Jim, Why does any electronic component fail? It could happen for any number of reasons. But, to answer your implied question, open diodes don't blow fuses; shorted diodes do. If one of the diodes in a full-wave rectifier opens, the output voltage drops and the ripple increases significantly. Other than a shorted transformer- which is still a remote possibility- the most likely candidates are the ones I listed.
Disconnect one end of each diode, and measure the forward and reverse resistance of each- or use the diode test function of a good DVM. If you find a bad diode, replace both in that pair. Also disconnect and measure the high-voltage capacitor's resistance (and its capacitance, if you have such a meter). While you have the diodes disconnected, but with the capacitor in place, plug in the power supply to see if the 10 amp fuse holds and nothing gets hot. If it blows, either the transformer or the capacitor is bad. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, February 24, 2009 12:11 PM To: [email protected] Subject: [Repeater-Builder] Motorola Micor Power Supply - TPN1110B Thanks Eric for the correction on the model #. Why would CR1,CR2, or CR3, CR4 short? I would think they would open, or one/some would open, not short. I will call our local Mot. Repair to locate the these diodes. I guess I could work on separate the secondary from C1, to check if C1 is shorted. Thanks, 73's, Jim Kh6jkg. Jim, It took me a while to figure out what you have. TLN5123B is not the model of the power supply; it is the part number of the Chassis and Hardware Kit in a TPN1110B Power Supply. If your power supply blows the 10 ampere fuse F1 with no load connected to TB1 and both F2 and F3 pulled, you have greatly narrowed the possibilities. The most likely candidates, in order, are shorted CR1 or CR2, then shorted CR3 or CR4, and finally a shorted C1. If capacitor C1 is either open or shorted, the ferroresonant transformer cannot regulate properly. Note that more than 600 VAC appears across C1 during normal operation, and you must replace this capacitor with a similar unit designed for this application. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of [email protected] <mailto:kh6jkg%40netscape.net> Sent: Monday, February 23, 2009 8:36 PM To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> Subject: [Repeater-Builder] Motorola Micor Power Supply - TLN5123B I have a Micor power supply, that stopped working. I removed the power supply, currently no load on the bench. Back plane fuse - OK F3 - 13.8v fuse - OK, 0vac, Voltage 4.7vdc before F3 F2 - 9.6v fuse - OK, 0vac, Voltage 2.2vdc before F2 F1 10 amp. opens if left powered on. I am able to measure the above voltages before F1 opens. With no AC power, I measured the resistance across TB1, (After temporally shorting to ground to remove any stored voltag e, and opening F2, & F3.), 15.3 ohms. There are not many components before F2, and F3. I guess the next components to check are CR1, CR2, CR3, CR4. Although, I have not seen many power supplies with C1 across one of the secondary, like Motorola P.S. It would be best to replace all four. Please send me your input, on the likely faulty component(s) to check. Thanks for your emails. 73's, Jim Kh6jkg. ________________________________ A Good Credit Score is 700 or Above. See yours in just 2 easy steps! <http://pr.atwola.com/promoclk/100126575x1218822736x1201267884/aol?redir=htt p:%2F%2Fwww.freecreditreport.com%2Fpm%2Fdefault.aspx%3Fsc%3D668072%26hmpgID% 3D62%26bcd%3DfebemailfooterNO62>
