Sansui 441 buzzes and blows fuse

[bankara]

I recently found a Sansui 441 out on the street and brought it home to see if I could repair it. The fuse cover was missing and I hoped that I'd get lucky and all it needed was a new fuse. I ordered some Littelfuse 1.5A 3AG slow blow fuses from PartsExress to replace the missing one. The back of the receiver stated that it wanted to have a 1.5 amp, 250V fuse.

I Popped it in and turned on the receiver and it buzzed loudly for about 2 seconds before the fuse died. To rule out a dud fuse I tried again with the same result.

I am looking for advice for next steps to troubleshoot the problem. Thanks!

 

[petehall347]

which 411 is it ?

 

[bankara]

It is a classic 411, not the R-411. I am on my way home and can look at the model # for more specifics when I get there

 

[petehall347]

need service manual or schematic

 

[bankara]

I have that at home as well, will post a link when I get there.

 

[bankara]

Found the service manual: https://www.manualslib.com/manual/950094/Sansui-441.html

 

[maxhifi]

A few ideas:

Shorted rectifier diode
Shorted filter capacitor
Bad STK module

 

[petehall347]

will be back soon . have been busy .

 

[bankara]

Have done a little research, read the schematics, and I am still wondering where to begin testing. Other fuses on the boards are intact so I can rule that out. I have a multimeter, a soldering iron, a basic understanding of electronics, and really just need a little advice about where to start.

I have taken some pics of the receiver which I am putting up here.

 

[Oldsansui441]

Hi, l have a 441 also, l would have to say it is definately worthwhile getting yours up and running, they sound great amd have a super FM section.

I would have to say it was prob the transformer humming due to the extra current being drawn by a short somewhere. I would start by checking the rectifier diodes, then possibly the main filter cap and the STK module.

 

[petehall347]

first make sure the voltage is set correctly for your area . there is a small cover plate on the rear .selector is under it

 

[petehall347]

is it the eu or la model ?

 

[Oldsansui441]

Yes, good call by petehall347 .

 

[bankara]

Solid advice PeteHall347, I will check the selector when I get home today. How would I check for whether it is EU or NA model? It appears though it is for the US market.

 

[petehall347]

looks like one difference is eu model has double power switch .. 4 wires to switch
la has single switch . 2 wires to switch .

 

[bankara]

Selector switch is definitely set to US standards so that rules that out. It also appears as though the model is LA because I see two wires attached to the power switch. attaching pics for reference. The on switch is also wired into the speaker selector knob on this model.

 

[bankara]

Just tested for continuity on diodes B01 thru B04 in the power board (F-1508) and they all seem to give me continuity. Checked the tuner board (F1506 -F) and it I am not getting continuity for D02 or D04.

I am using this (admittedly cheap and shabby) multimeter and checking using the Diode tester on the dial:

http://www.parts-express.com/digital-multimeter-with-battery-tester--390-730#lblProductDetails

Perhaps there is something else I should be using to test? I can give specific readouts for each diode, if that helps.

 

[petehall347]

set it on diode test and test diodes both ways .

 

[bankara]

Hi, l have a 441 also, l would have to say it is definately worthwhile getting yours up and running, they sound great amd have a super FM section.

I would have to say it was prob the transformer humming due to the extra current being drawn by a short somewhere. I would start by checking the rectifier diodes, then possibly the main filter cap and the STK module.

Noted, thank you for the advice. Should be looking at the power board for the rectifier diode? I have been going through the service manual I attached here but it doesn't let me know which of the diodes is the rectifier. I am guessing that it is D4 on the power board, since that is the only one that is different (to my totally untrained eyes). It has three prongs going into the board and is nearest the power intake. Thanks!

 

[bankara]

Testing D04 diode on the power board and I am seeing continuity in both directions so that may be the source of my short. Hard to tell since I cannot find any info on testing a 3 prong diode for continuity but I am guessing that I should only be seeing current move in one direction.