Magnavox 37mf437d/37 chirp

[intimidator]

I have Magnavox 37mf437d/37 and when I turn it on I hear a chirping. The green power light is on but the screen is black. I looked at the power supply and there are three capacitors that look like they are a little bulging. Could the bulging capacitors cause the tv not to work?

[multimeter]

Re: Magnavox 37mf437d/37 chirp

chirping can be a sign of a bad start-up capacitor,(33-50 uf 50v),or a sign of short,check voltages on psu,and check them to GND also,you want to see a high resistance in K OR MEG OHM,the ground pins will give you a reading of 1.5ohm.the startup caps will be in the primary section,check all your caps in the secondary esr and capacitance.

also check secondary diodes,these can cause a chirp if one or more have shorted.

and yes bulging caps can cause this issue,replace with panasonic fr/fm or fc series,fr being the best,fm second,and fc third choice

[intimidator]

Re: Magnavox 37mf437d/37 chirp

I have checked all the diodes and they all show current going through them but I am just not sure if they are the correct voltage.

[aaronwt6]

Re: Magnavox 37mf437d/37 chirp

If you have the chirping noise, you will most likely need to replace the 3 capacitors as well as diodes ZD902, ZD904, ZD906, and ZD908. I've repaired at least a dozen of these and my experience has been if it simply won't power up but has the standby light, it's just the capacitors. If it advances to the chirping phase, then the diodes have also failed.

[intimidator]

Re: Magnavox 37mf437d/37 chirp

I have a couple of 1N4007 diodes laying around. Could I use those to replace the bad diodes?

[multimeter]

Re: Magnavox 37mf437d/37 chirp

I have a couple of 1N4007 diodes laying around. Could I use those to replace the bad diodes?

depends where in the circuit the diodes are,you need to check the part number written on them,you will find they may be UF4007 ETC ETC,which are ultra fast recovery diodes.

unsolder one leg of each diode and set meter to diode test,normal readings in diodes are reading one way when reversing probes,shottky diodes will have readings both ways but not shorted readings.

[multimeter]

Re: Magnavox 37mf437d/37 chirp

also we could do with some good pics of the PSU to show you what,where,and how to test,without it its like the blind leading the blind.also a pic of mainboard could be helpfull.

[aaronwt6]

Re: Magnavox 37mf437d/37 chirp

ZD902 and ZD904 -- P6KE120ACT-ND TVS DIODE 102VWM 165VC AXIAL
ZD906 -- P4KE250A-E3/54GICT-ND TVS DIODE 214VWM 344VC AXIAL
ZD908 -- 568-7930-1-ND DIODE ZENER 18V 400MW ALF2

Got all those at digikey

[intimidator]

Re: Magnavox 37mf437d/37 chirp

ZD902 and ZD904 -- P6KE120ACT-ND TVS DIODE 102VWM 165VC AXIAL
ZD906 -- P4KE250A-E3/54GICT-ND TVS DIODE 214VWM 344VC AXIAL
ZD908 -- 568-7930-1-ND DIODE ZENER 18V 400MW ALF2

Got all those at digikey

Thank you for the part numbers. I was just going to ask about the part numbers especially with the ZD908 diode.

[aaronwt6]

Re: Magnavox 37mf437d/37 chirp

If you change those 4 diodes along with the bad caps, you will almost certainly have a working board again. You can try the caps first but I doubt you'll have any luck without the diodes. My experience has been that once the chirping develops, you need to change the diodes too.