Toshiba TV29C90 problem; Image fades to black...

[Arfa Daily]

"rockinnomo" <hlbucklin@verizon.net> wrote in message
news:985e8812-c3ce-47ab-a362-8179bd548e48@q27g2000prf.googlegroups.com...

I posted this a while back and am still needing help so here it is
again. PLEASE E mail me directly hlbucklin@verizon.net

My electronics tech is having trouble fixing an SAE Two amplifier
model A-14. It has no audio output. If he shorts across a relay the
audio works fine. He has a good service manual but can't track down
what the problem is. Does anyone know what the problem may be
specifically? It was repaired for the same problem by another tech
and
the repair didn't last long. I do know that 4 ohm speakers are a no-
no. He's testing with headphones. Sure would appreciate some help
here. Please eMail me at hlbuck...@verizon.net.
Harvey

If there is no obvious problem, such as DC offset, that is causing the
protect relay driver circuit to fail to drop in, and the amp is otherwise
producing good audio, then this must actually be a very simple problem, that
should not be any problem for an experienced engineer, armed with a full
service manual, to track down. If your service tech is unable to do this,
then I would have to suggest that he is not the right person to be looking
at it.

Assuming that it uses a TA7317 as the protect IC, then common problems are
the timing cap for the switch-on delay, and the high(ish) value resistor
that charges said cap. There is also usually a quite high value resistor
between the relay coil, and the drive pin of the IC, and don't forget the
relay coil itself. Rarely, the IC might be faulty. If your tech does not
understand the inner workings of the 7317, he should download a spec sheet
for it, where all will be revealed ...

Arfa

 

[Arfa Daily]

"rockinnomo" <hlbucklin@verizon.net> wrote in message
news:985e8812-c3ce-47ab-a362-8179bd548e48@q27g2000prf.googlegroups.com...

I posted this a while back and am still needing help so here it is
again. PLEASE E mail me directly hlbucklin@verizon.net

My electronics tech is having trouble fixing an SAE Two amplifier
model A-14. It has no audio output. If he shorts across a relay the
audio works fine. He has a good service manual but can't track down
what the problem is. Does anyone know what the problem may be
specifically? It was repaired for the same problem by another tech
and
the repair didn't last long. I do know that 4 ohm speakers are a no-
no. He's testing with headphones. Sure would appreciate some help
here. Please eMail me at hlbuck...@verizon.net.
Harvey

If there is no obvious problem, such as DC offset, that is causing the
protect relay driver circuit to fail to drop in, and the amp is otherwise
producing good audio, then this must actually be a very simple problem, that
should not be any problem for an experienced engineer, armed with a full
service manual, to track down. If your service tech is unable to do this,
then I would have to suggest that he is not the right person to be looking
at it.

Assuming that it uses a TA7317 as the protect IC, then common problems are
the timing cap for the switch-on delay, and the high(ish) value resistor
that charges said cap. There is also usually a quite high value resistor
between the relay coil, and the drive pin of the IC, and don't forget the
relay coil itself. Rarely, the IC might be faulty. If your tech does not
understand the inner workings of the 7317, he should download a spec sheet
for it, where all will be revealed ...

Arfa

 

[James Sweet]

Yes, I only like to fix a problem once. Varo used to make some nice
3 KV PIV rectifiers that looked like the larger microwave oven diodes.
They were great for upgrading old broadcast and high power commercial
two wy radio systems. Using four of them and moving the meters allowed
me to reduce two full six foot racks into a single four foot outdoor
rack. It was bolted to the base of the tower and was still in use when
the owner died, years later. I did all the HV wiring with 25 KV second
anode wire.

Jeez, how big were the seleniums? The biggest ones I've seen were only a
couple inches square.

 

[James Sweet]

Yes, I only like to fix a problem once. Varo used to make some nice
3 KV PIV rectifiers that looked like the larger microwave oven diodes.
They were great for upgrading old broadcast and high power commercial
two wy radio systems. Using four of them and moving the meters allowed
me to reduce two full six foot racks into a single four foot outdoor
rack. It was bolted to the base of the tower and was still in use when
the owner died, years later. I did all the HV wiring with 25 KV second
anode wire.

Jeez, how big were the seleniums? The biggest ones I've seen were only a
couple inches square.

 

[Pilgrim]

In article
<b8ec8e3c-4c72-4a4e-b892-fb3962620934@f63g2000hsf.googlegroups.com>,
EricM <ew_morr@hotmail.com> wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!

Your PIV rating for the new diodes is much too low. You should have at
least a 1KV diode. Also you don't need that high a current diode.

Chuck P.

 

[Pilgrim]

In article
<b8ec8e3c-4c72-4a4e-b892-fb3962620934@f63g2000hsf.googlegroups.com>,
EricM <ew_morr@hotmail.com> wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!

Your PIV rating for the new diodes is much too low. You should have at
least a 1KV diode. Also you don't need that high a current diode.

Chuck P.

 

[Jerry G.]

The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.


"EricM" <ew_morr@hotmail.com> wrote in message
news:b8ec8e3c-4c72-4a4e-b892-fb3962620934@f63g2000hsf.googlegroups.com...
I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!

 

[Jerry G.]

The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.


"EricM" <ew_morr@hotmail.com> wrote in message
news:b8ec8e3c-4c72-4a4e-b892-fb3962620934@f63g2000hsf.googlegroups.com...
I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!

 

[Arfa Daily]

"Jerry G." <jerryg50@NOSPAMhotmail.com> wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecommunications...

The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.

I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable running
voltage drop to compensate for the higher DC that will be produced by the
replacement silicon diodes over the original selenium stack. As far as
grafting in a 5U4 goes, I think that I would want to know a bit more about
the actual AC supply level, as this device is rated maximum 450-0-450, and
if the HT supply was up at over 600v DC off load (ie before the delay
circuit had applied the DC to the output stage) by the time that the variac
was at 70%, this would indicate that more than this was being produced by
the transformer whilst it was off load.

Depending on the voltage rating of the main filter caps, I would feel
inclined to use 3 x 1000v PIV 1 or 2 amp diodes in series, as Jerry
suggests, with a couple of high voltage 3 watt zeners in inverse series with
each rectifier string, before the filter caps. That will ensure that the
forward voltage drop of the original seleniums, which will have been taken
into consideration by the designer when he specced the caps and the output
stage supply, is effectively preserved by the replacement rectifier
arrangement. The zener value would be chosen to provide a similar drop to
that which the selenium stacks produced

Another possibility might be to use microwave oven diodes, which are also
constructed as multi-diode 'stacks', so might better emulate the original
selenium stacks for forward voltage drop. They are extremely high voltage
working and quite meaty, current-wise. I must add, however, that I have
never tried any in this sort of application, so they might have more or
less voltage drop than you need.

Jerry's advice to bypass the diodes with suitably rated caps is good, and I
would absolutely concur on that point. Also, on not re-using the diodes that
you have in there at the moment, and on making sure that there is not some
other problem that led to the demise of the seleniums. These were never the
most robust devices, if subjected to long term overload ...

Arfa

 

[Arfa Daily]

"Jerry G." <jerryg50@NOSPAMhotmail.com> wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecommunications...

The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.

I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable running
voltage drop to compensate for the higher DC that will be produced by the
replacement silicon diodes over the original selenium stack. As far as
grafting in a 5U4 goes, I think that I would want to know a bit more about
the actual AC supply level, as this device is rated maximum 450-0-450, and
if the HT supply was up at over 600v DC off load (ie before the delay
circuit had applied the DC to the output stage) by the time that the variac
was at 70%, this would indicate that more than this was being produced by
the transformer whilst it was off load.

Depending on the voltage rating of the main filter caps, I would feel
inclined to use 3 x 1000v PIV 1 or 2 amp diodes in series, as Jerry
suggests, with a couple of high voltage 3 watt zeners in inverse series with
each rectifier string, before the filter caps. That will ensure that the
forward voltage drop of the original seleniums, which will have been taken
into consideration by the designer when he specced the caps and the output
stage supply, is effectively preserved by the replacement rectifier
arrangement. The zener value would be chosen to provide a similar drop to
that which the selenium stacks produced

Another possibility might be to use microwave oven diodes, which are also
constructed as multi-diode 'stacks', so might better emulate the original
selenium stacks for forward voltage drop. They are extremely high voltage
working and quite meaty, current-wise. I must add, however, that I have
never tried any in this sort of application, so they might have more or
less voltage drop than you need.

Jerry's advice to bypass the diodes with suitably rated caps is good, and I
would absolutely concur on that point. Also, on not re-using the diodes that
you have in there at the moment, and on making sure that there is not some
other problem that led to the demise of the seleniums. These were never the
most robust devices, if subjected to long term overload ...

Arfa

 

[Arfa Daily]

"Jack00" <SPal508596@aol.com> wrote in message
news:28b7878e-0cbe-4b9a-8a61-e4923ef5de13@p39g2000prm.googlegroups.com...

I've got this digibox which does not respond to the Sky remote but if
this remote is tested on another digibox then it works fine. But if i
press the front buttons on the DRX300 digibox then it seems to work
but with the remote nothing happens. Any help appreciated.

Thanks

First, if you haven't already, you need to do a full power-down reset.
Unplug from the wall for at least 10 minutes. If still no joy, follow this
with a forced software update. If still no joy, then it's time to get the
lid off, and dust off your 'scope to check what's coming off the remote
sensor. If you don't have a 'scope, then you won't get very far tracking
down the problem, if it is a 'real' fault.

Arfa

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:OGbMj.54818$Ge4.42958@newsfe1-win.ntli.net...

"Jack00" <SPal508596@aol.com> wrote in message
news:28b7878e-0cbe-4b9a-8a61-e4923ef5de13@p39g2000prm.googlegroups.com...
I've got this digibox which does not respond to the Sky remote but if
this remote is tested on another digibox then it works fine. But if i
press the front buttons on the DRX300 digibox then it seems to work
but with the remote nothing happens. Any help appreciated.

Thanks

First, if you haven't already, you need to do a full power-down reset.
Unplug from the wall for at least 10 minutes. If still no joy, follow this
with a forced software update. If still no joy, then it's time to get the
lid off, and dust off your 'scope to check what's coming off the remote
sensor. If you don't have a 'scope, then you won't get very far tracking
down the problem, if it is a 'real' fault.

Arfa

Beware the mains voltages can be relatively exposed in such boxes , when the
cover is removed

Just a crystal (not magnetic) earpiece will probably tell if the remote
receiver is working.

connect one wire of the earpiece to the outer metal of a phono or coax
connector on the rear, the other then touch to each of the traces going to
the receiver block in turn.
Usually 3 traces,
a/ would stop the stray pickup noise on an open earpiece (ground)
b/ would just give a click on touching (supply V)
c/ would give a varying click noise on pressing buttons on the handset.
(signal line)

NB No stray wires that could bridge other traces, just neat single wire for
probing.

If more than 3 going to the receiver block then try each in turn , one
should be variable click, related to keypad presses.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Allodoxaphobia]

On Sun, 13 Apr 2008 07:18:06 -0700 (PDT), volcko@juno.com wrote:

On Apr 8, 11:01 am, Ken Layton <KLayton...@aol.com> wrote:
On Apr 7, 7:38 pm, "hr(bob) wrote:

They are widely used in magnet/reed switch intrusion detectors.

Also in 45 rpm jukebox applications as the end-of-record trip switch.

I need 1 or 2 of these and am having trouble finding a source. Does
anyone know of a source for small quantity? In the US.

http://www.danssmallpartsandkits.net/
Do a _browser_ search "reed". The best price. Recommended.

http://www.alltronics.com/cgi-bin/item/95B012/search/1-Amp-Reed-Switch

http://www.goldmine-elec-products.com/prodinfo.asp?number=G16648
http://www.goldmine-elec-products.com/prodinfo.asp?number=G13078

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: <http://jonz.net/ng.htm>

 

[James Sweet]

"Don Bowey" <dbowey@comcast.net> wrote in message
news:C4276FC2.B5260%dbowey@comcast.net...

On 4/13/08 7:18 AM, in article
df0ec16c-f2f2-491a-821e-3ad310d23304@f63g2000hsf.googlegroups.com,
"volcko@juno.com" <bvolcko@gmail.com> wrote:

On Apr 8, 11:01 am, Ken Layton <KLayton...@aol.com> wrote:
On Apr 7, 7:38 pm, "hr(bob) hofm...@att.net" <hrhofm...@att.net
wrote:



They are widely used in magnet/reed switch intrusion detectors.

Also in 45 rpm jukebox applications as the end-of-record trip switch.

I need 1 or 2 of these and am having trouble finding a source. Does
anyone know of a source for small quantity? In the US.
Thanks.
BV

Search "reed relay"

I've bought a number of them on ebay, they're cheap.

 

[James Sweet]

"Don Bowey" <dbowey@comcast.net> wrote in message
news:C4276FC2.B5260%dbowey@comcast.net...

On 4/13/08 7:18 AM, in article
df0ec16c-f2f2-491a-821e-3ad310d23304@f63g2000hsf.googlegroups.com,
"volcko@juno.com" <bvolcko@gmail.com> wrote:

On Apr 8, 11:01 am, Ken Layton <KLayton...@aol.com> wrote:
On Apr 7, 7:38 pm, "hr(bob) hofm...@att.net" <hrhofm...@att.net
wrote:



They are widely used in magnet/reed switch intrusion detectors.

Also in 45 rpm jukebox applications as the end-of-record trip switch.

I need 1 or 2 of these and am having trouble finding a source. Does
anyone know of a source for small quantity? In the US.
Thanks.
BV

Search "reed relay"

I've bought a number of them on ebay, they're cheap.

 

[Jimmie D]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:Hh8Mj.54775$Ge4.33926@newsfe1-win.ntli.net...

"Jerry G." <jerryg50@NOSPAMhotmail.com> wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecommunications...
The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.


I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable
running voltage drop to compensate for the higher DC that will be produced
by the replacement silicon diodes over the original selenium stack. As far
as grafting in a 5U4 goes, I think that I would want to know a bit more
about the actual AC supply level, as this device is rated maximum
450-0-450, and if the HT supply was up at over 600v DC off load (ie before
the delay circuit had applied the DC to the output stage) by the time that
the variac was at 70%, this would indicate that more than this was being
produced by the transformer whilst it was off load.

Depending on the voltage rating of the main filter caps, I would feel
inclined to use 3 x 1000v PIV 1 or 2 amp diodes in series, as Jerry
suggests, with a couple of high voltage 3 watt zeners in inverse series
with each rectifier string, before the filter caps. That will ensure that
the forward voltage drop of the original seleniums, which will have been
taken into consideration by the designer when he specced the caps and the
output stage supply, is effectively preserved by the replacement rectifier
arrangement. The zener value would be chosen to provide a similar drop to
that which the selenium stacks produced

Another possibility might be to use microwave oven diodes, which are also
constructed as multi-diode 'stacks', so might better emulate the original
selenium stacks for forward voltage drop. They are extremely high voltage
working and quite meaty, current-wise. I must add, however, that I have
never tried any in this sort of application, so they might have more or
less voltage drop than you need.

Jerry's advice to bypass the diodes with suitably rated caps is good, and
I would absolutely concur on that point. Also, on not re-using the diodes
that you have in there at the moment, and on making sure that there is not
some other problem that led to the demise of the seleniums. These were
never the most robust devices, if subjected to long term overload ...

Arfa

 

[Jimmie D]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:Hh8Mj.54775$Ge4.33926@newsfe1-win.ntli.net...

"Jerry G." <jerryg50@NOSPAMhotmail.com> wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecommunications...
The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.


I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable
running voltage drop to compensate for the higher DC that will be produced
by the replacement silicon diodes over the original selenium stack. As far
as grafting in a 5U4 goes, I think that I would want to know a bit more
about the actual AC supply level, as this device is rated maximum
450-0-450, and if the HT supply was up at over 600v DC off load (ie before
the delay circuit had applied the DC to the output stage) by the time that
the variac was at 70%, this would indicate that more than this was being
produced by the transformer whilst it was off load.

Depending on the voltage rating of the main filter caps, I would feel
inclined to use 3 x 1000v PIV 1 or 2 amp diodes in series, as Jerry
suggests, with a couple of high voltage 3 watt zeners in inverse series
with each rectifier string, before the filter caps. That will ensure that
the forward voltage drop of the original seleniums, which will have been
taken into consideration by the designer when he specced the caps and the
output stage supply, is effectively preserved by the replacement rectifier
arrangement. The zener value would be chosen to provide a similar drop to
that which the selenium stacks produced

Another possibility might be to use microwave oven diodes, which are also
constructed as multi-diode 'stacks', so might better emulate the original
selenium stacks for forward voltage drop. They are extremely high voltage
working and quite meaty, current-wise. I must add, however, that I have
never tried any in this sort of application, so they might have more or
less voltage drop than you need.

Jerry's advice to bypass the diodes with suitably rated caps is good, and
I would absolutely concur on that point. Also, on not re-using the diodes
that you have in there at the moment, and on making sure that there is not
some other problem that led to the demise of the seleniums. These were
never the most robust devices, if subjected to long term overload ...

Arfa

 

[Jimmie D]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:Hh8Mj.54775$Ge4.33926@newsfe1-win.ntli.net...

"Jerry G." <jerryg50@NOSPAMhotmail.com> wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecommunications...
The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.


I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable
running voltage drop to compensate for the higher DC that will be produced
by the replacement silicon diodes over the original selenium stack.

I agree, 100 ohms is probably a more reasonable value.
When working on old equipment like this I try to add enough resistance to
keep the B+ at least 10% below the rating of the filer caps
If the filter caps were rated at 450 I would add enough resistors after
replacing selenium diodes to keep the voltage around 410 or so.
This is just kind of a best guess way of doing things when a minimum amount
of information is available.

Jimmie

 

[Arfa Daily]

"Thor" <Thor@nospam.net> wrote in message
news:m1p504ps3mf87slrn65rqo7ppijdh22i2j@4ax.com...

What are some simple and reliable methods of checking the laser in a DVD
player?
By definition the laser would include the layer that also plays audio cd's
as
well, but I am really interested in the video layer. I have DMM's and
such, even
a laser power meter but that is on the bulky side.

How much trouble is it to replace the laser(assembly?) and what equipment
is
needed? How about alignment, if it is needed?

I am looking at a finicky Sanyo DWM-400, about 3 years old.

I will give more info as needed.

Thanks for any help,
Thor

In general, there's not an awful lot you can do to 'test' an optical block,
as such. In general, if the unit plays CDs but not DVDs, or, more rarely,
the other way round, you have a better than even chance that it's the laser
(optical block) that's at fault. If your player is used a fair bit, then 3
years is not at all uncommon for the laser to be showing signs of wear.
Another good pointer is if the player starts freezing up after about 3/4 of
a full length feature film has played. This is when the player has switched
to reading layer 2 on the disc, which has to be read through the
semi-transparent layer 1, so consequently has less reflectivity of the laser
beam.

Other causes of poor playability are bad spindle motors, when they are the
brushgear'd little Mitsumi DC types, and (very) occasionally deposits on the
outer surface of the lens, particularly if it's a heavy smoking household.
Geoff in Israel who posts here, also tells me that it is more common to have
a dirty laser, if you live in a climate like his.

As far as replacing lasers goes, on most players, it's not a difficult job.
Often, the laser comes pre-mounted and aligned on a sub-deck, which also
includes the spindle and sled motors, and limit switch. Where this is the
case, it is pretty much guaranteed that it is just a 'drop-in' replacement.
Some lasers are supplied as just a 'bare bones' optical block. In most
cases, these will also just drop in, but some players, such as Panasonic for
instance, require the tilt to be mechanically adjusted. Some other players
have electronic setups to match in the replacement laser to the machine.
Most machines also have a degree of self diagnosis built in, but it's often
hard to get at unless you have a service manual, and sometimes a service
remote. In my experience, unless you have a particular liking for a player,
or if it's a HC system, and you have all its speakers and cabling 'plumbed
in' to your walls, the cost of a replacement laser is prohibitive, and you
might as well go and buy a new player, with a new 2 year warranty, at the
cheapest place you can find ...

Arfa

 

[Mark D. Zacharias]

"Gary L. woodruff" <woodruffrepair@frontiernet.net> wrote in message
news:ORLMj.1638$Cn4.394@news02.roc.ny...

Howdy, Thanks again Mark for the advise. Am I going to measure resistance
across E-B? If so, do I have to remove the transistor so I do not seen it
in the circuit?

Thanks, Gary

The (good) transistor will not affect the measurement of the 220 ohm
resistor.

Mark Z.