I've replaced a few of those ICs back in the day. Not so much anymore compared to other parts, mainly lyric/ tantalum caps and V regs. The control ICs are very sensitive to overvoltage and static discharge into the inputs and supply line. I've seen them fail from carpet shocks discharged into the front panel controls and headphone jack. Make sure you're using a good quality soldering station if poking around in the front panel area.
As you did mention the headphone jack wasn't working, check the supply lines of the op amp feeding it. May be worth considering, as a bad oo amp can drag down the associated supply rails.
Put your scope on AC coupling and dial the input way down to look at the residual noise of the regulator output. You will see the supply dip a tiny bit by a few mV when pressing play and seeking tracks. This is normal.
I've only 4.4V instead of 5 as I should have on +2.
Here the residual AC.
The setting is 10mV / div and 1uS / div.
I have about 6 wave peaks in 1uS, so a 6 MHz noise (according to my calculation) of 20mV peak-to-peak.
I start to love the scope, actually 🙂
Here the residual AC.
The setting is 10mV / div and 1uS / div.
I have about 6 wave peaks in 1uS, so a 6 MHz noise (according to my calculation) of 20mV peak-to-peak.
I start to love the scope, actually 🙂
Scope all power supply lines, plus don't use low ESR caps at the regs and in place of the axial caps, especially on the laser board.
Check the voltage with a DVM on pin 28 of the MAB. It should be higher than 4.4v which is 12% down from 5 volts. What's the tolerance on these regs? I think 4.8 to 5.2 volts approx from memory.
🙂 Nice.
I got to go on the Sony residential course at Thatcham. A lot of number crunching and paper rolls of numbers to show how the error correction worked.
That sounds OK tbh. It is from the +2 rail via a small inductor which itself is direct from a 7805 reg.
Trust the DVM. Measure some of the other regs to be sure. Make sure the scopes 'cal' control for the vertical amp is in the 'Cal' position.
If the scope setting or accuracy is wrong then you really might have a problem with excess amplitude of the RF because you measured 1.2 volts pk/pk I think. Ideally the RF should be measured with a divider probe (a 10:1 probe that has low capacitance loading).
Check the scope accuracy first.
Your scope should have 'Cal' output on the front, typically a 1kHz squarewave of 1 volt peak to peak level that is used as a reference signal for checking the accuracy of the vertical amplifiers.
This is the +1 rail as it comes from the connector on the servo board. I have 15mV of noise here.
When the drive skips, the noise becomes even greater. I'll post a video of that.
When the drive skips, the noise becomes even greater. I'll post a video of that.
Do we need more resolution of the noise? I have another scope with more bandwith (but also with many more knobs...) that I did not use so far (gift from my son).
Here is the video of the noise including skipping: https://www.dropbox.com/s/v07u94y748ihyqk/IMG_1732.MOV?dl=0
The noise is wobbling around quite a bit.
Here is the video of the noise including skipping: https://www.dropbox.com/s/v07u94y748ihyqk/IMG_1732.MOV?dl=0
The noise is wobbling around quite a bit.
In calibration mode, the image shows indeed a little less than the 2V it should. Like 1.85V. I did not see if I could manually calibrate the image to the value.
The noise looks fine. Its normal to see that kind of level of noise and variation of supply. A lot also depends on grounding of the test equipment and where you actually measure.
Don't try this 🙂 but ideally you measure from the ground pin of the regulator involved and measure the voltage directly at the output pin. The resistance of the print and wires makes a big difference to how much the voltage fluctuates at one end of the wire/print compared to the other.
Don't try this 🙂 but ideally you measure from the ground pin of the regulator involved and measure the voltage directly at the output pin. The resistance of the print and wires makes a big difference to how much the voltage fluctuates at one end of the wire/print compared to the other.
With the 'Var' control turned (hmm... and whichever way that is on your scope) the switch positions on the attenuator should be automatically correctly calibrated to be what the markings say such as 1v/div, 2v/div and so on.
If that 'uncal' marking in red is a light it should not be lit.