Re: What are the differences between the P6302 and A6302 current probes?


Atillo: I have had many of these probes and the other similar.

On ebay BEWARE as it is VERY easy for a probe to be dropped even 5 cm and break the thin ferrite core.

The damage can be invisible but the pulse and response will be bad, and impossible to fix.

Suggest to bid ONLY buy if they are guaranteed new or use 100% working with chance to return.

I have paid $35..65 but perhaps in 1990s..2000s

If ANY physical damages in photos, avoid.

fai attenzione al compratore



Re: [Tek 485] No intensity control



from the schematic for the CRT circuit <13> it looks like you could measure the value of R1603-R1609 by either lifting only one leg of either R1603 or R1604, or by lifting one leg of both R1605/R1606 and R1608/R1609. If you could easily disconnect the DD connections then there would be no need to lift any legs of any resistors.

-- Jeff Dutky

Re: What are the differences between the P6302 and A6302 current probes?


Thank you very much David for the information.

-- Cheers

FS: Tektronix 492 to 492P Spectrum Analyzer mod kit 040-1038-03 plus manuals

Ken Eckert

Deane Kidd put this mod kit together for me years ago. It was an official Tek kit p/n 040-1038-03. Auction also includes all the original 492/492P manuals: OP, Service Vol 1, Service Vol 2 and Programming along with the mod sheets/documentation. Photos on request.

This kit includes everything (Deane was meticulous) including all the cables, screws and cable clamps.

I never installed it, I sold the 492 a while back.

Asking USD$250 or best offer

Re: What are the differences between the P6302 and A6302 current probes?


AFAIK, A6302 and P6302 are the same thing.


Re: Tek 567 trace wandering

Michael W. Lynch

On Fri, Jan 29, 2021 at 04:33 AM, <> wrote:

The second issue is the looping compensation seems very stiff, and turning it
has no visible effect at all. Is it likely to have seized, and how does one
get at it - again it doesn't look easy to access.
That looping compensation control is usually stuck where the shaft passes through the chassis on the capacitor itself. You can access this a little better by removing the bottom panel, still a pain, but does give more room to work and better access. I used a bit of penetrating oil on mine and finally got it freed up.

Michael Lynch
Dardanelle, AR

Re: Tek 576 possible power supply failure

Michael W. Lynch


Did you disconnect the 100V to the HV section? Sounds like another shorted HV transformer.

Michael Lynch
Dardanelle, AR

Re: [Tek 485] No intensity control


Ok. As Mark Vincent suggested, I'll replace them with 1N4937.

One question : Mark sugested to check R1603-9 carbon resistors... I guess it is pointless to try to check them without desoldering one lead : right ?


Re: Sloppy front panel BNC connector - 475


Interesting about the resistor material. The original definitely looks like carbon film, and the service manual confirms that (well, it states that resistors used in this model with 4 bands are carbon film, 5 bands are metal film).

Audiophiles claim that carbon composite resistors are noisy. Does that also apply to electrical noise in the scope front end?

Re: Tek 7T11A issues


Thanks all for the valuable input - I now have a few things to try/look at. Since my original post I decided to try the 7S11 with my 7S12. Since that, the 7S12 has developed its own problem - It no longer will show rise times. Instead, it only brightens a portion of the trace corresponding to the time/division setting, but does not expand the trace anymore to enlarge in on the leading edge. There's always something! I've never had the 7S11 in with the 7S12, always just used the 7S12 stand alone as a TDR to measure cables or look for opens/shorts - Now I'm wondering if the 7S11 could have caused some damage to the 7S12?

What are the differences between the P6302 and A6302 current probes?


Greetings to all,
I have an AM503 current amplifier and I want to buy a P6302 current probe, but I see that maybe now they are called A6302. Is there a difference or are they the same?

Thanks for the attention.


Re: broken coupler


One of the 577 units that I worked on had a coupler from a rc boat
propeller installed on a control shift. If there is enough room. If
electrical isolation is not needed I like this idea part was dirt cheap
from Amazon $1.75 - 6.75 and was metal.


On Thu, Jan 28, 2021, 7:33 PM Larry McDavid <> wrote:

Qservice lists them and there are some offered on eBay but pricey.


On 1/28/2021 3:51 PM, DaveH52 wrote:
This may be a long shot, but I'm looking for a suitable replacement for
a "376-0050-00 CPLG,SHAFT,FLEX:0.081 & 0.127 ID.PP" for an SC502 scope. the
max OD is about .375" and the max length is about .5" and it must support
axial loads as well.

Best wishes,

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

Re: Tek 567 trace wandering


On a 576 only the side panel needs to be removed to get at the invert zero
and cal switches. If I remember correctly easier access can be attained by
removing the control that covers up the switches. This can be done by
removing the knob. And pulling the entire module out gently. There is
enough slack in the wiring harness to do this with out unplugging anything
but just barely. It is not an awful job as far as I remember.


On Fri, Jan 29, 2021, 5:33 AM <> wrote:

The 576 I recently acquired is on the face of it in good condition, but
it's got a couple of issues. The first is the trace wanders over the screen
randomly at times. Pressing the Zero button does bring the trace to a
central dot OK, but it seems there is an issue with the Cal button. Any
movement and the trace starts/stops wiggling. So I'm assuming the switch is
dirty - is that a fair assessment? And what needs to be removed to get at
it easily? Any tips on how to remove and clean it appreciated.

The second issue is the looping compensation seems very stiff, and turning
it has no visible effect at all. Is it likely to have seized, and how does
one get at it - again it doesn't look easy to access.

TIA, Keith.

7854 revived with a new CRT - how to correctly calibrate Z circuit (was: #157693 -


Hi all,
more than a year ago, I initiated that discussion: about my 7854 with severe focus/intensity problem.

Finally I got a replacement CRT guaranteed working some days ago.
I replace old CRT with the new one and.. finally!!! Trace is brilliant, sharp and focused. The readout also is very well focused, even at high intensity.

Undoubtedly Albert Otten was right when he hypothesized the phenomenon of CRT's double-peaking for my case!

Now, with this new CRT, some re-calibration is necessary, due to slight changes in deflection sensitivity, step response, etc. So I started from scratch.
I want to clarify that the scope actually works well, I have not noticed obvious anomalies (for now).

I follow the calibration step-by-step as per manual.
I have come to section B, "Z axis and display - page 4-47" and here I found two things that baffled me.

Section B-3 "Adjust Z-axis DC levels": I correctly managed steps a thru g obtaining an 80 Vp.p. signal at TP122, board A21.
Continuining to next steps I read this:

i. Connect the test oscilloscope 10X probe to TP183 (located on the Z-Axis Board) with the probe ground connected to chassis ground.
j. Set the 7854 B INTENSITY control fully clockwise.
k. EXAMINE—Test oscilloscope display for a waveform baseline between 8 and 12 volts above ground reference.
I. ADJUST—The Output Level adjustment, R135 (located on the Z-Axis Board A21), for a waveform base line at 10 volts above ground reference.

Question: what is "baseline"? The bottom portion of the waveform? If this is the case, R135 has no effects on the level of bottom portion.


m EXAMINE— The test oscilloscope display for a 68 to 72 volt peak-to-peak vvaveform. (Do not move the test oscilloscope vertical Position control.)
n ADJUST—The Z-Axis Ampl Gain adjustment, R125 (located on the Z-Axis Board A21) for a 70 volt peak-topeak vvaveform displayed on the test oscilloscope.

Here I can adjust: I set for 70 Vp.p. But the lower portion of waveform is at approx 7-8 V about GND.

Can be the manual wrong? I think the the regulation at points j/k/l should be made witch INTENSITY fully CCW, adjusting the R135 (Z axis output level) for top waveform level about 10 V from GND. I'm thinking wrong?

The second problem arose during the calibration of the Good SIgnal Flip-FLop GSF (page 4-50, section B5 of the manual): using a DVM I set the voltage at TP103 (board A21) 40 mV less than the voltage at TP122 with no problems.
Using two identical timebases 7B53A in slot A and B, I connected the probe of my test oscilloscope at TP106, board A21.
7854 set to Horizontal mode B: I see a good pulse signal, with levels approx. -0.2V and +3V. The signal is stable while rotating B INTEN through its range.
7854 set to Horizontal mode A: I see a the same pulse signal, same levels, but it's "slippery". For a few instants is stable and triggered, then become jittery, slips and then return somewhat stable. Adjusting GSF Level, R102 (located on Z-Axis Board A21) has no noticeable effects.
Thinking about some problem in the 7B53 in A slot, I swapped the two plugins: same result: GSF signal is stable in HORZ MODE B. Unstable when set to HORZ MODE A .

I don't see any motivation for this behavior since the FF circuit is very simple.
Really I don't know why this happens, since the scope seems to work normally. I will follow the Z signal back to schematics <4>

The 7854 manual seems very unclear in this cases. I do not have another 7854 to compare the signals and I don't remember what the signals on A21 Z axis board was, since my last tests two years ago...

What do you think? Am I doing something wrong or is the manual to be wrong?
Any suggestion is welcome.


Re: Tek 465B ch 2 var broken coupler repair


Be careful to make sure that the flexible coupler is not being used for electrical isolation also. I find that sometimes I can use a solid coupler in place of the flexible, but if it is on a POT with high voltage on it, and the shaft to the knob is metal, I will replace the shaft with a fiberglass shaft of the same diameter. Just out of caution...


TM500 Latch Tab fix


There have been a few threads on TM500 latch repairs. Depending on which specific problem you have, this idea might be of interest.

I needed to replace/repair the latch on a TR502. The latch was of the old-style grey plastic one-part jobbie and the external part had sheared off leaving the tab with a short bit of the grey plastic inside. I managed to find some other broken latch parts in my bits box, including a larger grey tab and a smaller off-white one as well as a complete grey latch.

I discovered, as some of you will already be aware, that the tab is held on via two claws on the external end of the latch which is retained by a plastic insert so that the jaws can't spring out of the tab when pulling on it. It happens that this plastic insert is 3/32" diameter (or about 2.4mm). The insert is hidden underneath the tab, so usually invisible.... you may need to look very carefully. If you carefully centre-punch or centrally dent the insert you can carefully drill it out, preferably with incremental drill sizes, until you "almost" reach the top side of the tab. With care you can successfully remove what is left of the insert. The remains of the latch can be dudiciously removed via the side-slots in the tab.

You'll be left with a 3/32" diameter hole which extends through the end of the latch. Now, once you've swapped the "new" and old bits around you're left with the job or replacing the insert; if you don't use an insert the tab will simply pull off again next time round (as I discovered). So, what to use? Initially I tried a very short self-tap screw; this worked but didn't look very nice even though it was on the underside of the tab. I thought of a M2.5 machine screw, which would have been a better choice but decided to investigate the sourcing of 3/32" plastic rod, only to find that unless you were a very keen modeller you would be buying 5' of plastic rod in order to only use only a few millimetres of it!

Suddenly one of those light-bulb moments happened...... in the UK (and I suppose the USA and elsewhere) you can buy Johnsons Baby Cotton Buds, and guess what.... they are made using a white plastic rod of exactly 3/32" diameter! I had initially thought they might have been some compressed paper product, but no, it's plastic.

My wife now has one less in her pot and I just cut off one end and then with a scalpel cut myself a 1/8"/3.5mm length and inserted it into the hole in the tab and latch with a pair of long-nose pliers, and hey presto it works. It's not grey but hey, who uses their TM500s upside down to see????

If you are a perfectionist (and what Tek geek isn't??) then you can carefully shave it back flush with the under-side of the tab with the scalpel.

Re: Tek 485: Was dead. Was fixed. Clumsy me killed it again. (from a lurker :) ) #photo-notice

Roy Thistle

On Thu, Jan 28, 2021 at 09:30 PM, Ron Rossi wrote:

You might find it interesting nontheless.
I watched the video.
Those are some possible symptoms of damage to the circuits that the dropped BNC might have momentarily grounded (Focus DC Restorer circuits, Fig. 8016, A11 Partial Horizontal amplifier board) ... There is also some possible interaction with the Auto Focus circuitry (Fig. 8-15, A13 Partial Power Supply board.)
Also, I still think you might have damaged the diode package(s) (CR1601 + CR1602) on the 3kV line. (Possibly more on that in another post.)

[Tek 485] No intensity control


Hi *,

I start this new thread on the new issue seen after fixing the PSU issue from now ended topic:


Hands back on the 485and starting from some Service Manual reading! This one gives some hints on troubleshooting some issues (p.4-8) including "No intensity control / Poor focus control".

I checked all the DC restorer diodes (list from the description in p. 3-13) with my DMM Diode test function..

List is: CR1646/1651/1652/1656/1660/1663/1664/1666

It turns that CR1646 / CR1666 / CR1651 look open (0L) on both directions.

Probably the first thing to do is replace this 3 diodes. Service manual I have, points that these are NDP341. But trying to see the ref, I seem to read 282 marking on them (but not sure at all about that !!).

What would be the replacement diode ? CR1652, CR1656 and CR1660 were already changed to BAV21. So i guess this ref will do ? Will order some.

Are there some more checks I can do in the meantime ?


PS. My scope as zome TI IC marked "M 7519". This lead me to think the scope is from 75/76...

Re: Tek 485: Was dead. Was fixed. Clumsy me killed it again. (from a lurker :) ) #photo-notice

Roy Thistle

On Thu, Jan 28, 2021 at 10:55 PM, Tom Miller wrote:

I agree with Merchison.
I agree with both Tom M. and Mechison.
I was going to say read the "Beam Current Limit" section (page 3-14, in 070- 1193-00)
But, I was assuming you read the entire section on the CRT circuits. (I mean since you "momentarily" grounded out some of those circuits.)

Re: Tek 7T11A issues

Albert Otten

Hi n49ex,

Are you using a sampling head with trigger signal output? If not (for instance S-6) then you have to supply external triggering to the 7T11A.


9121 - 9140 of 186258