MAGNAVOX FUNAI 32MF301B/F7 blows fuse

[triplefour]

picked up a few more tv's today and started on this one first.
on the front it says magnavox, but on the back it says funai.
when i got it, it had no standby light and did not respond to pushing power.
i opened the case and realized first thing that the fuse had blown.
i was able to find a similar fuse lying around so i figured i'd take a chance.

shoulda built that light bulb fuse saver thing budm was telling me to because of course it just blew the new fuse right away. cant count on getting lucky every time i guess! gotta think if a fuse blew, theres usually a reason.

anyway i was able to find the service manual and in the diagnosis flow chart it does have a couple things to say about if its blowing fuses...

it says two things:
"Check the presence that the primary component
is leaking or shorted and service it if defective."

and

"Check the presence that the rectifying diode or circuit
is shorted in each rectifying circuit of secondary side,
and service it if defective."

can someone tell me what they mean by "primary component" ?
and i guess im supposed to know what the rectifying diode or circuit is, but i could probably use a little help there too...

i started checking diodes and i did notice one that seemed to be shorted (reading 0 resistance both ways) but ill have to lift a leg to be sure.

this power supply is so huge and strange looking.
everyone has their own way i guess.

[Th3_uN1Qu3]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

The primary transistor is the thing on the little heatsink next to the large yellow transformer. What a sad, empty looking PSU though.

[triplefour]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

i know, right? all that space and just a few components...mostly diodes and resistors...theres only that one transistor so naturally i took it out and tested it.
it has shorts from all 3 legs to each other...im guessing that means its no good.
im hoping i just replace this transistor and fuse and ill be fine? what else can i test to be sure i wont just blow the transistor again though?

[Caleb]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

q600 will be shorted, d604 will be shorted, d640 on back of board will be shorted, d610 maybe shorted, you will also probably need to replace q601, several of the other zeners may be bad as well, you should also check those two big cement resistors as well as the low value resistor near d604 for opens. big thread on this power supply HERE When you order up replacements get spares.

[budm]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

You need to check evrything (diodes, transistors, opto, resistors etc) in those red section.
This is very similar circuit that is used in the Sylvania that you are still working on.
https://www.badcaps.net/forum/showthread.php?t=40071
Sylvania/Magnavox/Emerson/Funai are made by Funai.

[Andrew F. Ali]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

I can't remember anybody being successful in repairing these 'worrisome' Pwr Supp bds. IMHO best fix is to locate one on e-bay and replace that dead one.

[triplefour]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

Thanks burn yea I did notice the similarity to the sylvania board...thanks for the tips everyone. I'll test all those parts n report back...

[triplefour]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

ok q600 was shorted as i said
d604 was shorted
d640 reads shorted but i didnt desolder it yet
d610 i lifted one leg, seems to be fine on diode check i get 707 (what does that mean, voltage drop?) one way, and infinite the other way..
i removed q601 and tested it with my test thing (the kit i built that can test capacitors for ESR and also tests transistors and mosfets and stuff)
but i still dont really understand the numbers it gives. one reading i got called it an NPN and another said its a Diode... guess i gotta find the datasheet
markings: C 5344 Y201

jeez from reading these other posts, it seems like a nightmare....too bad the board isnt cheap for only a 32" tv....i would pay 20$ maybe 25

[budm]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

2sc5344, npn.

Japanese transistors:
2SA, 2SB = PNP
2SC, 2SD = NPN

[triplefour]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

is this the correct datasheet?
when my meter reads it correctly as an NPN, it says
B=19 and uf=533mv

not sure what to read in the datasheet to verify this....

[budm]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

is this the correct datasheet?
when my meter reads it correctly as an NPN, it says
B=19 and uf=533mv

not sure what to read in the datasheet to verify this....

I am not familiar with your meter so I have no Idea what the:
B and uF are for when testing the transistor.

[triplefour]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

yea this kit really came with no instructions except how to build it and how to use it, but not any description of what the readings mean in certain non obvious situations...
i know others have bought this kit, and maybe know more about it...
any other easy test i could do on this thing?

[Caleb]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

I was able to sub a bc337 for that transistor, I have a cricket transistor tester and it looks at gain as well as leakage. Both of the last two sets I repaired had good gain on that q601, but both failed the leakage test. I think when the mosfet shorts it passes too much voltage to the transistor and causes damage to the junction. if you use the bc337 you will need to insulate the emitter and wrap it around the back of the transistor to get the correct pinout.

Make sure you check all these parts
Q600- TK10A50D mosfet
Q601- 2sc2120y transistor
D604- 27v zener
D610- 36v 1w zener
D609- 4148
D640- rectifier diode
D648- 36v 1w zener
D645- 22v 1w zener
R602- 2.2 ohm 5w
R611- 2.2 ohm 5w
R608- .18 ohm 2w
Fuse

[budm]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

+1 with Caleb, when this thing blow up, lots of parts will need to be replaced, just a really bad design. BTW, check the Opto-isolator also or just replace it.
When I work on this one I use VARIAC, lamp, and AC Amp meter to power up the set.

[Caleb]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

Hey Bud, I was thinking about building some kind of current sensing add on for these, -thinking a current sensor could feed into a resistor network on an opamp and when it passes 3.5 amps it would send signal to pnp inline with opto and shut down power supply before it destroys itself. Do you think it would be worth the effort? Or just resign these to the junk pile.

@Triplefour make sure to get a 3amp replacement for D640 as I think the consensus is that it shorting drives the entire chain of failure

[budm]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

There are lots of circuits out there (but not verified if they actually work or not).
For example:
http://www.engineersgarage.com/contr...ircuit-breaker

[triplefour]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

oh man what a nightmare psu... for profit its not worth the time...for education maybe

[Caleb]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

It really isn't that bad normally, Ive fixed 3 out of 3. This last Emerson was the worst out of all of them but someone without a clue had been in it messing around and burned out more stuff than normally fails. Should only be about 10$ in parts including shipping.

[triplefour]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

ok i will test the rest of the parts n see...thanks!

[Caleb]

Re: MAGNAVOX FUNAI 32MF301B/F7 blows fuse

ha ha, you thought this one was bad check out the repair kit for the 40" version of these poorly designed power supplies. Pic attached below