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Marantz CD-73: not recognizing disc, laser seems fine, voltages differ oddly from SM?
Marantz CD-73: not recognizing disc, laser seems fine, voltages differ oddly from SM?
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Old 23rd November 2020, 03:53 PM   #11
joydivision is offline joydivision  Portugal
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I found the problem!!! Have kind of very little time right now to post this, so just a quick note that the problem is localized, player reads great now. It was a tiny cap in the wobble oscillator which had dry solder joints, making it open circuit so the whole oscillator was knocked out! Without wobble oscillator, the tracking and error correction is totally compromised, so it would work in a limited way, but only on very good pressed CD, as the tracks are narrower than CD-R, where it would work "Kind of"! ! It all makes sense now!!! Later I will post how I found the problem and what I learned with this repair.
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Old 24th November 2020, 12:00 AM   #12
joydivision is offline joydivision  Portugal
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So, this is what I did and how I found the problem:
- I followed the advice (and common sense, taking into account age of player) here and on other places and cleaned and lubricated the swing arm (carefully, so not to take it totally apart), it now swings much more freely. I tried to lubricate the spindle motor, but was unable to get oil into it (no holes in bottom, top is inaccessible due to "turntable"). This improved reading on outer tracks of CD, it would "lose tracking" and return to track 1 before much more easily

- I adjusted the spindle motor height via its screw in the motor shaft (focus adjustment), following SM indications (measuring voltage at 3240 and also watching eye pattern on scope), BUT: even though I set it almost perfect, it would never get right for all CDs. The CD-R was most tolerant. Two pressed (good condition) CDs I tried, when one was acceptable (still very sensitive to mechanical impact), the other failed, and vice-versa.

- I tried again to check laser adjustment (watching eye pattern and control voltage at 3308), was fine. Had no influence, unless set too low.

- played with focus gain pot, not really useful, no real difference.

- discovered (by accident) that connecting the metal frame of CDM to case of player (ground) would improve reading. Very odd. This made me think - it HAD to be a problem in electronics.

- I then came across a part in SM where it said: if the offset and error correction circuits are defective, the player might function acceptably with a very good condition CD, but fail with minimal errors or mechanical impact. This made me think again and I started to measure around on servo board, comparing voltages to SM indications.
I quickly noticed something was really wrong around IC6212 and IC6213, which together form the wobble oscillator. IC6212 was outputting 10,8V DC at pin 8 and at pin 9 there was only 1,25V and also at pins 10 and 8 of IC6213 there was 5V instead of 2,5V. Also, there was NO 650Hz signal at all! So, no wobble signal! That explained EVERYTHING!
Voltages at other parts of these ICs were fine, this made very unlikely that the ICs would have failed, so I started measuring passive components.
The wobble oscillator contains two 1% caps, I remembered reading that they tend to fail. But no, they were fine. As were the resistors. But then I measured C2237 (33nF) and yes, it gave weird values of fluctuating low capacity on my DMM! Then it struck me: it was one of a few components which had "dark" dots (little cavities?) in the middle of the solder joint (which would only be visible with little light), as basically the end of their leg had corroded a little, making it appear in a different color compared to the solder joint (which wasn't dry). I had noticed them before, but the ones that I measured were fine. I missed this one! If I had measured before, I'd got to the problem many hours before...
I resoldered the legs, and yes, now 33nF! So, I switched player on and BINGO! On my scope I now could see 650Hz signal at test points of wobble osc and now read perfectly all the CDs I threw at it!

What I've got left to do with the player: resolder the other few components with "darkened" legs, seal radial arm nut with nail laquer, tighten correctly spindle motor security nut, give it a good clean and (hopefully I will get green light from owner) do a comprehensive recap, maybe not complete, but at least the power supply, audio signal path and nasty blue axial Philips caps... Then, I'm sure it will work well another 20 years, if well treated! These old mechanisms and lasers are superb.
I will report back then and post some photos.
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Old 24th November 2020, 04:02 PM   #13
Guerilla is offline Guerilla  Denmark
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That was good detective work - And nice dudging derailing atempts . I guess I was lucky with my fixes decades ago. Those drives were not as old at that time.

Cheers!
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Old 24th November 2020, 08:15 PM   #14
joydivision is offline joydivision  Portugal
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Thanks
But the task is not done yet: now that it's reading nicely, I tried it out connected to amp, and noticed that only one channel is playing muisc! Probably a bad cap or bad solder joint. Owner gave me green light to do a (almost) full recap, so still a lot to do, but now I'm confident it will be restored to great condition.
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Old 3rd December 2020, 11:01 PM   #15
joydivision is offline joydivision  Portugal
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Well, I'm now almost done with the recap. But this had a surprising (and unnerving) turnaround in the meanwhile: the damn wobble oscillator failure occurred again, suddenly! And it would go away and come back intermittently, as I would "resolder things" around the wobble oscillator section (heat/cold).

I was getting desperate, decided taking out one or another leg of resistors so to isolate the problem, which didn't help, as I was now suspecting (wrongly) of the LM324, which I unsoldered and replaced with a new one, just to see the same exact wrong 10,3V on pin 8 and NO wobble signal! I also resoldered the 33nF cap again, nothing. Just before starting to (wrongly) suspect of the 4070 IC, and having tested all resistors, I measured again all voltages in the surroundings and started thinking. And by deduction it suddenly struck me: no way that there could be 5V at pin 10 of 4070 and around 0,6V after the 120k resistor R323, and this made me focus on the two 1% film caps (5,6n) which are part of the wobble oscillator and are of the flimsy old type which I heard before does sometimes go open or short! And YES! one of them measured 22k-80k widely floating according to temperature/position of the moon?? lol... it would short against ground, so no oscillation possible!
Strangely enough, it would still measure with acceptable capacity on my DMM! That's why I wouldn't find it before, I had measured it before!

Below are some photos were you can see the bad boy. And yes, only one of them was bad!
I changed them and bingo! All voltages normal and stable and perfectly reading all discs.

I then proceed and tested again and don't know why, but now audio output is fine on both channels, player is working! So I went ahead with the recap which is almost done (and tested, doing it in parts). Oddly enough, while doing the recap (as this player is kind of hard to service, just have a look at the complicated work bench setup), one lead of the HF cable just broke off the PCB and made me live half an hour of "panic", as the player would now totally refuse to read! Then I noticed the broken wire! Always pay attention to details and bend old cables as little as possible...

Will make final report and some more photos when all is done and back together.
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Old 4th December 2020, 03:03 PM   #16
Markw4 is online now Markw4  United States
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Nice troubleshooting story and pics. Thanks!
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Old 6th December 2020, 02:17 PM   #17
joydivision is offline joydivision  Portugal
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So,here's the final report, player is reassembled and working great, playing Pat Metheny right now
I'll be kind of sad when it will go back to its owner, haven't had anything like this here before yet... it's a real museum piece now.
It even plays CD-Rs, which is amazing, because this is CDM-0, but, which is natural, not every CD-R, some of them are quite skippy in the first tracks, getting better towards the outside. Others play perfect. Might have to do with brands or velocities at which they were burned. It may even be possible to further tweak the settings of focus/laser powrr and make it read them better, but this would take hours (and this player is a nightmare to service and adjust, as you can see from the images), also the owner has NOT requested this kind of service (nor is paying at this kind of level), so it will stay as it is: playing pressed CDs perfectly (no matter how scratched they are) and some CD-Rs.
Regarding sound quality, it astonished me. I wasn't expecting it to sound that good, because of TDA1540 lacking the two bits, also because of weird Sony decoder version (I know there was a Philips only version), which looks like patchwork, but it DOES sound great. I can't really say it sounds inferior to my heavily modded TDA1541 and CDM-4 based Marantz. Btw, sounds much better than the B&O CD50 which is shown below it (also not mine, repaired for a friend, will return soon), which is more or less from the same time. So, if anyone is hesitating if this kind of ancious player will be satisfying (they ARE expensive now) for the listener: yes, it is, at least this kind of player. But then again, they ARE slow, at least for track change, and at least this model doesn't have time display, only single LEDs for track, and only up to 15 tracks, so yes, it's kind of a special experience to play CDs on this. Is appears alomost as if it was some kind of hybrid between a tape/record player and a CD player... Here are some photos.
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Old 6th December 2020, 03:37 PM   #18
Guerilla is offline Guerilla  Denmark
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Most importantly, it has numeric Buttons for direct track-choice. Later they disapeared from nearly all players
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Old 7th December 2020, 03:57 PM   #19
N101N is offline N101N
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You have done impressive work. I don`t regard the TDA1540 (lacking two bits) and the weird Sony decoder version as degrading factors for sound quality. What heavy modifications have been made to the TDA1541 player?
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Old 9th December 2020, 11:05 AM   #20
joydivision is offline joydivision  Portugal
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Quote:
Originally Posted by Guerilla View Post
Most importantly, it has numeric Buttons for direct track-choice. Later they disapeared from nearly all players
Actually it doesn't have numeric buttons, it only allows selection of the track to go to (the LED for the track will light up, each press of key will select next track until track 15 and then you hit PLAY again and it will then seek until that track (very slow compared to later mechs). You can't do this backwards, unless you jump back to start... it's not very practical, but it's part of all the vintage, retro feeling
But yes, numeric keys were often available in earlier models, very practical, and on later models almost disappeared.

Quote:
Originally Posted by N101N View Post
You have done impressive work. I don`t regard the TDA1540 (lacking two bits) and the weird Sony decoder version as degrading factors for sound quality. What heavy modifications have been made to the TDA1541 player?
Thanks

I was just saying this because I've listened to other TDA1540 players, and though they sounded very good, sound was a little inferior to good TDA1541. But then again, these players were not of the league of this one, nor did they have the fantastic CDM0 (or CDM1) mech, so all this influences the sound, this one is definitely on the same level as my TDA1541, which has a new low jitter clock, NOS mod (which has its pros and cons, I know, but it can be switched to OS for direct comparison... went through a lot of work at the time) and better opamps and caps.
What I especially like about the CD73 is that is sounds so analog, natural and has a huge sound stage and depth, also you can easily pick up with you ears each of the instruments (which often is hard to do on players with higher levels of jitter, even if they have good DAC like TDA1541 or 43). Also NO digital harshness. Really good.
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