RX-900U needs some love

ASPEC

Aspiring Auddict
I picked up a pristine RX-900U online over the holiday. When I unboxed it I could not believe how clean it was. Then I noticed the volume knob seemed to be sitting at a wierd angle. I pulled the cover off and found the bracket for the volume control knob assembly was bent back and the knob assembly was pushed back into the chassis. The receiver had been dropped on it's face or set down roughly enough in shipping. The knob still turned freely (as free as a motorized knob does) and there were no parts rattling around so I pulled the pre-main jumpers and plugged her in. The receiver turned on and all the functions were working/switching so I turned it off and put the jumpers back in. I hooked up a pair of minimus 7's I had sitting on the shelf and made sure the volume was turned down all the way and turned the receiver on. There was no sound coming from the speakers set to FM so I made sure all connections and settings were right and tried again and nothing. Fearing a dead tuner I grabbed an iPod an hooked up to the CD in and tried that and nothing. At this point I made sure there was not a tape monitor setting screwing things up just in case and no sound. So now I start thinking "is the protection relay clicking after I power up?", I was so excited when I got it I never paid any attention. I turned the unit on once more and after the initial click when switched on there is no second click so I think it's in protection mode.

What do you folks think? Should I unplug the volume control and check it? Would a damaged volume control throw it into protection?

I've got a DVOM, a service manual and enough beer to get into trouble. What should we do first?

Thanks in advance. :)
 
Thoroughly check it over for damaged or cracked circuit boards especially around screws and fasteners.
 
Is there any indication of power on? Like lit LED's?
 
Refer to page 4 of the service manual.
1. Check power supply voltages at the various points as outlined in the SM.
2. Check the idle current setting at the test points indicated in the "idle current adjustment" procedure.

Don't adjust anything at this point. Anything! Just check for the voltages.:thmbsp:
 
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Is there any indication of power on? Like lit LED's?

Yes. Power is on to everything. All features work in tuner (narrow,wide,mem set, signal meter etc) it will tune to and lock stations. All other controls and source switches turn on their respective LEDs. Even the remote volume and all features controlled by the remote respond. Just no sound.
 
Refer to page 4 of the service manual.
1. Check power supply voltages at the various points as outlined in the SM.
2. Check the idle current setting at the test points indicated in the "idle current adjustment" procedure.

Don't adjust anything at this point. Anything! Just check for the voltages.:thmbsp:

I'll jump on that as soon as I get home.

Thank you sir. ;-)
 
Well... Whatever was going out just totally went. The displays and LEDs no longer light up or respond. You can still hear relay RY101 on main 3 click when you hit the power button.

If I have measured correctly the numbers are as follows:

Q152 : .42 V

Q153 : .42 V

Q155 : .2 MV

Q154 : 35 MV

R245 : 0 V

R246 : 0 V
 
If fuses are good. Look for R291,275,276 in the power supply. Check for continuity across them. They are basically fuseable resistors.
291 and 275 --1 ohm
276 -----------2.2 ohm
 
The only fuse I can find is the 7.0 amp F101 on main 3 and it is okay. There is no F102 on main 3 like the service manual shows.
 
Thoroughly check it over for damaged or cracked circuit boards especially around screws and fasteners.

Did you look over the soldered side of the boards real good ? A cracked solder connection or broken circuit board trace would be a likely cause of your present condition.
 
If fuses are good. Look for R291,275,276 in the power supply. Check for continuity across them. They are basically fuseable resistors.
291 and 275 --1 ohm
276 -----------2.2 ohm

Missed that post. On it now.




Did you look over the soldered side of the boards real good ? A cracked solder connection or broken circuit board trace would be a likely cause of your present condition.


Yup. but it won't hurt to look again.


Thanks again for your help. Your always on top of it. :thmbsp:
 
I find a bright light and magnifier very useful for inspecting circuit boards. Shine the light through the board from the top side while looking at the solder side and vice-versa.Cracks show up better that way.
 
If fuses are good. Look for R291,275,276 in the power supply. Check for continuity across them. They are basically fuseable resistors.
291 and 275 --1 ohm
276 -----------2.2 ohm

Got our numbers:

R291 : 1k ohm

R275 : 1k ohm

R276 : 2.4 ohm


I find a bright light and magnifier very useful for inspecting circuit boards. Shine the light through the board from the top side while looking at the solder side and vice-versa.Cracks show up better that way.


* Just found a cracked trace just after J105/J104 between it and J102/J162/J164/J163 on the other end. :D



.
 
Got our numbers:

R291 : 1k ohm

R275 : 1k ohm

R276 : 2.4 ohm





* Just found a cracked trace just after J105/J104 between it and J102/J162/J164/J163 on the other end. :D



.

Jumper across the crack with a bit of wire.

R291 and 275 -- pull one leg of each resistor and recheck there resistance. According to the schematic they are suppose to be 1 ohm.Either its a typo error on the schematic or they are both open.
R276 is close enough.
 
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