Hi,
I have a Revox B225 with a Philips CDM-0 swinging arm drive. It works for three or four minutes then stops playing with symptoms similar to a 'no CD' .
I checked the voltage to the laser today and found it was set way too high, adjusting it down to the correct 500mV got the machine to play for about ten minutes before it stopped. I was monitoring the HF output on the 'scope and the laser voltage on a DVM at the time it stopped playing the CD, the HF stopped and the laser voltage went up to about 1.5V.
Does this sound like a faulty laser, or something in the control circuit?
Thanks for any input,
Richard
I have a Revox B225 with a Philips CDM-0 swinging arm drive. It works for three or four minutes then stops playing with symptoms similar to a 'no CD' .
I checked the voltage to the laser today and found it was set way too high, adjusting it down to the correct 500mV got the machine to play for about ten minutes before it stopped. I was monitoring the HF output on the 'scope and the laser voltage on a DVM at the time it stopped playing the CD, the HF stopped and the laser voltage went up to about 1.5V.
Does this sound like a faulty laser, or something in the control circuit?
Thanks for any input,
Richard
I wouldn't immediately blame the laser mechanism, the CDM-0 is a very robust unit. Lasers also tend to work better with increasing temperature (so that the player will only work after some warm up time), rather than what you are experiencing.
The first step I would take on a player like this is replacing all of the electrolytic capacitors. They will be faulty by now, as these have a service life of about ten years, and could well be causing the fault with your player.
The first step I would take on a player like this is replacing all of the electrolytic capacitors. They will be faulty by now, as these have a service life of about ten years, and could well be causing the fault with your player.
Yes, I already replaced all of the electrolytics. The ones in the PSU were particularly bad - I tested a couple for fun and they were very leaky! There's a crude voltage doubler in there too which wasn't working until I replaced the caps. There's a scattering of nice Philips tants which I haven't changed, they seem to be more robust!
I've replaced all the 33µF caps on the CD control board this morning with no improvement.
I'm wondering if I can put the CDM-1 from my Philips CD104 into the Revox as a test. Would it be a direct swap?
Richard
I've replaced all the 33µF caps on the CD control board this morning with no improvement.
I'm wondering if I can put the CDM-1 from my Philips CD104 into the Revox as a test. Would it be a direct swap?
Richard
Okay, just to confirm, you replaced every last electrolytic capacitor, including the three or four on the PCB attached to the laser mechanism itself?
The next step I would suggest is probing various important points on the PCB with an oscilloscope (such as power supply rails, HF signals, etc), and note any changes between when it will and won't read a CD. My guess is that your fault will be due to a faulty passive or IC that is failing when it heats up. Unfortunately, I can't think of much more than this, as these first generation Philips players are so complex, there are so many things it could be.
You can try swapping in the CDM-1 from your CD104 if you like. The two are compatible, the B225 actually could have come with either. The only problem is that some of the newer CDM-1s can with different connectors to a CDM-0, which will complicate installing it.
The next step I would suggest is probing various important points on the PCB with an oscilloscope (such as power supply rails, HF signals, etc), and note any changes between when it will and won't read a CD. My guess is that your fault will be due to a faulty passive or IC that is failing when it heats up. Unfortunately, I can't think of much more than this, as these first generation Philips players are so complex, there are so many things it could be.
You can try swapping in the CDM-1 from your CD104 if you like. The two are compatible, the B225 actually could have come with either. The only problem is that some of the newer CDM-1s can with different connectors to a CDM-0, which will complicate installing it.
>erin: This is not a Philips player and doesn't have the eyelet problem. It does, however, suffer quite badly from expired electrolytics!
>amc184: No real news yet. The good weather has precluded any playing with important things (we install photovoltaic systems at work!) but I have discovered:
1. Swapping the CDM-1 from my Philips didn't work - I haven't had time to investigate why. The connectors are the same on both, the only real difference seems to be the turntable motor drive circuit. Might just be a different type of motor.
2. I have bought a Thurlby logic analyser which I'll be using to make sure both the microprocessors are doing what I expect them to do. Might be a bit easier than probing all the data and address lines with the 'scope! It's a long time since I did any troubleshooting with microprocessors though.
3. I did try to buy another, working, B225 on ebay so I could do board swaps but the price went too high :-(
I'll post again when I have more news!
Richard
>amc184: No real news yet. The good weather has precluded any playing with important things (we install photovoltaic systems at work!) but I have discovered:
1. Swapping the CDM-1 from my Philips didn't work - I haven't had time to investigate why. The connectors are the same on both, the only real difference seems to be the turntable motor drive circuit. Might just be a different type of motor.
2. I have bought a Thurlby logic analyser which I'll be using to make sure both the microprocessors are doing what I expect them to do. Might be a bit easier than probing all the data and address lines with the 'scope! It's a long time since I did any troubleshooting with microprocessors though.
3. I did try to buy another, working, B225 on ebay so I could do board swaps but the price went too high :-(
I'll post again when I have more news!
Richard
Sounds good. I don't think you'll need the logic analyzer though, I'd consider that superfluous when repairing CD players. Sometimes you can have problems with a logic bus (like I did a week ago with a Philips CD150), but nothing you can't spot with a scope. The first thing I'd do is 'scope the power supply rails on each daughter board.
The laser power control circuit is usually pretty much self contained... is it discrete on this, a couple of transistors with just a Laser on/off line from the servo IC.
If the laser power is going haywire that suggests the "servo loop" from photo diode to power control may be being broken... something as simple as the flexiprint or connector with a break etc, or failure of one of the transistors... assuming it's discrete.
Have you a circuit showing that part of the player ?
If the laser power is going haywire that suggests the "servo loop" from photo diode to power control may be being broken... something as simple as the flexiprint or connector with a break etc, or failure of one of the transistors... assuming it's discrete.
Have you a circuit showing that part of the player ?
I do have the full Studer / Revox service manual. Unfortunately, the servo control has a microprocessor in the loop so although 'self-contained' there are other functions associated with that processor which do work. One symptom is that the user display shows a 'no cd' indication when the turntable motor stops and the laser voltage rises.
I suspect there may be a break in the servo loop. I thought it was a thermal fault, but I haven't been able to find one in spite of using most of a can of freezer spray!
As you say, it could be something simple, but so far I'm unable to find it!!
Oh well, it keeps me out of trouble!
I suspect there may be a break in the servo loop. I thought it was a thermal fault, but I haven't been able to find one in spite of using most of a can of freezer spray!
As you say, it could be something simple, but so far I'm unable to find it!!
Oh well, it keeps me out of trouble!
Maybe if you could post that part of the circuit on here it might gives some clues as to faultfinding.
Revox B225 update
I managed to buy another B225 on ebay which works just fine. Board swapping proved that all the boards in the faulty unit are working properly.
Checking the CDM-0 mechanism, there was no light showing at the laser lens. I took the laser out of the machine and tested across the laser with a multimeter, no indication on the laser, normal diode reading on the monitor diode. Tried out the laser with an external power supply, no visible light, no current drawn from the power supply.
Looks like I have two options:
1. Find a new SHARP LT022 laser diode and fit it,
2. Get another CDM drive and rob the drive or the laser assembly.
In pursuit of (1), has anyone any ideas about getting an LT022, or a more available substitute?
In pursuit of (2) does anyone have a reference for which CDM drives use a suitable donor light pin?
TIA
Richard
I managed to buy another B225 on ebay which works just fine. Board swapping proved that all the boards in the faulty unit are working properly.
Checking the CDM-0 mechanism, there was no light showing at the laser lens. I took the laser out of the machine and tested across the laser with a multimeter, no indication on the laser, normal diode reading on the monitor diode. Tried out the laser with an external power supply, no visible light, no current drawn from the power supply.
Looks like I have two options:
1. Find a new SHARP LT022 laser diode and fit it,
2. Get another CDM drive and rob the drive or the laser assembly.
In pursuit of (1), has anyone any ideas about getting an LT022, or a more available substitute?
In pursuit of (2) does anyone have a reference for which CDM drives use a suitable donor light pin?
TIA
Richard
You tested the LD on a multimeter... arghhh. You can't do that and hope that it will live to tell the tale. All it takes is a spike of a few picoseonds... yes that quick... and the facets of the LD can suffer permanent damage turning it into little more than an LED.
As to fitting a new LD. Well if you can get one... and there were threads on here with folk with them I'm sure, was it here,
http://www.diyaudio.com/forums/digi...d-philips-cdm-x-mech-they-want-resurrect.html
the Sharp LT022MC was used in many first generation players. It's how critical the mechanical alignment is that could be interesting... and it's something I have never done with a pickup.
As to fitting a new LD. Well if you can get one... and there were threads on here with folk with them I'm sure, was it here,
http://www.diyaudio.com/forums/digi...d-philips-cdm-x-mech-they-want-resurrect.html
the Sharp LT022MC was used in many first generation players. It's how critical the mechanical alignment is that could be interesting... and it's something I have never done with a pickup.
Well, yes, a multimeter can be a bit drastic, but since the laser wasn't working anyway, I had little to lose. When one is faced with a scrap £300 CD player for which the parts are rarer than pure unobtainium, some diagnostic methods which may be inappropriate in other circumstances might just be the only thing left.
I have a working CDM-1 out of a Philips CD104 but it has a different turntable motor so I'm not sure whether it would be a direct replacement. The connectors are the same. Of course, that means the Philips will be non-functional which is a shame because it is a nice little player, especially after I'd changed all the electrolytics and the op-amps and done the NOS mod.....
Check also the flat ribbon cable that links the drawer to the stationary intermediate PCB. The conductors in the ribbon break & give NO CD symptoms intermittently.
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