Sony Rcvr STR-DE675 random loud pops

[G. Paul Ziemba]

My Sony STR-DE675 Receiver (at least ten years old by now) has started
to make random loud pops to the speakers (I have only the main L and R
speakers attached). The "protect" mode activates and so far, my speakers
are still functional.

The pops started out few and far between, but over the course of
the past year they have become more frequent, to the point that
now, within a few minutes of powering on, the device goes into
protect mode. I did not perceive that the pops were restricted to
one or the other channel, although they were so loud and brief
I can not be certain. Their loudness is independent of the setting
of the volume control.

Even with all cables disconnected (no speakers, nothing), the unit
eventually goes into protect mode within a few minutes.

The output transistors all check good (base-emitter and base-collector
junctions all about .6v forward-biased, emitter-collector resistance
does not show any shorts) and the resistance of the emitter resistors
seems normal (fraction of an ohm).

I visually inspected the underside of the board and did not see any
apparently-bad solder joints. Nonetheless I did touch up the output
transistor solder joints. I reinstalled the board in the chassis and
made all mounting screws snug. No improvement.

I visually inspected the electrolytics from the top of the board,
but none appeared swollen.

I have schematics, but I am stumped as to how to proceed further. Has
anyone encountered this kind of problem and found a fix?

Many thanks!
--
G. Paul Ziemba
FreeBSD unix:
9:06PM up 48 days, 21:38, 11 users, load averages: 0.70, 0.64, 0.65

 

Physically check the connecions to the main filter caps. The big ones.

 

[Dave Platt]

In article <mjm9t5$2kd2$1@usenet.ziemba.us>,
G. Paul Ziemba <paul+usenet@w6yx.stanford.edu> wrote:

I visually inspected the electrolytics from the top of the board,
but none appeared swollen.

Caps can (alas) go quite bad even if they don't swell. 10 years of
steady use could be enough to cook the electrolyte, especially if
they're located in a hot section of the chassis and weren't of
terribly good quality in the first place.

I have schematics, but I am stumped as to how to proceed further. Has
anyone encountered this kind of problem and found a fix?

This could indicate the presence of "leaky" electrolytic capacitors,
possibly ones in a DC-blocking role in the signal path. They could
occasionally "flash over" and conduct when you don't want them to.
'Lytics can become leaky with age, especially if they're being
operated with a low DC bias across them (i.e. far below their WVDC
rating).

Cracked or "cold" solder joints are (as you obviously know) another
prime suspect. Your receiver is new enough that it may use lead-free
solder, which is less flexible than leaded and more prone to cracking
under stress. "Ring fractures" around component leads would be one
thing to look for.

It would help you a great deal if you could determine whether the pops
are specific to one channel or the other. If so, you know where to
start looking. If not, that suggests common circuitry (e.g. the power
supply, bias circuitry, etc.).

Since they're independent of the volume control setting, odds are that
they're in the later portion of the preamp circuitry or in the amp,
not in the input stages.

One of my favorite debugging tools, for faults like this, is a wooden
chopstick. Hook the receiver up to test speakers, power it up, and
then start tapping around the PC board with the chopstick. If tapping
in a particular area of the board elicits a POP, or otherwise changes
the behavior, there's a good chance that there's a bad solder junction
somewhere within mechanical-shock distance of the point of tapping.

I had an audio amp which was prone to such popping, some years ago.
The fault turned out to be at the driver transistors... they were
metal-can types, which ran hot, and they'd been snugged down right to
the PC board before being soldered... no "give" in the wire leads.
Differential heating/cooling cycles eventually cracked the solder
joints on the board.

 

[Phil Allison]

G. Paul Ziemba wrote:

My Sony STR-DE675 Receiver (at least ten years old by now) has started
to make random loud pops to the speakers (I have only the main L and R
speakers attached). The "protect" mode activates and so far, my speakers
are still functional.

The pops started out few and far between, but over the course of
the past year they have become more frequent, to the point that
now, within a few minutes of powering on, the device goes into
protect mode. I did not perceive that the pops were restricted to
one or the other channel, although they were so loud and brief
I can not be certain. Their loudness is independent of the setting
of the volume control.

** Try with only one speaker connected - then you will see if the pops are coming from just one or both channels.

Even with all cables disconnected (no speakers, nothing), the unit
eventually goes into protect mode within a few minutes.

** This usually means there is DC voltage on one of the speaker outputs causing the relays to open and bringing on the "protect light".

Finding the exact cause is a process of elimination and one that makes repair techs really earn their money. Typically it comes down to one of the small transistors in the power amp or a zener diode, bad solder joint or almost anything.


..... Phil

 

[M Philbrook]

In article <mjm9t5$2kd2$1@usenet.ziemba.us>,
paul+usenet@w6yx.stanford.edu says...

My Sony STR-DE675 Receiver (at least ten years old by now) has started
to make random loud pops to the speakers (I have only the main L and R
speakers attached). The "protect" mode activates and so far, my speakers
are still functional.

The pops started out few and far between, but over the course of
the past year they have become more frequent, to the point that
now, within a few minutes of powering on, the device goes into
protect mode. I did not perceive that the pops were restricted to
one or the other channel, although they were so loud and brief
I can not be certain. Their loudness is independent of the setting
of the volume control.

Even with all cables disconnected (no speakers, nothing), the unit
eventually goes into protect mode within a few minutes.

The output transistors all check good (base-emitter and base-collector
junctions all about .6v forward-biased, emitter-collector resistance
does not show any shorts) and the resistance of the emitter resistors
seems normal (fraction of an ohm).

I visually inspected the underside of the board and did not see any
apparently-bad solder joints. Nonetheless I did touch up the output
transistor solder joints. I reinstalled the board in the chassis and
made all mounting screws snug. No improvement.

I visually inspected the electrolytics from the top of the board,
but none appeared swollen.

I have schematics, but I am stumped as to how to proceed further. Has
anyone encountered this kind of problem and found a fix?

Many thanks!

time for a recapping....

You have one that is shorting, it does not need to be swollen as you
say, most likely a small package cap with a lot of F for its size.

Jamie

 

[Mark Zacharias]

"G. Paul Ziemba" <paul+usenet@w6yx.stanford.edu> wrote in message
news:mjm9t5$2kd2$1@usenet.ziemba.us...

My Sony STR-DE675 Receiver (at least ten years old by now) has started
to make random loud pops to the speakers (I have only the main L and R
speakers attached). The "protect" mode activates and so far, my speakers
are still functional.

The pops started out few and far between, but over the course of
the past year they have become more frequent, to the point that
now, within a few minutes of powering on, the device goes into
protect mode. I did not perceive that the pops were restricted to
one or the other channel, although they were so loud and brief
I can not be certain. Their loudness is independent of the setting
of the volume control.

Even with all cables disconnected (no speakers, nothing), the unit
eventually goes into protect mode within a few minutes.

The output transistors all check good (base-emitter and base-collector
junctions all about .6v forward-biased, emitter-collector resistance
does not show any shorts) and the resistance of the emitter resistors
seems normal (fraction of an ohm).

I visually inspected the underside of the board and did not see any
apparently-bad solder joints. Nonetheless I did touch up the output
transistor solder joints. I reinstalled the board in the chassis and
made all mounting screws snug. No improvement.

I visually inspected the electrolytics from the top of the board,
but none appeared swollen.

I have schematics, but I am stumped as to how to proceed further. Has
anyone encountered this kind of problem and found a fix?

Many thanks!
--
G. Paul Ziemba
FreeBSD unix:
9:06PM up 48 days, 21:38, 11 users, load averages: 0.70, 0.64, 0.65

Wow - I was typing a big long reply and my mail program crashed, lost it
all.

OK.

1. It would be helpful to know if the pop is on one channel or all.
All channels would point to a power supply problem, such as perhaps bad
solder at a fixed voltage regulator. Probably a good idea to resolder all
your TO-220 style voltage regulators for good measure.

2. The base voltages should be around 1.1 volts or so. Although the service
manual incorrectly drew the ouputs as bipolar, they are Darlingtons, the
voltages shown in the schematic are correct. I have serviced Sony receivers
of this general type for over 20 years, and this has virtually always been
the case.
If you really read 0.6 volts on the bases, you may need a new multimeter.
The MUTE function of the driver IC's would have resulted in 0 volts at the
base, and it's not a bias problem, so there you go.

3. The uPC 2581 driver ic's do run quite hot and dry out nearby caps.
The IC's should be resoldered and any suspect caps replaced. The STK350-230
(IC501) is a VERY common troublemaker - although not often intermittent,
usually just bad (at least by the time I see them).

Mark Z.

 

On Saturday, May 23, 2015 at 7:23:16 AM UTC-4, Mark Zacharias wrote:

"G. Paul Ziemba" <paul+usenet@w6yx.stanford.edu> wrote in message
news:mjm9t5$2kd2$1@usenet.ziemba.us...
My Sony STR-DE675 Receiver (at least ten years old by now) has started
to make random loud pops to the speakers (I have only the main L and R
speakers attached). The "protect" mode activates and so far, my speakers
are still functional.


3. The uPC 2581 driver ic's do run quite hot and dry out nearby caps.
The IC's should be resoldered and any suspect caps replaced. The STK350-230
(IC501) is a VERY common troublemaker - although not often intermittent,
usually just bad (at least by the time I see them).

Mark Z.

I will second Mark's comment here. Many a Sony has been "fixed" by resoldering the uPC 2581. I usually remove the solder and resolder. Very common problem.

Dan

 

[G. Paul Ziemba]

dplatt@coop.radagast.org (Dave Platt) writes:

determine whether the pops are specific to one channel or the other

One of my favorite debugging tools, for faults like this, is a wooden
chopstick.

Oh, very good. I wasn't clever enough to think of that! So far I
have determined the pops are in the left main channel but not the
right. Still trying to localize the area of greatest mechanical
sensitivity - almost anywhere on the board generates a pop, and
then it's 30-60 seconds or so until I can reset the "protect" mode
by power-cycling. Working on lighter taps!

Thanks to everyone else for excellent ideas as well. I'll report
back once I get a better idea of the location.
--
G. Paul Ziemba
FreeBSD unix:
5:36PM up 2 days, 5:06, 7 users, load averages: 0.73, 0.88, 0.85

 

[G. Paul Ziemba]

dansabrservices@yahoo.com writes:

On Saturday, May 23, 2015 at 7:23:16 AM UTC-4, Mark Zacharias wrote:
3. The uPC 2581 driver ic's do run quite hot and dry out nearby caps.
The IC's should be resoldered and any suspect caps replaced. The STK350-230
(IC501) is a VERY common troublemaker - although not often intermittent,
usually just bad (at least by the time I see them).

Mark Z.

I will second Mark's comment here. Many a Sony has been "fixed" by resoldering the uPC 2581. I usually remove the solder and resolder. Very common problem.

Dan

I used a plastic rod to tap around the board to localize the problem.
The two big capacitors were fine, but almost everywhere else wasn't.

Connecting only one speaker at a time was a good idea - left main
channel only.

There were multiple solder joint faults. The big cap in the 30v
circuit, c819 (on the PCB layout but not on the schematic), the
coil of the headphone relay near it, and the driver ICs (uPC 2581)
all had unstable solder (not visible to the naked eye).

Working through all of these required multiple disassembly and
reassembly iterations (no easy-access panel from below, grr) but
now the amp has been running for an hour without a pop.

Thanks to all for the various suggestions - all were helpful in
reaching a satisfactory conclusion.
--
G. Paul Ziemba
FreeBSD unix:
10:11PM up 2 days, 9:41, 9 users, load averages: 0.74, 0.71, 0.74