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Diabolical Artificer · 17th Aug 2018, 7:32 am

Firstly how experienced are you? Do you have a DMM (digital multimeter) and soldering iron?

Is the voltage selector set to the correct voltage in your area?

1) If you have a meter set it to DC resistance (ohms) take out F901 to F903 making sure you note what fuse goes where. Attach your DMM leads to the tfmr (transformer) side of the F901 and 902 fuse holders, note the reading and post here. Now attach your black lead to E4 of connect to the chassis, red lead to tfmr side fuse holder F903, take reading and post.

2) Next with DMM still on DC resistance put leads on fuse holder F901/2 but on the circuit side, note reading, post. Next black lead to E4/ground/chassis, red lead circuit side of F903 holder, same again. This is with fuses still out.

Fuses still out switch DMM to AC volts, repeat # 1) but turn on amp briefly and check you have AC from the tfmr. The schematic doesn't say but you'd expect around 40v for F901/2 and a lower voltage for E4/F903

You say you tested OP (output) transistors for shorts, is this so?

Lastly take some good quality pictures of the circuit board etc and post here, we might spot something.

Good luck, Andy.

17th Aug 2018, 7:32 am	#6
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: Fuses keep blowing on Rotel RX400 amp Firstly how experienced are you? Do you have a DMM (digital multimeter) and soldering iron? Is the voltage selector set to the correct voltage in your area? 1) If you have a meter set it to DC resistance (ohms) take out F901 to F903 making sure you note what fuse goes where. Attach your DMM leads to the tfmr (transformer) side of the F901 and 902 fuse holders, note the reading and post here. Now attach your black lead to E4 of connect to the chassis, red lead to tfmr side fuse holder F903, take reading and post. 2) Next with DMM still on DC resistance put leads on fuse holder F901/2 but on the circuit side, note reading, post. Next black lead to E4/ground/chassis, red lead circuit side of F903 holder, same again. This is with fuses still out. Fuses still out switch DMM to AC volts, repeat # 1) but turn on amp briefly and check you have AC from the tfmr. The schematic doesn't say but you'd expect around 40v for F901/2 and a lower voltage for E4/F903 You say you tested OP (output) transistors for shorts, is this so? Lastly take some good quality pictures of the circuit board etc and post here, we might spot something. Good luck, Andy. Attached Thumbnails __________________ Curiosity hasn't killed this cat...so far.