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On Tue, Mar 12, 2019 at 12:52 PM, Raymond Domp Frank wrote:

1 mega-sample

sorry... typing too fast... that should be 100 mega-samples

I was simply using a hand held DMM (craftsman 82400) to test the voltage at
C2202. I do not own another bench scope. So if I understand correctly, I
can connect the DUT to the isolation transformer using all three prongs.

I will check the value at this capacitor this evening

Nick

Hi all I picked up a SG503 and a PG506 just recently for a very decent price. Haven't tested or used them yet as both have some issues broken knobs missing parts some cosmetic damage. Have checked with Sphere and Qservice and neither has what I need so will list here to see if anyone has some spare bits for one of them.
PG506 SR# B059635 later version
1 - 366-2082-00 Knob gray volts/Div.
1 - 378-2030-06 Lens Red LED Dspl Printed PG506
1 - 337-3039-00 Shield Elec Side complete w/latch
1 - 386-2843-00 Subpanel Front (optional)

SG503 SR# B068393
1 - 386-2848-00 Subpanel Front ( broken a lot)
1 - 366-1527-00 Knob Gray tuneing

Any subs that can be used recommended will be appreciated.
Also am planing to replace the Sprague 30D caps on the 506 and all the multi color tants on the 503. tants on the 506 all are tan color AVX type like the new ones from Mouser.

Any other recommendations offered?

Jim O

On Wed, Mar 13, 2019 at 03:17 PM, Nicholas Keller wrote:

Is this what you describe as “floating the 2247A”?

Hi Nicholas,
Glad you bought an isolation transformer!
My advice to "float your 2247A" actually was very badly formulated. I meant to say something like "float the hot (primary) circuits of your 2247A", meaning the circuits directly connected to the mains *and* I should have added *not* to float your testing equipment (like your testing 'scope).
Many people disconnect safety ground on their measuring 'scope but that's *very* bad and dangerous practice.

Always make sure all instrument chassis are connected to safety ground if at all possible.

Your 2247A is an example where you can get the protection of your isolation transformer and still connect the chassis of both your testing 'scope and the device under test (DUT) to safety ground. This is because T2204 takes care of isolation of all low-voltage circuits from the mains, *including* the 'scope's chassis, which is connected to low-voltage/ secondary ground.
The isolation transformer makes everything directly connected to the two mains input wires (the hot circuits) float i.e. galvanically disconnected from "the rest of the world".
Since the 2247A's chassis is isolated from the hot circuits, it's safe and actually a good idea (safe) to connect that chassis to safety earth. The ground connection on your isolation transformer always connects that transformer's housing to safety earth and the ground wire you're mentioning is supposed to connect that earth ground through to the 'scope's ground (3rd pin in 3-prong adapter).

If you connect things this way, your testing instruments will remain connected to ground, as will your 2247A's chassis.
Only the hot (primary) circuits of your 2247A will be isolated from mains via the isolation transformer on their input and from the 2247A's chassis through T2204 on their output.

Four final notes:

1. In most instruments, there are one or more capacitors between the mains connection(s) and chassis. These are there for EMC reasons but they may present a high-impedance voltage on the chassis (of Vmains/2) if safety ground is disconnected in that instrument.
2. Providing safety earth continuity to your DUT (where possible) provides protection in case of leaks or one of the capacitors as in 1. short-circuiting.
3. In most (older) instruments with linear supplies, like the 465 'scope, providing this earth continuity while using an isolation transformer won't do much good. In those instruments. By all means use an isolation transformer but skip the earth continuity.
4. Be aware that, though disconnected from mains, hazardous voltages still exist inside hot circuits connected via an isolation transformer!

Good luck with your repair!

Raymond

/g/TekScopes/album?id=86536

I tested a Toshiba A1962 PNP transistor to assess the overall condition of the step generator. It works as you can see from the link, however the trace becomes garbled with lower step sizes of the generator and higher vertical sensitivity. I am using 15 inch clip leads from the test fixture so that is probably not helping. Finally I have a strange reading when I set the step generator to 0.05 and 0.1V

Hi Tom,

Yep, and even under magnification it looks perfect.

No glass, no elements akimbo.

It doesn't look like it has been abused... except for
the trace, that is.

-Chuck Harris

Tom Miller wrote:

I just got my trusty 7904 and tried the same test with squarewave.

Same result as the 7104 , precisely rectilinear, no visible distortion.

Cheers,

Jon

I just paid $150 USD for one with several issues. Now that I fixed it I expect to get $200-250 pretty easily.

If you dont want it, I will take it.

Good idea, I have an oscilloscope, I will put it to good use

Have you worked through the adjustment procedure, checked the waveforms against the manual? I usually find any faults/oddities that way, The step generator waveforms should be very clean. Getting the sockets out is very time consuming, I avoid it if possible. Some Deoxit on the ic's and a couple of insertions cures almost all but the worst sockets. Also deoxit into the pushbutton switches cures a lot of problems.

296-1403-5-ND? x 3
LM741CNNS/NOPB-ND? x 1

I believe I will give this a try from Digi Key

If this doesn't work I might look at replacing all the socket for the IC's on the step generator board

Hi Chuck,

Have you had the tube out of the scope and inspected for bits of broken glass inside the tube?

Regards

I already own 2 of them, but I would snap up another for that price.

UK pound is roughly equal
to $1.30 At the moment.
Jim
Ei2BB.

On Wed, 13 Mar 2019 at 06:55, Craig Sawyers <c.sawyers@...>
wrote:

I have a chance to buy a 465B which seems to work fine Both time bases

show good traces etc The

owner is asking 100.00

I was going to ask a stupid question: is the USD, UKP or EUR. But they are
all about the same thing
now!

Craig

Thanks

Also I checked and I definitely have the TI IC sockets with the narrow pin inserts, I will look them over

And a thank you to all who commented here, your input is helpful and appreciated

If you look at it shows use of the pocket signal generator with the DSA602. It is a single frequency, single level output. I have one but it didn't work properly with my DSA602 scope.I believe it is kaput and I haven't tried to repair it.
Leonard

Raymond,

Per your advice (and that clearly marked on the PCB!), I have purchased an
isolation transformer. After watching a few videos online, I am still
unsure whether I should connect ground from the Tek to the transformer.
One video showed use of a 3-prong to 2-prong adapter where the ground wire
is left unattached. Is this what you describe as “floating the 2247A”?

Thanks for your help!

Nick



On Sun, Mar 3, 2019 at 8:48 PM Nicholas Keller via Groups.Io <Nirokeforums=
[email protected]> wrote:

No, I was not using an isolation transformer (I don’t have one) and yes I
was measuring between cap and chassis. I will look into getting a
transformer before testing across c2202 or doing other troubleshooting.

Thanks for the warning

Nick


On Sun, Mar 3, 2019 at 6:49 PM Raymond Domp Frank <hewpatek@...>
wrote:

On Mon, Mar 4, 2019 at 12:17 AM, Nicholas Keller wrote:

I measured 120-122VAC up to the diode ring. Does this
suggest that C2202 is bad?

I guess you realise you're measuring in an area that is directly

connected

to the mains, no isolation? Take great care! *Do* use an isolation
transformer and *float your 2247A*.

Did you measure the 77 V across C2202 or between C2202 and chassis? The
latter would be incorrect, because the chassis is floating (with

exception

of some C's) against C2202 (since that has a galvanic coupling to the
mains).

Raymond

PSU is most likely culprit, you will have fun digging down to get to it. Search the archives for info on this, there were many threads regarding the way to test the PSU out of the scope (carefully) and likely suspects for replacement. Personally I had no problem with the 3 legged caps in the PSU (You will see which when you get in there) however others on this board disagreed. There is also a battery on the digital board which leaks (depends on version) that can cause problems. Its been a while since I repaired any of these so working from (poor) memory here.

U360 is a plain vanilla 741 opamp

Dave,
I recently stripped mine with acetone. That and gloves, a mask, and loads of paper towels had it stripped and sorted in a reasonable time. Work outdoors for best safety.
My mistake was using an abrasive attack at the start. Don't do that.
After a couple of coats of 'Etch Primer' the paint went on a treat. Sadly not the exact Tek blue but close enough to make me happy. Getting the right paint here to Australia (or the UK) is just too expensive.
Cheers, Brian.