Hi all,
I have a problem with my Rotel RA-930BX. It simply is totally off!
Fuses are ok, I measured the AC in the board and it is ok also.
Maybe it's an easy thing, but I can't find where's the problem!
Just stopped listening to the music!
Any help will be much appreciated.
I have a problem with my Rotel RA-930BX. It simply is totally off!
Fuses are ok, I measured the AC in the board and it is ok also.
Maybe it's an easy thing, but I can't find where's the problem!
Just stopped listening to the music!
Any help will be much appreciated.
Attachments
units like that fail once in a million years
If you need a free schematic please email me
things to look at
---Check mains fuse ( Caution required at all mains operated devices )
--- depress tape monitor switch
--- make sure that pots and switches are clean and not scratchy
---selector switch is open onatop and doesn't like dirt
---Tape monitor switch is sealed though might get oxidized or dirty
---Verify all voltage according to the schematic
---Verify connections remember that you have direct speakers and switched speakers
---Verify proper speaker switch pressed
do this and let us know
Kind regards
sakis
If you need a free schematic please email me
things to look at
---Check mains fuse ( Caution required at all mains operated devices )
--- depress tape monitor switch
--- make sure that pots and switches are clean and not scratchy
---selector switch is open onatop and doesn't like dirt
---Tape monitor switch is sealed though might get oxidized or dirty
---Verify all voltage according to the schematic
---Verify connections remember that you have direct speakers and switched speakers
---Verify proper speaker switch pressed
do this and let us know
Kind regards
sakis
Schematic for the RA-930AX can be downloaded from: B&W Group North America Service & Support - Service Manuals
There is very little (if any!) difference between the AX and BX that I can tell.
You should have around +/- 38V supplies at the capacitors. The power LED is powered by the +38V supply, so if that is not lit, you are missing 38V.
I have seen instances where the bridge rectifier has failed in these amps. They are only 4A rated units and that is a bit tight. Replace with at least an 8A one if it has been damaged.
There is very little (if any!) difference between the AX and BX that I can tell.
You should have around +/- 38V supplies at the capacitors. The power LED is powered by the +38V supply, so if that is not lit, you are missing 38V.
I have seen instances where the bridge rectifier has failed in these amps. They are only 4A rated units and that is a bit tight. Replace with at least an 8A one if it has been damaged.
Fantastic. The unit is missing +38V. No voltage at the power capacitors.
And for the rectifier, I put my MM at the "beep" sound position and it sounds at all the 4 pins. It should block current at least in one phase, right?
If so, I'll get tomorrow same an 8A rated rectifier...
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You will need to take the rectifier out to test it, as it would be shunted by the windings on the transformer. I'd say its quite likely that it's toast though.
I'm not sure if those Black Gate's are stock - to me, it looks as if the unit has had all of the capacitors replaced. Still, thats a bonus for you My 930AX is a good sounding amp, and my only complaints with it are the stupid plastic base that has shattered.
I'm not sure if those Black Gate's are stock - to me, it looks as if the unit has had all of the capacitors replaced. Still, thats a bonus for you
My 930AX is a good sounding amp, and my only complaints with it are the stupid plastic base that has shattered.
Right, I'll take the rectifier out to test it. I can tell it's not "clean" as the other components... Looks a bit burned, but who knows...You will need to take the rectifier out to test it, as it would be shunted by the windings on the transformer. I'd say its quite likely that it's toast though.
I'm not sure if those Black Gate's are stock - to me, it looks as if the unit has had all of the capacitors replaced. Still, thats a bonus for you
Looking at the other side of the PCB, I see no signs of components replaced. All the soldering points seem to be still "original". Also the capacitors still have that nasty glue surrounding them...
What happened is that Rotel always made a model and, after 2 or 3 years "upgraded" it with other components. The RA-930BX is an 1994 release. Like the RA-04 series, the first seems to be from 2006. Then Rotel released the RA-04 Special Edition in 2008 (with better capacitors and resistors). Now the company just released the "new" RA-10 model. Exactly same specifications and design, but different components.
upgrade remarks correct
rectifier can be confusing from trafo windings but also voltage that is stored inside the caps
Again it seems that Rotel got rectifiers that where overestimated or lower quality than supposed to be ..Generally and many Rotels have a history on bowing rectifiers .
A blown rectifier will also mean a mains fuse gone ....carefully with all those
Kind regards
Sakis
rectifier can be confusing from trafo windings but also voltage that is stored inside the caps
Again it seems that Rotel got rectifiers that where overestimated or lower quality than supposed to be ..Generally and many Rotels have a history on bowing rectifiers .
A blown rectifier will also mean a mains fuse gone ....carefully with all those
Kind regards
Sakis
Bad news, my friends! The rectifier is still good! But I measured the Transformer's secondary output and there's no voltage! Is that possible it is the transformer?? The main power switch is working normally...
I'm assuming when you say "the main power switch is working normally", that you are seeing the correct voltage across the transformer's primary.
The transformer will have a thermal fuse in the primary. Check and see if the primary is open circuit. If it is... the thermal fuse has blown. It will be practically impossible to replace this as it will be buried deep inside the primary winding.
The transformer has 28-0-28VAC secondaries. A standard 2x25VAC toroid would work to replace it, with only a tiny loss of power output - a watt or two, nothing to worry over. I'd guesstimate the VA rating is about 120VA, judging by the size of the transformer.
The transformer will have a thermal fuse in the primary. Check and see if the primary is open circuit. If it is... the thermal fuse has blown. It will be practically impossible to replace this as it will be buried deep inside the primary winding.
The transformer has 28-0-28VAC secondaries. A standard 2x25VAC toroid would work to replace it, with only a tiny loss of power output - a watt or two, nothing to worry over. I'd guesstimate the VA rating is about 120VA, judging by the size of the transformer.
Yes, correct! But I found that the WHITE wire (from primary bottom windings) is NOT closed or connected to any other (BLUE, BROWN or RED). It is OPEN to them. The other RED, BLUE and BROWN terminals (primary) still are closed circuits between them. According to the manual service on line you provided some would go for the 120VA. However, there's an open winding at the primary... The secondaries are ok...
I found a toroid of 30VAC secondaries and rated 3.75A (???) In Holland we have 230VA mains, although I just measured 254VA right now!!
Now a question is if a 30VAC secondaries would force to a change with some resistor or is it still in the "good limit"?
Another question is linked to this page (type the code to access). The original Rotel transformer (model TT-240GF-2) has 2 REDS and one BLACK wires for its secondaries. How would be for the toroidal replacement having it 4 different colors for its secondaries?
Thank you so much, guys!!
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Dont confuse VA rating of the transformer (secondary voltage * current) with voltage...
The transformer you linked to is 225VA, which means 2 * 30V * 3.75A = 225VA. Higher VA is OK electrically, the problem is only that the size of the transformer may be too large to mount in the case.
30V AC secondaries would be a bit too high in my opinion, this would produce 42V DC supplies, and probably more like 45-48V with ~250V AC on the primary. You would risk causing too much heat in Q901/902 short term, and in the long term risk damage to the output transistors.
The original transformer has a centre tapped secondary. Referencing the diagram on that website, you would connect the Yellow and Blue wires together, and this would connect where the original Black wire connected. The Red and Grey wires would connect where the original Red wires connected.
The transformer you linked to is 225VA, which means 2 * 30V * 3.75A = 225VA. Higher VA is OK electrically, the problem is only that the size of the transformer may be too large to mount in the case.
30V AC secondaries would be a bit too high in my opinion, this would produce 42V DC supplies, and probably more like 45-48V with ~250V AC on the primary. You would risk causing too much heat in Q901/902 short term, and in the long term risk damage to the output transistors.
The original transformer has a centre tapped secondary. Referencing the diagram on that website, you would connect the Yellow and Blue wires together, and this would connect where the original Black wire connected. The Red and Grey wires would connect where the original Red wires connected.
i stand corrected about the fuse thanks JC you are right .
if mains measure for some reason above 240 obviously the transformer is toasted ( count this worst in case that happens in long term )
But sure you need to check this out there is going to be more failure coming in case and for any reason your mains is 254 volts
happy holidays
sakis
PS
The amp will make it also in case of rail voltage is a bit higher than specified though 2X24 will e also easy to find ..That high rails will not support loads specified lower than 8 ohms , then heatsink will be too small to handle the extra power ( already heatsink is small ) ,secondary power supply via zener and resistor might suffer more ... so yes if its for casual listening in low power and easy load ....if pushed or low loaded the amp will eventually fail and take with , precious speakers since the 930 features also no DC protection
if mains measure for some reason above 240 obviously the transformer is toasted ( count this worst in case that happens in long term )
But sure you need to check this out there is going to be more failure coming in case and for any reason your mains is 254 volts
happy holidays
sakis
PS
The amp will make it also in case of rail voltage is a bit higher than specified though 2X24 will e also easy to find ..That high rails will not support loads specified lower than 8 ohms , then heatsink will be too small to handle the extra power ( already heatsink is small ) ,secondary power supply via zener and resistor might suffer more ... so yes if its for casual listening in low power and easy load ....if pushed or low loaded the amp will eventually fail and take with , precious speakers since the 930 features also no DC protection
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Sakis, wouldn't a 230 V transformer be safe even if it runs hot at 254 V ? I'd expect the transformer designer to allow for a +/- 10% variation on mains supplies. Is this a real problem in practice ?
Here we never have that problem as the voltage is always on the lower side like 210 to 220 V. Sometimes hovers around 260 V for short periods of time !
But many people have ( controlled) motorised Auto transformers that could apply high voltages for short periods of time while it corrects itself.
Here we never have that problem as the voltage is always on the lower side like 210 to 220 V. Sometimes hovers around 260 V for short periods of time !
But many people have ( controlled) motorised Auto transformers that could apply high voltages for short periods of time while it corrects itself.
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