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Old 26th May 2008, 03:23 PM   #11
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Kchu by power driver they most probably mean final output transisistors which are the big 2sb817 and 2sd1047, it could also mean the drivers for these output transistors which are the smaller 2sa1507 and 2sc3902 but I ve never found a case where the drivers *2sa1507, 2sc3902 have blown and not the bigger transistors.
From your pic the blue transistors with the wires to heatsink you marked are called drivers and the big ones with the legs into pc board are alled output transistors.
If those drivers are blown, for sure the output transistors are blown too.
The repair shop is just using diffrent terminology to call the parts which is confusing.

Can you get the parts???

Try google and search for datasheet for those transistors i mentioned, will give you good idea which is which.

After close inspection of your pics it seems to me that the zobel network is just fine, can you tell me what the amp does when you switch it on and what happened when it stopped working. Dont connect the speakers to it though, can cause damage. I wonder if their diagnostic is correct as these amps are very robust and only zobel problems. I have a model 972 for over 12 years no problems. Im trying to help you according to what repair shop said but it could also be something else.
You have to test the transistors mentioned, the site given by john is good or use google and search testing BJT transistors and learn, its not that complicated.
I will send you similar schematic, watch your mail.
Alex
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Old 26th May 2008, 06:04 PM   #12
Quattor is offline Quattor  France
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Regarding those 2SA1507/2SC3902, they are most defenetly predrivers for the output transistors. Very popular replacement should be, as mentioned, 2SD600K/2SB631K, as well as excellent 2SA1209/2SC2911 wich were used by Rotel in more than a few models. These last ones mentioned are stocked by Farnell, all originals if I may say so. One thing though, check those two additional transistors on the main heatsing (beside 2SD1047, 2SB817, 2SA1507 and 2SC3902). There should be two of them, with the same marking. In most of their models, Rotel used darlington transistor 2SD1953 as a Vbe multirplier. In few of them, 2SD600K which is quite ordinary low to medium power transistor. So be sure, what it is, it will be helpfull in testing phase.

As for the datasheets, try http://www.datasheetcatalog.net/
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Old 26th May 2008, 06:10 PM   #13
Quattor is offline Quattor  France
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One thing more - those one letter markings on the transistors are DC current gain groups. For example, 2SA1507 is made by Sanyo, and it comes in 3 hFE groups - R, S and T (R with the DC current gain from 100-200, S from 140-280 and T from 200-400). So be sure to get complementary transistors from the same hFE group.
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Old 27th May 2008, 12:58 AM   #14
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Hi Alex,

Basically the amp will not power up with no lights or anything. I first open the amp and found the 3 fuse blown. I replaced the fuses and turned it back on. It lights led up for half a sec and the fuse are blown again.

The repair shop told me it would cost Usd $400 to repair as the power drivers must be replaces in matched pairs although only one is blown. I think I know which one it is as I can tell the driver the repair shop soldered.

What would consider an upgrade to the amp if I replace all transisters with better ones?

Thanks,

Kevin
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Old 27th May 2008, 03:32 PM   #15
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Hi Kchu

400 us dollars, they gotta be crazy or otherwize all the transistors in that amp are blown

Is the power driver as you call it one of those that you marked in blue on your picture???? Better yet tell me the marking on the faulty one.

Rotel uses excellent quality parts when it comes to transistors youll find it very hard if not impossible to get better parts. You can however substitute the output transistors to higher powered ones but you wont get better sonic results or power output with them. As it is Rotel amps are very conservatively rated and can give a number of watts more than stipulated. My 972 is rated 70 watts but gives me more than 100watts, but watch out for the heat. Those heatsinks are too small for such higher power operation. I wouldnt go that route. Theres plenty of mods you could do but first get it working.

Can you get the part from a supplier?? How did the amp blow, short circuit the outputs or blow when playing for hours on high volume. Has the repair shop worked on the amp before??? Why did they solder on it and tell me the part number. I need to know to be able to help you out here.
Yes its preferable to get matched parts so in minimum you looking at 2 transistor substitutions at maybe 4 to 5 dollars each. You can just replace the faulty one, will work but this can cause output offset voltages, not good for your speakers.

Alex
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Old 27th May 2008, 03:54 PM   #16
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Hi Alex,


I think the faulty ones are 2sc3902 and 2sd1047. I'm not sure how they got blown as it just stoped working one day I got off work.

Anyway I found this site and I found all the parts I listed in my first post. I order all 8 transister that are soldered onto the PCB and the 6 drivers for 16 sterling pounds. But it doesn't mention the marking on the transistors that come in 3 hFE groups. I thought I mind as well change all transisters. I got my parts here
http://www.dalbani.co.uk/index.php

I hope they are right??

BTW that's the Rotel service centre that wanted to charge me USD$400, that's why I got a new amp. I bought a Denon 3808, it's good for surround sound playing my blue-ray discs but in terms of music the Rotel is much better.


Kevin
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Old 28th May 2008, 12:00 AM   #17
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Default Rotel RA-1062

Hello,

f you post or send me the serialnumber of your RA-1062.

I will get you the servicemanual.

bestregards Michael
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Old 28th May 2008, 12:21 AM   #18
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Hi Michael,

I'll send you the serial number when I get home tonight.

Thanks,

Kevin
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Old 28th May 2008, 11:17 AM   #19
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Hi kchu

Good that you found transistors and thats a good price. I am not familiar with that supplier but i truely hope that they dont supply fakes as that price for so many seems a bit low. If you post a pic of them when you recieve i can let you know.

Anyway if derguteton can get you a manual i suggest you have a carefull look at it and pinpoint the exact transistors which are faulty. They are marked on the pcb board and you can then identify them on the manual. This is important as i would highly recommend that you only substitute the faulty ones and maybe its complement. I say maybe because you wont know yet whether the supplier sent you matched complementary pairs. If the other channel is in working order dont substitute the transistors, and youll have spares if anything goes wrong again.
One of the reasons Rotel charge that much for repairs is that match all complementary transistors but it can be done at home with ohms meter with a hfe test. Not 100 percent but close enough. With any luck the supplier will furnish you with same batch transistors and the hfe markings will be the same. Regardless of differences in hfe the amp will still work, ive had to do this in the past sometimes.

If derguteton could supply me with a manual id very very grateful.

Alex
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Old 28th May 2008, 03:22 PM   #20
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While waiting for the parts to arrive I took apart the amp and noticed the soldering of the transistors are quite bad. It might be shorted because of the solder or it might be the repair person didn't take the time to put my amp back together knowing I will not be repairing the amp.
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