Topics

Need Help Troubleshooting Tektronix PS280

daven9ooq
 

Hi everyone I recently purchased a Tektronix PS280 power supply for my bench projects, just looked at all the old posts on the 280 ,there seem to be an awefull lot of bad ones on ebay as they show no voltage readings or low volts on the variable channels.

That is the problem with mine, after doing a full recap on the two variable channels , still have voltage issues low to no volts .

I dont have much experience troubleshooting just a basic electronics background and need help troubleshooting this supply please!
Many thanks in advance

Dave.

Siggi
 

Hey Dave,

Do you have the service manual already (
http://w140.com/tek_ps280_ps283_service.pdf)? If so, the first thing to
check is power supply voltages. I see the "AC INPUT, TRANSFORMER & FUSE
BOARD" on page 93, schematic <1>. In your shoes, I'd check all the AC
voltages from the transformer and validate that all the fuses are good as a
start.

Assuming those are good, you can move on to page 94, schematic <2>. This is
the part of the circuitry that's responsible for generating the voltage
rails for the control circuitry, and for selecting the appropriate AC
voltage tap for the expected output voltage.
Check easy things to start, like is there a reasonable DC voltage after
each diode bridge, are the +24V, -24V, +15V and -15V DC voltages correct.

Note that you have two independent channels, so you have to be careful to
measure the voltages against their respective ground/zero points.

I find it helpful to go about this in an organized manner, by e.g. printing
the schematic and annotating the printout with the readings.

Siggi

On Fri, Aug 16, 2019 at 7:34 AM daven9ooq via Groups.Io <daven9ooq=
yahoo.com@groups.io> wrote:

Hi everyone I recently purchased a Tektronix PS280 power supply for my
bench projects, just looked at all the old posts on the 280 ,there seem to
be an awefull lot of bad ones on ebay as they show no voltage readings or
low volts on the variable channels.

That is the problem with mine, after doing a full recap on the two
variable channels , still have voltage issues low to no volts .

I dont have much experience troubleshooting just a basic electronics
background and need help troubleshooting this supply please!
Many thanks in advance

Dave.



Dave Seiter
 

Hi Dave,
I looked at the manual the other day- wow, it's definitely not a real Tek product!  Assuming the displays are working correctly, I would work my way from the transformer secondary, looking at the voltages, and from the front panel backwards looking for voltage change from the controls.  I think you said that the schematics didn't match the PCB, and that makes it much harder.
Good luck!
-Dave

On Friday, August 16, 2019, 04:34:44 AM PDT, daven9ooq via Groups.Io <daven9ooq=yahoo.com@groups.io> wrote:

Hi everyone I recently purchased a Tektronix PS280 power supply for my bench projects, just looked at all the old posts on the 280 ,there seem to be an awefull lot of bad ones on ebay  as they show no voltage readings or low volts on the variable channels.

That is the problem with mine, after doing a full recap on the two variable channels , still have  voltage issues low to no volts .

I dont have much experience troubleshooting just a basic electronics background and need help troubleshooting this supply please!
Many thanks in advance

Dave.

daven9ooq
 

Hi Dave, Many thanks! For your comments, I did make some headway today ,haven't found any bad components yet but did get some smooth voltage adjustment from the Master side, No the metering is not working correctly! Could be my fault got some connectors mixed up for the metering shouldn't be too hard to figure out. 
The metering does light up and appears to work but not reading correctly, I dlo have extra chips if needed.I took my measurements right from the Master output terminals ,in place of relying on the internal meters, seems like at first I has full range to 31volts but when I checked again it was only half of that, not sure whats going on , when you adjust voltage the relays are clicking like a pinball machine!
Hope I dont have a bad relay could be hard to replace, actually the relays and the transformer are the only difficult components to replace everything else is commom easy to get stuff.
Earlier I took a look at tekscopes for other threads on the PS280 there were some, I would really like to hear what users think about the relibality and Quality of it , I see no one learned their lesson on using counter sunk screws in cheap plastic!
How about using a counter bore, And pan head screws!
I'm working one handed due to a couple strokes, doing well considering but work is slow!
On the plus side there is a Theroy of design in the manual I got from Tekwiki , Many Thanks to whoever did that nice work!
Unfortunately the manual is the wrong revision for the one I have.  Seems there was 3 versions or revisions mine seems to be the latest and has the heatsink inside  and one main board with a zillion connectors.
The schematic is usefull in a general way just the connections are wrong fot the revisions, I looked for a different manual but wasn't able to come up with anything usefull. If anyone has one Please post it!
I'll do my best to keep you posted on my progress or lack of it.
There are a ton of these on ebay most bad which makes me think there is a design flaw ? Any comments welcome!
The PS 280 is branded with the Tek Name but wasn't built or designed by Tek , It was aftet sold out to Danaher I think and built and designed by Goodwill a Taiwaneese company Wich explains the Asian capacitors and transistors in it.
Best regards to all.
Daven9ooq

Larry McDavid
 

I have two Tektronix PS280 power supplies; both work well. The fan is a bit noisy...

I have an Operator Manual 070-8355-00 and a User Manual 070-8355-02 in paper print format. I also have a PS280-PS283 Service Reference 070-8356-00 with schematics in pdf format.

I have a friend who has modified a unit to add a thermal switch to the fan so that it runs only if necessary.

Will these manuals help anyone?

Larry

On 8/16/2019 4:48 PM, daven9ooq via Groups.Io wrote:
Hi Dave, Many thanks! For your comments, I did make some headway today ,haven't found any bad components yet but did get some smooth voltage adjustment from the Master side, No the metering is not working correctly! Could be my fault got some connectors mixed up for the metering shouldn't be too hard to figure out.
The metering does light up and appears to work but not reading correctly, I dlo have extra chips if needed.I took my measurements right from the Master output terminals ,in place of relying on the internal meters, seems like at first I has full range to 31volts but when I checked again it was only half of that, not sure whats going on , when you adjust voltage the relays are clicking like a pinball machine!
Hope I dont have a bad relay could be hard to replace, actually the relays and the transformer are the only difficult components to replace everything else is commom easy to get stuff.
Earlier I took a look at tekscopes for other threads on the PS280 there were some, I would really like to hear what users think about the relibality and Quality of it , I see no one learned their lesson on using counter sunk screws in cheap plastic!
How about using a counter bore, And pan head screws!
I'm working one handed due to a couple strokes, doing well considering but work is slow!
On the plus side there is a Theroy of design in the manual I got from Tekwiki , Many Thanks to whoever did that nice work!
Unfortunately the manual is the wrong revision for the one I have.  Seems there was 3 versions or revisions mine seems to be the latest and has the heatsink inside  and one main board with a zillion connectors.
The schematic is usefull in a general way just the connections are wrong fot the revisions, I looked for a different manual but wasn't able to come up with anything usefull. If anyone has one Please post it!
I'll do my best to keep you posted on my progress or lack of it.
There are a ton of these on ebay most bad which makes me think there is a design flaw ? Any comments welcome!
The PS 280 is branded with the Tek Name but wasn't built or designed by Tek , It was aftet sold out to Danaher I think and built and designed by Goodwill a Taiwaneese company Wich explains the Asian capacitors and transistors in it.
Best regards to all.
Daven9ooq
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)

Dave Seiter
 

My main bench supply is an old single output 0-80V Kikusui that has always had an issue with it's fan controller (once it comes on in an overload situation it never turns off).  A few days ago the top segments of the LED display decided to go out and I wondered if maybe I should replace it with something from Tek.  I was surprised to see all the PS280s on ebay, especially since so many seem to have problems.  The Kikusui LEDs were all working this morning, so it's probably just getting cranky with age.
-Dave

On Friday, August 16, 2019, 04:49:05 PM PDT, daven9ooq via Groups.Io <daven9ooq=yahoo.com@groups.io> wrote:

Hi Dave, Many thanks! For your comments, I did make some headway today ,haven't found any bad components yet but did get some smooth voltage adjustment from the Master side, No the metering is not working correctly! Could be my fault got some connectors mixed up for the metering shouldn't be too hard to figure out. 
The metering does light up and appears to work but not reading correctly, I dlo have extra chips if needed.I took my measurements right from the Master output terminals ,in place of relying on the internal meters, seems like at first I has full range to 31volts but when I checked again it was only half of that, not sure whats going on , when you adjust voltage the relays are clicking like a pinball machine!
Hope I dont have a bad relay could be hard to replace, actually the relays and the transformer are the only difficult components to replace everything else is commom easy to get stuff.
Earlier I took a look at tekscopes for other threads on the PS280 there were some, I would really like to hear what users think about the relibality and Quality of it , I see no one learned their lesson on using counter sunk screws in cheap plastic!
How about using a counter bore, And pan head screws!
I'm working one handed due to a couple strokes, doing well considering but work is slow!
On the plus side there is a Theroy of design in the manual I got from Tekwiki , Many Thanks to whoever did that nice work!
Unfortunately the manual is the wrong revision for the one I have.  Seems there was 3 versions or revisions mine seems to be the latest and has the heatsink inside  and one main board with a zillion connectors.
The schematic is usefull in a general way just the connections are wrong fot the revisions, I looked for a different manual but wasn't able to come up with anything usefull. If anyone has one Please post it!
I'll do my best to keep you posted on my progress or lack of it.
There are a ton of these on ebay most bad which makes me think there is a design flaw ? Any comments welcome!
The PS 280 is branded with the Tek Name but wasn't built or designed by Tek , It was aftet sold out to Danaher I think and built and designed by Goodwill a Taiwaneese company Wich explains the Asian capacitors and transistors in it.
Best regards to all.
Daven9ooq

Harvey White
 

On 8/16/2019 7:48 PM, daven9ooq via Groups.Io wrote:
Hi Dave, Many thanks! For your comments, I did make some headway today ,haven't found any bad components yet but did get some smooth voltage adjustment from the Master side, No the metering is not working correctly! Could be my fault got some connectors mixed up for the metering shouldn't be too hard to figure out.
I have a CPS250 (5v 2A, dual 0-20 500ma) that arrived broken (bought it knowing it didn't work, but didn't pay much).


The metering does light up and appears to work but not reading correctly, I dlo have extra chips if needed.I took my measurements right from the Master output terminals ,in place of relying on the internal meters, seems like at first I has full range to 31volts but when I checked again it was only half of that, not sure whats going on , when you adjust voltage the relays are clicking like a pinball machine!
IIRC, the design clicks in different voltage taps on the transformer to minimize dissipation in the power transistors.
Hope I dont have a bad relay could be hard to replace, actually the relays and the transformer are the only difficult components to replace everything else is commom easy to get stuff.
Earlier I took a look at tekscopes for other threads on the PS280 there were some, I would really like to hear what users think about the relibality and Quality of it , I see no one learned their lesson on using counter sunk screws in cheap plastic!
How about using a counter bore, And pan head screws!
Asian stuff is frequently made for an entirely different market. This is experimenter quality with a $$$$ label on it.  IIRC, I had to replace some of the rectifiers in the bridges, not sure if I put a whole bridge in or just good diodes.  May have had to replace a pass transistor, not sure about the main filter caps.

Design is fairly straight forward, a standard series pass regulator, so pretty much the voltage at the base of the pass transistor is about 0.6 volts more than the output.  The current limiting puts a sense resistor across the BE junction of a transistor, so more than 0.6 volts there turns on the transistor and lowers the output voltage regardless of settings.  Mine has analog meters, one voltage, one current.  Supplies can be series, parallel, or independent.

It's been pretty reliable, and not all that badly designed.  I have another chinese made design that uses a similar relay switching scheme, but at a higher voltage and current rating.  It has held up well.

Harvey

I'm working one handed due to a couple strokes, doing well considering but work is slow!
On the plus side there is a Theroy of design in the manual I got from Tekwiki , Many Thanks to whoever did that nice work!
Unfortunately the manual is the wrong revision for the one I have.  Seems there was 3 versions or revisions mine seems to be the latest and has the heatsink inside  and one main board with a zillion connectors.
The schematic is usefull in a general way just the connections are wrong fot the revisions, I looked for a different manual but wasn't able to come up with anything usefull. If anyone has one Please post it!
I'll do my best to keep you posted on my progress or lack of it.
There are a ton of these on ebay most bad which makes me think there is a design flaw ? Any comments welcome!
The PS 280 is branded with the Tek Name but wasn't built or designed by Tek , It was aftet sold out to Danaher I think and built and designed by Goodwill a Taiwaneese company Wich explains the Asian capacitors and transistors in it.
Best regards to all.
Daven9ooq



Chuck Harris
 

I have fixed many of this design power supply. They are
typically badge engineered by name brand companies, but are
made in China by GoodWill company.

They are made up of three basic boards, one is a current meter,
one is a voltage meter, and the third is the actual regulator
control.

The regulator uses a tapped secondary transformer to get the
unregulated voltage to be very close to the regulated voltage
so that the linear regulator won't dissipate too much power.

The biggest failure I have found is the meter assemblies have
their own bridge rectifier, and filter cap power supply, and
the capacitors they use are pure Chinese S-Crap. They go open
circuit, flood the meter with ripple, and it either blanks out,
or goes on a wild counting spree. Usually, the ripple upsets
the meter IC into blowing the fuse, and the screen is blank.

The fix is to replace the capacitors with something good, and
replace the wired in fuse.

Sometimes, the problem will be a blown track on the control
circuit board, due to one of the relays that switches the
transformer taps being both on and off at the same time... This
is caused by the contact mounting block melting and letting
one of the contacts come down and touch both the armature and
the other contact. Replace the relay with a good OMRON and
you will be back in business.

-Chuck Harris

Harvey White wrote:


On 8/16/2019 7:48 PM, daven9ooq via Groups.Io wrote:
Hi Dave, Many thanks! For your comments, I did make some headway today ,haven't
found any bad components yet but did get some smooth voltage adjustment from the
Master side, No the metering is not working correctly! Could be my fault got some
connectors mixed up for the metering shouldn't be too hard to figure out.
I have a CPS250 (5v 2A, dual 0-20 500ma) that arrived broken (bought it knowing it
didn't work, but didn't pay much).


The metering does light up and appears to work but not reading correctly, I dlo
have extra chips if needed.I took my measurements right from the Master output
terminals ,in place of relying on the internal meters, seems like at first I has
full range to 31volts but when I checked again it was only half of that, not sure
whats going on , when you adjust voltage the relays are clicking like a pinball
machine!
IIRC, the design clicks in different voltage taps on the transformer to minimize
dissipation in the power transistors.
Hope I dont have a bad relay could be hard to replace, actually the relays and the
transformer are the only difficult components to replace everything else is commom
easy to get stuff.
Earlier I took a look at tekscopes for other threads on the PS280 there were some,
I would really like to hear what users think about the relibality and Quality of it
, I see no one learned their lesson on using counter sunk screws in cheap plastic!
How about using a counter bore, And pan head screws!
Asian stuff is frequently made for an entirely different market. This is experimenter
quality with a $$$$ label on it. IIRC, I had to replace some of the rectifiers in
the bridges, not sure if I put a whole bridge in or just good diodes. May have had
to replace a pass transistor, not sure about the main filter caps.

Design is fairly straight forward, a standard series pass regulator, so pretty much
the voltage at the base of the pass transistor is about 0.6 volts more than the
output. The current limiting puts a sense resistor across the BE junction of a
transistor, so more than 0.6 volts there turns on the transistor and lowers the
output voltage regardless of settings. Mine has analog meters, one voltage, one
current. Supplies can be series, parallel, or independent.

It's been pretty reliable, and not all that badly designed. I have another chinese
made design that uses a similar relay switching scheme, but at a higher voltage and
current rating. It has held up well.

Harvey

I'm working one handed due to a couple strokes, doing well considering but work is
slow!
On the plus side there is a Theroy of design in the manual I got from Tekwiki ,
Many Thanks to whoever did that nice work!
Unfortunately the manual is the wrong revision for the one I have. Seems there was
3 versions or revisions mine seems to be the latest and has the heatsink inside
and one main board with a zillion connectors.
The schematic is usefull in a general way just the connections are wrong fot the
revisions, I looked for a different manual but wasn't able to come up with anything
usefull. If anyone has one Please post it!
I'll do my best to keep you posted on my progress or lack of it.
There are a ton of these on ebay most bad which makes me think there is a design
flaw ? Any comments welcome!
The PS 280 is branded with the Tek Name but wasn't built or designed by Tek , It
was aftet sold out to Danaher I think and built and designed by Goodwill a
Taiwaneese company Wich explains the Asian capacitors and transistors in it.
Best regards to all.
Daven9ooq






daven9ooq
 

Many Thanks to all who have replied, My wife is off work for the next 3days ,so I probably won't be able to get much more done until then  From the sound of it seems like it's worth fixing  ,I did recap both variable supplies the 5volt fixed supply Was working so left it alone.
I used good quality Nichicon throughout ,off hand I forgot the series, using a  ebay cheap transistor \ component tester I found the esr of the smaller electrolytics  worse than the larger ones around 1ohm on the 4.7 uf 50 volt , and about the same for the 47uf ,the 470's didn't look that grate either didn't check the main filter as too big for the zif socket on my tester.
Since I'm working one handed and it was pretty difficult to get the board out  so I replaced everything , Don't want to do it again 6months down the line, also want something I can depend on.
 I have plenty of 50-60 + year old Tek equipment with Sprague electrolytics that still work , That said + the tons of  bad PS280's on ebay don't speak well of the Tiawan capacitors I did take the time to look up the company Jamicon.
My wife is Asisn ,so I have nothing against Asian except cheep coppies of good stuff. That said there has long been a need in this contry for good affordable test equipment.
So I can and do appreciate the need to keep a tight budget on stuff, the overall quality of the PS280 isn't bad  but I have a Astron VS50M  a 37 Amp 50 surge it is slightly adjustable .it uses a LM723 regulator and 8-2N3771 RCA pass transistors it has current limiting and most Hams in the Group can speak to thequality of it,  when you have a 4thousand dollar radio hooked up to it you need a good quality supply!
It seems to me the multi tap relay switching is  helpfull but maybe  unnecessary as one single heatsinked 2N3055 is good up to15 amps!I don't know enough about the heat dissapation to say for sure.
Also the constant voltage/ current switching is only a gimick as it a function of settings not selectable by user togeather they over complicate what should be a straightforward supply! And could save money. 
But that is just my thinking, I could be wrong!
Thanks guys for the insights!
At this point I think everything is basically working but there are a lot of adjustments to do and you need a slew of load resistors to do. Some I have some I have on order, others I need to find and order.
Thanks again!Dave n9ooq

Harvey White
 

Power supply design is a series of tradeoffs.  It may be that size and cost (for a heatsink, let alone other things) suggested using a common design with a tapped transformer.

About the worst case for a linear supply is a very low output voltage at the maximum current.  The pass transistor is getting rid of the difference as heat.  This design would certainly fix that.

A switching regulator would work reasonably well, but has more noise, more complexity and the like.  If you were going to do a massive enough power supply, it might be better to have a switching pre-regulator, then a linear regulator to make the output behave.  I may have seen a design like this with an SCR bridge feeding a linear regulator.

Harvey

On 8/17/2019 2:48 PM, daven9ooq via Groups.Io wrote:
Many Thanks to all who have replied, My wife is off work for the next 3days ,so I probably won't be able to get much more done until then  From the sound of it seems like it's worth fixing  ,I did recap both variable supplies the 5volt fixed supply Was working so left it alone.
I used good quality Nichicon throughout ,off hand I forgot the series, using a  ebay cheap transistor \ component tester I found the esr of the smaller electrolytics  worse than the larger ones around 1ohm on the 4.7 uf 50 volt , and about the same for the 47uf ,the 470's didn't look that grate either didn't check the main filter as too big for the zif socket on my tester.
Since I'm working one handed and it was pretty difficult to get the board out  so I replaced everything , Don't want to do it again 6months down the line, also want something I can depend on.
 I have plenty of 50-60 + year old Tek equipment with Sprague electrolytics that still work , That said + the tons of  bad PS280's on ebay don't speak well of the Tiawan capacitors I did take the time to look up the company Jamicon.
My wife is Asisn ,so I have nothing against Asian except cheep coppies of good stuff. That said there has long been a need in this contry for good affordable test equipment.
So I can and do appreciate the need to keep a tight budget on stuff, the overall quality of the PS280 isn't bad  but I have a Astron VS50M  a 37 Amp 50 surge it is slightly adjustable .it uses a LM723 regulator and 8-2N3771 RCA pass transistors it has current limiting and most Hams in the Group can speak to thequality of it,  when you have a 4thousand dollar radio hooked up to it you need a good quality supply!
It seems to me the multi tap relay switching is  helpfull but maybe  unnecessary as one single heatsinked 2N3055 is good up to15 amps!I don't know enough about the heat dissapation to say for sure.
Also the constant voltage/ current switching is only a gimick as it a function of settings not selectable by user togeather they over complicate what should be a straightforward supply! And could save money.
But that is just my thinking, I could be wrong!
Thanks guys for the insights!
At this point I think everything is basically working but there are a lot of adjustments to do and you need a slew of load resistors to do. Some I have some I have on order, others I need to find and order.
Thanks again!Dave n9ooq



John Crighton
 

Hello Daven9ooq,

I will chuck in my 2 cents worth to help you.

One of the previous posters suggested that you print out the schematics. I am going to adopt a Judge Judy attitude here.
Have you printed out enlarged copies of the circuit diagrams? That is a YES or a NO

Another poster suggested that you start at the transformer and work your way forward.
Have you tested the transformer? That is a YES or a NO

Have you checked the bridge rectifiers as the other poster suggested? YES or NO

The previous helper asked you to make notes on your printed out circuit diagram and component layout drawings?
Have you done as he suggested?

We know your power supply is slightly different from the diagrams. This is the beginning of the "Fun Part." for us hobbyists.
Find a big piece of paper and start drawing the main parts of the circuit as you find it.
Turn this repair job into a learning excercise. Make it fun.

Start with the transformer.
Load test it with say a 2 amp load.
Note the open circuit volatge and loaded voltage as Dave suggested. Write your results down on your big hand drawn diagram.
Load test the ouput of the rectifier stage. (cut the track or wire to the filter capacitor)
Check for a nice fullwave rectifier display on oscilloscope. No Load and full 2 amp Load. This will show up any cracked tracks or
dodgy wiring connctions.
Reconnect the filter Capacitor to the bridge rectifier. Put your 2 amp load resistor across your filter capacitor.
Check the ripple, No Load and Full Load. Record your results as Dave or the other poster suggested.

I want you to tell me that you have tested the transformer, the rectifiers, the filter capacitors and it is all good because you have
test results to prove it. That to me would be a good concrete start on this fun filled interesting repair job.

Regards,
John Crighton
Sydney

----- Original Message -----
From: "daven9ooq via Groups.Io" <daven9ooq=yahoo.com@groups.io>
To: <TekScopes@groups.io>
Sent: Saturday, August 17, 2019 9:48 AM
Subject: Re: [TekScopes] Need Help Troubleshooting Tektronix PS280


Hi Dave, Many thanks! For your comments, I did make some headway today ,haven't found any bad components yet but did get some smooth voltage adjustment from the Master side, No the metering is not working correctly! Could be my fault got some connectors mixed up for the metering shouldn't be too hard to figure out.
The metering does light up and appears to work but not reading correctly, I dlo have extra chips if needed.I took my measurements right from the Master output terminals ,in place of relying on the internal meters, seems like at first I has full range to 31volts but when I checked again it was only half of that, not sure whats going on , when you adjust voltage the relays are clicking like a pinball machine!
Hope I dont have a bad relay could be hard to replace, actually the relays and the transformer are the only difficult components to replace everything else is commom easy to get stuff.
Earlier I took a look at tekscopes for other threads on the PS280 there were some, I would really like to hear what users think about the relibality and Quality of it , I see no one learned their lesson on using counter sunk screws in cheap plastic!
How about using a counter bore, And pan head screws!
I'm working one handed due to a couple strokes, doing well considering but work is slow!
On the plus side there is a Theroy of design in the manual I got from Tekwiki , Many Thanks to whoever did that nice work!
Unfortunately the manual is the wrong revision for the one I have. Seems there was 3 versions or revisions mine seems to be the latest and has the heatsink inside and one main board with a zillion connectors.
The schematic is usefull in a general way just the connections are wrong fot the revisions, I looked for a different manual but wasn't able to come up with anything usefull. If anyone has one Please post it!
I'll do my best to keep you posted on my progress or lack of it.
There are a ton of these on ebay most bad which makes me think there is a design flaw ? Any comments welcome!
The PS 280 is branded with the Tek Name but wasn't built or designed by Tek , It was aftet sold out to Danaher I think and built and designed by Goodwill a Taiwaneese company Wich explains the Asian capacitors and transistors in it.
Best regards to all.
Daven9ooq




---
This email has been checked for viruses by AVG.
https://www.avg.com

Lawrance A. Schneider
 

Hello,

On Aug 16, 2019, at 9:27 PM, John Crighton <john.crighton@...> wrote:

One of the previous posters suggested that you print out the schematics. I am going to adopt a Judge Judy attitude here.
Have you printed out enlarged copies of the circuit diagrams? That is a YES or a NO

Another poster suggested that you start at the transformer and work your way forward.
Have you tested the transformer? That is a YES or a NO

Have you checked the bridge rectifiers as the other poster suggested? YES or NO

The previous helper asked you to make notes on your printed out circuit diagram and component layout drawings?
Have you done as he suggested?

We know your power supply is slightly different from the diagrams. This is the beginning of the "Fun Part." for us hobbyists.
Find a big piece of paper and start drawing the main parts of the circuit as you find it.
Turn this repair job into a learning excercise. Make it fun.
I’ve ben doing this for three days. on my E3630A HP power supply. Still no luck. I don’ have the schematic for the daughter board meter section of the supply. Further, there are NO TEST POINTS! But, I’ll continue working.

larry

Steve Lindberg
 

These puppies were OEMed by Tek. The one I got had banana plugs broken loose from PCB.

Steve Lindberg


Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10

Lawrance A. Schneider
 

Hi,

Do you know the model number for the Tea version? I would expect a more thorough schematic from them.

Thank you, larry

On Aug 20, 2019, at 11:01 AM, Steve Lindberg <steve_tech@...> wrote:


These puppies were OEMed by Tek. The one I got had banana plugs broken loose from PCB.

Steve Lindberg


Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10



daven9ooq
 

Sent from Mail for Windows 10

Hi the schematic from the TekWiki shows reference to PS28—512-1 my main board showsGPC-848A-1 B the schematic is component wise fairly accurate but all the jumpers and connections are completely different. Some versions had a separate fuse board my main board consists of the 2 variable supplys with filters bleeders rectifiers and 4relays and fuses.
Nothing is blown all traces intact.

Voltage readings on the main reference 7815 are pin 1-29.7vdc. 2-14.98vdc 3 40.5 vdc this is weird as pin 2 is supposed to be ground even says so on the schematic, but appears to be output pin 3 should be out , but it works! Slave side is similar like a symmetrical reverse image , and looks to be independent but in fact some adjustments do have a relationship with the other side.
The last stage before the series pass transistor is labeled dynamic load control.

The first 741 op amp readings are pin 1 .0043vdc, 2-14.98v 3-14.98 4 gnd 5.044 6-5.483v. 7- 29.72v 8.NC
That is as far as I got so far.

Many thanks Dave

daven9ooq
 

I would stick with what you have, maybe it's time to do a little service on it, sometimes you need a dual supply or even 3voltages it's rare though.
I should have done more resurch on this before I bought it. But it's the same  era as my TM500 equipment so it should fit right in. Around 1981.Many thanks !Daven9ooq

daven9ooq
 

Thanks for the comment I Think we established the PS280 was not made by Tektronix although it carries their  name, and was out sourced toGoodwill industries.
I really could use some help troubleshooting this supply  I did a full recap on the 2 -0-30volt supplies, they do go down to 0 volts and in fact will go negative if you adjust it so, At present I am getting about 15 volts max. on the main side and little to nothing on the slave side, waiting for load resistors to come, maybe about a week more,  There is a Theroy of operation in the manual one Tekwiki although the manual is for a different  version, all versions seem to use the same circuitry , just different construction and appearance.
I'm quite busy at the moment and in the near future, I really could use to get this off my bench quick but could use help with Ideas on what to check and how to proceed.
Many thanks in advance!
Daven9ooq.

daven9ooq
 

Hi Steve , Can you tell me more, were the banana plugs over tightened? , or its it a manufacturer defect, have you repaired it ,if so how, please tell us more! 
Many ThanksDaven9ooq

daven9ooq
 

Hi John, Yes Thanks this is the kind of help I need , Yes did check the secondaries voltage wise but not under load,   I'm rather busy lately and I have to confess I have not done the math to calculate the resistance I need for a 2amp load. I dought I have the resistors in the wattage I need,  I do have a 2ohm 100 watt resistor handy. I have a bunch of others on order from china expect them in about a week. 
I'm expecting my stepson   to immigrate to the U.S. From the Philippines Thursday the 28th . so lots to prepare and hard to predict how much time I will have in the future.  Hopefully next week I will have more time  but working one handed due to strokes , so it will have to be spread out over days if not weeks!
But yes this is the correct methods  for troubleshooting taking nothing for granted.
 Yes I did print out the schematic but did not page them togeather as I should have.
I do see the +and - 15volts comming of the references on both sides , there are 4 fullwave bridge rectifiers I have checked both variable sides I recapped all filters , Im forced to kind of short cut  testing everything, due to time constraints and lack of a variable load.
I do very much appreciate your methods though and will go back ,when time permits  and report the results so others can learn  from this , This is what this group is for. 
Many Thanks John!Daven9ooq

daven9ooq
 

Hi, John, Wow you really want to make me work hard , but I understand your logic, Which is the proper procedures to troubleshoot any piece of equipment. 
This should help any one of us who are new or less experienced.
To try to answer some of your questions Yes I did print out the schematic  and I even printed out datasheets for all the opamps, but no I did not enlarge it, I have a magnifying lamp ,I dont have any way to print anything larger than 8.5x11 .
Yes I did check the transformer, that is to say I  measured ac voltage at the secondary for the 2 variable supplys,  to be honest I did not write it down on the schematic, and I dont recall what it was exactly, For the sake of thouralness I will go back and do this over, but if you read my earlier posts , what is the point of doing steps 1-5 if I measure + and - 15volts at both references? 
This is a multi tap transformer with no less than 10 secondaries, all terminated with connectors , I'm using pieces of stiff wire or paperclips to get into the connectors and jumpers to my probes, and there are 7 full wave bridge rectifiers 
I did look at the waveform of the two variable supplies ,they both looked good,  I did not check the ripple as I just finished a full recap!
Back to the transformer, the first thing I do when opening up a piece of equipment is do a very thoural visual inspection of each component using all senses, sight sound and smell in doing this I did not find anything unusual , I noted everything look quite clean  there was very little dust which suggests light usage.
The Serial #is TW50125 which I gather is an early ,late version , going by appearance and the photos on the TekWiki site  round push button and internal heatsink, I conclude a early late revision and one piece main board, as opposed to the schematic on Tekwiki that has a seperate fuse board.
 John I am prepared to proceed With Troubleshooting in this manner if your willing to see me through untill I get it working, If  I can streach it out at my own pace, and with the understanding that 1 I am handicapped ,working one handed  from a stroke and my short term memory took a hit with a burst anurism, so as to say I work slow and my short-term memory is falty. I haveCML Leukemia but after 8years of Gleevec a truly miracle drug, I'm happy to report my Leukemia has disappeared , undetectable , maybe just to small to detect or just hiding , but at least for the last 3 or 4years undetectable!
I am able to walk and drive , pretty much independent. So doing exceptionally well considering what I been through, I owe it to my hobby in electronics and amateur radio and my Wife Esther a Filipina I meet and married after my first stroke due to an elergic reaction to Cartizem a family of blood pressure medication, just one pill one time nearly killed me! N9OOQ is my call sign.
I usually dont  work on my hobby when Esther is off work, she will be off the next 8days due to my stepson immigrating to the U.S. From the Philippines, so we have a lot of activity planned for him , Mark is 35 ,Esther hasn't seen him in the Flesh for nearly 20 years,
So I will be busy for about the next week or so, I will be reading the mail though, and may even get some brief time troubleshooting, I was trying to get done before Marks home comming!
I have the Job of Chauffeuring everyone around and teaching Mark 35 to drive, so yeah I up for Challenges!Should make a good learning experience for most!
Thanks John and everyone for your understanding and patients!
Best Regards to all!73's Daven9ooq