Rotel RA-940BX distorted sound

[SteveNielsen]

Re: Rotel RA-940BX distorted sound

The last schematic doesn't show the AC3 & AC4 connections. I haven't looked at the manual yet, it's taking a while to DL for some reason.

[SteveNielsen]

Re: Rotel RA-940BX distorted sound

This part of the manual schematic shows that AC3 is connected to AC4 via power switch, which has nothing to do with voltage selection. For voltage selection AC4 should be connected to the appropriate transformer primary tap for your line voltage.

[holmzy]

Re: Rotel RA-940BX distorted sound

hi guys, the smoothing caps are fine i have replaced them alread no effect. ac3 is mains cable live and ac4 is connected to ac3 via power switch and capacitor. ac4 is live mains IN 240v on transformer

[R_J]

Re: Rotel RA-940BX distorted sound

When you turn on the amp. do you hear the relay (RY601) click after a few seconds?
Did you try switching the record/listen and tone switches back and forth, they could be dirty (oxidized) I find a lot of these older amps need the switches cleaned.

[holmzy]

Re: Rotel RA-940BX distorted sound

hi I did try switching back and forth a lot and air blew the switches. Could this explain the 0v at the bias adjust?

[R_J]

Re: Rotel RA-940BX distorted sound

The bias test points are T1 to T3 and T2 to T4, there should be about 12 milli volts aprox.
If you check accross the speaker terminals it should be 0 volts. adjusting vr601(L) or vr602(R) should vary the voltage accross the speaker terminals. it should go a bit positive one way and then a bit negative the other, setting it to 0 volts is where it should be
The bias adjust should increase or decrease the voltage acrosss accross tp1 & tp(vr603) tp2 & tp(vr604)

Does the relay click?
and blowing air into the switches does nothing, you need a control cleaner/deoxidizer (DO NOT USE WD40!)

[holmzy]

Re: Rotel RA-940BX distorted sound

I get 0v across the test terminal! I will have to invest in this detox spray. If I could test the switch via speakers or something would be good to confirm fault. yes the relay does click

[stj]

Re: Rotel RA-940BX distorted sound

test the switch with the meter set to ohms.

your in the u.k. - go to maplins for a can of contact-cleaner / switch-cleaner.

NEVER spray WD40 near electronics btw - it will slowly rip the layers of the board apart by getting between the tracks and the glue holding them down!!!

[R_J]

Re: Rotel RA-940BX distorted sound

I get 0v across the test terminal! I will have to invest in this detox spray. If I could test the switch via speakers or something would be good to confirm fault. yes the relay does click

What do YOU consider a test terminal??? are you talking about the Speaker TERMINALS or are you talking about the BIAS TEST POINTS
0 volts accross the SPEAKER TERMINALS is Correct.

[holmzy]

Re: Rotel RA-940BX distorted sound

I will give maplins a shot later hopefully and yes I do mean bias adjust test points 1-4

[holmzy]

Re: Rotel RA-940BX distorted sound

got switch spray from maplins. sprayed everything no change what so ever!