Rotel RA931 Amplifier

[clapster]

Hi There

My amplifier over heated this weekend , even though i have a fan blowing on both my amplifiers and it is now dead . Ive checked the fuse in the plug and all the fuses in the amplifier with a voltage meter and they are all ok . Is there anything else i can look for or is it terminal .

Many Thanks

 

[moamps]

Hi clapster and welcome to the forums!
I moved your post from the Everything Else forum to the Solid State, where it is more appropriate and should get you more feedback, IMO.
With some basic knowledge of electronics and a DVM, it shouldn't be too difficult to detect and repair the problem. First you should download a copy of the service manual from http://www.eserviceinfo.com/downloadsm/27338/ROTEL_RA931.html . After that we may be able to give you some specific pointers on where to look.

Regards,
Milan

 

[clapster]

Thats brilliant

Many thanks , ill download the manual and have a good read through and with any luck ill be one step closer to repairing my amplifier .

Thanks again

 

[anatech]

Hi clapster,
Check the continuity of the power transformer primary windings. They have a thermal fuse that will open if the transformer gets too hot.

-Chris

 

[clapster]

Hi There Chris

Thanks for the tip and you were spot on . The power transformer is the problem as there is no continuity so the thermal fuse must be blown . Only problem is , were do i buy a power transformer from or will it be cheaper just to buy a new amplifer which would have to be the very very last resort .

Many Thanks

 

[anatech]

Hi clapster,
Sometimes you can get to the thermal fuse and replace it. It will make an opening in the windings and can normally be found on the outer layers. Access it between the layers without damaging any insulation.

Make sure that it is okay by your local code to replace this fuse. DO NOT SHORT IT!!!!!!!! Otherwise you must buy a broken unit and use it's transformer or buy a new exact replacement transformer. I suspect that this is the only legal option you have. It is also the only truly safe way to get your unit working.

-Chris

 

[jaycee]

In the UK if you bypass a safety feature and your house burns down etc, you are liable.

Contact Rotel themselves - they might well be willing to sell you a spare part.

You could also use a standard 2x25V 225VA transformer. The rail voltages would be slightly lower (35v instead of 37v) but i doubt it would make any big difference.

 

[clapster]

Thanks for the replies .

Will the standard 2x25V 225VA transformer fit inside the amplifier ( in the place of the old one ) or will it have to be external .

Thanks

 

[anatech]

Hi clapster,
Do yourself a favour and make sure you can install it inside the original location.

-Chris

 

[clapster]

Hi There Chris

Thanks for that , i will do . I managed to find someone who sells the transformer mentioned in one of the replies , so ill have a look and see if it will fit in the place of the broken one .

Thanks Again , Clapster

 

[clapster]

Hi There

Does anybody know of a U.K. based complany that sells second hand amplifier parts .

Thanks Clapster

 

[clapster]

Or even brand new

Thanks

 

[AndrewT]

Hi,
you could try the Forum's Market Place.

Add UK to your title.
I really hate looking at adds to find that postage from the other side of the world makes it uneconomic to entertain sending back to UK.

 

[jaycee]

If you are talking about the transformer, here are a few suitable places:

Rapid - http://www.rapidonline.com (part num 88-2642)
Farnell - http://uk.farnell.com (part num 9532846)
RS - http://rswww.com (part num 22-5332)

Out of these, Rapid is probably best as they deal with small orders.

All of those sites have data sheets that show the dimensions of the transformers. Simply measure the old one and compare with the data sheets.

 

[clapster]

Hi There Jaycee

Well what else can i say but thank you for that great bit of info . I went onto the rapid site and found exactly what im looking for and its not going to cost an arm and a leg . Will order it and let everbody know the outcome .

Many Thanks Clapster

 

[twinney12]

Rotel RA931 (Not MKII)

Hi I have a Rotel RA931 beauty; but the amp has just given up the ghost!
It blows the first fuse on the PCB every time I switch it on.
I suppose that would indicate a short, but where to look?!
I have checked the amp power supply, and found the U23 themal fuse but it appears OK and passes a continuity check.
I know that I need a Service Manual but 'moamps' link (post #2) above:http://www.eserviceinfo.com/downloadsm/27338/ROTEL_RA931.html
does not work - it only comes up with "File Not Found"
I have searched the web and cannot seem to locate the manual anywhere.
I know that I should now check the other components, but am wary of touching the 2 big caps, next to the amp as I don't know if they are charged or not. - Does that sound daft? I am a retired lecturer in computing, but have little experience of audio circuits - is it likely that the caps would still be charged, or would any charge be dissapated by switching off?
Do I just go through each component (not many on the Rotel) checking for shorting, and 'dry solder joints' etc.?
Any help would be greatly appreciated. Kind Regards, To AL!
Tony Swaine

 

[twinney12]

Rotel RA 931 service manual

If anyone is interested, I 'phoned Rotel and the nice lady sent me a Rotel RA 931 intergrated amp schematic diagram. I have it, and will post it on my web site; if you're interested, let me know.
Argen:
Hi ! I have bought a few things from you in the recent past, and I am interested in this MKIII Tripath.
What is the significance of the change to air inductors - does the change affect the bass?
What is the significance of the 2 improved higher rated 400v capacitors?
What is the improvement in the 'buffer capacitor over the previous component?
Can you explain, Arjen, what effect higher voltage, higher capacitence and higher/lower ampage of a component has on overall sound?

Can anyone give a graduate, (M.Sc.Conputer Science) a rundown on what the various components contribute to the overall sound, that comprises a T-Class amp?
I love this learning thing and am grateful for all the help I have already received. All I wannna do is ROCK!
KInd Regards, Tony Swaine, Chester, UK (Floyd etc., - no hope for me!)

 

[jaycee]

The big caps will discharge in about an hour or so.

In all likelihood, the fault is that one or more of the output transistors mounted on the big heatsink has died, and gone short circuit.

 

[nigelwright7557]

Hi There

Does anybody know of a U.K. based complany that sells second hand amplifier parts .

Thanks Clapster

www.farnell.co.uk
www.rswww.co.uk

 

[twinney12]

Rotel RA-931

Thanks jaycee! I have ordered the transistors - only couple quid each.
If anyone wants the schematic for the Rotel RA-931 it's

here:http://newtownsaints.co.uk/freestuff.html

Thanks again! Tony