Hi all,

I was recently repairing my SA-HT70 dvd player because the subwoofer kept
cutting out. I fixed the problem. Then, I was about to remove a little piece
of plastic that had fallen onto the circuit board with my tweezers. I
accidently dropped the tweezers onto the circuit board - this caused a big
spark with some smoke. Now, when plugged in, the unit displays the red stand-
by light, but when I press the power button, it goes green for about 2
seconds then back into standby (red), whilst the relay near the power input
clicks once or twice. Does anybody know what that means and if I can fix it?
Thanks.

"aarpay" u36611@uwe wrote in message news:76a5cdc83293f@uwe...
Hi all,

I was recently repairing my SA-HT70 dvd player because the subwoofer kept
cutting out. I fixed the problem. Then, I was about to remove a little
piece
of plastic that had fallen onto the circuit board with my tweezers. I
accidently dropped the tweezers onto the circuit board - this caused a big
spark with some smoke. Now, when plugged in, the unit displays the red
stand-
by light, but when I press the power button, it goes green for about 2
seconds then back into standby (red), whilst the relay near the power
input
clicks once or twice. Does anybody know what that means and if I can fix
it?
Thanks.


Check for +28v on pin 14 of IC502. If missing, safety resistor FP549 is
open. Failing that, you've probably fried IC502. I've got the relevant part
of the schematic as a pdf if you need it. Contact me off group with a valid
e-mail if you do.

Arfa

I'm sorry, but I'm a bit of a novice....

Should I be testing the voltage difference between pins 1 and 14? What is the
reference? Thanks

Arfa Daily wrote:
Hi all,

[quoted text clipped - 11 lines]
it?
Thanks.

Check for +28v on pin 14 of IC502. If missing, safety resistor FP549 is
open. Failing that, you've probably fried IC502. I've got the relevant part
of the schematic as a pdf if you need it. Contact me off group with a valid
e-mail if you do.

Arfa

--
Message posted via http://www.electronicskb.com

"aarpay via ElectronicsKB.com" u36611@uwe wrote in message
news:76af1547ad2b4@uwe...
I'm sorry, but I'm a bit of a novice....

Should I be testing the voltage difference between pins 1 and 14? What is
the
reference? Thanks

Arfa Daily wrote:
Hi all,

[quoted text clipped - 11 lines]
it?
Thanks.

Check for +28v on pin 14 of IC502. If missing, safety resistor FP549 is
open. Failing that, you've probably fried IC502. I've got the relevant
part
of the schematic as a pdf if you need it. Contact me off group with a
valid
e-mail if you do.

Arfa

--
Message posted via http://www.electronicskb.com


The reference is ground ie any piece of metalwork on the unit such as the
antenna socket outer, which will definitely be ground. However, I must say
that if your level of expertise with this equipment is actually such that
you are not aware that ground is the standard reference point unless
otherwise stated, then it is unlikely that you are going to be able to
troubleshoot the unit to the point of being able to fix it. Also, you should
be aware of the safety angles of working on a piece of live equipment.
Whilst the 'HT70 is better than some for safety in that it uses a linear
rather than switch mode supply, there is still exposed line voltage in
places around the power supply, so do take care ...

Arfa

Also, I would like that schematic. How do I contact you off group?

aarpay wrote:
I'm sorry, but I'm a bit of a novice....

Should I be testing the voltage difference between pins 1 and 14? What is the
reference? Thanks

Hi all,

[quoted text clipped - 8 lines]

Arfa

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/For...epair/200708/1

Thanks for your reply:
I figured the frame was reference, but just wanted to make sure. Pin 14 is
NOT reading +28V. In fact, it has no voltage. Does this mean I need to
replace the FP549? If so, how much resistance (in ohms) does the FP549 have?

Arfa Daily wrote:
I'm sorry, but I'm a bit of a novice....

[quoted text clipped - 16 lines]

Arfa

The reference is ground ie any piece of metalwork on the unit such as the
antenna socket outer, which will definitely be ground. However, I must say
that if your level of expertise with this equipment is actually such that
you are not aware that ground is the standard reference point unless
otherwise stated, then it is unlikely that you are going to be able to
troubleshoot the unit to the point of being able to fix it. Also, you should
be aware of the safety angles of working on a piece of live equipment.
Whilst the 'HT70 is better than some for safety in that it uses a linear
rather than switch mode supply, there is still exposed line voltage in
places around the power supply, so do take care ...

Arfa

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/For...epair/200708/1

"aarpay via ElectronicsKB.com" u36611@uwe wrote in message
news:76af5fca07a7b@uwe...
Also, I would like that schematic. How do I contact you off group?

aarpay wrote:
I'm sorry, but I'm a bit of a novice....

Should I be testing the voltage difference between pins 1 and 14? What is
the
reference? Thanks

Hi all,

[quoted text clipped - 8 lines]

Arfa

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/For...epair/200708/1

Right click on one of my posts' headers, then left click on properties,
where you will find my address.

Arfa

"aarpay via ElectronicsKB.com" u36611@uwe wrote in message
news:76af827026e1d@uwe...
Thanks for your reply:
I figured the frame was reference, but just wanted to make sure. Pin 14 is
NOT reading +28V. In fact, it has no voltage. Does this mean I need to
replace the FP549? If so, how much resistance (in ohms) does the FP549
have?


First you should locate FP549, and check the voltage ( with respect to
ground ) on either side of it. If there is +28v on one side, and nothing on
the other, then it is open circuit, and will need to be replaced.
Officially, it is a 500mA fuse, but is actually shown on the schematic as a
fusible resistor. It is quite common for such wire-ended circuit protectors
or 'fuses' to actually be special low value resistors which are designed to
go rapidly open circuit once their nominal power rating is exceeded. I would
expect this one to be around 1 ohm at 0.5watt - but a fusible type, not a
standard resistor. If you can obtain an official wire-ended 500mA circuit
protector, then fit that. If not, the fusible resistor. If you're lucky,
there will be no other damage. But make the checks first, before proceeding
to replacing it.

BTW, it is common convention to bottom post on newsgroups ( without wishing
to start another furious debate on the subject |:-\ ) as it makes the
thread a lot easier to follow

Arfa

Arfa:

I rechecked the voltages on the unit.

With the unit in standby mode, pin 14 on IC502 reads about +2.0 V. FP549 also
reads about +2.0 V on either side.. The voltage on both of these gradually
drops the longer the unit has been plugged in. Also, If I unplug the unit, I
get the same readings. I suppose charge is stored in the capacitors somewhere.
If I press the power button, the voltage reading (for both IC502 and both
ends of FP549) jumps to about +12.0 V, then the unit goes into standby mode
after 1 second, and the readings go back to about +2.0 V (dropping gradually).
Any suggestions? Thanks

By the way, I can't figure out the right place to right-click. I'm not seeing
an email address.

--
Message posted via http://www.electronicskb.com

"aarpay via ElectronicsKB.com" u36611@uwe wrote in message
news:76bed0e7b9a57@uwe...
Arfa:

I rechecked the voltages on the unit.

With the unit in standby mode, pin 14 on IC502 reads about +2.0 V. FP549
also
reads about +2.0 V on either side.. The voltage on both of these gradually
drops the longer the unit has been plugged in. Also, If I unplug the unit,
I
get the same readings. I suppose charge is stored in the capacitors
somewhere.
If I press the power button, the voltage reading (for both IC502 and both
ends of FP549) jumps to about +12.0 V, then the unit goes into standby
mode
after 1 second, and the readings go back to about +2.0 V (dropping
gradually).
Any suggestions? Thanks

By the way, I can't figure out the right place to right-click. I'm not
seeing
an email address.

--
Message posted via http://www.electronicskb.com


OK. Well that basically tells us that the problem is not the protector, or
probably its feed either, so it will be necessary to start checking the
output voltages of IC502, which is where it gets complicated, because as it
only stays on a second or two, before dropping back to standby, you don't
have long to evaluate what is appearing on the chip's outputs. As it is also
possible that the input voltages never have time to reach their normal
running level, it takes a degree of experience to determine if output pins
that are reading low in that second or two, are *heading* for the right
level ...

For an e-mail direct to me, use

Arfa

Ok. What do you recommend as my next step? Should I try and measure the
voltages on all 14 pins and post the results?




Arfa Daily wrote:
Arfa:

[quoted text clipped - 17 lines]
seeing
an email address.

OK. Well that basically tells us that the problem is not the protector, or
probably its feed either, so it will be necessary to start checking the
output voltages of IC502, which is where it gets complicated, because as it
only stays on a second or two, before dropping back to standby, you don't
have long to evaluate what is appearing on the chip's outputs. As it is also
possible that the input voltages never have time to reach their normal
running level, it takes a degree of experience to determine if output pins
that are reading low in that second or two, are *heading* for the right
level ...

For an e-mail direct to me, use

Arfa

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/For...epair/200708/1

OK. Well that basically tells us that the problem is not the protector, or
probably its feed either, so it will be necessary to start checking the
output voltages of IC502, which is where it gets complicated, because as
it
only stays on a second or two, before dropping back to standby, you don't
have long to evaluate what is appearing on the chip's outputs. As it is
also
possible that the input voltages never have time to reach their normal
running level, it takes a degree of experience to determine if output pins
that are reading low in that second or two, are *heading* for the right
level ...

For an e-mail direct to me, use

Arfa


Ok. What do you recommend as my next step? Should I try and measure the
voltages on all 14 pins and post the results?


You should have the schematic that covers this part of the machine now, and
all of the voltages are printed at the pins of IC502. However, as I said,
it's probably going to be difficult for you to interpret what you're seeing
in the brief time it remains out of standby, but you can give it a try, and
I'll see if anything leaps out at me.

Arfa