ok sounds good,if i could ask a favor of you mr mooly, can you explain some thing for me. i have a service manual from hifi engine,
please can you also look at this info and teach me where it says to hook my scope up to,
i have both a digital single channel scope and a rather large dual channel scope,
then i guess i will need to know what setting to use on said scope,
is there any chance of you being so kind?
mike
Page 22 shows how to measure the RF but I would suggest in the first instance you just ground the scope to the chassis and simply probe the RF test point.
I was going to suggest you look here:
https://www.diyaudio.com/community/threads/sony-cdp790-and-kss240-restoration-project.226288/
but I see all the images have broken again (the move to XF forum software). I'll try and get Jason and or Gerard to look that asap
The RF can be found here:
This is from the web. You are looking for around 1.2 to 1.5 volts peak to peak. The diamond shape in the signal should be clearly distinguishable and free of noise and jitter.
I was going to suggest you look here:
https://www.diyaudio.com/community/threads/sony-cdp790-and-kss240-restoration-project.226288/
but I see all the images have broken again (the move to XF forum software). I'll try and get Jason and or Gerard to look that asap
The RF can be found here:
This is from the web. You are looking for around 1.2 to 1.5 volts peak to peak. The diamond shape in the signal should be clearly distinguishable and free of noise and jitter.
i have found the test points rf and vc, it would seem i am to solder tails on to these to hook up scope, so i am going ahead
You need to be very aware that VC could be a virtual ground point (I haven't studied the circuit but that would be typical) and so grounding that via the scope (if that is mains grounded) could cause a short to be applied to that point and possible cause damage.
If you measure any DC voltage on VC then it is NOT a ground point and you must not use that unless you are familiar with how to do so safely. It's much easier to measure from ground. The only downside is you may see a little more noise but it gets you 95% of the way there usually.
If you measure any DC voltage on VC then it is NOT a ground point and you must not use that unless you are familiar with how to do so safely. It's much easier to measure from ground. The only downside is you may see a little more noise but it gets you 95% of the way there usually.
ok ,im getting nothing like the pic ,the wave form is nice and sloping in pic,im getting lots of ups and downs ramdomly. do i need a special cd?
Any decent commercial music disc is fine but you should never use CDR or RW for tests. The RF always looks the same regardless of content.
If you are using a divider probe (X10 probe) then a good initial setting would be 50mv/div, if using a standard probe (X1) then 0.5v/div. Divider probes are preferred because they have much lower capacitive loading but the RF test point is low impedance and so either should be OK.
If you are using a divider probe (X10 probe) then a good initial setting would be 50mv/div, if using a standard probe (X1) then 0.5v/div. Divider probes are preferred because they have much lower capacitive loading but the RF test point is low impedance and so either should be OK.
some thing must be up with it as its just one single line being very wiggley ,im guessing this is what it looks like when things are bad?
at the moment its playing very well ,but when it skips back you can here the laser fall out of focus (the laser makes a click sound and the then the disc reads again and continues playing from a few secs back on the cd
When it is playing the RF will be at least something like it should be. So use that as a baseline. It should and will look at least somewhat like in the image I posted. If the amplitude drops below around 0.9 volts peak to peak then the player gives up and will not play.
If it is playing correctly and the RF looks wildly different to in that image then something is wrong with the measurement technique.
It is very hard to say what is going on without seeing it for real but remember most faults are usually fairly simple and most tend to be mechanical.
Is it possible the problem is something like the sled sticking, the player throws a fit and then just stops?
If it is playing correctly and the RF looks wildly different to in that image then something is wrong with the measurement technique.
It is very hard to say what is going on without seeing it for real but remember most faults are usually fairly simple and most tend to be mechanical.
Is it possible the problem is something like the sled sticking, the player throws a fit and then just stops?
well i got my other one out and it is just displaying a think line with is just a blur, no detail at all
If its playing OK then the RF must be basically correct. There is little room for it not being if the thing is playing. Something has to be amiss with the measurement in some way. The amplitude will be at least 0.9 volts peak to peak if its playing.
So much depends on the scope settings as well. You need internal trigger with NO HF reject selected and you need the time base wound out enough to resolve the detail. The scope should trigger easily on the RF signal. An analogue scope needs to have at least a 10Mhz bandwidth.
So much depends on the scope settings as well. You need internal trigger with NO HF reject selected and you need the time base wound out enough to resolve the detail. The scope should trigger easily on the RF signal. An analogue scope needs to have at least a 10Mhz bandwidth.
i have got the signal now,it is blury as my focus button is giving trouble ,repairing it now,only take a min more
i dont think its a mech problem as i have had it all to bits and cleaned and freed up what looked sticky,i have worked on many cd players mech and have got it right, do you think its a problem with the servo pcb,i was thinking of recapping it,
i have also been super careful with this player as its a part of my personal collection,(i collect es gear)
why i ask about the servo pcb is that if it was not getting the right voltage from power supply that might cause it to stop and start would it not? when it skiped and i had the oscilloscope hoked up the signal stopped along with the skip,is this normal?
i have also been super careful with this player as its a part of my personal collection,(i collect es gear)
why i ask about the servo pcb is that if it was not getting the right voltage from power supply that might cause it to stop and start would it not? when it skiped and i had the oscilloscope hoked up the signal stopped along with the skip,is this normal?
That was a very good scope back in the day and way better than most modern digital ones for resolving detail.
The RF should not be excessively fuzzy. One possible cause is using chassis ground (as I mentioned earlier) rather than the VC point but it is a much easier option. If you can measure on the scope a lot of noise between chassis and VC then that is the answer.
The RF signal is a direct signal from the disc itself and so any problem with disc rotation will show in the RF. The signal is only stable and clear while the servo's are locked.
The focus servo (lens up and down) always has to be correct. Any focus problems will show as a lower amplitude signal.
The tracking servo (lens moving in horizontal axis) brings it all into sharp focus.
When you jump tracks on the CD such as going from beginning to end of the CD then the tracking servo is partially disabled (tracking gain is lowered). What you see on the scope during that time is a blurred RF signal. If that is the sort of effect you see happen when playing a CD (when it fails) then it suggests a tracking issue.
Any supply voltage problem will cause all kinds of problems and this is why supplies should always be checked, not just with a DVM but with a scope as well.
The RF should not be excessively fuzzy. One possible cause is using chassis ground (as I mentioned earlier) rather than the VC point but it is a much easier option. If you can measure on the scope a lot of noise between chassis and VC then that is the answer.
The RF signal is a direct signal from the disc itself and so any problem with disc rotation will show in the RF. The signal is only stable and clear while the servo's are locked.
The focus servo (lens up and down) always has to be correct. Any focus problems will show as a lower amplitude signal.
The tracking servo (lens moving in horizontal axis) brings it all into sharp focus.
When you jump tracks on the CD such as going from beginning to end of the CD then the tracking servo is partially disabled (tracking gain is lowered). What you see on the scope during that time is a blurred RF signal. If that is the sort of effect you see happen when playing a CD (when it fails) then it suggests a tracking issue.
Any supply voltage problem will cause all kinds of problems and this is why supplies should always be checked, not just with a DVM but with a scope as well.
Do not replace any capacitor or any other component without any suspect of failure. Replacing components without any criteria is source of anymore failures.
regarding the scope im not so sure its working well,, i have a signal generater so i am going to try hook that up to see how clean that signal looks, im worried that i may be using a faulty unit, i hope its ok as i hoped to learn on it,
is tracking a adjustment? or do you think it is a faulty part?
thanks so much for your advice as this is making sence to me kind of.
do you think i should not hook the scope on the two test points listed in the service manual? if i did would that tell me if the wave form is cleaner at its source,, or is it two dangerous for me to try? i do understand that i am not very good at using this machine, so if you say dont i wont,
how will a test be done on the power supply with the scope,?
i purchased the scope to learn on it so i could one day adjust the laser on my phillips cd204 i recapped about a year ago, it works but i noticed that the adjustments did not look right ,looked like some one had been adjusting the tracking , so i have not used it since i noticed ,
but i rabble
mike