"Dead" Sony MZ-N707 Minidisc - faultfinding advice sought

[Parkie1472]

I have a Sony MZ-N707 which hasn't been used for quite a number of years. In fact it had very little usage from new before it was consigned to a cupboard for storage (yes, the battery was removed beforehand - I've been caught by leaky cells before!) as my job changed and was no longer travelling for business.

Unfortunately it is now dead, not working when powered by any of the internal battery, external charger, charger stand or USB cable. It doesn't try to spin-up if I go to play a disc. Well, it isn't completely dead - the LCD display (either internal or on the remote control) at first glance appears to remain blank but it does actually show all characters and segments at the same time in a very dim light grey for a few seconds, before going off. So something is happening internally but not much. Maybe the display is enabled but receives no data to display.

Before I breakout the oscilloscope and service manual to explore the inner workings, is this a known fault mode that is easily fixed or is it likely to be beyond redemption?

I hope that it proves to be repairable as it is in immaculate condition, comes with all the accessories, multilingual manuals and original box and it would be a shame not to be able to save it.

Hoping for some positive responses from contributors to this forum.

Thanks in anticipation.

[kgallen]

Give it some power for a while with a disc in. 

[Parkie1472]

Hi kgallen,

Thanks for your suggestion. I'll give it a try but I'm not sure what effect it will have on the internal electronics so that they can spring back into life. I've already tried it with a fully charged NiCd and a new alkaline cell with no joy.

Have you had success in the past by doing this? How long do I need to have it connected to the charger?

Cheers

[kgallen]

Hi Parkie,

We're assuming a fully functional unit that's been asleep for a long time.

Just want to give it the best chance of coming out of hibernation before we start pulling the poor thing about.

Also I would work the clamshell open and closed with a disc being inserted. There is a small switch that detects this happening and wakes up the units, so if we give this a bit of movement we might see some life.

Kevin

[sfbp]

I noticed you mentioned NiCd - haven't seen those in a while. Was this one of the units that did NiCD as an alternative to NiMH?

[Parkie1472]

Hi sfbp,

The unit, bought in 2003, was originally supplied complete with a 1.2V 700mAh NiCd AA cell, which amazingly still takes and holds charge. Extended operating time can be achieved by the use of an alkaline AA cell instead. It is noted however that the charging stand has a label indicating compatibility with NiMH so that should be possible, all be it with a longer charging time due to their larger capacity.

Cheers

 

[sfbp]

Exactly. It's almost the only one that does, IIRC.

So, the question is, does your problem somehow arise from something connected to the NiCd technology? You won't get any power from USB, that is in the definition of NetMD (and USB 1.1).

Are you sure your charger is working?

Have you measured battery output voltage both unconnected and under (presumably) load in the device? Seems to me this smells of power failure. Even if it doesn't work with Duracells, the chances are something in the power circuitry is messed up. I wonder whether you have any battery decomposition perhaps?

Kind regards

[Parkie1472]

Hi sfbp,

Charger is checked out working on and off load and the battery voltage holds up OK, whether NiCd or alkaline. 

Thanks for the reminder about not getting power via USB. It's got to be 16 years since I last used it and I expected it to work like more modern USB connected devices. Maybe I should have read the manual!

There are no signs of leakage visible within the battery compartment.

I'll be whipping off the back cover later today to have a look around for obviously failed components and check a few levels.

Cheers, Brian

[sfbp]

OK if we've eliminated all of those, I'd now be inclined to check the microswitches. There's one that turns off the power when the device is opened. Section 1, page 4 of the service manual.

[Parkie1472]

Hi sfbp,

Success!

Following an axiom I adopted in my previous career in industrial electronics - check the mechanical interfaces first - I removed the rear cover and set about the microswitches.

The one you suggested was working OK. This seems to enable the main internal power supplies which were at the correct levels. However the one on the top that is activated by the "Open" slider mechanism (Half Lock) was stuck in the down position so its changes of state when opening and closing the clamshell were never registered. A couple of squirts of switch cleaner soon freed it off and then everything started to work as advertised. Normal service has been restored.

Thanks to all for your advice and assistance. I'm glad that it proved to be a mechanical problem rather than electronic as, although I don't normally shy away from unfamiliar circuits, I would probably draw the line at trying to do any repairs to this item's main board as the SMD components are sooo small!

Cheers, Brian

[sfbp]

You're very welcome and doubtless if you hang around we shall be calling on your expertise in due course.

As to *small*, you ain't seen nuffin' in that generation. The HiMD and all-flash devices are way worse than the good ol' N707.

Well done and welcome to the board!

[Aj J]

My 707 was previously working. Was kept in a drawer for a year or so. When i tried to use it, it  won't  turn on even with new batteries. I connected it to the pc and it woke up. It's now working fine.