Well here is the funny part. On one of the supplies, I did indeed find a bad 3771, but before I changed it, there was still 12 volts at the lugs. I then took the 723 and put it in another ps, which it caused the resistor connected to tip29 npn transistor to smoke. So back to the first power supply. I replaced the bad 3771, all the rest are ok, put in a new NTE923 chip, and now no voltage at all out the lugs. Pull the SCR from the bottom, left it hang, and still no voltage. Only thing left is the TIP29. Any thoughts.
Mathew -----Original Message----- From: Charles Miller [mailto:[EMAIL PROTECTED] Sent: Tuesday, January 25, 2005 5:17 PM To: [email protected] Subject: Re: [Repeater-Builder] Transistor Checking Mathew, Depending on the meter that you have you should get a reading of between 400 and 700. My Fluke 77 shows 453 on most Astron's that I have serviced. If you have a short between any pin and case or between pins the transistor is defective and must be replaced. Also check the resistors in the output stage, as you will probably find one or more open. If the transistor blew to the base it probable took out the 723 as well. I most if not all cases we change out all the transistors and the 723. Only in a couple of cases did we find other damage that required more parts. Good Luck, Charles Miller ----- Original Message ----- From: "w9mwq" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, January 25, 2005 4:02 AM Subject: [Repeater-Builder] Transistor Checking > > > Just need a short memory replacement here please. I'm working on an > Astron 35 amp power supply, hope to get it going again. I'm > checking the transistors in the unit, and not sure if I remember > correctly. On my vom, in the diode checking position, I should have > a dead short from case to one pin, and nothing from case to the > other pin, but should there be a reading from pin to pin. These are > on the 2N3771 transistors. Thanks. > > Mathew > > > > > > > > > > Yahoo! Groups Links > > > > > > > > Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
