I found a helpful thread here to change the Sony kss-240a laser when it started skipping all the time and cleaning wasn't helping.
First impressions were great, no more skipping, then after about 3 minutes the power tripped off (including the main green power light) then came back again. So it sounds good now but only lasts a few minutes before it trips. Anything I might check? I tried a different power source already, tried reseating the ribbon cables. Would be delighted to get it working again. My electronics skills are limited but I do have a multitester.
When I plugged it back in, in my haste to check the result of changing the laser, the power button was already on whereas I would normally be careful to check first. Could the elderly circuits have suffered from that initial surge?
Any suggestions much appreciated!
Cheers,
Dave
First impressions were great, no more skipping, then after about 3 minutes the power tripped off (including the main green power light) then came back again. So it sounds good now but only lasts a few minutes before it trips. Anything I might check? I tried a different power source already, tried reseating the ribbon cables. Would be delighted to get it working again. My electronics skills are limited but I do have a multitester.
When I plugged it back in, in my haste to check the result of changing the laser, the power button was already on whereas I would normally be careful to check first. Could the elderly circuits have suffered from that initial surge?
Any suggestions much appreciated!
Cheers,
Dave
First suspect might be a bad joint, possibly on a regulator or some other such part... a good visual inspection is needed to see.
Look at the last images in post #1 here:
Sony CDP790 and KSS240 Restoration Project
If the main power light is going out then it suggests a rail is going down. You could also check ALL the rails while it is in the faulty state to see what if any disappear.
The components themselves should not be affected by what you mentioned.
Look at the last images in post #1 here:
Sony CDP790 and KSS240 Restoration Project
If the main power light is going out then it suggests a rail is going down. You could also check ALL the rails while it is in the faulty state to see what if any disappear.
The components themselves should not be affected by what you mentioned.
It could be the power switch contacts oxidising or mucky, I’ve seen that before. And I’ve also seen a couple with a break in the contacts on the transformer primaries. Worth checking those too
I decided to have a look again though I'm not really confident with electronics. I can't see any weak joint issues on the underside of the PCB. It all looks factory fresh. I have an old multi meter so I tried measuring the voltages in a few places. On TP7 (labeled -30v) with it applied between D18 and lk13 I got a reading of -42v which goes to -55v or so when the power cuts out. Any clue there?
That sounds a little strange. The neg 30v supply is all related to the VFD (vacuum fluorescent display). First double check the measurement points are correct.
The 7915 is a -15v regulator. The 15v Zener diode D17 artificially raises the regulator output by adding the Zener voltage to the regulator thus giving negative 30 volts.
Work with what you are measuring. It could be a break in a ground connection between the analogue and digital grounds.
If the regulator output really is going to those high voltages then it should be possible to see why. Measure from the same ground point you are using now and when the fault occurs check that the ground going to D17 (the Zener) is showing zero volts.
Conversely check that there is zero volts between the Zener ground and 'Analogue Ground) which can found at the top of the diagram.
The 7915 is a -15v regulator. The 15v Zener diode D17 artificially raises the regulator output by adding the Zener voltage to the regulator thus giving negative 30 volts.
Work with what you are measuring. It could be a break in a ground connection between the analogue and digital grounds.
If the regulator output really is going to those high voltages then it should be possible to see why. Measure from the same ground point you are using now and when the fault occurs check that the ground going to D17 (the Zener) is showing zero volts.
Conversely check that there is zero volts between the Zener ground and 'Analogue Ground) which can found at the top of the diagram.
As a long time servicer, I can only speculate on things from across the internet, because the unit is not on my service bench...
It's likely that the regulator IC Z209 is at fault, or it's ground-through-the-zener D17 is intermittently loose and requiring re-soldering.
Or the zener itself is opening up when it gets warm.
It's likely that the regulator IC Z209 is at fault, or it's ground-through-the-zener D17 is intermittently loose and requiring re-soldering.
Or the zener itself is opening up when it gets warm.