Hi,

As the subject line states, our Technics A/V receiver is experiencing
an intermittent video condition. The unit is only 2 years and 8
months old, i.e. it's just past the 2 year manufacturer's warranty
:-(. My previous receiver, a Pioneer SX-580, lasted about 25 years!!
Anyways...

The video signal output from the RCA jack labeled "TV Monitor out" is
fine upon power-up, but after a handful of seconds, the video signal
drops out. In other words, the TV screen goes black. After a
seemingly random period of between 5 seconds and several minutes the
video signal reappears for a few seconds, and then blanks out again.

This problem occurs when the selected video source is either the "VCR
in" RCA jack, or the "TV in" RCA jack. BTW, our DVD player video
output is directly connected to the S-video input of the TV, i.e. the
A/V receiver is not used to switch the DVD video signal.

It seems the problem gets worse as the unit heats up, i.e. the
interval between when the video signal appears increases.

The audio output is fine, i.e. even when the video signal drops out,
the audio from the VCR or TV can be heard.

Given that the problem is intermittent, I assume that there is a good
probability that the source of the problem is cold solder joints. In
order to locate cold solder joints (or a bad connection in general), I
have prodded the circuit board with a wooden stick, and jiggled
various wires. As of yet, I haven't been able to isolate the supposed
bad connection.

Does anyone have any ideas or suggestions?

Is anyone aware of specific components whose solder joints seem to
have a high failure rate on Technics A/V receivers? For example, I am
aware that a large number of Sony TVs have cold solder joints on the
HOT drive transistor (and/or transformer) which eventually leads to a
blown HOT. Is anyone aware of a similiar situation for Technics A/V
products?

Thanks in advance,
Andrew

I would be inclined to believe that your fault is more some component(s)
became thermo sensitive. If you are prodding at the board, and there is not
intermittency, then most likely it is not a cold solder connection.

To follow this logically, you would have to use a scope while the fault is
occurring to track down where the intermittent is. Or, you can try getting
some cold spray and a heat gun, and use the technique of heating and cooling
the various components to find this.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"hecubus" wrote in message
om...
Hi,

As the subject line states, our Technics A/V receiver is experiencing
an intermittent video condition. The unit is only 2 years and 8
months old, i.e. it's just past the 2 year manufacturer's warranty
:-(. My previous receiver, a Pioneer SX-580, lasted about 25 years!!
Anyways...

The video signal output from the RCA jack labeled "TV Monitor out" is
fine upon power-up, but after a handful of seconds, the video signal
drops out. In other words, the TV screen goes black. After a
seemingly random period of between 5 seconds and several minutes the
video signal reappears for a few seconds, and then blanks out again.

This problem occurs when the selected video source is either the "VCR
in" RCA jack, or the "TV in" RCA jack. BTW, our DVD player video
output is directly connected to the S-video input of the TV, i.e. the
A/V receiver is not used to switch the DVD video signal.

It seems the problem gets worse as the unit heats up, i.e. the
interval between when the video signal appears increases.

The audio output is fine, i.e. even when the video signal drops out,
the audio from the VCR or TV can be heard.

Given that the problem is intermittent, I assume that there is a good
probability that the source of the problem is cold solder joints. In
order to locate cold solder joints (or a bad connection in general), I
have prodded the circuit board with a wooden stick, and jiggled
various wires. As of yet, I haven't been able to isolate the supposed
bad connection.

Does anyone have any ideas or suggestions?

Is anyone aware of specific components whose solder joints seem to
have a high failure rate on Technics A/V receivers? For example, I am
aware that a large number of Sony TVs have cold solder joints on the
HOT drive transistor (and/or transformer) which eventually leads to a
blown HOT. Is anyone aware of a similiar situation for Technics A/V
products?

Thanks in advance,
Andrew

I would be inclined to believe that your fault is more some component(s)
became thermo sensitive. If you are prodding at the board, and there is not
intermittency, then most likely it is not a cold solder connection.

To follow this logically, you would have to use a scope while the fault is
occurring to track down where the intermittent is. Or, you can try getting
some cold spray and a heat gun, and use the technique of heating and cooling
the various components to find this.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"hecubus" wrote in message
om...
Hi,

As the subject line states, our Technics A/V receiver is experiencing
an intermittent video condition. The unit is only 2 years and 8
months old, i.e. it's just past the 2 year manufacturer's warranty
:-(. My previous receiver, a Pioneer SX-580, lasted about 25 years!!
Anyways...

The video signal output from the RCA jack labeled "TV Monitor out" is
fine upon power-up, but after a handful of seconds, the video signal
drops out. In other words, the TV screen goes black. After a
seemingly random period of between 5 seconds and several minutes the
video signal reappears for a few seconds, and then blanks out again.

This problem occurs when the selected video source is either the "VCR
in" RCA jack, or the "TV in" RCA jack. BTW, our DVD player video
output is directly connected to the S-video input of the TV, i.e. the
A/V receiver is not used to switch the DVD video signal.

It seems the problem gets worse as the unit heats up, i.e. the
interval between when the video signal appears increases.

The audio output is fine, i.e. even when the video signal drops out,
the audio from the VCR or TV can be heard.

Given that the problem is intermittent, I assume that there is a good
probability that the source of the problem is cold solder joints. In
order to locate cold solder joints (or a bad connection in general), I
have prodded the circuit board with a wooden stick, and jiggled
various wires. As of yet, I haven't been able to isolate the supposed
bad connection.

Does anyone have any ideas or suggestions?

Is anyone aware of specific components whose solder joints seem to
have a high failure rate on Technics A/V receivers? For example, I am
aware that a large number of Sony TVs have cold solder joints on the
HOT drive transistor (and/or transformer) which eventually leads to a
blown HOT. Is anyone aware of a similiar situation for Technics A/V
products?

Thanks in advance,
Andrew

"Jerry G." wrote in message ...
I would be inclined to believe that your fault is more some component(s)
became thermo sensitive. If you are prodding at the board, and there is not
intermittency, then most likely it is not a cold solder connection.

To follow this logically, you would have to use a scope while the fault is
occurring to track down where the intermittent is. Or, you can try getting
some cold spray and a heat gun, and use the technique of heating and cooling
the various components to find this.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================

Jerry,

Thanks for the suggestion. Using cold spray I isolated the
intermittency to a single transister (Q352). Just the slightest spray
on this transistor brought back the video signal.

Inspecting the solder connections of this transistor revealed cold
solder joints. However, even after reflowing the solder on the
transistor (and Q351) the same intermittency occured.

Okay, so I figured that in addition to the cold solder joints, the
transistor itself has become heat sensitive (as Jerry mentions). Q352
is marked with "B621A", but the parts counter guy cross-referenced
this part to NTE159 (instead of NTE294). Installing the NTE159 part
did not improve the situation, in fact, a video signal never appeared
at the output :-(

No parts dealer in town (that is open today) has an NTE294 in stock,
but one shop had a 2SB544 in stock, which also cross-references to
NT294. Hmm... perhaps the 2SB544 will work. Installing the 2SB544
had the same results as with the NTE159, i.e. no video signal at all.

I now realize that simply because 2 parts cross-reference to the same
part (NTE294 in this case), that the 2 parts themselves may not be
interchangable since the maximum ratings may be significantly
different. Live and learn.

Anyways, I'm wondering if any other component(s) may have been damaged
due to my experimentation, particularly Q351 (D592A). I'm guessing
that Q351 and Q352 form a push-pull video amplifier configuration.

Any suggestions on the next step. Should I just find exact
replacement parts for both Q351 and Q352? If so, do I need to find a
matched pair?

Thanks,
Andrew

An NTE 159 has a different basing. It goes E-B-C when viewed from the front,
the 2SB transistor would go E-C-B viewed from the front.

Mark Z.

--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.


"hecubus" wrote in message
om...
"Jerry G." wrote in message
...
I would be inclined to believe that your fault is more some component(s)
became thermo sensitive. If you are prodding at the board, and there is
not
intermittency, then most likely it is not a cold solder connection.

To follow this logically, you would have to use a scope while the fault
is
occurring to track down where the intermittent is. Or, you can try
getting
some cold spray and a heat gun, and use the technique of heating and
cooling
the various components to find this.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================

Jerry,

Thanks for the suggestion. Using cold spray I isolated the
intermittency to a single transister (Q352). Just the slightest spray
on this transistor brought back the video signal.

Inspecting the solder connections of this transistor revealed cold
solder joints. However, even after reflowing the solder on the
transistor (and Q351) the same intermittency occured.

Okay, so I figured that in addition to the cold solder joints, the
transistor itself has become heat sensitive (as Jerry mentions). Q352
is marked with "B621A", but the parts counter guy cross-referenced
this part to NTE159 (instead of NTE294). Installing the NTE159 part
did not improve the situation, in fact, a video signal never appeared
at the output :-(

No parts dealer in town (that is open today) has an NTE294 in stock,
but one shop had a 2SB544 in stock, which also cross-references to
NT294. Hmm... perhaps the 2SB544 will work. Installing the 2SB544
had the same results as with the NTE159, i.e. no video signal at all.

I now realize that simply because 2 parts cross-reference to the same
part (NTE294 in this case), that the 2 parts themselves may not be
interchangable since the maximum ratings may be significantly
different. Live and learn.

Anyways, I'm wondering if any other component(s) may have been damaged
due to my experimentation, particularly Q351 (D592A). I'm guessing
that Q351 and Q352 form a push-pull video amplifier configuration.

Any suggestions on the next step. Should I just find exact
replacement parts for both Q351 and Q352? If so, do I need to find a
matched pair?

Thanks,
Andrew