Topics

1502 TDR project - using bench supply

Mark Pilant
 

Hi Tom.

Got around to testing the 1502 using a bench supply. As you suggested,
when hooked up, the 1502 power supply started operating as expected. All
the voltages appeared to be to spec. Although still no trace on the CRT.

I guess there may be some issues with the TekWiki suggested modification
of a 2200uf cap in parallel with a 270 10W resistor.

So now I need to figure out what to do. I'm thinking of possibly using
a 12V 2A "wall wart" supply connected to the banana plugs instead of the
nor mal AC power cord. The main problem is how to actually connect it
all up.

There is room on the rear panel for one of the ubiquitous coaxial power
connectors, but I'm a little reluctant to drill a hole for it. I could
terminate the power card in the supply in a female banana jack attached
to some sort of "paddle" to make it easier to connect / disconnect; but
it would be "a bit" ugly :-)

Any other ideas out there?

- Mark N1VQW

Tom Gardner
 

On 12/12/19 16:59, Mark Pilant wrote:
Hi Tom.

Got around to testing the 1502 using a bench supply.  As you suggested,
when hooked up, the 1502 power supply started operating as expected.
:)

Repeat after me: Tom is wise and omniscient. If you repeat it enough times, maybe/I'll /start to believe it.


All
the voltages appeared to be to spec.  Although still no trace on the CRT.
Check all the voltages/ripple.

Suspect the EHT; those components can be easily replaced since they aren't potted.

I guess there may be some issues with the TekWiki suggested modification
of a 2200uf cap in parallel with a 270 10W resistor.
If you put a storage scope on the 12V line, then you can observe the switch-on transients. That will aid tweaking the R&C, but personally I think that's a waste of time.


So now I need to figure out what to do.  I'm thinking of possibly using
a 12V 2A "wall wart" supply connected to the banana plugs instead of the
nor mal AC power cord.  The main problem is how to actually connect it
all up.

There is room on the rear panel for one of the ubiquitous coaxial power
connectors, but I'm a little reluctant to drill a hole for it.  I could
terminate the power card in the supply in a female banana jack attached
to some sort of "paddle" to make it easier to connect / disconnect; but
it would be "a bit" ugly :-)

Any other ideas out there?
Remove the transformer. Mount an 240Vac - 12Vdc brick on a PCB in place of the transformer, and connect it to the IEC socket and the battery "pins" or similar. No case mods required.

Keep the transformer in case you want to revert the mod and use tagged NiCd cells. Over here they are ~£30 for 9.

Greg Muir
 

Mark,

If you are going to continue to work on 1502/1503 units in the future it is wise to build up an external bench supply power adapter for these units. I did the very thing and also built up an extender for the chart recorders as well.

For the connection to the banana plug in the battery compartment I modified a standard dual banana plug by cutting off the plug end, turning it around and attaching it to a handle. If you do this be sure that you mark the insertion position on the handle so as not to incorrectly connect it to the TDR. The other end is simply a dual banana plug for connection to a bench supply. Of course the negative side is indicated by the little flag on the side of that connector.

I just posted photos in the album section titled “Tek 1502/1503 Test Adapters.”

Greg

Greg Muir
 

Mark,

PS - I never have tried any of the passive component ":cheat" methods to trick the TDR into thinking it has a battery attached. The bench supply method works every time.

You also may be aware that there have been others who have come up with minor modifications to the TDR power supply circuitry itself to bypass the "battery present" detect circuit so that you don't need to have any connection to the battery compartment contacts whatsoever when operating the units off of 120V.

Greg

Paul Amaranth
 

The pack was missing on my 1502 and prices on those are silly (I paid $12 for
the 1502, I wasn't going to pay $50 for a dead battery pack). I made up
a frame out of sheet metal bent like this:

-+ +-
| |
+--+

to hold a couple of banana plugs and put in some subC nicads. Then I made
a cover plate that holds it all in. Works fine. I should put a little
slide switch on the cover plate to disconnect the battery when it's in
storage.

If you made up a bracket like that, there's probably room to put in a
small 12V power supply with an IEC connector on the back. Then just
swap in the battery when you need portability.

Paul

On Thu, Dec 12, 2019 at 11:59:25AM -0500, Mark Pilant wrote:
Hi Tom.

Got around to testing the 1502 using a bench supply. As you suggested,
when hooked up, the 1502 power supply started operating as expected. All
the voltages appeared to be to spec. Although still no trace on the CRT.

I guess there may be some issues with the TekWiki suggested modification
of a 2200uf cap in parallel with a 270 10W resistor.

So now I need to figure out what to do. I'm thinking of possibly using
a 12V 2A "wall wart" supply connected to the banana plugs instead of the
nor mal AC power cord. The main problem is how to actually connect it
all up.

There is room on the rear panel for one of the ubiquitous coaxial power
connectors, but I'm a little reluctant to drill a hole for it. I could
terminate the power card in the supply in a female banana jack attached
to some sort of "paddle" to make it easier to connect / disconnect; but
it would be "a bit" ugly :-)

Any other ideas out there?

- Mark N1VQW





!DSPAM:5df2721f306015243021362!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix & Windows

ehsjr
 

On 12/12/2019 11:59 AM, Mark Pilant wrote:
Hi Tom.
Got around to testing the 1502 using a bench supply.  As you suggested,
when hooked up, the 1502 power supply started operating as expected.  All
the voltages appeared to be to spec.  Although still no trace on the CRT.
I guess there may be some issues with the TekWiki suggested modification
of a 2200uf cap in parallel with a 270 10W resistor.
So now I need to figure out what to do.  I'm thinking of possibly using
a 12V 2A "wall wart" supply connected to the banana plugs instead of the
nor mal AC power cord.  The main problem is how to actually connect it
all up.
There is room on the rear panel for one of the ubiquitous coaxial power
connectors, but I'm a little reluctant to drill a hole for it.  I could
terminate the power card in the supply in a female banana jack attached
to some sort of "paddle" to make it easier to connect / disconnect; but
it would be "a bit" ugly :-)
Any other ideas out there?
Yes. First see Paul's reply. It's good for building a
battery pack AND for the cap/resistor mod AND for
mounting a jack for a 12V supply. NO internal mods
to the 1502.

Another way (but Paul's is better in my opinion) is
what I did years ago with a method a little different
than Paul's: two plates, connected by a threaded
rod and held apart by nuts on the rod. The distance between
the plates is adjusted so they exactly fit the depth of
of the battery compartment, then the nuts are tightened.
The inner plate has the dual banana plug and the outer
plate has the jack for the wall wart supply. There's
tons of room between the plates for the cap and resistor.

Inside Outside
Plate Plate
|............|
|==========={|}=
|............|

The = signs are the threaded rod, the {} are the nuts.
Ignore the periods - they are there to make the spacing
appear correctly for those with different font settings.

Ed


- Mark  N1VQW

EB4APL
 

Greg,

After searching for your album, I realized that there is typing error in the name, "Tex" instead of "Tek"

Regards,

Ignacio

El 12/12/2019 a las 18:45, Greg Muir via Groups.Io escribió:
Mark,

If you are going to continue to work on 1502/1503 units in the future it is wise to build up an external bench supply power adapter for these units. I did the very thing and also built up an extender for the chart recorders as well.

For the connection to the banana plug in the battery compartment I modified a standard dual banana plug by cutting off the plug end, turning it around and attaching it to a handle. If you do this be sure that you mark the insertion position on the handle so as not to incorrectly connect it to the TDR. The other end is simply a dual banana plug for connection to a bench supply. Of course the negative side is indicated by the little flag on the side of that connector.

I just posted photos in the album section titled “Tek 1502/1503 Test Adapters.”

Greg

Mark Pilant
 

Success.

After using the bench supply, and giving the unit a couple of minutes to warm up,
I started rotating the intensity control. As I swept to the upper end, I could see
evidence of a trace, although off the CRT. By adjusting the vertical position, I
was able to finally see the trace on the CRT.

I decided to check a couple of RG-58 test cables I had laying around, and the TDR
got them right.

So, here is a list of what I tried and whether or not it "worked":
1) Used the TekWiki cap/resistor replacement for the battery. Did not work.
2) Checked all the 470uf caps on the underside of the power supply board. Two
checked fine on my ESR/cap meter and one checked open. I replaced the
"open" cap with a new one. Not certain it "worked".
3) Power supply still not functioning, so I hooked the 1502 to a bench supply.
Success, all voltages correct.
4) I checked the supposed "open" cap out of circuit it checked fine. So I put it
back. Non-problem.
5) Left the 1502 powered up for a bit while I checked the power supply voltages.
After a bit (a minute or two) on a whim I tried rotating the intensity control and
saw evidence of a CRT trace.
6) Using the vertical position, intensity, and focus controls I was able to get a nice
clean trace on the CRT.

So now to figure out what I want to do about the battery pack and then put everything
back together (mostly put the case on).

Thanks for all the suggestions.

- Mark N1VQW

Paul Amaranth
 

When I was putting mine back together a while ago after fixing a HV
issue, I had the IEC extender that's screwed into the cabinet just fall
apart on me. I was able to use the terminal pieces to fabricate a
replacement using a urethane rubber casting compound, but some recent
experience leads me to think that you could also use hot melt glue as a
thermal casting material to mold the item.

It's probably not waterproof anymore, but I don't plan on dunking it anyway.

Be careful putting it back together - that extender is NOT available anywhere that
I could find.

That is one neat little box.

Paul

On Thu, Dec 12, 2019 at 12:59:15PM -0800, Mark Pilant wrote:
So now to figure out what I want to do about the battery pack and then put everything
back together (mostly put the case on).

Thanks for all the suggestions.

- Mark N1VQW
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix & Windows

Greg Muir
 

Ignacio,

Oops! Fumble fingers here. The correction has been made.

Thanks!!

Greg

<<<<<
Ignatio EB4APL mentioned:

Greg,

After searching for your album, I realized that there is typing error in the name, "Tex" instead of "Tek"

Regards,

Ignacio

ehsjr
 

On 12/12/2019 3:59 PM, Mark Pilant wrote:
Success.
After using the bench supply, and giving the unit a couple of minutes to warm up,
I started rotating the intensity control. As I swept to the upper end, I could see
evidence of a trace, although off the CRT. By adjusting the vertical position, I
was able to finally see the trace on the CRT.
I decided to check a couple of RG-58 test cables I had laying around, and the TDR
got them right.
So, here is a list of what I tried and whether or not it "worked":
1) Used the TekWiki cap/resistor replacement for the battery. Did not work.
Two things come to mind on that.
First, do not attempt to power on the 1502 immediately after plugging
in the AC cord or wall wart supply. Give it a few seconds to charge
the cap, then turn the 1502 on.

Second, the cap may be too small. I used 4700uF which works
fine for me - I think the wiki recommends 2200.

Finally, if using an external supply (wall wart or otherwise),
put a diode in series between the supply and the cap/resistor
combo. The diode is to protect the 1502 against plugging in a
wall wart or supply with the opposite polarity, and protect "backfeeding" the wall wart or supply. The TDR tries to put
about 17 volts across the bananna jacks to charge the battery.

Ed

<snip>

Tom Gardner
 

On 13/12/19 02:54, ehsjr via Groups.Io wrote:
On 12/12/2019 3:59 PM, Mark Pilant wrote:
So, here is a list of what I tried and whether or not it "worked":
    1)   Used the TekWiki cap/resistor replacement for the battery.  Did not work.
Two things come to mind on that.
First, do not attempt to power on the 1502 immediately after plugging
in the AC cord or wall wart supply.  Give it a few seconds to charge
the cap, then turn the 1502 on.

Second, the cap may be too small.  I used 4700uF which works
fine for me - I think the wiki recommends 2200.
The problem is that if the capacitor is too large it takes too long to charge up. The PSU interprets the low voltage as a failed cell, and shuts down.

The required C (and R) seems to be select-on-test, varying from one 1502 to another. Even if suitable values are found, it makes me wonder if it will switch on /next/ time :(

Mark Pilant
 

Just to wrap this up....

Since I have been only having marginal success with the cap/resistor
NiCd substitute, I have decided on my alternative.

My plan is to cut some aluminum blanks the same size as the finned
end plate of the original battery pack. From there, I'll drill the
necessary holes to allow the new plate to be screwed to the TDR (with
the original thumb screws) as well as the original plastic battery
frame.

I'll then drill a hole in the new plate for a standard coaxial power
connector to allow an external wall supply to be connected to the
banana plugs of the original. The original end plate will just be
kept in the cover; so it doesn't get separated from the unit.

I was thinking of making up one battery pack, but so far, all the
"C" side NiCd flat top batteries are too long by about 0.1". In
looking around, the "shorter" ones appear to have all been flat top
batteries, while the "longer" ones were the button top batteries.
However, now even the flat top batteries seem to have the same length
at the button top batteries. Sigh.

- Mark N1VQW

Tom Gardner
 

Sounds like a good plan; nothing original is destroyed.

I think I would use a standard IEC C14 "kettle lead" panel mounted male plug, simply so I can reuse the many kettle leads I already have.

Happy holidays.

On 24/12/19 18:17, Mark Pilant wrote:
Just to wrap this up....

Since I have been only having marginal success with the cap/resistor
NiCd substitute, I have decided on my alternative.

My plan is to cut some aluminum blanks the same size as the finned
end plate of the original battery pack.  From there, I'll drill the
necessary holes to allow the new plate to be screwed to the TDR (with
the original thumb screws) as well as the original plastic battery
frame.

I'll then drill a hole in the new plate for a standard coaxial power
connector to allow an external wall supply to be connected to the
banana plugs of the original.  The original end plate will just be
kept in the cover; so it doesn't get separated from the unit.

I was thinking of making up one battery pack, but so far, all the
"C" side NiCd flat top batteries are too long by about 0.1".  In
looking around, the "shorter" ones appear to have all been flat top
batteries, while the "longer" ones were the button top batteries.
However, now even the flat top batteries seem to have the same length
at the button top batteries.  Sigh.

- Mark  N1VQW

Harvey White
 

Be very careful with the amp hour ratings on the C size cells. Some manufacturers put an AA sized cell in a big wrapper for the C form factor.  You might be just as happy with AA, depending.  You may find that *real* C sized batteries have a significantly larger rating then the fakes.  We're talking name brands here.

Harvey

On 12/24/2019 1:17 PM, Mark Pilant wrote:
Just to wrap this up....

Since I have been only having marginal success with the cap/resistor
NiCd substitute, I have decided on my alternative.

My plan is to cut some aluminum blanks the same size as the finned
end plate of the original battery pack.  From there, I'll drill the
necessary holes to allow the new plate to be screwed to the TDR (with
the original thumb screws) as well as the original plastic battery
frame.

I'll then drill a hole in the new plate for a standard coaxial power
connector to allow an external wall supply to be connected to the
banana plugs of the original.  The original end plate will just be
kept in the cover; so it doesn't get separated from the unit.

I was thinking of making up one battery pack, but so far, all the
"C" side NiCd flat top batteries are too long by about 0.1".  In
looking around, the "shorter" ones appear to have all been flat top
batteries, while the "longer" ones were the button top batteries.
However, now even the flat top batteries seem to have the same length
at the button top batteries.  Sigh.

- Mark  N1VQW