We did have this...
We have done all we reasonably can to try and 'prove' its a a tracking (radial) fault but you have to also look at the possibility it just might not be.
If you look at the circuit you will see a 100 ohm between B and E. If you isolated pin #1 of the IC then both of those transistors should have read faulty if tested in circuit. In circuit testing at best just tells you if there is a catastrophic failure. Even a 10k or 100k between B and E should still give a 'faulty' result because that would be classed as a leaky junction.
Ok will do that – but start with the supply voltages first (I measured them right at the beginning of all this and found nothing particular, but maybe I did not look well enough. There is a lot of power rail wires in this after all).
what is the op amp output to servo amp? the output of 6208 to the focus motor?
6208 op amp is for the focus coil. 6218 is for the radial arm motor, which is was referring to before. If you can figure out if the u-con is commanding the radial arm servo to advance, you can likely conclude there's something else telling the u-con there's a reason to freak out ie one of the photo sensors in the beam amplitude detecting array doing weird things, eother from contamination or another issue in the detection circuit. I seriously doubt the laser is weak or going bad. The player isn't behaving like it is. Most laser failures show up with consistent mistracking when the player is warmed up or right from the start. Some skipping issues show up from too much laser current being commanded to compensate for dirty optics. It would be an expensive endeavor to replace the laser and find out it was in vain. The fact you get clean and consistent RF at the correct amplitude alomst certainly rules out the laser on its own.
I just read Moolys comment about the eye pattern collapsing down before the unit skips. That can be an indicator of the u-con freaking out or something else ie 3 pin V reg oscillating / collapsing. They use alot of separate supply voltagws in these earlier players, which is great for isolation from noise, but horrible to trouble shoot. I've seen alot of power supply related issues in Philips CDPs cause all sorts problems, mainly worn capacitor related, but sometimes from supply regs behaving strangely. The clock oscillator for the u-con can cut out and cause weird intermittent issues too. Due to the intermittent nature, my gut instinct points to a supply voltage dropping out or sagging. Again, the biggest suspects are the 3 pin regs and the peripheral circuitry. If you replaced ALL of the tantalums, that would rule part of it out, but I've seen fancy low esr caps after 3 pin regs cause oscillation, sometimes dependent on load or operating temp. Just out of kicks, have you tried varying the AC line voltage with a variac? That may tell you something if its a supply related issue. Are all the V regs running at reasonable temps? A player skipping forwards by multiple frames at a time can be frustrating to figure out.
I just read Moolys comment about the eye pattern collapsing down before the unit skips. That can be an indicator of the u-con freaking out or something else ie 3 pin V reg oscillating / collapsing. They use alot of separate supply voltagws in these earlier players, which is great for isolation from noise, but horrible to trouble shoot. I've seen alot of power supply related issues in Philips CDPs cause all sorts problems, mainly worn capacitor related, but sometimes from supply regs behaving strangely. The clock oscillator for the u-con can cut out and cause weird intermittent issues too. Due to the intermittent nature, my gut instinct points to a supply voltage dropping out or sagging. Again, the biggest suspects are the 3 pin regs and the peripheral circuitry. If you replaced ALL of the tantalums, that would rule part of it out, but I've seen fancy low esr caps after 3 pin regs cause oscillation, sometimes dependent on load or operating temp. Just out of kicks, have you tried varying the AC line voltage with a variac? That may tell you something if its a supply related issue. Are all the V regs running at reasonable temps? A player skipping forwards by multiple frames at a time can be frustrating to figure out.
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Thanks!
Ok true, I got confused. We look at 6218.
What is the u-con?
I admit putting low ESR caps after the regulators in 2020, but it worked well with those for nearly three years.
Yes, I replaced all NEARLY tantalums – apart from those in the TDA1540 decoupling, but those should not get in the way (or do they? The DAC chips also hang on the +2 supply line).
The tantalums are as orange as the MKT's, which makes it confusing.
I don't have a variac unfortunately. But what I did not (I think I was afraid to mess something up on the mains line side) is soldering the transformer to 240 Volts. It still runs on the 220V setting. But again did so for years without problem.
I'll check the supply regs and lines as soon as I find a moment and will report back. How would I spot a regulator that is somehow intermittently causing problems? It would not be so complicated to just swap the one related to that power line (I think I even have some in my stash).
Thanks again for providing all this in-depth experience and knowledge!
Ok true, I got confused. We look at 6218.
What is the u-con?
I admit putting low ESR caps after the regulators in 2020, but it worked well with those for nearly three years.
Yes, I replaced all NEARLY tantalums – apart from those in the TDA1540 decoupling, but those should not get in the way (or do they? The DAC chips also hang on the +2 supply line).
The tantalums are as orange as the MKT's, which makes it confusing.
I don't have a variac unfortunately. But what I did not (I think I was afraid to mess something up on the mains line side) is soldering the transformer to 240 Volts. It still runs on the 220V setting. But again did so for years without problem.
I'll check the supply regs and lines as soon as I find a moment and will report back. How would I spot a regulator that is somehow intermittently causing problems? It would not be so complicated to just swap the one related to that power line (I think I even have some in my stash).
Thanks again for providing all this in-depth experience and knowledge!
I partially agree. The reason i harp on the radial tracking is to discount it as a possible cause itself being a directly observed symptom. I once had a player like this intermittently skip forward due to a bad oscillator crystal at the control IC. Ive also seen sticky radial arms cause similar intermittent skipping. The thrust bearing preload can be hard to adjust right on a swing arm pickup and they're very sensitive to shock damage from mishandling the player in transit without the little red transport locking devices in place. Can the laser supply circuit be the culprit? Absolutely, but working in that area is very risky for someone who isn't familiar with the proper procedures to keep the laser diode from being damaged.
The fault started to occur after the player had stayed for about three months nearly without playing in a warm to hot room (hot summer of 2022). It had not been moved at all.
If you check supplies then I would use a scope as well to look for anything untoward appearing. Problems with 78/79 regs are fairly common in commercial gear for some reason.
Just seen @profiguy reply... its very difficult pinning the problem down to a specific area.
Random thought. If the player is left paused (do they have a timeout?) then that would tend to eliminate mechanical issues with the arm as it would be static.
Just seen @profiguy reply... its very difficult pinning the problem down to a specific area.
Random thought. If the player is left paused (do they have a timeout?) then that would tend to eliminate mechanical issues with the arm as it would be static.
When the player is paused (it seems to stay paused infinitely) it has no tracking problems whatsoever. It always stays at the same spot and does not skip. It starts where it has paused.
You wan4 to monitor the supply rails that feed the transport u-con IC. This is the main 5V supply and th e clock oscillator. You want to verify the 3 pin regs aren't oscillating, getting too hot or sagging in output. You can also touch the tip of your soldering iron (only if its uses an ungrounded / isolated tip) to the vreg tabs and heatsinks and warm them slightly. That may provoke the issue of its temp related.
So you don't see a track here related to those tantalums I left as decoupling?
I'll have to check the schematic and get back to you... time for a bathroom break.
u-con is short for micro control IC. It's the one that runs the transport functions with a crystal next to it.
It would seem to point that way but its not 100% absolutely conclusive. It is part of the general 'evidence' though 🙂
The MAB 8440
uP (Microprocessor), SysCon (system controller). The big chip with a weird number 😉
Only if the skipping occurs at the same or similar elapsed time of the CD, indicating a binding spot in the bearing ie debris or similar.
The radial arm motor can draw alot of peak current when its binding. That will show up in the drive waveform as clipping from the servo circuit.
The only reason I know this is I went to Philips training classes for servicing their CD players. It was a week long seminar in Belgium back in the early 80s.