TekWiki says 2200uF in parallel with 200 to 270 Ohms/10W.

I've got two questions:

1. Why the (lowish value) parallel resistor?

2. Why 10W? Under normal operating conditions it will have about 12V across it so just over 1/2W for a 270R

Dave

It’s easy to rebuild the battery pack. The cells are C-size. It can be handy if you get stuck in the field without AC power available.

I also built up a double banana plug on a handle to plug into the battery contacts to connect to a bench power supply when servicing 1502 & 1503 TDRs. Also built up an extender cable for the chart recorder to be able to service it outside the unit as well.

As for no power up when the proper battery present condition is met, I will frequently find a unit with those little dipped tantalums in a shorted condition inside.

Using the optional 013-0169-00 balanced output isolation transformer for this unit will allow you to connect directly to a metallic telephone circuit and take TDR measurements with a DC voltage present on it. On occasion I have been able to pinpoint the location to a confused telco tech where a bridge tap is located on a DSL phone line miles between the central office and the subscriber demarcation point. DSL needs a clean straight line from the central office with no additional branch connections in order to work correctly with no errors.

With the ability to look out to 50,000 feet away from the test site, this unit can be quite handy.

Greg

Pessimists NEVER have unpleasant surprises!  A motto I live by! JK

I have the switch set to front. The manual regarding this is super
confusing.

Thanks,
Michael

On Tue, Nov 12, 2019 at 8:06 PM Don Bitters via Groups.Io <donbitters=
yahoo.com@groups.io> wrote:

Gentlemen, a quick question - how are the outputs strapped (usually on the
back of the PS)? Local sense is on the back of the unit, remote sense is at
the end of the power cabling - it must be one or the other. This can give
the symptoms you have if it is not strapped for local sense.
Don Bitters

Oh crap, now it looks like its working. I am definitely gonna run through
the calibration and see what happens. I wonder if my 34401A has issues,
like the ammeter is grounding the positive and its tripping over currrent.
I just tried it right now with just the receiver as the load, and it is
drawing 600 ma, and the voltage is rock solid. I put the unit in parallel
mode to try and transmit, set the OCP to 5 amps, transmitted, and it drew
just under 4 amps and the voltage was pretty much rock solid, dropping just
about 100 millii volts. Arggggg, now confusion sets in.

On Tue, Nov 12, 2019 at 7:08 PM Michael Yellin via Groups.Io <michaelhq54=
gmail.com@groups.io> wrote:

Siggi,

That is what is confusing to me. The fact that every output has the
problem, yet the DACs are individual to each output. I guess its possible
all three went out, but unlikely I think. Perhaps there is an issue with
the serial communications.

As a load, I have a receiver, which draws 500ma in receive. I also use my
34401A multimeter. I have set the current limit to various numbers, high,
low, mid range, nothing changes. The readings on the PS appear to be
accurate when measured by my multimeter. Even when loading the PS well
below the setting, the voltage still drops.

I traced the schematic back from the individual DACs, and they come
together on the command board. It looks like "upstream" of all 3 DACs is
U301, 302, 306, 309, 310, 305 and 308. 309 and 310 are ram chips. 301 is
an octal D flip/flop (No idea what that is) 306 is an OCTAL D-TYPE
TRANSPARENT LATCHES AND EDGE-TRIGGERED FLIP-FLOPS (Again no idea what that
is) 302 is a Dual 2-line to 4-line Decoder/Demultiplexer (Yeap, you
guessed it, no idea), 305 is a 27C256 (I know that's an EPROM) and 308 is
an 8bit Microcontroller (I know what that is also, YAY)

Gonna grab the control board out of the unit, and see if I see anything
physically wrong with it. Unfortunately, I don't think I know how to
figure out if the parts are working. :( I'll start prixing out the parts,
I doubt they will be too expensive. But, I have a feeling I will need
firmware images for 305 and 308, which might be difficult to find.

Thoughts

Thanks,
Michael

On Tue, Nov 12, 2019 at 5:37 PM Siggi <siggi@undo.com> wrote:

Hey Michael,

I can’t think of anything common to all three channels other than the
digital logic. What are you using for load? What’s the current limit you
set? Are the current and voltage read back displays accurate?
What happens if you set the current limit at max, and then load the

supply

below max current?

The design of the digital control and read back is pretty old school.
There’s a single DAC per channel, and a serial communication protocol to
it. There’s MUXing downstream from the DAC. Read back is by successive
approximation, by comparing the DACs output against measured current or
voltage.
I assume there’s also dedicated read back of CC/CV/OVP, though I haven’t
studied the schematic in that regard.

Siggi

On Tue, Nov 12, 2019 at 18:28 Michael Yellin <michaelhq54@gmail.com>
wrote:

Siggi,

Thanks for the response, and the link. Yes, the CC lights when the

load

is

connected. However, I believe I have properly set the current limits.
From memory, I choose the output I want to adjust, then choose volt

set,

and input the voltage I desire and enter. Then press current set,

enter

the current I want, and enter. Then enable the outputs. I also would
assume user error, its my go to most of the time. But in this case, I
actually RTFM.

Thanks,
Michael

On Tue, Nov 12, 2019 at 2:12 PM Siggi <siggi@undo.com> wrote:

Hey Michael,

the schematics for the PS2520G/PS2521G recently surfaced. See
http://bama.edebris.com/manuals/tek/ps2520g/.
When your outputs collapse, do you see the CV/CC indicators change? I
wonder if this is - ehem - operator error and you're in fact tripping

over

the previous owner's (inherited) low, low current limit.
I have one of those supplies and I can say that the user interface on

these

power supplies is ... hard to love.

Siggi

On Tue, Nov 12, 2019 at 4:58 PM Michael Yellin <

michaelhq54@gmail.com>

wrote:

Hello,

Recently acquired a Tek 2521G, which appears to be in great shape.
Inspected the inside, and nothing jumps off and the caps looks

fine.

However, whenever a load is placed on any of the outputs, the

voltage

drops. With no load, the voltage is accurate as set, and when a

load

is

placed, the amperage is dead on for the setting. But, as

mentioned,

as

soon as a load is placed on any of the outputs, the voltage for

that

output

drops significantly. I have run through the calibration, with out

fixing

the unit. I plan to do the complete calibration shortly (all

outputs

in

order), but am beginning to think it is not a calibration issue.

Can

anyone think of what might cause all the outputs to act exactly the

same.

My understanding is that the unit essentially is three separate

"boards"

so I find it strange that all three outputs are behaving the

same. I

have

some basic repair skills, and a fair compliment of test equipment.

Any

help would be greatly appreciated.

Thanks,
Michael

Gentlemen, a quick question - how are the outputs strapped (usually on the back of the PS)? Local sense is on the back of the unit, remote sense is at the end of the power cabling - it must be one or the other. This can give the symptoms you have if it is not strapped for local sense.
Don Bitters

Siggi,

That is what is confusing to me. The fact that every output has the
problem, yet the DACs are individual to each output. I guess its possible
all three went out, but unlikely I think. Perhaps there is an issue with
the serial communications.

As a load, I have a receiver, which draws 500ma in receive. I also use my
34401A multimeter. I have set the current limit to various numbers, high,
low, mid range, nothing changes. The readings on the PS appear to be
accurate when measured by my multimeter. Even when loading the PS well
below the setting, the voltage still drops.

I traced the schematic back from the individual DACs, and they come
together on the command board. It looks like "upstream" of all 3 DACs is
U301, 302, 306, 309, 310, 305 and 308. 309 and 310 are ram chips. 301 is
an octal D flip/flop (No idea what that is) 306 is an OCTAL D-TYPE
TRANSPARENT LATCHES AND EDGE-TRIGGERED FLIP-FLOPS (Again no idea what that
is) 302 is a Dual 2-line to 4-line Decoder/Demultiplexer (Yeap, you
guessed it, no idea), 305 is a 27C256 (I know that's an EPROM) and 308 is
an 8bit Microcontroller (I know what that is also, YAY)

Gonna grab the control board out of the unit, and see if I see anything
physically wrong with it. Unfortunately, I don't think I know how to
figure out if the parts are working. :( I'll start prixing out the parts,
I doubt they will be too expensive. But, I have a feeling I will need
firmware images for 305 and 308, which might be difficult to find.

Thoughts

Thanks,
Michael

On 11/12/2019 3:53 PM, Chuck Harris wrote:

Also, unless they are modified, they will NOT work if the
nicad battery is dead.
-Chuck Harris

Right. And the mod is super easy: a 2200uF 25v or higher,
across the battery banana plugs, plugged into them from
the battery compartment. Correct polarity is mandatory.
No circuit mod needed inside the 1503.

Ed

When I buy something on ebay, unless it's new, I buy it with the assumption and expectation that it don't work. Its broke. Period. That way I'm never disappointed. I look at a ham radio, and wonder how much is this broken radio worth to me? Same thing with any test equipment. Is it worth having to fix it? You'd be surprised at how many things I've bought over the years that said it didn't work and it actually did!

Vince.

--
K8ZW http://www.metalworkingfun.com http://www.hamradio.fun

Hey Michael,

I can’t think of anything common to all three channels other than the
digital logic. What are you using for load? What’s the current limit you
set? Are the current and voltage read back displays accurate?
What happens if you set the current limit at max, and then load the supply
below max current?

The design of the digital control and read back is pretty old school.
There’s a single DAC per channel, and a serial communication protocol to
it. There’s MUXing downstream from the DAC. Read back is by successive
approximation, by comparing the DACs output against measured current or
voltage.
I assume there’s also dedicated read back of CC/CV/OVP, though I haven’t
studied the schematic in that regard.

Siggi

Sorry, I meant "squegging" which means an unsteady oscillation.

Thanks to everyone who mentioned that the thing needs a filter capacitor
instead of that chemical coffin of a battery.
That explains the symptoms perfectly. Will try that ASAP.

Reminds me of an old forties GE portable radio that used a two volt wet
cell as a battery and filter capacitor.

On Tuesday, November 12, 2019, ArtekManuals <manuals@artekmanuals.com>
wrote:

George

By "squeezing" I am going to guess you mean "ticking" a common symptom of
a switching power supply going in to protection mode because there is high
current drain. Typically this is caused by shorted bypass capacitors
usually tantalums on a DC bus somewhere but shorted transistors and IC's
are usually right behind the caps as likely suspects

Dont know the history of the name, maybe because oscilloscopes was/is
Tektronix strong suit. At any rate in general anything designed and
manufactured by Tektronix has traditionally been discussed on here.

As another poster suggested go to the group web site and do a search. The
one flaw with that approach is netiquette is not the strong suit of the
group membership. Threads are often hijacked and you will find the contents
of some of the messages with 1503 in the subject line have absolutely
nothing to do with the 1503 . Other threads with info about the 1503 have
nothing in the subject line because they in turn were hijacked threads from
another topic.

If it were me I would do a search in the group archives first, if you dont
find the solution to your problem then come back here with as much detail
about what your problem looks like and I am sure we will try and help you

Cheers
and good luck

Dave
manuals@artekmanuals.com

On 11/12/2019 3:03 PM, george gonzalez wrote:

Is the Tek 1503 in this group's bailiwick? Not exactly a scope…

It seems to have “issues”. The switching power supply is squeezing more
than switching.

Thanks,

George

AG0I

--
Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com

Hey Peter,
Have you really been working on this for 8 years? That’s dedication.

I apologize, after looking at your pics I realized you are working on 576, and I have a 577. The 577 is much simpler in some regards. But the analog display information is essentially identical. However, as Dennis indicated, the looping is in all likelihood accurate. Miller effects and hysteresis along with wire loops can be the cause. Your 36” leads are going to be a nightmare at low current. Your modest current curves are the best I think you can expect.

Kevin

On Tue, Nov 12, 2019 at 12:04 PM, george gonzalez wrote:

Is the Tek 1503 in this group's bailiwick? Not exactly a scope…

Hi All:
It is, is it not? (all be it, with an internal pulse generator, and a dedicated (if you use it for what it was intended) use.
Many a traditional Tek scope has been on the end of some TDR setup. Probably, that is what initiated the design idea?
Regards to All.
Roy

Siggi,

Thanks for the response, and the link. Yes, the CC lights when the load is
connected. However, I believe I have properly set the current limits.
From memory, I choose the output I want to adjust, then choose volt set,
and input the voltage I desire and enter. Then press current set, enter
the current I want, and enter. Then enable the outputs. I also would
assume user error, its my go to most of the time. But in this case, I
actually RTFM.

Thanks,
Michael

Hi Guys:
Great!
It's great to see somebody getting some reasonably good deals from Ebay.
Whenever my ship is in port at Ebay, I always for some strange reason (maybe trauma in my childhood) hear the B-9, Class M-3 say "Danger Will Robinson. Danger!"
Or maybe it is just my wallet moaning from the beating it has taken over the years.
Either way, its safer to assume the worst.... and not hope too much for the best.
Regards and best wishes.
Roy

On 12/11/19 21:54, Harvey White wrote:

You can replace the NICD battery by a DC supply of the appropriate voltage for testing purposes, but the original design needs the battery in there for filtering purposes.

Easily achieved by using 4mm banana sockets on a flying lead, connecting to the plugs at the other end of the hole into which the battery is inserted. Make sure you get the polarity right :)

On 12/11/19 21:47, ArtekManuals wrote:

By "squeezing" I am going to guess you mean "ticking" a common symptom of a switching power supply going in to protection mode because there is high current drain. Typically this is caused by shorted bypass capacitors usually tantalums on a DC bus somewhere but shorted transistors and IC's are usually right behind the caps as likely suspects

In a 1502, have a look at C6246, C6341 on the +25V line. I've had them spew acid over the nearby tracks.

Direct replacement tants are prohibitively expensive, but modern electrolytics can be used. Be careful about the diameter; there isn't much headroom in the case.

Hey Michael,

the schematics for the PS2520G/PS2521G recently surfaced. See
http://bama.edebris.com/manuals/tek/ps2520g/.
When your outputs collapse, do you see the CV/CC indicators change? I
wonder if this is - ehem - operator error and you're in fact tripping over
the previous owner's (inherited) low, low current limit.
I have one of those supplies and I can say that the user interface on these
power supplies is ... hard to love.

Siggi

On Tue, Nov 12, 2019 at 4:58 PM Michael Yellin <michaelhq54@gmail.com>
wrote:

Hello,

Recently acquired a Tek 2521G, which appears to be in great shape.
Inspected the inside, and nothing jumps off and the caps looks fine.
However, whenever a load is placed on any of the outputs, the voltage
drops. With no load, the voltage is accurate as set, and when a load is
placed, the amperage is dead on for the setting. But, as mentioned, as
soon as a load is placed on any of the outputs, the voltage for that output
drops significantly. I have run through the calibration, with out fixing
the unit. I plan to do the complete calibration shortly (all outputs in
order), but am beginning to think it is not a calibration issue. Can
anyone think of what might cause all the outputs to act exactly the same.
My understanding is that the unit essentially is three separate "boards"
so I find it strange that all three outputs are behaving the same. I have
some basic repair skills, and a fair compliment of test equipment. Any
help would be greatly appreciated.

Thanks,
Michael

Hello,

Recently acquired a Tek 2521G, which appears to be in great shape. Inspected the inside, and nothing jumps off and the caps looks fine. However, whenever a load is placed on any of the outputs, the voltage drops. With no load, the voltage is accurate as set, and when a load is placed, the amperage is dead on for the setting. But, as mentioned, as soon as a load is placed on any of the outputs, the voltage for that output drops significantly. I have run through the calibration, with out fixing the unit. I plan to do the complete calibration shortly (all outputs in order), but am beginning to think it is not a calibration issue. Can anyone think of what might cause all the outputs to act exactly the same. My understanding is that the unit essentially is three separate "boards" so I find it strange that all three outputs are behaving the same. I have some basic repair skills, and a fair compliment of test equipment. Any help would be greatly appreciated.

Thanks,
Michael

As far as I remember there are two supplies, the LV and the HV. I know the HV has a transformer and seems to run hot (I've seen somewhat cooked boards).  The HV multiplier is made of discrete parts, and can be replace individually.  IIRC, some microwave oven diodes seem to be a good fit.

You can replace the NICD battery by a DC supply of the appropriate voltage for testing purposes, but the original design needs the battery in there for filtering purposes.

Harvey