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Reidar5 · 17th Aug 2018, 7:54 pm

Hello,

and thanks for your help so far

Answer to David:

The F902 and 901 are the ones that keep blowing. The fuses blow although the A & B switches for the speakers aren’t pressed in.

Answer to Alan:

I’m not able to turn the amplifier on at all. Once I turn the power on, the fuses blow instantly. Neither capacitor nor bridge rectifier seem to have any sign of swelling, but there is small amounts of some kind of substance that seems to have leaked out of all of the capacitors at the bottom.

Answer to ‘Turretslug’:

I set the DMM to the diode-test function.
Then, I checked the bridge rectifier, and got ca. 0.002 for the positive and negative DC outputs, in both directions (black probe on + DC output, red probe on – DC output and vice versa)

Next, I touched the one probe lead to + DC output and the other probe lead to one of the AC inputs. I got 0.634 in the one and 0.654 in the other direction.

One probe lead to – DC output and the other to AC input gave 0.683 in one and 0.664 in the other direction.

In the next step I followed Andy’s instructions:

“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.”

Here I got ca 00.20 in all cases. (Strange number. The DMM was set to 200 ohms)

“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.”

Here, I got 1 in all cases, which I believe means that my DMM measured no connection.

“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”

Here I got 40 V for F901 and F902 and 12.7 V for F903/E4.

I’ll upload some pictures of the circuit board later

Reidar

17th Aug 2018, 7:54 pm	#8
Reidar5 Triode Join Date: Mar 2014 Location: Tromsø, Norway Posts: 21	Re: Fuses keep blowing on Rotel RX400 amp Hello, and thanks for your help so far Answer to David: The F902 and 901 are the ones that keep blowing. The fuses blow although the A & B switches for the speakers aren’t pressed in. Answer to Alan: I’m not able to turn the amplifier on at all. Once I turn the power on, the fuses blow instantly. Neither capacitor nor bridge rectifier seem to have any sign of swelling, but there is small amounts of some kind of substance that seems to have leaked out of all of the capacitors at the bottom. Answer to ‘Turretslug’: I set the DMM to the diode-test function. Then, I checked the bridge rectifier, and got ca. 0.002 for the positive and negative DC outputs, in both directions (black probe on + DC output, red probe on – DC output and vice versa) Next, I touched the one probe lead to + DC output and the other probe lead to one of the AC inputs. I got 0.634 in the one and 0.654 in the other direction. One probe lead to – DC output and the other to AC input gave 0.683 in one and 0.664 in the other direction. In the next step I followed Andy’s instructions: “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.” Here I got ca 00.20 in all cases. (Strange number. The DMM was set to 200 ohms) “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.” Here, I got 1 in all cases, which I believe means that my DMM measured no connection. “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” Here I got 40 V for F901 and F902 and 12.7 V for F903/E4. I’ll upload some pictures of the circuit board later Reidar