Yamaha RX-V673 - No Power - Blowing T2.0A Radial fuse each time power is applied

[ACRO]

Good morning/afternoon all!

Firstly, I am a newbie to electronics so please forgive me! However 2 weeks ago we had some issues (potential neutral fault) in our building (comprising of 26 apartments) that led to a number of electronic devices failing to power on. So far, I have managed to repair our 2 Sonos speakers which were relatively easy to diagnose and repair (blown capacitors and radial fuses).

Next up is our Yamaha RX-V673, I was hoping to have a go at repairing it myself before resorting to either paying someone else to have a look. Upon visual inspection on the Video-2 PCB when power comes in to the system, I noticed that F3701 (T2.0A Anti-surge Slow blow radial fuse) had blown, as well as capacitor C3706 (KXJ 400V 68uF) which had a bulge in the side and lid. I replaced both of these and reapplied power, unfortunately however the fuse at F3701 keeps blowing each time in quite spectacular fashion (loud pop, smoke and flash).

In the photos of the solder side, I had removed the safety capacitor at C3704 to test, however from my reading it appears X2 capacitors rarely fail. From what I can tell, it should not be too complicated to identify the issue as there is only a limited number of components that could be at fault - considering it appears to be an issue with actually getting power into the system.

Unfortunately I am limited in terms of electronics knowledge and equipment (other than a cheap soldering iron and basic multimeter).

Any pointers would be greatly appreciated!

Many thanks,
Adam

[ambrosia heart]

See PM, just FYI.  Don‘t post it.   
Tell me your result if you wanted.

[mzacharias]

Diode bridge D3701 or switching IC IC371, I would think.

[George Edmonds]

Hi

If you have suffered a neutral fault in a large building which will be supplied with a three phase supply it is possible under some circumstances to have an incoming mains supply of up to 400VAC.  No switch mode power supply will tolerate this, they will just virtually destroy themselves.

About two years ago I tried to sort out  an Office in London that the same had happened to, what I found was that the repaired items, which included high end photocopiers, even when repaired failed again within a short time.

Unless you are very experienced with the repair of switch mode supplies, you say you are not, find someone who is, they can be very dangerous to work on as there  some 360VDC at high currents present throughout the entire supply.

It is very easy to get into a situation where the supply repeatably blows up and possibly spraying molten copper.

George G6HIG Dover UK