I've got a 30 year old Sony STR-DE310, which stopped powering on. I've opened the case, and done basic checks- 120v ac is reaching the unit. I haven't checked any voltage otherwise...I don't know how, but have a dmm.

There is one capacitor that has sticky brown leakage on its top, C950 on a board with IC950, labeled "reset".

The service manual for model DE305 is available, and I grabbed an image.

C950 is circled in red. I need to replace at least that cap, but I need to get to the underside of the board first. How do I disassemble the blue circled part?

How does one fix this? Is there a good reference?

 

I've opened the case, and done basic checks- 120v ac is reaching the unit.

What does reaching the unit mean? Voltage measured at the receptacle or inside of the unit?

The service manual for model DE305 is available, and I grabbed an image.

I really dislike schematics drawn like that. It does nothing to convey circuit intent.

How do I disassemble the blue circled part?

It looks like it lifts out of the blue part of the connector.

 

I measured 120v inside the unit on the pins somewhere inside of the case, not sure where offhand, will need to check again tonight.

There's a service manual here, for what it's worth....https://www.manualslib.com/manual/753266/Sony-Str-De305.html

Thanks on the connector, looks maybe like a simple molex type thing?

I need to order at least the one cap online, but might be iterative process... Would like to get all in one order if I can

 

I measured 120v inside the unit on the pins somewhere inside of the case, not sure where offhand, will need to check again tonight.

Be careful. 120VAC is a lethal voltage.

I'd measure the voltage on pin 5 of IC950 before, and after, replacing the capacitor. Most electrolytic caps fail open (after possibly failing short and being blown open).

I need to order at least the one cap online, but might be iterative process

And expensive when you factor in shipping cost. Before ordering the 1000uF/16V cap, check to see if there are any others used somewhere so you could order more than 1. Also measure the diameter, height, and lead spacing, and get one with the same, or higher, temperature rating. Tolerance won't likely be an issue because it's just a filter cap.

If you have any electrolytic caps in that capacitance range (e.g. 470uF, 680uF, ...) with at least a 16V rating, you could use them as a temporary replacement to see if things change.

 

C950 definitely needs to be replaced. But before you do anything, have a look at the power input.
Q951 is a power transistor, next to C950.
Input voltage is 12.7 V.
Output voltage is 5.8 V which can also be measured at inductor L402. Voltage measurements at these test points should give a clue as to what is happening.

You can measure the voltages with respect to ground at each side of R950 with your DMM.
R950 is just below C950 as shown in your photo of the board.

 

@MrChips : On one side of R950 - 10.6V, on the other side - 5.8V.

 

@MrChips : On one side of R950 - 10.6V, on the other side - 5.8V.

Thanks. That’s useful information.

In future, don’t use minus symbol when you mean to say “is” or “=“.
You need to reserve ”-“ when you need to distinguish between positive and negative voltages with “+” and “-“.

 

sorry, not negative voltages. sloppy punctuation

 

Do those voltages seem to indicate problems beyond C950?

Also, R950 is 10mm diameter, 17mm long, 85degC, 1000uF, 16V. I found a bunch here, but not sure what to pick other than Panasonic, Nichicon, wurth? 105C, 5000 ish hours..not sure about other specs Digikey

 

R950 is 10mm diameter, 17mm long, 85degC, 1000uF, 16V. I found a bunch here, but not sure what to pick other than Panasonic, Nichicon, wurth?

You mean C950.

Fit is more important than brand. I'd have no problems with Nichicon or Panasonic.

 

Yes! Was before my morning coffee! Thank you for the reply. The OEM caps are a blend of Panasonic, nichicon, elna, possibly others. I'll get the order going.

I take it that bad cap is all it would take to drop the voltage to 10.6 instead of 12.7?

Sorry for the basic questions guys. My last exposure to this was in (civil) engineering school, 30 years ago... Basic EE class! I recall using the loop and node equations to analyze circuits, basic caps, resistors, inductors , etc... Enough to get me in trouble

 

What has likely happened is the capacitance value of C950 has fallen from the nominal value of 1000 μF. Hence the reading of +10.6 V instead of the nominal value of +12.7 V is an indication that the ripple voltage has increased. The DMM records an average value which is now lower than if C950 were doing a better job of holding the voltage steady.

Go ahead and replace C950.

 

That makes sense. Thanks for breaking it down in that detail.

Thanks for the help!

 

OK, that capacitor C950 did look failed on the top! So replacing it is a good start. Years ago I was give a failed Kenwood stereo amp that "just quit working." A top inspection showed nothing to attract attention. Opening the bottom VENT cover allowed seeing half the PCB, and on one direction a solder joint looked a bit questionable. Could not reach it though.
It took a complete removal of the case to get to that part of the PCB.

Evidently there had been a wave soldering machine problem.

NONE of the soldered connections on that part of the PCB were adequately soldered!
I heated up the soldering pen and had at it. SIX INCHES of solder off the roll and ten minutes of re-soldering carefully, and I had a repaired PCB assembly. There certainly were a couple of failed joints open, and a whole lot that would have failed any inspection. Put it all back together and it all works. The very strange part is that I had searched for service information and it seemed that KENWOOD did not even acknowledge having made that product. WAS it a bootleg item? A fake?? or?? I never did find out. But I never had to repair it again either.

 

So I just replaced C950, and plugging it in, getting a clicking relay, and display flashing "protect". What next?

 

So I just replaced C950, and plugging it in, getting a clicking relay, and display flashing "protect". What next?

Tried it a few more times, and it did power on a few times, intermittently, but then the relay would click and put into protect mode...

 

So I just replaced C950, and plugging it in, getting a clicking relay, and display flashing "protect". What next?

Go back and measure DC voltages around Q951.

 

@MrChips , thanks. 14.5ish volts on the one side, it varies up and down with clicking of the relay. Other side: 6.11 volts, steady thru all the clicking

 

Does MrChips know what you mean?
Base, Emitter and Collector voltages.

 

Good point. Those are measured on each side of R950: 14.5 volts on one side (maximum, it varied downward with clicking relay during measurement) and 6.11 V on the other side, steady during the 10 seconds or so of measurement.

I'm wondering where to look next?