Project 940

[M1JWR]

found a 940 at a boot sale, how rare is that, cumbria was never a minidisc paradise in the first place so peoples interest in them here is not great.

guy said it dosent come on, thats ok, so took it home, when i checked, he's dead right, its dead jim !

good project i think, power supply problem, thats a new one, no light no click of relay no nowt. main fuse and power cable ok.

got what i will call the relay board out now so going to check over that first, got some elna caps on there, they are not good, could be anything though.

drive looks ok and owh looks ok, will get to that later at some point, no belt though, no suprise there, can easy service that up and stick it in another

deck, to check that, still have a couple of 470's around.

have parts off decks i have broken for spares in the past for psu parts, eg psu's out of an s50/520 and 470, so as long as its not the toroidal

all is not lost.

[kgallen]

Wish you well @M1JWR I hope you get the beauty working. Here if you need me!

[BearBoy]

Good luck with the repair @M1JWR!

 

If you get a chance, take a few photos as you go. Might help others with similar issues in the future.

[M1JWR]

cheers gents, hope you are all well.

i have made some progress, as you may remember there is another 940 here so thats handy,

took a shortcut and put its relay board into this player, its a non uk one and the boot sale one is a uk one

but as we know apart from the two obvious bits, internally there is no difference.

plugged it in and you hear the satisfying click of the relay and the red light and it switches on with good display.

its not a minter this 940 there some scratches and marks on it.

now to the drive unit, closer look revieled lots of dust, crap and hair and somebody thought, its not working dear

ill put some wd40 on it that'll sort it, took some time to get rid of as much as possible of that lot, then cleaned the laser,

put a bit of lube on the sled, i use that stuff thats used on hornby trains, its very fine, just put a little on a cotton bud,

then a bit of switch cleaner on that switch sensor for eject etc, remenents of the old belt were lying in the bottom below

where belt goes, removed whats left of that and put a new one in, stuck it all back together and switched it on, and.....

it works, plays no probs, sound no probs, now as we all know the biggie, record, i usually go via optical and rec, i mean

stream off a well known platform, mustve done a good job on the drive as it records and writes toc with no fault.

so defenetly a duff component on its own relay board, my money is on the 5v regulator, dont think ive got one of those,

they are a 4 pin jobbie, this time fleabay is your friend about 5 quid for one on there from the uk

will post a pic of offending board later

[BearBoy]

3 hours ago, M1JWR said:

somebody thought, its not working dear

ill put some wd40 on it that'll sort it

 

🤯🤦‍♂️

 

Good to hear you're making progress and the drive etc are (now) sound.

 

[kgallen]

Sounds good!

 

No active components on the relay board is there? (I should check the schematics before waffling on…!).

 

Great you narrowed it down and the rest of the machine seems to be working now you’ve cleaned it up. Great work!!!

[kgallen]

Which regulator John, IC902?

 

Checked all the rails? 5V, 3.3V etc?

 

See if 3.3V out of Q904 emitter which is the ‘standby’ regulator. Ie is the standby PSU rail ok. 
 

Then maybe have a look at the base and collector of Q902 to see if that turns on. That switches the relay. 

[M1JWR]

Hi kevin

havent gone deep into this board yet, was busy with drive unit

ive nicked a pic off this site from an older post, hope thats ok

firstly i will tell you what i have that is the same or similar to whats on here

the white filter, the transformer, which looks the same but different part number

and the relay itself plus various other generic bits like caps etc, the only bit i dont have for certain

is the ic on the heatsink.

later i will check the two trannies for shorts as the board is out of the deck, dont see q902 as such,

q906 is connected directly to it, easy spot on this pic

i might even have those trannies if it comes to that i will have to check against s50/520/470 part lists

saw another 940 go on fleabay last week spares or repair around 90 quid seems the going rate these days,

3 years ago they were 60 quid'ish

was suspecting the 5v because of a marantz cd player that did the same a few years ago, and thats what was shot

[kgallen]

Hi John

 

You said the standby led wasn’t on so I'd work through the standby power supply (the small transformer) against the schematic. You can do some buzzing out (and checking for opens and shorts) with they unit unplugged. Then you’ll need power to check voltages. I see +3.3V for the standby DC rail, so I’d check for that first. That gets used to enable the relay that puts mains into the main transformer to awaken the whole deck.

 

I don’t think I saw a +5V rail for standby but I’ll check again (on a proper computer rather than a phone!). Of course there are 5V rails when the machine is alive but since you said standby wasn’t coming up I’d start there. 
 

Of course apologies if you already know all this, you’re hardly a first-timer! But the good thing is hopefully this is just a simple fault then another great 940 comes alive!

[kgallen]

Looking more, that 4 pin IC902 regulator only kicks in with the main transformer. 
 

Also from that photo above looks like some of the small transistors have different refdes to the schematics. Those two TO220 trannies to the right of the relay (black rectangle) should be Q904 and Q901 but on the photo I’m sure I can read Q932. That one I recon is Q901 on the schematic since the other one has the 100uF cap and zener diode near it so that would be the discrete 3.3V reg.

 

I’d have a look around those ‘green’ diodes near the main input connector. They are the standby supply bridge rectifier. With power disconnected check none are short or open circuit (should drop around 0.6V when forward biased). You can poke on their legs from above.

 

I agree the IC400 multi-rail regulator is on for standby but since this is on the main board and you swapped the relay board and got the machine working I conclude IC400 is working ok and in the failed machine it’s just not getting any power from the faulty relay board.

 

So initially I would focus on T900 (standby transformer), D904/5/6/7 (bridge rectifier) and C401 (10000uF smoothing cap). That’s all there is to the standby power supply on the relay board (regards power towards IC400).

 

On IC400 you could see if there is about 7V dc on pin 7. Also check there is something on pin 2 (schematics say 2.4V, but it will be very lumpy as it’s just half wave rectified ac, not smoothed).

[M1JWR]

did do one or two simple things last night, diddent find any shorts on the to220 trannies

i diddent find any short/connection between any pin on the transformer

i am no expert on transformers but from a unknolwedgable point of view i would think there

should be a connection through it eg from the 4 pins on one side to the two pins on the other

one thing, it dosent smell right this board, especially in that area.

wonder if somebody has wrong wired plug at mains and burnt it out, it dosent have the original plug,

the same wd40 guy, simplistic i know but you never know

ive got to go and look at a car, so will be around later on

usually ok with psu's, but in the past i would have a suspect and swap it out, process of elimination,

sometimes a good way, if you catch it early, and not if you dont, we've all done that

[kgallen]

A transformer should *NOT* have continuity from the primary to the secondary. That is their main attribute for isolation.

 

If it smells funny and you have continuity from the primary to secondary then I would agree with you that the transformer has been burned by some suspect mains (UK mains applied to a US/CND/JP transformer being typical). Note it needs to really smell funny/acrid. Transformers usually smell a little bit weird so there needs to be a significant acrid smell to suggest it's damaged.

 

On that standby transformer, the primary and secondary windings come out on opposite sides of the bobbin. So with the power OFF you should find continuity (some low resistance) between the 3 pins on the primary side (this is the side nearest the left edge of the PCB). You should also find continuity between the two pins on the secondary side (this to the "inside" of the PCB). This transformer only has a single secondary winding - one coil of wire, the two pins being each end of that winding wire.

 

This is the schematic I'm on about. In this post, transformer T900 is what I'm referring to.

 

 

 

 

 

 

[M1JWR]

yes there is no continuity between any pin in the transformer, will get to the diodes later

originally when i did electronics so to speak it was with radios, cb's years ago 99% of them

used a seperate power supply, so therefore little knowledge about them, all i ever knew

was that they dropped the 240v to say 30v for example and then on to the regulators which dropped it further

say 5v for the circuits that need that, on an now old cb the 240 came in via a protection diode and ash filter

then to the vol/on/off pot and through cb/pa switch to a avr which was usually 8v output there would be others

5v etc for various circuits that needed whatever, remember the last one was a tristar 777, but thats now in

another galaxy far far away

[kgallen]

To clarify

 

no continuity between primary and secondary is good and essential for safety and operation

 

no continuity of primary or secondary windings is definitely not a good thing - no operation

[M1JWR]

my bad memory there is no continuity between pins 1,2,3,4

there is continuity between 6 and 8

my mistake sorry kevin

so from that we can deduce its gone to another planet

these others i have i think are same fitment, mds s50 one looks identical

different part number and no red tape will be back if ive found others

3 years ago i bought a mdm7a off a guy ex 470 he also sent me the main board(now robbed)

and a broken power board and i bought a 520 that was smashed for its drive unit and broke it for

spares, thats the one you ended up with parts, ill go and have a ratch for those, the s50 one is handy,

i know where that is and i know its ok. can only but try

[kgallen]

Sounds like the primary is bu**ered then!

 

I had that on one of my MDS-E10 that had been abused. 

[M1JWR]

went for a ratch found the ex 470 power board and the s50 board, there are subtle differences,

transformer is identical almost off s50 and the 470 one is a tad bigger, more unused points on secondary side,

only differences with s50 one is that two of the part numbers are opposite way round and the windings are covered

in lacquer or whatever and 940 one is wrapped with red tape

the relay on the 470 board is identical to that of the 940, s50 one different make but would say the same,

checked those diodes one way on all reads around 190 and the other is very high 1600 ++

replaced the transformer with one out of s50 and for good measure replaced the relay itself as further checks on both

transformers were the same, primary side no contact between pins, no contact between pins from primary to

secondary side, but there was contact between the two pins on secondary side, which was confusing because i knew

the s50 one worked and because of that i think its the relay itself that was shot.

youve probably gussed by now its all up and running, will keep an eye on that transformer for a while to see if the lacquer

stuff bubbles up with heat, seen that with stressed parts in radios years ago.

thanks kevin, ive learned a bit about transformers, because i knew little about those, and now others with the same problem

with 940's etc will be rushing out and paying top dollar for s50's, now where did i put the other one !!!

[kgallen]

The primary side winding will have a higher resistance than the secondary. Maybe it’s above what your continuity meter allows - unless you have an ohmmeter as you gave numbers for the diodes. 
 

Worth having a look at the removed transformer again. You’re just looking between pins 1 and 4 (which I would presume are the outer ones if they populated all 4).

 

The relay would only affect coming out of standby into full powered up (since it switches mains into the big transformer).
 

But excellent news you have it working, great stuff!!!

[kgallen]

On 8/26/2023 at 9:58 PM, M1JWR said:

saw another 940 go on fleabay last week spares or repair around 90 quid seems the going rate these days,

I wanna know where you see these sub-100 940's. I rarely see one sub-200 these days!

 

However, no, no, no, I'm not looking... I'm not. No.

[BearBoy]

1 hour ago, kgallen said:

However, no, no, no, I'm not looking... I'm not. No.

 

🤣 I believe you, @kgallen. Honestly...

 

I've been making a conscious effort not to look at decks on eBay recently but the BIN prices do seem to be the wrong side of £200 these days (not that I'm sort of looking either 😉). Not sure what they're actually selling for, and eBay is a tad misleading in this regard as it seems to show the original advertised price against its sold listings, rather than any lower offer the seller may have accepted.

 

Glad to hear you've rescued another defunct 940 @M1JWR 👍

 

I suppose one positive of the increase in value of these decks is that people are possibly more likely to try to sell non-functioning ones, rather than just take them to the tip.

[M1JWR]

4 hours ago, kgallen said:

I wanna know where you see these sub-100 940's. I rarely see one sub-200 these days!

 

However, no, no, no, I'm not looking... I'm not. No.

all i ever did in the past was have a bookmark on the firefox or whatever from ebay "sony mds" or sony mds-jb940 if you prefer, and every few days have a look see what crops up, looked in past listings and somebody bought a spares or repair one for 47 quid a week or 3 back, so they do crop up, but yes usually over 200 quid for a full working one, me and bear boy are waiting with bated breath on when you increase your vast collection, and i am sure you will have a deck with an mdm7a that you are willing to sacrifice if in the rare situation that somebody has been inside and knackered it, that does happen, owh is first to die, 930's are worth a bash aswell, i got one about 4 years ago, seller said no sound output,, figured he was using mdlp discs and was correct, exellent nick and nowt wrong with it 35 quid, 980's will go over a ton spares or repair, and what i call a sleeper, the 920, exellent quality machine, not big money, and if spares or repair a lot less and a 330/520 drive goes stright in.

me, i am still whittling down my once vast collection of 440 and 470's

[kgallen]

Don’t start me off!!! I thence started looking at 930 and then 920.  Fortunately they are all way too expensive at the moment.

 

I must resist putting a notify search in place…

 

Hmmm good question, not sure I do have a fully working 7a in ‘stock’. The one in the 440 has some intermittent issue.

 

I do have a NOS 7AX2 though and I notice they are no longer available on AliExpress…

 

Love the story on the 930 @M1JWR, fab catch!

 

@BearBoy I’m brain synching with you to resist a purchase!

[BearBoy]

12 hours ago, kgallen said:

@BearBoy I’m brain synching with you to resist a purchase!

 

Last time we brain sync'd on anything I ended up buying far too many MDW80Ts from Amazon Japan 😲 🤣

[BearBoy]

I've boxed myself into a bit of a corner as far as decks go by making frequent use of the Group function on my MDs. Although there's a fairly large selection of the later portables with this functionality, the only full size Sony decks that have it are the MDS-JB980, MDS-JE780 and MDS-JE770.

 

Every time I have seen a reasonably priced QS deck recently, I've ended up talking myself out of it. The 920 and 930 because they lack MDLP and the 940 because it doesn't have Group. The 940 I do have gets some use if I'm recording from a CD with CD Text (via the Control A1 cable connected to a CDP-XB740) but otherwise I use a 980 most of the time. Unfortunately they tend to command the higher prices, presumably because of the NetMD functionality (for which I use portables).

 

I've stopped looking at any of the lovely ES decks for similar reasons. Only the MDS-JA333ES has MDLP but it lacks the Group function. Well, that and the fact they're in an entirely different ballpark price wise 😲

 

I probably don't want to know the answer to this but do any of your Pro decks have Group @kgallen? 🤣

[sfbp]

There are lots of machines with Group function if you don't stick to "pure" decks  Anything that runs M-Crew for a start. This includes the MDS-PC3, the PX3/5/7 and many other bookshelf models. Missing from your list is the MXD-D5C, I think. I'm pretty sure the MXD-D400 does too.

 

One of these days, I will tell the story of my PX7, which Kevin and I have worked on (he from afar). It's a beautiful piece of equipment, with a wonderful sound (quite high quality amplifier, I think), and it does groups. It's the only machine I've ever seen with TWO PS/2 sockets (one for PCLink, one for Keyboard or PCLink). We had quite the adventure.

 

The only annnoying thing about Group function in M-Crew is it always comes up turned off when you stick a new MD in. Unless there's a magic way to default it on?

[kgallen]

35 minutes ago, BearBoy said:

I probably don't want to know the answer to this but do any of your Pro decks have Group @kgallen? 🤣

No they don't. Consider the MDS-E12 and MDS-E10 as a MDS-JB940 in rack mount format. Ok the I/O is different and there is the SCMS stuff, plus some other features in the setup menu, but under the hood audio wise they are pretty much a 940.

 

There, that's calmed your nerves a bit now hasn't it! Means you won't go looking for an E10 or E12 on eBay! 😄

[kgallen]

12 minutes ago, sfbp said:

I will tell the story of my PX7, which Kevin and I have worked on (he from afar).

That's very much over-over-stating my contribution. Mostly I've been a sympathetic but largely impotent ear.

 

No Service Manual for the thing that I can dig through... @sfbp is probably a bit mad at me for all of the chatter above, but then I can easily look at a SM for the 940 and thus chip in repeatedly with a modicum of usable input.

[BearBoy]

2 minutes ago, kgallen said:

No they don't. Consider the MDS-E12 and MDS-E10 as a MDS-JB940 in rack mount format. Ok the I/O is different and there is the SCMS stuff, plus some other features in the setup menu, but under the hood audio wise they are pretty much a 940.

 

There, that's calmed your nerves a bit now hasn't it! Means you won't go looking for an E10 or E12 on eBay! 😄

 

Phew. I can hold off setting up eBay notifications 😂

 

Shame actually, I really like the aesthetics of the grey Pro decks.

[BearBoy]

16 minutes ago, sfbp said:

There are lots of machines with Group function if you don't stick to "pure" decks  Anything that runs M-Crew for a start. This includes the MDS-PC3, the PX3/5/7 and many other bookshelf models. Missing from your list is the MXD-D5C, I think. I'm pretty sure the MXD-D400 does too.

 

Yeah, you're absolutely right @sfbp - I was only referring to the "pure" MD only, full width, Hi-Fi separates type decks. I've never really looked at any of the dual CD/MD machines tbh or any of the myriad of bookshelf devices. Some of the bookshelf units look great but wouldn't really fit with the way I have either my office or living room systems set up.

[BearBoy]

22 minutes ago, sfbp said:

One of these days, I will tell the story of my PX7, which Kevin and I have worked on (he from afar). It's a beautiful piece of equipment, with a wonderful sound (quite high quality amplifier, I think), and it does groups. It's the only machine I've ever seen with TWO PS/2 sockets (one for PCLink, one for Keyboard or PCLink). We had quite the adventure.

 

Please do, if you get the time 🙂 

[M1JWR]

wonder if kevin had pressed the trigger on that cheap 920 a couple of days ago on for 40 quid with best offer

needed work to drive unit, it had a remote aswell which was for a 480/980

maybe offered 30 or less, for educational experimental purposes of course !!!!

[kgallen]

Nope, missed that one. I’m not very good at this it seems. Against better judgement I have eBay watchers on 920/930/940, but eBay considered not to tell me about any new listings..