Sony STR-D590 input stage problem

[CapLeaker]

I've picked this Sony STR-D590 up. It's in good shape and cleaned a 1/4 inch of dust off at the inside. It powers up, the relays click, display o.k.. Both channels don't have the power output they should have if I use any of the input channels. Left channel has either no sound or always white noise. The right channel has no noise, but audio is low. Both channels are bleeding through, regardless of input jack and front panel selection and are never that what it should be on audio.
Here is the twist. I press any of the input selector buttons and I get on both channels a loud "pop pop" sound. Loud as what I think the audio level out actually supposed to be. Balance, bass and treble work fine. Never saw an input selection problem like this.
Anyone had an issue like this before? Could IC402 do that?

Just measured IC402 (LC7822) analog switch. All pins that should have 0V all have 12.3V. The negative voltage on pin 12, I have -11.3 I guess something is up.
Yep... have 10.8V on all the RCA jacks on the input. :-(

[Longbow]

Re: Sony STR-D590 input stage problem

You are correct to start measuring voltages around IC402. This is a serial data controlled analog switch. The switch i/o pins have to be 0 volts dc for it to work. So you need both + and - supplies to be correct and ripple free. Reset pin #18 has to be high, otherwise your IC is in reset.

Since all your analog i/o pins are 12v, there is something wrong with the power supply or with the ground returns on that board. With power off, confirm that you have low ohms to the power supply (-) at c953. If all power supply voltages are correct, I would replace the IC.

[CapLeaker]

Re: Sony STR-D590 input stage problem

Well, I did some more measuring, as I couldn't quite remember if the reset pin was hi and it was. Then I took IC402 out. Now of course the dc is gone on all the inputs and absolutely no audio, as expected and no more pop pop sound while pressing input sources or bleed over or anything that way related. So I do think the problem is the LC7822 unfortunately.

[Longbow]

Re: Sony STR-D590 input stage problem

Yes, the IC is bad. It probably received a pulse directly from one of the inputs. With 12v on all the pins, it is no wonder you have loud popping in the output. No instructions from the uPC would make all the i/o pins go to 12v. Average audio through the switches is probably on the order of 1 volt p-p with FET gates switching the outputs on and off using the +/- 12v. Looks like you will have a nice working amp.

[CapLeaker]

Re: Sony STR-D590 input stage problem

I just hope whatever damaged the IC, damaged the IC only.

[CapLeaker]

Re: Sony STR-D590 input stage problem

It's been a while and I just got a new LC7822 (IC402). Put that in and I finally get audio. Sounds good too!
However something is still not right with this puppy. The input selector does not seem to work. I can feed audio lets say into the CD input, but can press any input on the front panel (for example phono or tape or even the tuner) and I still have the CD input. The radio tuner does not work either. It scans but doesn't receive anything. Also if I select tuner I get every 10 seconds a static burst. Oh well... back to the schematic diagram.

Poking around the LC7822 for voltages and some are not correct.
Pin 18 & 19 are 12.5V (11.5V)
pin 12 is -12.03V (-13.5V)
pin 13 is 0.91V (0V)
pin 14 is 3.69V (0V)
pin 15 is 3.29V (supposed to have 0.5V)

Pin 13 to 15 are latch, data and clock. Clock supposed to have 0.5V. Data and latch not supposed to have any voltage? I checked IC 304, data, latch and clock do have the same voltage is there too.

[CapLeaker]

Re: Sony STR-D590 input stage problem

I had a few minutes to remove the radio tuner. That got rid of the static bursts on the tuner setting. Rest stayed the same. Any RCA input I use on the back, the audio comes over to any setting other like tape, video, cd, phono etc. on the front panel. So either that new lc7822 is bad, or the is something wrong with the latch data and clock signal. I wonder what would be the best way to test this?

[redwire]

Re: Sony STR-D590 input stage problem

I think the input mux IC402 serial (data) control comes from MCU IC101 on the display board. You can look for cold solder joints or a ribbon connector problem, ohmmeter the three lines between the IC's.
But a slight chance the surge that took out IC402 made it back to the MCU and damaged its serial port. You need a scope on the CLK/DATA/CE lines to look for that.

[CapLeaker]

Re: Sony STR-D590 input stage problem

The data line on lc7822 pin 14 is messed up. There is voltage that shouldn't be on there and I see a bunch of noise on it with my oscilloscope as well. When I press an input button on the front, I'd expect a burst of data and that isn't happening, just a bunch of noise always. So I guess that MCU IC101 of the back side of the front panel is bad. I may lift that data leg on the MCU and see if the noise and DC disappears on the lc7822.

Edit:
There is more screwed up. So I lifted the data pin 48 on the MCU IC101. Same noise on that pin but the voltage is 2.4V DC. Measured pin 14 on the lc7822 and I've got now 4.9V on that and still noise. So verdict is the MCU is bad and there must be still one of the other IC's on the main board bad. Oh well...

By now I figure that there was a surge through the radio tuner (I found a bad transistor), went through the LC7822, ripped through one or more IC's on the main board and the MCU on the front panel. Nice. :-(

[CapLeaker]

Re: Sony STR-D590 input stage problem

I had some more time to play with it. So I am trying to isolate, why I see now almost 5V on the Data pin. This is driving me bonkers. Theory I got is to take all the IC's off the data pin to see if I could get rid of the voltage I am seeing on the pin. So far I haven't been successful.

I took out:
- the tuner module
- IC 402 (LC7822)
- IC 304 (LC7535)
lifted jumpers for data and clock on IC302
lifted data pin on MCU IC101

... and I still got 5V and noise on the data line? Cording to the schematic, the data line should be empty now. I guess I must miss something somewhere.

Edit:
I removed that ribbon cable between the display board and the main board. Plugged the power back in and I got damn 5V on the data line with the ribbon cable to the head removed. I guess somehow I get the 5V STBY voltage on the data line on the main board. Doesn't matter if I plug the head back in and turn the stereo on or off. As long it is plugged in, as long I got 5v on that damn data line. GRRR!

Editing the Edit:
Found where the 5V came from. Barked up the wrong tree... R438 10k right at the tuner pins. Anyway... now I need a replacement MCU and can't find one.

[Longbow]

Re: Sony STR-D590 input stage problem

Good work troubleshooting the problem so far. I think you are speeding through a bit too fast. The main micro seems to control lots of IC's with the 3 lines you have been following (CE, Data, and Clock). These use 5v logic, so you expect either a 0v or a 5v condition on the scope. Measuring the lines with a multimeter probably won't be useful. On ANY digital output such as these lines, a baseline 2.5 volt d.c. value indicates a problem.

Edit:
There is more screwed up. So I lifted the data pin 48 on the MCU IC101. Same noise on that pin but the voltage is 2.4V DC.

That's your next problem. Is that voltage present on IC101 with the pin disconnected from everything else? Bad micro. There may be other stuff, but be sure the pin is actually disconnected.

Measured pin 14 on the lc7822 and I've got now 4.9V on that and still noise.

Noise where? Are you saying the noise is still on IC101 with pin 48 disconnected? (If pin 14 on the 7822 shows 5 volts when disconnected, this does NOT indicate a problem because there is an internal pullup. Which transistor was bad?)

[Longbow]

Re: Sony STR-D590 input stage problem

Theory I got is to take all the IC's off the data pin to see if I could get rid of the voltage I am seeing on the pin.

Nope. Unless you are dealing with a BGA, just gently desolder and lift pin 48 IC101, rather than pull everything else out. If the pin has anything other than 0v or 5v, then IC101 is faulty. It might also be interesting to see what is on the DATA trace with pin 48 lifted! It might give you some information about more problems down the line.

At this point you can try replacing the chip if it is available. (The chip is programmed, so you will have to get it from Sony.) I'd say chances are 50/50. Once I see a chain reaction like this it indicates that a power surge or lighting pulse ran through some or all of the circuitry. It is likely, based on what you have found, that a number of things connected to the serial data lines may be toasted. Unless you can find a parts unit to play with, time to cut your losses.

[CapLeaker]

Re: Sony STR-D590 input stage problem

yeah... I only ended up lifting pin48 on IC101 and got something like 2.5V. There was no data going out that I could see with my oscilloscope. Usually one would see a "burst" of data once one presses a button, but in this case it was just flat, no output at all. Anyhow... not being able to get a replacement MCU, I cut my losses and parted it out. Lightning went through the amplifier all right. Also the tuner had a bad transistor, but I didn't bother fixing it, unless the amp was running. All the other chips that had a serial line are not that bad to get, just the MCU. Oh well... can't win everytime! Thanks for all the help Longbow and I appreciated all the input!