[Vintage[_2_]]

I got hold of a Sony PCM 7050 dat recorder in good condition.
The only thing is that sometimes the recorder does not power up.
I have been measurning the voltages on the power pc-board in the unit, under
the power transformer, and these are OK.
Therefore I now have the idea that the switching power supply is the cause
of the problem and regularly does not "boot up".
More and more it points in that direction.
It simply does not "start"...
There are times that the PCM-7050 powers up normally and can be switched off
and on several times without any problem.
When the PCM has been switched off for about half an hour it does not power
up anymore.

Does anybody have had similar problems and/or repaired the switched power
supply at the back of the unit ?
Are there parts in such a psu that must be checked first, I mean are there
components that regularly fail in this psu ??
There are no schematic diagrams of the psu in the Sony manual, because Sony
used a psu from a third party supplier and only gives the input and output
connector pin configurations.
The PCM is powered by 240Volts AC (Europe) and that is what I measure on one
of the small white psu connectors.
On the other small white psu connector I measure approx 120 Volts AC. And
of course no output voltages on the larger red connector.
The psu is still available from Sony Professional, but the price is quite
high.
Somebody having a spare for me ?
Sending the PCM to Sony service is quite complicated here and apart from
that also quite expensive.

Richard,
the Netherlands.

[Bigguy[_2_]]

Vintage wrote:
I got hold of a Sony PCM 7050 dat recorder in good condition.
The only thing is that sometimes the recorder does not power up.
I have been measurning the voltages on the power pc-board in the unit, under
the power transformer, and these are OK.
Therefore I now have the idea that the switching power supply is the cause
of the problem and regularly does not "boot up".
More and more it points in that direction.
It simply does not "start"...
There are times that the PCM-7050 powers up normally and can be switched off
and on several times without any problem.
When the PCM has been switched off for about half an hour it does not power
up anymore.

Does anybody have had similar problems and/or repaired the switched power
supply at the back of the unit ?
Are there parts in such a psu that must be checked first, I mean are there
components that regularly fail in this psu ??
There are no schematic diagrams of the psu in the Sony manual, because Sony
used a psu from a third party supplier and only gives the input and output
connector pin configurations.
The PCM is powered by 240Volts AC (Europe) and that is what I measure on one
of the small white psu connectors.
On the other small white psu connector I measure approx 120 Volts AC. And
of course no output voltages on the larger red connector.
The psu is still available from Sony Professional, but the price is quite
high.
Somebody having a spare for me ?
Sending the PCM to Sony service is quite complicated here and apart from
that also quite expensive.

Richard,
the Netherlands.


Check electrolytic capacitors in the PSU - look for doming or leakage.

Guy

[Scott Dorsey]

Vintage oldaudio-at-planet.nl wrote:
I got hold of a Sony PCM 7050 dat recorder in good condition.
The only thing is that sometimes the recorder does not power up.
I have been measurning the voltages on the power pc-board in the unit, under
the power transformer, and these are OK.
Therefore I now have the idea that the switching power supply is the cause
of the problem and regularly does not "boot up".
More and more it points in that direction.
It simply does not "start"...
There are times that the PCM-7050 powers up normally and can be switched off
and on several times without any problem.
When the PCM has been switched off for about half an hour it does not power
up anymore.

Look at the kickstart circuit.

Does anybody have had similar problems and/or repaired the switched power
supply at the back of the unit ?

This is the typical symptom of a switcher with a kick start issue.

Are there parts in such a psu that must be checked first, I mean are there
components that regularly fail in this psu ??

Well, electrolytic caps are always suspect.

Sending the PCM to Sony service is quite complicated here and apart from
that also quite expensive.

Find a local tech who specializes in switching supplies if you are not
willing to work on it yourself. They are out there.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Vintage[_2_]]

Thank you, Scott,
I will check the electrolytic capacitors. (There are two big ones in the
primary circuit).
What components form the kick start circuit ? I mean: Where do I look ?

Richard.

"Scott Dorsey" schreef in bericht
...
Vintage oldaudio-at-planet.nl wrote:
I got hold of a Sony PCM 7050 dat recorder in good condition.
The only thing is that sometimes the recorder does not power up.
I have been measurning the voltages on the power pc-board in the unit,
under
the power transformer, and these are OK.
Therefore I now have the idea that the switching power supply is the cause
of the problem and regularly does not "boot up".
More and more it points in that direction.
It simply does not "start"...
There are times that the PCM-7050 powers up normally and can be switched
off
and on several times without any problem.
When the PCM has been switched off for about half an hour it does not
power
up anymore.

Look at the kickstart circuit.

Does anybody have had similar problems and/or repaired the switched power
supply at the back of the unit ?

This is the typical symptom of a switcher with a kick start issue.

Are there parts in such a psu that must be checked first, I mean are there
components that regularly fail in this psu ??

Well, electrolytic caps are always suspect.

Sending the PCM to Sony service is quite complicated here and apart from
that also quite expensive.

Find a local tech who specializes in switching supplies if you are not
willing to work on it yourself. They are out there.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Vintage oldaudio-at-planet.nl wrote:
Thank you, Scott,
I will check the electrolytic capacitors. (There are two big ones in the
primary circuit).

They are probably poorer than they were when they were new, but they are
not the problem.

What components form the kick start circuit ? I mean: Where do I look ?

Depends. Look for an RC pair with a very small capacitor attached somewhere
to the transformer primary. It provides a little turn-on pulse when the
supply is turned on, to provide enough current on the secondary to turn on
the regulator electronics that provide the pulse that turns on the switching
transistor on the primary. It "kicks" the supply into operation. Without
some power to operate the low voltage electronics, it cannot turn the high
voltage section on.

It will help you to draw out the high voltage section of the supply.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."