Sony HCD-MJ1 receiver died on me while on standby

[Jean-Pierre]

It is a design piece and I cannot part from it so .....cheerful I thought of the fuse. But no.
The thing is always on and shows a the time. I checked the AC-board and AC is coming in, but nothing passes through the fuse, so the problem could well be in one of the components of this tiny board
This is a picture of the AC-board, then the diagram form the service manual.
In the manual diagram there is a switch to change from 110 tot 220. In reality this is absent on my device. It is setup for use in a 220 world only.
So the AC-board no longer has this function it only serves as AC entrance and delivers the power to the transformer.
I did some tinkering on drones, but my knowledge of electronic components is very limited .
Who can help me to get this baby running again.

 

[Les Jones]

It is possible that there are two transformers, One very small one supplying the clock/timer part and a larger one that powers the main part of the unit. Posting the full schematic would give us a much better idea of what area the fault lie in. It would also show if my guess of there being two transformers was right or wrong.

Les.

 

[Jean-Pierre]

Hi Les,
That was quick. In Belgium we are diving into the night now. Here is the service manual so you can study the workings. I really hope that, with you're help, I can get the beauty running again.

 

[rjenkinsgb]

That board should have direct connectivity from the two input terminals to the two outer terminals on the three pin connector.

Do you have a multimeter you can use to check continuity of the fuse and filter choke, measuring from the underside of the board?
The choke should show as a short circuit, zero ohms or nearly so, if you measure between the top and bottom pin at each side.

The only other possibility is a dry joint, but none look particularly suspect. There are some shadows under the connector pins that make those joints difficult to see.

 

[Jean-Pierre]

Yes I have a multimeter and I'll check for continuity. Even with a magnifying glass I can see no dry joints, but the little transformer thing smells burnt and the plastic around the feet looks like melted or scorched. What puzzles me is that the fuse is ok, that makes me think that the standby circuit, clock display, is dead, but the power circuit may still be alive, as Les says.
Can this power board be safely bypassed ?

What is that filter choke ? Is it to filter current spikes ?
Thanks for your help, it is much appreciated !!

 

[rjenkinsgb]

First thing, just check continuity from the input of the PCB to the output.

Call the connector pins one through five across the board, starting at the two pin connector side.

Pin one should connect to pin five and pin two should connect to pin three; nearest and farthest across the two connectors in other words.

Look at you underside photo of the PCB:
The nearest inside pins connect only through the choke, the outside ones go via the fuse, some jumper links and the other side of the choke.

The choke is a "common mode filter", it's to reduce electrical noise emitted from or passed through the power cable.
I'm guessing the scorched appearance is from the original manufacturing, when the coil wire ends were soldered to the bobbin pins, possibly by dipping or wave soldering. If that process did not fully burn off the lacquer insulation on the wire at some point, it could be causing a problem.

Check continuity through the entire board first, then the inductor if one of the board circuits is open.

 

[Nigel Goodwin]

First thing, just check continuity from the input of the PCB to the output.

Call the connector pins one through five across the board, starting at the two pin connector side.

Pin one should connect to pin five and pin two should connect to pin three; nearest and farthest across the two connectors in other words.

Look at you underside photo of the PCB:
The nearest inside pins connect only through the choke, the outside ones go via the fuse, some jumper links and the other side of the choke.

The choke is a "common mode filter", it's to reduce electrical noise emitted from or passed through the power cable.
I'm guessing the scorched appearance is from the original manufacturing, when the coil wire ends were soldered to the bobbin pins, possibly by dipping or wave soldering. If that process did not fully burn off the lacquer insulation on the wire at some point, it could be causing a problem.

It's VERY, VERY unlikely to be that, they basically never go wrong - there's nothing to go wrong really.

 

[rjenkinsgb]

It's VERY, VERY unlikely to be that, they basically never go wrong - there's nothing to go wrong really.

I agree completely - but the OP says the board has power at the input terminals and not at the output terminals, some something must have failed!

They say they have changed the fuse, so what else can it be - unless the fuse clip is sprained and not making contact?

 

[Les Jones]

My theory that there may be two transformers was wrong. The first thing I would check is the output of all the voltage regulators.
I am not sure what you mean that it always shows the time. Do you mean that now the only thing it will do is show the time or do you mean that when it was working it always showed the time. Is it totally dead now ? If so then check the output of the three bridge rectifiers first.

Les.

 

[Jean-Pierre]

Les, I'll try to explain. When the device is off, the display dims slightly and shows only the time. When I turn the device on, I hear a click, the display gets brighter and all the functions appear. A month ago I noticed that the display was not showing anything while the device was connected to the mains. So whatever went wrong, it happened while the Sony was off. I understand that at that moment only a small part was under tension and failed. As I have no basic knowledge of electronic components I might be capable of identifying the rectifiers, but then checking their output ...... Besides this design machine is so densely packed that it is hard to open it and maintain the connections between the different boards.

 

[Jean-Pierre]

Robert, your step by step advice is within my reach. So I have my multimeter ( TEK DMM150) at hand. My remark that there is something at the input side and nothing at the output side might have to do with the fact that I misunderstand the difference between AC and DC. I'll come back to you when I followed your pin by pin check.

 

[Jean-Pierre]

Nigel, Even if it is very unlikely that something on that power board went wrong, if I succeed in testing it then I can go further to the mains transformator and the rectifiers. But there the water will soon be too deep for me, but hey, that's what you guys are for.
Thanks for your advice

 

[Nigel Goodwin]

Just use your meter on the low ohms range (200 ohms FSD?) - DON'T plug the unit in the mains.

Without touching anything the meter should read 'over range', on my meter here that is '0L.' - if you then touch the probes together it should the read near '00.0' (mine reads '00.3').

On the AC board there are two connectors, a two pin (CN801) and a three pin (CN802) you should be easily able to get your probes in the top of them. So place the probes in CN801 pins 1 and 2 - if it reads over range, then there's a fault. Now try the same on CN802 pins 1 and 3, again does it read over range or a low resistance (anything less than over range). If it reads over range it's likely the thermal fuse (non-replaceable) inside the transformer has failed.

But if it reads low, then the transformer should be OK. In which case put the probes in CN801 pin 1 and CN802 pin 3, this should read low - if not try from CN801 pin 1 to the fuse (F802), it should read low to both sides.

So try that and report back.

 

[Jean-Pierre]

Robert, I’ve checked the power board and the multimeter happily beeps. So what goes in, goes out. Problem must be down the road..

 

[Jean-Pierre]

Nigel, both stay OL. But I have the power board on my knee, disconnected. Do I have to connect it back in the device and do the same test again ?

 

[Nigel Goodwin]

Nigel, both stay OL. But I have the power board on my knee, disconnected. Do I have to connect it back in the device and do the same test again ?

Yes, if it's not connected then you can't read read through the connections I suggested.

What do you mean by 'power board'?, do you mean the AC Board (as it's called on the circuit - the one with the fuse on). If that board is removed, you could test the transformer by putting the meter across the pins of the plug that goes on CN802 (pins 1 and 3).

 

[Jean-Pierre]

Yes, I said power board, but I is the AC-board. Now I'll do the test on the transformer and hope for good news. Because in the manual they take about a 'non-replaceable item'. As with many old things, I would like them to work, even if I never, ever use them again. Must sound familiar to most tinkerers.
I'll report back.

 

[Jean-Pierre]

Brushed my teeth, combed my hair and took the transformer out.
I measured the outer pins of the input plug and this is what I got :

No smell, no sign of heat, look brand-new to me.
What does that tell you ?

 

[Nigel Goodwin]

Well you didn't need to take the transformer out

The transformer looks OK then, so put it back in, and put the other board back in - then do the tests I mentioned in post #13

 

[Jean-Pierre]

Thanks. At least I could visually inspect the transformer and it looks ok. I attached the AC board and did the test of post #13.
First CN801 pin 1 on CN802 Pin 3

Then CN801 PIn1 to fuse

Now I'll put them back.