Hi,

This is the power board from a Sony CD / Radio player.

The unit stopped working with AC power and only worked with batteries. I opened it up and saw that the pads for power prongs were ripped from the board. I scrapped the lead and resoldered it (A). The power was flowing in at 120v (B), goes through the transformer, and comes out at 9.8v (C), but when reattached, power did not go on inside the unit. I took it back apart and noticed that power did not flow through the wires (D). I looked for a fuse but could not find one.

Any ideas I can try?

Thanks in advance,
Sam

 

Does your meter have a diode test function? One or more of the 4 rectifier diodes may haves failed.

 

@wayneh Thank you.

I removed all 4 diodes, tested them, and got about the same reading from each one. Photos attached.
Did I do that correctly?
Next steps?

Thanks,
Sam

 

@wayneh Thank you.

I removed all 4 diodes, tested them, and got about the same reading from each one. Photos attached.
Did I do that correctly?
Next steps?

Thanks,
Sam

Nuts, those seem OK. Make sure they read zero when connected in the reverse. Probably they are all fine but it's a simple test.

I thought for sure the diodes would be it. Now I wonder about the various PCB traces and connections to the output wires. I mean, you have AC voltage and apparently a working rectifier, you should be able to get DC at the output. Once you have it back together, probe voltages at all the diodes.

One thing you might also try is loading the 9.8V side of the transformer with, say, a 1K resistor. Measure the voltage then, under slight load. (Don't go too long, the resistor may get hot.) This test ensures that the 9.8V you measured is real and not just a ghost. Meters are incredibly sensitive and need almost no current. Putting a small load there requires current to flow.

 

I don't really know what I am doing so I am happy to try all your suggestions!
They were all at 1 (the equivalent of zero) when I tested in reverse.
When I wrote I was getting 9.8v that was AC, not DC.
I didn't quite follow about adding the resistor. Attached is a photo of the resistor I have. Will that do? I should solder each end to positions C?

Sam

Nuts, those seem OK. Make sure they read zero when connected in the reverse. Probably they are all fine but it's a simple test.

I thought for sure the diodes would be it. Now I wonder about the various PCB traces and connections to the output wires. I mean, you have AC voltage and apparently a working rectifier, you should be able to get DC at the output. Once you have it back together, probe voltages at all the diodes.

One thing you might also try is loading the 9.8V side of the transformer with, say, a 1K resistor. Measure the voltage then, under slight load. (Don't go too long, the resistor may get hot.) This test ensures that the 9.8V you measured is real and not just a ghost. Meters are incredibly sensitive and need almost no current. Putting a small load there requires current to flow.

 

I don't really know what I am doing so I am happy to try all your suggestions!
They were all at 1 (the equivalent of zero) when I tested in reverse.
When I wrote I was getting 9.8v that was AC, not DC.
I didn't quite follow about adding the resistor. Attached is a photo of the resistor I have. Will that do? I should solder each end to positions C?

Sam

That’s a 56k resistor, too high to place any significant load onto the transformer, although better than nothing if that’s all you have. Maybe you have a small 12V light bulb you could use? An automotive dome light would work. Visual feedback is handy. And yes, you want the dummy load across the secondary of the transformer, the same place you measured the AC voltage.

 

That’s a 56k resistor, too high to place any significant load onto the transformer, although better than nothing if that’s all you have. Maybe you have a small 12V light bulb you could use? An automotive dome light would work. Visual feedback is handy. And yes, you want the dummy load across the secondary of the transformer, the same place you measured the AC voltage.

Is this what I was supposed to do?

 

Have you checked the fuse (F902) between the transformer secondary and the bridge rectifier input ?
I am guessing that there is a TO220 device mounted on the metal plate just below the transformer in your picture of the component side of the board. I think this will be a voltage regulator or transistor. What is the part number on this device ?
Can you post a picture with the white cable moved so it is not obscuring the components below it ?

Les.

 

If you look into the end of the socket where the power cable goes, you should see that there is a moveable portion inside. This is a "switch" that disengages the battery and allows for AC power to be used. My first test would be to see if that switch is working. It may not be fully engaging and connecting the AC power. This switch will NOT shut off the AC to the transformer so you will get power there regardless of its condition. This is a common failure. The AC inlet assembly should still be available as it is a common part across many Sony models.

If you look at your marking A and follow the arrow marked 10.7 downward, you will see three connections in a row. This are the contacts for the switch. Using a meter for continuity, you should see pairs of these go open/short as the power cable is inserted (please only connect this end and do NOT have the other end in the wall).

 

Hi abrsvc, I had not thought about the mains connector switching between mains and battery. The three connections that I thought went to a TO220 device must the the ones that go to the switch contacts.
Sam11i, Ignore my comments in post #8 as I think abrsvc is right about them going to switch contacts.

Les.

 

I've been repairing these for over 30 years and have run across this many times. As I stated this is a very common failure. I stock these parts for that reason although I don't get much call for them these days. These switches can fail even with normal use, so given your description that the AC connections were broken, it suggests that this switch may also have been damaged.

 

@LesJones I followed abrsvc, but I also listened to you, and it seems like the fuse F902 is blown, as there is no continuity between the two sides. (photo attached)

@abrsvc That's good to know; I wondered what those 3 pins were when I took the whole socket apart. Your observations seem to be correct. When there is no plug inserted, positions 1 and 3 are connected, but when I insert the plug, they are closed, and there is no pair that allows for continuity.

It seems like I have two issues here. The fuse and the switch. Is there a way to bypass the switch and use AC without the batteries?

What are my next steps?

I really appreciate the time you are giving me and the knowledge I am gaining here.

Sam

 

I think abrsvc is in a better position to advise you as he has worked on them and all that I know about them is what I have deduced from you pictures. The only explanation I can think of for the fuse blowing is possibly when the power connector broke the internal parts of the switch shorted the power supply to the battery and passed more current that the fuse rating. I am assuming that the battery is an internal rechargeable one or primary cells in a battery holder. Identifying the rating of SMD fuses can be difficult.

Les.

 

I would not recommend shorting out any switching components. It is done this way so that you can't have both the battery and AC "connected" at the same time. If you short this out, then it would be possible to send power TO the batteries which would not end well. I am not aware of any mention of a blown fuse in this thread. Replace the inlet assembly and try again. If you post the model number I can provide the part number for you.

 

Is this what I was supposed to do?

Yup. Looks like your transformer is probably fine. Your diode testing showed the rectifier is probably fine. The problem is elsewhere and it looks like you're on it.

 

@abrsvc I tried putting the switch together again, and it looks good, but it did not help.
I found this piece (attached) floating around inside the machine when I opened it. Can it be part of the switch?
The model number of the player is Sony zs-rs60bt. Attached are some photos of the numbers on the part that didn't help me when I googled them.

In the meantime, to test if it is the switch, can I solder a wire from 1 to 3 on the switch to see if I get power? If that doesn't work, can I do the same for the fuse - to test?

Thanks again!

 

This is what I suggesting to try to test if it works. Makes sense?

 

This is what I suggesting to try to test if it works. Makes sense?

Did you say the fuse tested open (bad) with your meter? I'm always reluctant to bypass a blown fuse if I don't know why it blew. But I have to admit I've done it.

As for the switch, you should be able to probe out the logic of it and then simulate the condition you want. Inserting the AC jack usually breaks the battery circuit. I'm not sure what a jumper is going to accomplish? I may just be confused about what you're doing. If you plug in the AC, you should be able to tell whether AC is getting past the switch or not.

 

The switch on the AC input is NOT switching the AC input. It is switching the load between the battery and the output of the mains power supply. I would guess this is probably about 9 volts DC.
Sam, if you decide to add the link in post #18 (Against abrsvc's advice.) I suggest cutting the track that goes to the middle connection on the switch so there is no chance of the power supply being connected to the battery.

Les.

 

Looking at post#12, I would say it's the changeover switch on the mains socket.