Rotel RA-05 no sound

it doesn't appear to be getting power to pin 1. there should be around 30v dc according to the data sheet .
without a schematic its not too easy to suggest where to look next ..its maybe a power supply fail .
lets start at the beginning of the supply .
check acv at both fuses .
check dcv at the bridge rectifier .
i think these will be correct as they will be feeding the main amp .

next check voltages at the op amps . jrc 2114d .
data sheet here for 2114d http://html.alldatasheet.com/html-pdf/7259/NJRC/NJM2114D/67/1/NJM2114D.html
i see 2 diodes under the bridge rectifier and am thinking that will be a rectifier for one of the power supplies . check them . one side of each is going to be acv the other dcv .
 
Last edited:
Thanks pete, 30.6v ac on both fuses, Sorry but I am a bit lost in finding the bridge rectifier The op amps Ic 504 is a jrc 2114d i'm guessing Ic 502 is the second op amp it's an OPA2604AP

Voltages for IC 504 (200 mv scale) 1, minus 39.7 2, minus 39.7 3,minus 105.8 4, 1
5, minus 104.9 6, minus 39.4 7, minus 39.6 8, 1

Voltages for IC 502 ( 200mv scale) 1, 1.0 2, 0.09 3,0.02 4, minus 1 5, 0.02 6, 0.09
7,08.3 8,minus 1

hope this makes sense, many thanks
 
the bridge rectifier is the big square block with 4 legs ..next to the large capacitors . its marked with + - and the ac symbols that look like like S
try your meter on 200vdc setting and check the power in pins on the ic chips again ..pin 1 for TC9163ANG
pins 4 and 8 on the op amps ..
 
Last edited:
Thanks Pete,
Bridge rectifier 81.6v
PIN 1 tc9163ang 3.6V
IC 504 pin 4 16.5v pin 8 -16.4v
IC 502 pin 4 -16.6 pin 8 16.6v
 
ok the preamp is likely working then .
voltage is low on the input switcher PIN 1 tc9163ang 3.6V . whether its shorting or is not being supplied is anyone's guess at this point .data sheet says 30v .. i don't know if it would be working with 3.6v ..i guess not . any chance you could trace back from pin 1 and get voltage readings ? especially if it goes through a resistor . it should follow back to the power supply ..
just had a thought .......
switch the amp on for a few minutes and see if the chip is getting warm/hot .
i still wish we had a schematic .. am wondering if there is another rotel amp that would have a very similar schematic .. it would make things much easier .
ok i made a mistake ..i didnt read all the data sheet .. looks like it could run from +- 15v ..
pin 1 -15 pin 28 +15v .so if you could get pin 28 voltage please ...and pin 28 to ground ..
 
Last edited:
Traced pin 1 back to resistor R 921 16.6v one side -3.6v the other but traced back pin 28 to R 922 and its 16.6v one side and 0.7v the other.
Measured the resistors and they are about 450 ohm (in situ) not 470 ohm but appear to be ok? also in the same area are 2 capacitors c 922 and c923 25v 100 uf I dont have a meter that can check capacitance but I charged them with and ohm reading then switched to dc volts and they came down steady so perhaps ok? I checked pin 28 against pin 14 (ground) and it measured 0.7v
Chip doesn't appear to get hot or even warm.

I have added a couple of close up photo's of the area

Many thanks for the continued support
 

Attachments

  • DSC01017.jpg
    DSC01017.jpg
    72.9 KB · Views: 8
  • DSC01018.jpg
    DSC01018.jpg
    80.3 KB · Views: 7
if you could remove the solder from pins 28 and 1 then see what voltages there are at where they were connected .
and if you could check continuity between pins 28 1 and 14 ..
i think it is shorted inside the chip .
 
i will be away sat night so will catch up Sunday night .
i might have chance Saturday night though ..
if those voltages come back up then best bet is replace the chip ..then hopefully it will fix it .
it should be possible to connect 2 pins together to see if the rest of the amp is working . but without a schematic its just guessing . so not a good idea to try really ..
 
Hi Pete,
Solder removed from pads 1 and 28 and yes voltage on the pads + and - 14.7 So I will replace the chip, Does it matter if it doesnt have the G on the end of the chip number ie TC9163AN not ANG ?

Thanks again for all your help
 
not sure .will have to look at the data sheets to try and see the differences if any,
just had a look and can only find the an ..the datasheet links for ang redirect to an versions ,
 
Last edited:
New TC9163 AN chip fitted today (not ANG) and it works great !! :D
Very many thanks Pete your help has been much appreciated (this is the second time you have guided me to sucess).
 
phew ..glad i was correct with the diagnosis.
nice job well done:thmbsp:
i will give you a tip . do NOT unplug or plug inputs whilst its switched on . i have seen a few of these ic switches go bad by doing just that .
 
Thanks again Pete, Do you think I should try to get the DC down at the speaker terminals? Without a service manual I would be a bit lost though.
 
looking at the pics i dont see any provision for dc offset . only vr.s i see look like they are for bias current .
try warming it up for a while and see if offset lowers ..
i don't see it as being a problem anyway . although 62 and 69 mv are sort of borderline . i have had amps with 100mv and left them alone . they sounded fine to me .
yours may well have came out of the factory with similar values to what they are now .
 
Back
Top Bottom