing (with my 23.4 VAC to start from). On my board I discovered that U3 is too hot to touch, perhaps it's shorted and overloading the rail (I had no more sockets so I soldered it unsocketed... poor stupid, hard work now🤐. Anyway, -5.1 to +30.4 supply seems a hard beating for a TL081, isnt'it?) Changing the value of R13/R14, could the circuit work with a lower negative rail, say 2V7 or 3V3? Cheers,
  3. Thanks for your kind reply! I tried simulating that too (Simetrix), sorry for bad image without captions, top is D5 anode voltage, then D6 anode, then D7 anode, bottom: current in mA in negative rail. No zener regulation here too...
  4. Hi folks. I built this PSU in its original version, with 081 opamps and 5.1V zeners. I understand the circuit is rather old and has been improved over time, but I already had the PCB and the whole thing is getting me to learn something, so I'm trying a troubleshoot before tossing it into the waste. I have 23.4 VAC on input and 30.4 VDC on C1. Unfortunately the negative supply around D7 isn't working. Checking on multimeter and scope (old CRT with no measure function) I have: on D6 anode, a pseudo sinewave with -1.8/-8.7 V p/p on D7 anode a jagged, flatted top wave with 0.7/-1.5
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