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I have a 7D15 mounted in my 7904A and have noticed that the numeral "8" appears to be displayed in a strange way (to my view anyway).

Whereas all other numerals are displayed in a nicely rounded fashion (ie not precisely in squared-up LED 7-segment layout), the 8 shows like a H, with a flat top and bottom, and without any character rounding. So it always looks like a 7-seg display number rather than an alpha-numeric display.

Is this normal, am I paranoid, or is there an issue either in the 7D15 or the 7904A readout system? It does not matter in which character position the 8 is shown; so 88888 for example will always show as a series of Hs with flat tops and bottoms.

This of course is something you won't see on the regular PI readout displays because it is always 1,2,5 etc or mV, mS etc. 8 is the only character showing any form of "abnormality".

Is this normal or not?

On Wed, Dec 22, 2021 at 02:26 AM, Andy Warner wrote:

Does anyone on the list have experience or advice repairing damage such as
this?

I have several scrapped SG503's so if you would replace the drum instead you can have
one for the price of shipping (from Sweden). Contact me off list if you are interested.

/H?kan

Thanks for clarifying, Raymond.

How important is the exact value of these caps?

Hello George,
I bought my set of 3 boards in 2018 at Norway Labs for approx. $145 for my 2756P. You could try to contact Sue Breuner, Norway Labs, Inc. (503) 924-5846
I tried to get a picture in here, but I don't know how to do it. You can PM me for that.
Best wishes,
Jaap Rusticus
PA0JRK
Netherlands

Hi Zen,
Thank you for your reply.
I could find the white/green wire on the 577.
My question was where this point is shown in the schematics.
I guess it should be S120A , but I am not familiar with the way Tek represents rotary switches on them.

The good news is that I have one 177 that seems to be working and I could complete the 1st pass of the calibration procedure yesterday night.
Since I have had to adjust R617, I will have do start over the procedure again, as requested by the manual.

The question now is how to test the broken 177?
I have checked diodes for PN junction with the DMM (they all tested ok) and the two op amps in an test gadget that puts them to oscillate and they tested good also.
No signs of heat damage on any resistor.

Regards,
Roger

On Wed, Dec 22, 2021 at 08:02 AM, Stephen wrote:

I didn’t quite get which capacitors you’re referring to. Did you mean the
20pf input capacitors? Maybe a typo?

I was referring to C18 (Ch1) and C68 (Ch2) at the gates of Q20A and Q70A, through resistors R18 and R68, respectively. These immediately follow the input attenuators, on the vertical input boards. Their values are shown as 3.3pF in some versions of the SM and smaller (ca. 2.7pF) or even individually tailored in others.

Raymond

On Wed, Dec 22, 2021 at 03:58 AM, Dave Casey wrote:

CA glue and baking soda would be a good way to fill/build up.

The original cam material provides low friction against the switch levers. Maybe a small, partial (graft) transplant from another cam switch model is feasible: many Tek modules contain these switches.

Raymond

Thanks Raymond,

I assembled 2x 2.4M resistors from 2.2M and 220K 1W metal film resistors and it’s almost perfect at 0.996875KHz. Yes, I agree, the multiturn pots would be overkill. The purpose of the unit is stepped amplitude, not frequency.

I didn’t quite get which capacitors you’re referring to. Did you mean the 20pf input capacitors? Maybe a typo?

On Tue, Dec 21, 2021 at 10:05 AM, Dave Daniel wrote:

Did you measure the ESR of the old capacitors?

No, I didn’t.

My mistake again, it is indeed a TO-92. I misread the location diagram.

I'd like to register a successful conclusion to this project. Full signal amplitude is back after replacing Q1040.

My thanks to all who helped here, and especially to Gordian Sehrig who kindly supplied the replacement transistor.

Merry Christmas to all.

EJP

where are you located?

I received these two leaf contact assemblies recently without a part number attached. I have uploaded pictures fo the two identical parts to a photo album /g/TekScopes/album?id=270969

Does anybody recognize these parts, and know either the part number, or the instrument in which they are used?

-- Jeff Dutky

Chris,
I checked both carts and one is model 3 for 7000 series 4 bay and the other is model 203 for 7000 series 3 bay.? They both work but I need to clean them up a bit.? The 203 has a bit or rust.? Wheels turn fine.? Also want to get rid of all my 500 scopes except the 575 curve tracer at this time.? Have 1s1, 1s2, 1l5, 1l10, 1l20, 547s, 1a1s, 1a2s, and more.? Will not ship.? Need to get them a new home.
Carl Hallberg

Did not know about CA + NaHCO3 before now, looks promising. Will try it and
report back.

N0BUQ, you are correct, only 1 of the tracks needs rebuilding.

On Tue, Dec 21, 2021 at 20:58 Dave Casey <polara413@...> wrote:

CA glue and baking soda would be a good way to fill/build up.

Dave Casey

On Tue, Dec 21, 2021 at 7:48 PM n4buq <n4buq@...> wrote:

It's hard to tell, but it appears only one lobe would need to be
repaired. The other one looks like it did not have a lobe at that point
and all the might be done there is just smooth it out just a bit just to
make sure there's no plastic sticking up that would enable the switch

when

it shouldn't.

Perhaps some epoxy built up and then filed down to the radius for the
lobe? JB Weld makes a Plastic Repair formula that might work. I think

the

hard part might be to make a "form" such that the liquid will stay put
where it cures.

You might also find a replacement cam. I see several different part
numbers on eBay and one might be a direct replacement.

Good luck with it.

Thanks,
Barry - N4BUQ

----- Original Message -----

From: "Andy Warner" <andyw@...>
To: "tekscopes" <[email protected]>
Sent: Tuesday, December 21, 2021 7:26:48 PM
Subject: [TekScopes] Repairing damaged cams

I have an SG503 with a cam switch that has clearly been damaged by a
soldering iron at some point in it’s past.

Picture here:

Does anyone on the list have experience or advice repairing damage such

as

this?

I am thinking I dismantle the switch, remove the cam, and then fill the
damage with some kind of material, file/sand to make good, then

re-assemble.

--
Andy

--

Andy

CA glue and baking soda would be a good way to fill/build up.

Dave Casey

It's hard to tell, but it appears only one lobe would need to be repaired. The other one looks like it did not have a lobe at that point and all the might be done there is just smooth it out just a bit just to make sure there's no plastic sticking up that would enable the switch when it shouldn't.

Perhaps some epoxy built up and then filed down to the radius for the lobe? JB Weld makes a Plastic Repair formula that might work. I think the hard part might be to make a "form" such that the liquid will stay put where it cures.

You might also find a replacement cam. I see several different part numbers on eBay and one might be a direct replacement.

Good luck with it.

Thanks,
Barry - N4BUQ

I have an SG503 with a cam switch that has clearly been damaged by a
soldering iron at some point in it’s past.

Picture here:

Does anyone on the list have experience or advice repairing damage such as
this?

I am thinking I dismantle the switch, remove the cam, and then fill the
damage with some kind of material, file/sand to make good, then re-assemble.
--
Andy

On 12/21/21 15:36, Raymond Domp Frank wrote:

By dispersion in capacitors, in a non-formal sense, I mean the frequency dependence of the dissipation factor.

OK thanks, I get that now.

On Tue, Dec 21, 2021 at 10:51 PM, John Griessen wrote:

Are you meaning the term used on GR bridges? D for dissipation factor?

By dispersion in capacitors, in a non-formal sense, I mean the frequency dependence of the dissipation factor. In said 465, the small ceramic capacitors, which sit in parallel with the gate (impedance) of the input FET, caused huge distortion because of the frequency dependence of their dissipation factor; with (e.g.) abhorrent square wave representation as a result. Both channels had deteriorated almost the same, so I initially sought the cause in and after the channel switch circuits.

Raymond

On 12/21/21 14:25, Raymond Domp Frank wrote:

I once had a 465 portable 'scope where the dispersion of the two ca. 2.5pF
caps at*both* inputs had become ridiculously high, causing huge distortion. I
was surprised to see such high dispersion for such small (dogbone ceramic)
caps. The caps did*not* show DC leakage less than 50MOhm..

.... and their capacitance was still fine...

Are you meaning the term used on GR bridges? D for dissipation factor?