Today on the workbench: A beautiful designed ReVox CD player. Based on one of the first CD players of Philips and uses a CDM1 transport and two mono DACs TDA1540p.
This service friendly machine didn’t come in for a little maintenance, no it was brought in with a common symptom for a TDA1540 like CD player: Distorted sound.
To me this sounded like an easy fix, because I’ve seen this error a lot and it’s commonly cause by a power supply voltage that is to low. In most cases that is the -18 V or -17 V volt line, created by a voltage doubler circuit.
In order to know what we are dealing with, I opened up the device, did a visual inspection, found nothing disturbing and connected it to my test amplifier and have a test run.
Let have a look inside…
It appears there was a bit more going on. The right channel was in complete silence and the left channel experience a heavily distorted audio sound.
So that could be two defects in one. I decided to have a look at the distortion first, the dead channel next.
I’ve measured all the voltage rails and checked it with the service manual / schematics. All are OK and within specifications. So there goes the theory of a bad negative voltage line.
Since there is no digital out, I couldn’t directly rule out half the CD player. Luckily the device was so well build, I could easily take out the DAC board and put the scope on the digital signals.
At first they seem fine, there was a signal on all the required data and clock lines. But a scope isn’t really suitable to view multiple digital signals, even with a 4 channel scope. That’s where this device comes in:
It’s a cheap 8 channel USB logic analyser that can show 8 channels of digital data with a theoretical maximum of 24MHz.
The data signals that are the input of the DAC board is looking fine, all the signals are there and all looks very much like the signals in the service manual. This signal is then fed through the digital filter and 4x oversampling IC SAA7030.
So, lets see how the signals look like after they are processed by that chip.
What is it that this chip does? Well, it does the oversampling, so it will multiply the clock frequency by 4, does the digital filtering and creates new clock and strobe signals.
So basically what is expected to see at the output is that it will have quadrupled the data bitstream for left and right (not exactly, because of quantisation, etc) and created quadrupled clock and strobe signals.
I’ve recorded these signals (except the main clock, because I already ran out of the 8 channels on the logic analyser) with two different sources:
- 1 kHz calibration signal, which is a function of this CD player
- 1 kHz test signal from a test CD (Burosch)
Here you see the 1 kHz calibration signal with a Data clock in, Strobe (which indicates the start/end of a word) and two data channels.
What we would expect at the output is a repetitive data stream, like the output of channel L, but not a constant bitstream like channel R.
But that’s not all, the Data Clock out is not constant and is very slow and not constant.
With the test CD as a source the left and right channel may vary, but that is not uncommon. The outputs are similar as with the calibration signal.
That the right channel does not give any signal makes sense based on what we see here. So the cause of that could be this SAA7030.
The heavy distortion is likely caused by the inconsistent signal on Data Clock out. So it looks like both errors are caused by the same circuit: the SAA7030.
Since the SAA7030 is a very independent chip with not that many surrounding components like capacitors or oscillators, it most likely this chip is defect. Let’s have closer look:
After I soldered the SAA7030 out of the PCB there was definitely signs that it got very warm.
I’ve installed a IC socket and put in another SAA7030 which I salvaged from a CD104 PCB. Installed the DAC PCB and there was sound from both channels again and the distortion was also gone.
Have a b225 I bought new in 1986. Had very little use as I went back to vinyl. Took it out of the cupboard last week and astounded that everything still worked but left channel silent and right channel distorted. Would love to get it working properly again. Serial number 2503 with a Zero transport. Still completely original.
I live in PE South Africa. Could you please help with advice on what caps I could replace in the meantime to hopefully get things going. It is a beautiful piece of equipment and deserves the best!
You have an amazing blog.
The experience I have with Philips based cd-players that mostly the small blue axial capacitors are dried up after oll those years. Also for some players the -16~18V is to low because of bad 100uF capacitors in the voltage multiplier in the power supply section, but I think that the b225 does not have that.
The oversampling SAA could be the issue with your player, but thats a guess… Never guess, always measure.
In Dutch we say: Meten is weten, Gissen is missen. A free transformation would be like: to measure gives pleasure, to guess gives stress.
Replacing caps somewhat randomly on a player that already have issues is not the path I would follow.
You can test if the test-signal is working its way towards the output. That would rule out most of the transport electronics in the player.
You would need to be able to read the schematics and follow the signal, first digital, then analog.
Since you have different issues in both channels, it hard to compare signals between the two. So where in most cases a signal can be measured/compared with a decent multimeter, this time I thing you probably need an oscilloscope.
You can of course start with measuring the voltages from the powersupply. Unregulated power lines can be off by 10%, regulated lines should be within 5% tolerance.
Then also measure the AC component on those. (Multimeter on AC). For Unregulated power lines it should not exceed 20% of the DC component, in idle even lower. For regulated lines it should not exceed 50mV. < 10mV AC is what I mostly measure. Hope this can help you in any way. Regards, Mark
Apologies for the delay and many thanks for the assistance. Will keep you updated of progress.
a few days ago I’ve got a Revox C 126 cd player. I’ve never had a Revox before. Wonderful piece but the problem is that the CD drawer does not slide normally either when opening or closing. In fact, when it closes it has only a small intention to do it and stops, and when it opens the movement is fast but only about halfway, where it starts to play back and forth.
Have you ever encountered such cases? What could be the cause?
Thank you for your time!
In many cases such a symptom is caused by a worn belt. Especially when the player has been sitting idle for a long time.
So a new belt could solve the issue.
Also check the grease on the moving parts if they are not dried out.
Hi Mark – I am Mike from Munich, reed all your coms on that side.
I have a B225 with Troubles: both canels are heavy distorted. – the effect came over night!
All the capicitors are changed,
All voltages are OK – even the test tone is ok on all outputs. I planned to change the SAA7030 – but I am not sure that this would be ok. The sinus also runs thru the SAA – but it is ok.
So can got any idea what could be wrong. The decoder or a data prom from the reader? Thanks in advance – regards MIke
I’ve just had a look at the schematics of the B225. The test tone is created by a sine-wave generator around IC4 on The decoder. It is been switched between the generator signal and the signal from the decoder, SAA7000. So my guess would be that the problem is before that point.
With the test tone working fine, it could also be distortion on certain frequencies other than the test-tone. Do you have a test CD with serveral test sine waves on different frequencies?
In these special cases I usually connect a oscilloscope to the output and a test CD in the player to view the distortion in stead of listening to it. Don’t know if you have a scope available.
Hope this helps you a bit in fixing your B225!
Hi Mark and everyone! My 225 has a disc tray error, it can’t stop when the disc tray sticks out. I have cleaned the 2 limit switches and double checked the Jacks, screwed them tightly and correctly, the stroke iron is coordinated with the limit switch. Hope your message !
Hi. It looks like the tray is mechanically operating well and hits the limit switch, but the electronics fail to stop the tray motor.
Since the mechanics seems to be working, you will have to start measuring. First measure the resistance of the switch, it should measure near 0 ohms (let’s say, less then 10 ohms) when closed. When opened should be significantly higher, like in the order of thousands or milions of ohms (kOhm, MOhm).
When that’s measuring ok, you will have to dig a bit deeper in the system. You could then measure the voltage between both pins and/or relative to earth (player chassis). When measuring between the pins, you should measure something like 5v when the switch is open and nearly 0v when closed.
When measuring in relation to ground, one pin would measure always the same and the other should read the same when the switch is closed.
The best way to know exactly what you are measuring is checking the schematics and see how the circuit is created.
In this case you would need to know how to handle a multimeter and eventually how to read schematics and can interpret these. 🙂
Hope this points you in the right direction!
I had a similar problem. Normally, a metal plate is mounted on the rear of the carriage, transverse to the direction of thrust, and stops the transport motor when the carrier is extended. Is this part mounted with you – across?
Hi, about a month ago I got a Revox B225, when I first turned it on it did not read the loaded disc, then I moved the box a little and it was able to read but there was a lot of distortion coming out of the speakers, I replaced PSU caps and distortion was gone, it played discs ok but having a little trouble in reading some or definitely not reading others, CDRs were impossible to read, it just turn forever or suddenly turned off completely. After 2 or 3 days of normal use, no discs can be read but the funny things is that now the only ones that hardly recognizes/read (with difficulties) are CDRs, when first detecting/reading the cdr pick up seems to make a lot of noise until disc info it’s “found”, then noise stops, still, once the info of the disc is displayed the player acts weird, sometimes playing only a few tracks, if next track is selected or a different one via the numeric pads, it could just go there and play it or start “jumping” through tracks randomly until if “lucky” it starts playing the selected one. Sometimes the counter starts but no sound. If you could please help me try to found out whats wrong with my B225 I would be very thankful, with just 2 or 3 days of use I fell in love with this Revox. I’m in México and here it is very hard to find a good technician specialized in this kind of equipment. Thanks in advance. Best regards.
The distortion probably had to do with the -18V line or with bad solder joints. Especially because you experienced different behaviour while moving the cd-player.
You fixed that by replacing the caps in the power supply, well done!
Bad reading of CDs are in many cases caused by dried-out capacitors on the laser control board (mounted on the bottom of the laser assembly). It depends on the version of this PCB how many capacitors are on there and what value/orientation. Mostly there are five 33uF/16V capacitors on them. Some boards have one 68uF as well.
Mostly the blue Philips axial types are bad after all those years and their value will have dropped in value below 15uF in most cases. Best is to replace all the electrolytic capacitors on that board.
If that doesn’t fix the issue, you should check all other boards for those blue axial capacitors.
This is obviously not a real repair method, but is easier than to start measuring signals with multimeter, scopes and data loggers, which most people do not have lying around. 🙂
Good luck with your Revox B225!
Thanks a lot Mark 🙂 today I replaced all capacitors on servo 2 and DAC PBC, there was a little improvement (I think) since is kind of more “stable” when I select tracks, even though sometimes it goes from first through all the rest or from last in reverse until it “finds” the one selected, still only able to “read” one of the 3 CDR’s I have available, still no luck with originals, I noticed it struggles more with firsts and lasts tracks also very susceptible to the minimum vibration it would make the disc skip or totally freeze or the laser go “crazy” trying to stabilize, I guess. I will replace the ones on the laser control board and let you know. I’ve read that a broken/faulty laser will first stop reading CDRs, not originals, is that right?
I really appreciate your help.
Great to hear that you are making progress. 🙂
Since the reflecting surface of CDRs have pits and lands (digital 0 and 1) that are burned into the reflective material whereas pressed CDs have those pits and lands stamped into the die and then covered with reflective material. This makes it harder for a CDR to be read. When the laser degrades it will emit less laser light and the reflected light will be harder to read all the data from (tracing and data). The type of the reflective material (colour, reflectance) might also have some influence.
Philips lasers, especially CDM0, CDM1 will degrade not as much as lasers build these days. Also the detection electronics will be very accurate when all electrolytic capacitors are within specs ;).
Hello Mark, so I did replace blue capacitors (5) from cd drive mechanism and still no progress 🙁 laser is apparently working ok, I check it with a camera and there seems to be the pattern. What else should I check? When I select next track or any other, besides going crazy, sometimes it “starts playing” seconds before the one selected, I can tell it by the display and counter all of this with no sound, if it “finds” the one selected, either of 2 things can happen, it works for a few seconds before it goes crazy, if lucky, plays the whole track normally, or it “freezes” on 0:00 on counter (track won’t start).
Any advice on what could I do to bring my revox back to life will be appreciated 🙂
At this point it’s very hard to point to the cause of the problem. Assuming that you replaced the capacitors the right way and checked all boards voor bad solder joints, all common errors are now fixed. It seems like there is something different wrong with your player than the most common errors know to these type of cd players based on an CDM0/1 laser unit. Now is the time to start measuring/checking voltages, AC ripple voltages, HF eye pattern signal and other signals to determine the defect.
I’ve checked if there is a service mode you can bring the cd player into, but I haven’t found it. It looks like there isn’t one. Maybe you can bring it into service mode like it is with Philips CD100: press and hold stop button and power on the cd player. FFD button will the activate service mode 2.
You could try if that does something.
Hello Mark – thanks for the engagement. I checked where the problem came from IC1 switches between the sine wave generator and the drive. If I play 1kHz with a test CD, I can make out the sine on the scope – but with errors. Depending on the frequency, the vibrations are displayed in units of 3 to 6 pieces – in between a lot of undefinable things. The problem is the same at the input of IC1 as at the output. I tried to oscillograph all parameters. On SAA7000 point 2 & 3 are stable – just like a 4; on 5 turns off the signal on pause on the player – or the content is missing. What I also noticed is that the crystal at 7 & 8 only oscillates at about 2.5 MHz. I was just counting it by the vibrations. My old HAMEG still has a calibration at 2V & 1MHz. That was the reason. I’m trying to find the SAA7000 – it would be the first candidate to swap. Possibly the quartz. Do you have an opinion? thanks for your Input.
Thanks a lot for your help Mark. All electrolytics on all boards were replaced, , all but 8 blue “plastic” ones in DAC board, 2 of them with high values (15,000), also there are 9 axials in servo 2 pcb marked “n” on SM , should I replace all those too? Would a reversed electrolytic damage other components?, there was one at the decoder pcd, the player was on only for a few secs before I noticed. It seems there is no service mode just like you pointed 🙁 I’ll keep on trying.
Those axial capacitors are know to get very low in value after all these years (years of use and storage, makes no difference really). I would certainly replace those on the servo board because that’s the board that controls the reading of the disk.
A reversed electrolytic could damage the boards if it’s starts leaking electrolyte acid. It could then also damage other components. On the other hand, an electrolytic installed with the wrong polarity will charge a lot of current. It depends on the use of the capacitor and where it is in certain circuit whether it could damage other parts.
Great news Mark, it’s now reading both original and cdrs like a champ, I replaced op amps in servo 2 pcb and it’s back to life 🙂 Now ,since I “played” with some adjustments (height and scanning angle) in cd drive, I’m wondering if that could affect laser’s life, not sure if those adjustments have something to do with it. Could it damage the laser in anyway?
Thanks a lot for your help 🙂
That’s great news! Well done!
These opamps do not fail often. Maybe they died because of high load during another defect.
CD spindle high and angle will not influence the laser’s lifetime. But it could cause excessive load on the servo systems. Focus servo should be set to 0v in idle (if I’m not mistaken), that can be achieved by setting the correct spindle height. This is also described in the service manual of the Philips CDM-0 and CDM-1.
Angle should normally not need adjustment, should be set correctly during manufacturing. If you “played” with that as well, check the those service manuals.
It’s somewhat cryptically explained in there and officially you need a transparent adjustment CD.
I’ve heard that the transparent CD-like covers you find on either side of a CDR/DVD-R spindle would work fine.
I’ve never tried it though.
Hi Mark, so here is the update, it recognizes both original and CDR’s, plays ok first tracks but refuses to play last ones, guess has something to do with adjustments which it seems I have not been able to correct yet. Will keep on trying and let you know if succeed.
Hello again Mark, so after some adjustments and replacing some IC’s the player was behaving better, suddenly a new fault appeared, player would only respond to load button, luckily it turned out to be a faulty socket in slave microcomputer chip, now after that, player won’t spin 🙁 tried motor bearing height, no luck, it would seem like the swing arm and motor are not receiving voltage or signal even though the laser seems to be ok, laser light is there and pick up moves a few times trying to focus. Also, fuses 3 and 4 had blown a couple of times. I’m lost again and not sure where to point, hope you can help me, sorry to bother .
Too bad it broke again. When it tries to focus three or four times, it can’t see the CD. If it can’t see the CD it will also not start the spindle motor.
The player walks to several steps on startup. If one of those steps fail, it will stop and never reach the next step.
If swingarm servo does not get voltage, then the laser will not be put in starting position (close to the spindle). Then the TOC will never be found, but spindle should start if the spindle height is set correctly.
So the first thing to look at is if the swingarm (tracking servo) is activated so that the laser will move to the starting position.
Then the laser will be turned on and tries to find the CD by focusing a few times.
If that step is OK (focus lock), then the spindle should start.
If fuses are blown, then there could be a short circuit in any of the servo driving circuits. Check for shortages on solder joints etc. I’m unable to look into the schematics right now, so I don’t know in which circuit those two fuses are.
Fuses don’t blow suddenly. It’s a safety mechanism to avoid burning other components or to avoid causing fire.
I have a Revox B225 type 8001 #22866 not sure what year the unit was purchased approx. 1987.
#1entermittent hum emitted from l/speaker. problem occurs 3-4 times weekly.
#2 music sounds distorted at times like skipping.
#3 Intermittent unable to increase cd volume.
i replaced the RCA cables.
How can i get in touch with you.
Where are you located, do you have a repair shop.
Thank you for you message. Great to hear that you have an B225 of you own.
Let take a look at the problem symptoms your player has:
#1 Hum from left output. Since it’s not happening every time, I would expect a bad connection somewhere. Probably in the audio output stage, output connectors.
#2 Distorted music could be really everything, depending on the sound of the distortion. Possible causes: Dust on the lens, bad solder joints, bad capacitors somewhere in the device, unstable voltage from the power, broken DAC or oversampling chips, etc.
#3 Probably the same as #2.
I think the best option for you is to find a very good repair shop in your area and have it checked out. Preferably one with experience in repair on Revox cd-players or Philips cd-players in general.
For now I can only be contacted through this website. I have no repair shop, it’s just a hobby. 🙂
I’m located in The Netherlands.
at the time it was working perfect sounded excellent no problems ( dont have the remote) how ever i moved about a month ago and sure enough drop it about a foot high. now there is a humming noise and crackling noise , i havn.t hooked it up to my system yet i am using the headphones, it had an additional flaw all together with the drop that somehow corrected itself, when i hit the play the cd would jump out of the center nipple in the cradle/tray after 20-30 open and close putting the cd back in the center nipple then then finally it corrected itself and now it is playing without jumping off the nipple but sadly the humming and crackling noise is still there, any ideas. should i open it or……… help
This very much sounds like bad connections somewhere in the machine. Most likely the CD player suffers from bad solder joints. That’s probably why the previous error disappeared since the player was dropped.
Another thing that I have seen with different devices after a drop is a cracked printed circuit board (PCB). That is in some case very hard to repair.
If you have experience in opening devices, you could just have a look inside if you see any loose connectors or so.
If you have sufficient experience with soldering components on PCBs, then you could open it up and look for bad solder joints, loose cables or cracked boards and have those fixed. Otherwise it’s best to leave it up to a repair shop. I have seen a lot of devices that were beyond repair after someone thought he could fix it, but only made it worse.
A CD player like this is definitely worth saving!
My ReVox B225 has a similar problem: The left channel is ok, but right channel have a heavy distorted audio sound.
I found IC Philips SAA7030 on Mercado Livre (Brazilian eBay). I bought today. When I installed new IC, I tell you what happened.
I hope your B225 will be working again after replacing the SAA7030. I assume it’s a used SAA7030 that you’ve bought because it’s not very likely that these ICs are still in production. Or it might be a Chinese remake.
I really would love to hear from you again how the repair is going.
Good afternoon, Mark.
I have some great news! Today I left the DAC board half an hour in the sun (the brazilian sun is very strong). I installed and the cd player ran normally. I did not even need to change the ci. It was probably excessive humidity.
Great that you have your B225 working again! Moist could cause all kinds of strange behavior. Hopefully nothing got corroded, otherwise it will most likely start to malfunction again some day.