Diagnosing Faults on Sony MZ-N900 Portable Minidisc Players

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I nearly abandoned this one half way through the editing, it was just too long, and I didn't actually fix one, but I did learn the reason for a very common fault, and one not so common.
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Chapters
00:00 Unboxing
01:17 Testing
03:43 Lens cleaning
04:33 Troubleshooting
07:29 Lubrication
12:10 Top cover removal
13:34 Cleaning
15:15 Over-lubricating
16:35 Testing
18:03 Teardown
20:31 Mechanism
23:45 Reassembly
26:30 Testing
23:39 Fault diagnosis
33:36 What I've learned
34:59 Conclusion

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6 авг 2024

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Комментарии : 16

@missionnad1 4 месяца назад

Salutare din Romania V-am urmărit cu interes fiecare clip , sunt pasionat de tehnologia și echipamentele hi-fi stereo portabile din trecut. Nostalgie. Am un MZ-R900 , aceiași problemă la citirea md. Cauza nu a fost unitatea optică, ci motorul central care învârte discul. Axul central "the rotor" s-a deplasat in sus aproximativ 0,5 mm . Din această cauză discul atingea în carcasa de protecție ducând la mici vibrații și oscilații suficiente cât să facă probleme la citire. Trebuie să desfaceți motorul,ori înlocuit.

@sjm4306 4 месяца назад

I'm suspicious of the chewed up looking end of the laser ribbon just before the stiffener. Looks like someone tinkered with this unit and used tweezers to insert/remove the ribbon and may have inadvertantly severed some thin traces in that area.

@CBitsTech 4 месяца назад

Yes, looks like it to me too. In addition though, I swapped out the whole black part from another unit and that one didn't work either.

@HermanV 4 месяца назад

In my experience it's always better to remove the top so it's easier to clean. I currently use sewing machine oil to clean the movement mechanism of the head. And I found there are two small gears to move the spindle. they tend to get stuck most likely caused by the grease harden over time, same process, use sewing machine oil to clear the old grease. Move both the head and the spindle, leave it for a day and the next day every should be moving smoothly. From all the MD I repaired so far it's mainly the mechanism being stuck. I normally supply power, put in a disc and put the MD player to my ear and press the buttons. If all is well you should hear the mechanism move smoothly. If not you need to do more cleaning. Sometimes the spindle gears are very hard to reach.

@CBitsTech 4 месяца назад

Excellent advice, thanks. So, is the sewing machine oil the thing that cleans out the old grease? If so, do you need to apply new grease? And do you need to remove the oil before applying the new grease? It could be those spindle gears that are stuck on both those mechanisms, rather than the motor controller on one board.

@HermanV 4 месяца назад

@@CBitsTech I clean the sewing machine oil from the mechanism and apply lithium grease on the spindle.

@yajiu 4 месяца назад

The ribbon cable! Before you jump to the main board being the culprit, consider this: the ribbon cable to the laser sled can bunch-up and prevent the sled to travel! I’ve repaired 2 Sony CD walkmans just by dealing with the ribbon cables. Take a look on the underside of the ribbon: was there some double-sided tape installed at the factory that has failed? Remember, with many of these units, the ribbon cable is supposed to be stationary for 50% and bendable for 50% (guestimate) so that the sled can have full movement but the part that is below the sled does not interfere. You said it yourself: the cable is munched-there will be a reason.

@CBitsTech 4 месяца назад

Coincidentally, @technical iInitiative put up a video about a repair of one of these yesterday. Similar problem, solved by lubrication of the spindle of the round gears. Typical that his video goes live two days before mine lol BTW, there was no tape on the ribbon cable. Thanks for the suggestion.

@Tink-GB 4 месяца назад

@@CBitsTech On this model the voltage adjustment is on the pcb...so swapping sleds would not fix the read error issue....you would have to download and read the service manual to see how to get into the test mode first. You can then adjust the voltage up or down digitally using the display on the remote. It can also diagnose other errors and clear them... This model is so much more than you probably think...it even remembers discs inserted wrt certain settings...it was after all their top md player. Even the AA battery holder allows you to use a rechargeable AA powering through the socket on the side of it...only this player had that holder....so those battery holders are nearly worth more than the player itself...

@CBitsTech 4 месяца назад

Cool. Good info, thanks. I'm check the battery holder, I assume it's the original. I'll also look for a service manual and fit the diagnostic mode. Thanks.

@CBitsTech 4 месяца назад

I checked the AA battery holder, it has the input. I should read the user manual 🙂

@InsideOutElectronics 4 месяца назад

Make one out of 3 :) I have the same idea with mz 420d , make 1 out of 2.... May be ;)

@Synthematix 4 месяца назад

You've probably destroyed the laser diode by touching the ribbon, there are two tabs you're supposed to solder together when working with lasers to protect them from static damage. Also after you've taken these apart you need to go in the service mode to calibrate the laser and mechanism by using a shop bought disc (CD) and a brand new unused blank (MO)

@CBitsTech 4 месяца назад

Theoretically you're supposed to solder the tabs to protect from static, but practically I've never seen static kill anything. Thanks for the reminder though. Regarding calibration after taking them apart, would that only apply if I had taken apart the laser assembly itself? In any case, maybe calibration would help solve read errors. I'll look into that, thanks.

@Tink-GB 4 месяца назад

The other thing to consider is the laser head is wearing out, in that not enough voltage is getting to the head to read and receive... This is a generic problem for any cd player laser assembly but especially Sony... Solution...there is a tiny pot to adjust voltage usually found by the head assembly...adjusting it to supply more milli-volts to the head will solve most reading errors. Too much voltage will burn it out permanently, however what is needed is only a 1/8th of a turn, one way still no read...other way will sort it and if poss use a multimeter...but in general once they are on their way out with disc or read error, there is a point of no return... but it will make it last potentially for another 4 or 5 years depending on age.

@CBitsTech 4 месяца назад

If it's the laser, then it has to be the laser in both units, as I swapped in an entire replacement assembly and the result was identical. I'll consider it though, thanks.