The 723 regulator is probably bad. One way to confirm this is by measuring the voltage on pins 5 and 6 which should be around 7.1 volts. The 723 is powered separately from the main supply by its own DC source. There is a 2N3566 pass transistor supplying DC to pins 11 and 12. The base of this transistor is conncected to a 2N5060 thyristor to ground. The thyristor gate is connected to a PNP transistor, 2N4402 to the reference voltage of the 723 on pins 5 and 6. The PNP transistor gate monitors the PS-7 output voltage through a 2K voltage adjust pot. If the PS-7 output voltage should drop drastically from what is expected, the PNP transistor will pass some some of the reference voltage to the thyristor gate which will then trigger, bringing the base of the pass transistor within two diode drops of ground and therefore shut down the 723. The 723 minimum operating voltage to pins 11 and 12 is around 9.5 volts and as much as 37 volts. Unlike more modern solid-state regulators, the! 723 do es not have thermal shutdown. It also doesn not tolerate reverse voltage. For example, if you shut down the supply but you had it feeding a very large DC storage component such as a large electrolytic or capacitor bank, the electrolytics will start dumping voltage back towards the output of the 723 while the input is shut down. When this unlikely event occurs, you can smell it :-( -------------- Original message -------------- From: Lars-Åke Jansson <[EMAIL PROTECTED]>
> > =?iso-8859-1?B?TGFycy3Fa2UgSmFuc3Nvbg==?= made an utterance > to the drakelist gang > ---------------------------------------------------------------------- > Hello out there, > > Hopefully someone can give me an advice regarding my PS7. > > The problem is it only delivers 3 V. > There is 24,2 V out from the high current bridge (MDA3500). It is not > possible to adjust the output voltaged with the yellow potentiometer on PCB, > no response. After about 30 sec the IC MC1723 is hot like an oven. > > 73 de SM6CGI/Lars-Ake > > _________________________________________________________________ > Senaste nytt om Paris och Lindsey http://starlounge.msn.se/ > > ---------------------------------------------------------------------- > Submissions: drakelist@www.zerobeat.net > Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > ----------------------------------------------------------------------
