Marek No diagram included that I can see. The next comment may be totally wrong since I have nothing to go on. If the input voltage is 24 V and the supply is 10 V reg at .48A, then during the initial warm up the transistor easily dissipates 6 watts. That would be a power transistor and some form of heat sink to keep the junction temperature reasonable. Regards Paul WB8TSL
On Sun, May 8, 2022 at 2:14 PM Marek Doršic <[email protected]> wrote: > I would like to get your thoughts on my problem with OSA-5400 oscillator. > > I have on old unit, which is somehow broken. I was told it was overpowered > with voltages up to 32V (standard supply voltage is 24V) and even sourced > with reverse polarity supply power. > > When I first powered it up, it draws only 2mA. I replaced what I supposed > was a broken 10V voltage reference (how wrong I was), with a 10V zener > diode and voilà, I had a nice steady 5MHz, 14dB signal. But only for couple > of hours and then it died again. So I reverse engineered the schematics > below and the part in question (Q4) is what I suppose a PNP power > transistor. A bought a bunch of different types available. Solder in an > 2N2905A and powered the unit. The heater went on, the unit drew 480 mA > after power up but the output signal was still only some noisy 2mVp-p. > After a few minutes the transistor went broken and the heater and > everything went off. > Then I put there a BC160-10. This seemed to be good choice. The unit > worked again normally, with nice output signal, but again only couple of > hours and then the signal was lost. > But all the voltages at test pads remain as labeled on the PCB. The > thermistor output pins on front panel are always 2 Ohms. This part in > heated core of the unit is probably already broken. > > Do you have please any thoughts, what can be wrong with the unit or what > kind of power transistor should be used (Q4). The original part has gold > plated leads and TO-39 package. > The resistor values are only indicative measured with multimeter while > soldered in. > > .md > > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
