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In Reply to: RE: Problem with Rotel 855 after op amp swap. Help please! posted by twl168 on January 06, 2008 at 18:59:53
That could be it as it is a common way of grounding the pcb. Phenolic boards are problematic in this regard. I once found a broken corner like that in a new Kenwood tuner. Luckily it was not a ground point.
If it was the only point on the pcb tied to chassis (not likely) try to restablish the connection using a ring lug and a wire connected to the ground plane as close to the screw as possible.
Follow Ups:
Thanks.
I opened up the machine again and look at the corner. Can not tell if it is the ground point. But will do as your advice to put a metal ring and hope to establish ground.
On a separate note, any suggestion on re-solder another point where the pcb trace might be broken off due to excess heat from solder iron. As I mentioned in my reply to the others who offered their recommedation, two of the solder points are no good anymore. I guess my iron was too hot and not only melt the solder, but also the "green" part of the pcb. Not sure how to re-solder on those two point. Please help if you can.
Thank you so much.
That's not your problem (you're talking about the lower right corner as you are looking at the player from the back?). The PCB is grounded via a 100 ohm resistor to chassis up at the upper left corner of the board (same orientation, from behind the player).
Are you sure you plugged the opamps in in the right orientation? IIRC, from the back, pin 1 would be to the upper right of each opamp.
Thank you.
Yes, I was talking about the lower right corner. In that case, it is not the grounding issue and one monkey taken off the list.
I thought I did. Isn't the orientation determined by the half circle notch on the drawing of pcb and the half circle notch on the op amp? I did match up the female pin adapter to the notch drawing of the pcb. And when I install the op amp, the notch on the op amp match up to the female pin adapter.
Thank you
Yes, that is correct regarding the notches. Pull the opamps and see what the behavior is. If it's still the same, it probably isn't the opamps. Do you have a meter (DMM)? If so, check the voltages on the opamp sockets (pin4 to ground and pin 8 to ground). Should be -15V and +15V respectively. If those look OK, then you did something to another cable or elsewhere, not in the analog section.
I've got the service manual .pdf if you need it.
When I do the voltage checking, do I leave the power on? Do I leave the op amp in the socket? Just to make sure I do have the pin correct. With the notch facing left, pin 4 is on the lower left corner, pin 8 on the upper right corner. Correct?
Thanks
a) uhh, yes... power has to be on
b) doesn't really matter. I would try it both ways (opamps out, then in)
c) With the notch facing left, pin 1 is the lower left corner. Pin 4 is lower right, pin 8 is upper left
8-7-6-5
>
1-2-3-4
both pin 4 and pin 8 has reading of around 11.5v. I am pretty sure I am using the meter correctly. red to the pin and black to the ground.
What can be the cause of this? Looking back to what I did.
Use iron to remove the original op amp. insert the op amp socket. solder the op amp socket.
While I was doing this, I loose all the screws, chasis, pcb board. When I was soldering, I did not remove every cable, only the ones that were in the way of fliping the pcb. I move the front to the back of chasis, then stand up the pcb. While pcb is standing, I de-solder and solder the op amp. Then I turn around the pcb and put back the screws.
Does this sound like a cold solder problem. I did recheck all the connection on the op am sockets and non seems to be cold solder. I even went back and touch and melt and re-solder every point on the socket pins.
If this is cold solder job on the op amp socket, then how could the reading on both read the same? both op sockets, both pin 4 and pin 8 has a consistent reading of around 12v. no "-" for pin 4. Both show positive.
Please help!!
What were you using for your ground on your measurements? Pin 3 of either opamp is tied to ground, so that would be convenient. Pin 4 should definitely be negative wrt ground. And both should be around 15V, not 12 (unless Rotel changed something during their production of these.) IIRC, the TDA1541A needs +15V as well as +/-5V...
I guess my ground was wrong. I use chasis as ground.
Now I confirmed that the reading for both pin 4 and 8 are as advised. both -15 and 15 v.
So now what can be the issue. I am still getting the display with all the lights come up and the player is not responding. Does that mean the issue is with control board? But I did not work on the control board at all.
This reminds me of old game and watch game I played, when I hit the reset button, all the lights go up on the display. Is this has to do with some kind of reseting the control board? If so, how to do that? Or any idea?
Do you know other critical voltage that I need to check to make sure everything is correct?
Thank you so much for your help.
My guess would be similar to other posters at this point: your analog stage is probably working. You must have a connector either in the wrong place or something similar. Or you burned up a trace related to the control, etc. Only you know where exactly you worked when you were doing this, so I'd go back over those areas and look the traces over.
Do you have the service manual/schematics? If not, they are available online, and Rotel will email the pdf to you at no charge.
I thought the manual I have is the service manual, but turn out it is called tech manual. NO wonder I feel I do not get any idea about servicing the player other than looking at the diagram. Any idea where I can get one? I just posted another message to ask if anyone has it.
Tonight, I opened up the player again and checked everything as advised on the connections or posible cold solder ...etc. No luck so far. hmmmm, not sure what to do at this point.
Thanks
the manual list schematics only. Does not really provide testing requirement, or trouble shooting or where to look.
As green as I am about electronics, the experience I had were only kit building and follow directions. Still got lots to learn. Gotta say that I learn a whole lot this time as well.
I will recheck all the wiring again tonight. I am pretty sure I did not work on the control portion of the player. My only guess would be accidental solder on the other pins. Maybe the control wiring, due to age, were disconnected or pull when I was removing the chasis.
More trouble shooting tonight.
Thank you so much
It was working before you went in to do the opamp/sockets, correct? Usually these types of problems are simple and stupid... been there. Usually when I find it, it is a WTF? How could I... moment.
I am crossing my findgers. will check again tonight
Any progress?
I am totally clueless now. No progress. yet, it is even worse. now the display only show a few light up. i am convinced that it is the cable that connected the display to the pcb. but i check the connection and all but can not seem to find anything wrong with it.
I also look through all the connections as advised, but can not determine anything wrong.
The player is still opened up at my workbench. every night, I would check a few or play around with connnection. but no progress what so ever. I am almost at the point of through in the white towl.
Are you sure you have the cables in the right places? Also, if you pop the opamps out, any change in the display?
When you put the opamp sockets in, how far did you lift the PCB up? Any chance that you broke one of the transformer leads to the PCB, etc.? Are all voltages present (+/- 5Vdc, +/- 15Vdc)?
I could send pics of mine if you need to verify connections, etc.
Hmm,
I did not thing about the transformer leads. I did check voltage on pin 4 and pin 8 of each op amp socket. -15v and 15v, both correct. as far as anything else, not sure what the correct voltage should be, no way of checking.
Where are the +/- 5v and +/- 15v checking points?
I am certain that my connections of cables are correct because I do have a diagram from so called service manual.
When I was de-soldering the op amp, I did not fully disconnect all the wire, but enough so I can stand the pcb 90 degrees. Then I de-solder the op amp and solder the sockets in place. after that, the display showed all light up. after messing with the wires, that is checking for cold solder and wiggle them to see if there is any broken pcb solder joint, now the display only show a few light up.
What do you think?
Much appreciated.
The +/- 15V is correct, at least at the opamps
> > Where are the +/- 5v and +/- 15v checking points?
Check your schematics...
> > the display showed all light up. after messing with the wires, that is checking for cold
> > solder and wiggle them to see if there is any broken pcb solder joint, now the display only > > show a few light up.
Which wires? Sometimes you need to make things worse before you can figure out how to make them better. Seems like you did that. I take it that in order to get the board up for the socket swap, you unbolted the rear panel? That's the way I do it to get the transformer out of the way.
I'm trying to recall if there is any wiring to the front panel which is soldered into the PCB? Or is it all connectorized? I recall a pair of brown wires (IIRC) which runs on the case bottom up in front (I remember them because I always have to mess with them to get them to la right when I put the board back in. At any rate, at this point you might just want to redo the solder joints of anything running to the front panel.
When you turn it on, I take it none of the buttons works, etc.? What if you manually put a CD in the tray, and then with the tray in, turn it on? Does it spin, act like it is recognizing it?
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