Pioneer SA540 blowing fuse

[GytisB]

Good day AK members! I got this little Pioneer SA540 amp for cheap as not working. After some time inspecting it I found that speaker terminals have to be replaced (damaged, not working anymore). Did give this unit a good cleaning inside and outside. I have also replaced speaker terminals. The 1A fuse on the inside was blown, so I replaced it. Power up, and it immediately blow up again. Further inspecting, I found some "leaking caps", but in the end it turned out to be just glue on top. Anyway, did a whole recap using Silmic II and Nichicon FG. Put in a new fuse and it blows up immediately again. Did some searching on the internet, and I couldn't find any related threads. Just for being safe, I replaced 3 diodes (2 normal ones, and one bridge 4 pin). Also replaced 2SC2240 and 2SC2235 near the fuse (Q401 and Q405). Power up, and it still blows the fuse. While the fuse is blown, it still does output sound and works like it should I think? Would like to fix it anyway. Maybe someone has any ideas?

I was not able to attach the schematics pdf (too large file), but added a few screenshots that might help.

 

[Binkman]

While the fuse is blown, it still does output sound and works like it should I think?

HUH?

Anyway, did a whole recap using Silmic II and Nichicon FG.

I replaced 3 diodes (2 normal ones, and one bridge 4 pin). Also replaced 2SC2240 and 2SC2235 near the fuse (Q401 and Q405). Power up, and it still blows the fuse.

-----
Build a DBT.

 

[century tek]

Are you getting sound out of both left & right speakers? It looks like the bad fuse is for one speaker so I would think that one isn't working.

 

[GytisB]

Sorry for a late reply, was busy with other stuff.

Yes! I do get sound from both channels. And it makes no sense why it would work normally even though the fuse is blown. Although I had the same experience with my Sansui, where the fuse was blowing and still working fine. The problem was solved when the new diodes were in places. Here it doesn’t seem to do the trick.

I think I will build a dim bulb tester as @Binkman suggested. Will be easier to find out I guess

 

[Binkman]

I think I will build a dim bulb tester

G'day.. if getting normal playing from both channels the the there is no short but put on the too do list.

So with fuse blowing after recapping... fuse blows and still plays. (Thinking as I type) if the rated fuse for speakers blows (low amperage. for each speaker then ?????? If operating normally sounds whatever okay to you..don't put the fuse in.

 

[Ylli]

Are you trying to put a 1 amp fuse in both these locations circled in red? If so, one will certainly blow. The fuse installed is the proper one for when the unit operates from 240 VAC. The other set of fuse clips is for the when the unit operates from 220 VAC. The transformer has a tapped primary so it can use either voltage. Never put both fuses in.

 

[GytisB]

I think you guys might be right. All 3 fuses were there when I first opened it. So I thought they all have to be in a working condition. But it might make sense why the one blows and the other one doesn’t. Must be as you said the voltage related, since unit is working just fine in my opinion. Will leave it without the fuse then!

Will definetly build the dim bulb tester (for the future projects).