Date   
Re: 7904 excessive shadow/flare

unclebanjoman
 

O.K.! Thanks to everyone for the comprehensive answers, very instructive to me!

Undoubtedly the driving circuits of the 7904 and 7804 CRTs are completely different and this could partly explain the different behavior regarding the halo / flare effect.
Over time I will get used to the remarkable brilliance of my new 7904 (and his associated halo /flares) which, moreover, is really in excellent condition and after careful calibration it matches perfectly the manual's specifications.

My 7904 has serial number B269718; reading the manufacture date of a pair of TI SNxxxx ICs, it should be from 1979.

If another 7904 to be repaired happens to me, I will be curious to observe the halo / flare effect, whether it is identical or not. I will let you know if the case.

Thanks again,
Max

Re: 7B92A time-base plug-in odd behaviour

Colin Herbert
 

Thanks for the info, guys. I have now located where these switches go, but I am unclear as to what their functions are. Perhaps I don't really need to know, after all.

I am still perplexed by the odd behaviour of the plug-in in terms of the behaviour before warm-up. Once the scope has warmed-up, the time-base is still showing some instability which can be induced/stopped by wiggling the time-base "Time/Div" knob. I am now thinking that it might be caused by poor contact on one or more of the cam-switches. This looks like it will involve taking the cam-switch assembly out and doing the "paper-soaked-in-IPA" procedure. As there are about 50 of these, has anyone any idea which might be the dodgy one(s)?

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Roger Evans via Groups.Io
Sent: 22 May 2019 16:44
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7B92A time-base plug-in odd behaviour
On my 7B92A, the microswitch near the front panel is connected by a single wire to P911 on the interface board. P911 is to be found on schematic <4>, 'Delaying Sweep', near the top right >corner. It is marked as going to R334 on schematic <3> and the switch is marked as S490. S800 on 'Horizontal Logic', schematic <7> is marked with 'pull for alt, push for delay' and is surely the >second switch on that shaft, it connects through to the Readout board.
I noticed while investigating my 7B92A that the whte plastic 'cotton reel' that activates the microswitch didn't seem to be an entirely tight fit on the shaft but settled down happily after a few >iterations. I hadn't noticed any odd behaviour when it is operating in the mainframe.
Regards,
Roger

Re: 7B92A time-base plug-in odd behaviour

Albert Otten
 

Hi Colin,

Since most of the problem disappears after warming up I guess it's more like a semiconductor issue.
Do you have the model with "Alt Off" at the ccw position of the TRACE SEP knob, S/N B06-up? There are several ICs involved in processing the Alt Off position, like U635<5> and U856<7>.

Albert

On Fri, May 24, 2019 at 03:24 PM, Colin Herbert wrote:


Thanks for the info, guys. I have now located where these switches go, but I
am unclear as to what their functions are. Perhaps I don't really need to
know, after all.

I am still perplexed by the odd behaviour of the plug-in in terms of the
behaviour before warm-up. Once the scope has warmed-up, the time-base is still
showing some instability which can be induced/stopped by wiggling the
time-base "Time/Div" knob. I am now thinking that it might be caused by poor
contact on one or more of the cam-switches. This looks like it will involve
taking the cam-switch assembly out and doing the "paper-soaked-in-IPA"
procedure. As there are about 50 of these, has anyone any idea which might be
the dodgy one(s)?

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Roger
Evans via Groups.Io
Sent: 22 May 2019 16:44
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7B92A time-base plug-in odd behaviour
On my 7B92A, the microswitch near the front panel is connected by a single
wire to P911 on the interface board. P911 is to be found on schematic <4>,
'Delaying Sweep', near the top right >corner. It is marked as going to R334 on
schematic <3> and the switch is marked as S490. S800 on 'Horizontal Logic',
schematic <7> is marked with 'pull for alt, push for delay' and is surely the
second switch on that shaft, it connects through to the Readout board.
I noticed while investigating my 7B92A that the whte plastic 'cotton reel'
that activates the microswitch didn't seem to be an entirely tight fit on the
shaft but settled down happily after a few >iterations. I hadn't noticed any
odd behaviour when it is operating in the mainframe.

Regards,
Roger



Re: Latest firmware for TDS210 and TDS2CM?

Jared Cabot
 

Hmm, good info. I think I probably have a late firmware then, it had the earthing recall fix already done too, so it was post recall as well.

I guess I'll leave this as it is unless something turns up by chance, no point poking the bear without all the stuff needed seeing as it isn't a simple thing to upgrade without the right equipment.

497P owners-- bad RADIAL lead through-hole tantalum caps!

radioconnection@...
 

During trouble shooting, I've found several bad 50 uF at 25 VDC radial lead (not SMD!) on the first few boards I pulled for inspection.
All of those caps showed severe leakage and many had open leads due to corrosion. If you own a 497P it might be worth inspecting
the first few plug in boards (LO driver, Preselector driver, etc.) to see if your version has these caps (photo posted in library.)
Serial number of unit with bad caps is B020199 version 9.7--late production run. I

Re: 497P owners-- bad RADIAL lead through-hole tantalum caps!

Chuck Harris
 

That type of capacitor is a wet slug tantalum capacitor, and
it uses sulfuric acid as its electrolyte. Over time, the
positive lead gets etched away, and the acid leaks out. Lots
are starting to fail these days... more will in the future.

Wet slug tantalum capacitors are used because they have very
high voltage ratings for their size... much higher than dry
slug tantalum capacitors. They also can be very small in
size for their voltage and capacitance. You will often find
them in sub microfarad values, at relatively high voltages,
so don't be fooled.

You can recognize this type of capacitor, as the metal case is
silver plated, with usually a mossy silver color, and the positive
terminal will have a weld, or a ball on it right next to the case
insulator. The case insulator is usually teflon. The weld/ball
joint is there to separate the internal tantalum terminal from
the more easily soldered tinned copper, or copper clad steel, wire.

There is another type of capacitor that looks similar to the
wet tantalum, but is actually a hermetically sealed dry tantalum
slug capacitor. This type has a steel colored case, a glass
insulator that is soldered into the tinned steel case, and
may or may not have a ball on the positive wire. The clue is
the glass insulator, and the color of the case.

Hermetically sealed dry slug tantalum capacitors are space rated,
and will last about forever, if you don't reverse their polarity,
or exceed their rated voltage rating. I don't believe I have
ever found one to be bad in 40 years of messing with this stuff.

One you should consider replacing (wet slug), the other you should
keep (hermetic dry slug).

-Chuck Harris

radioconnection@... wrote:

During trouble shooting, I've found several bad 50 uF at 25 VDC radial lead (not SMD!) on the first few boards I pulled for inspection.
All of those caps showed severe leakage and many had open leads due to corrosion. If you own a 497P it might be worth inspecting
the first few plug in boards (LO driver, Preselector driver, etc.) to see if your version has these caps (photo posted in library.)
Serial number of unit with bad caps is B020199 version 9.7--late production run. I



Re: 7B92A time-base plug-in odd behaviour

Colin Herbert
 

Not totally the case, Albert. As I said, the instability can be present after warm-up and can be stopped or induced by "wiggling" the Time/Div knob. Specifically, if the delaying or delayed time-base is showing (i.e. the Time/Div knob is "IN") and the Time/Div knob is pushed in a little more firmly, the time-base stops and a vertical line or dot (depending on the Y input) at the left-hand side is shown.

Yes, It is the model with the "Alt Off" position on the Trace Sep knob; the S/N is B096566.

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Albert Otten
Sent: 24 May 2019 15:31
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7B92A time-base plug-in odd behaviour

Hi Colin,

Since most of the problem disappears after warming up I guess it's more like a semiconductor issue.
Do you have the model with "Alt Off" at the ccw position of the TRACE SEP knob, S/N B06-up? There are several ICs involved in processing the Alt Off position, like U635<5> and U856<7>.

Albert

On Fri, May 24, 2019 at 03:24 PM, Colin Herbert wrote:


Thanks for the info, guys. I have now located where these switches go, but I
am unclear as to what their functions are. Perhaps I don't really need to
know, after all.

I am still perplexed by the odd behaviour of the plug-in in terms of the
behaviour before warm-up. Once the scope has warmed-up, the time-base is still
showing some instability which can be induced/stopped by wiggling the
time-base "Time/Div" knob. I am now thinking that it might be caused by poor
contact on one or more of the cam-switches. This looks like it will involve
taking the cam-switch assembly out and doing the "paper-soaked-in-IPA"
procedure. As there are about 50 of these, has anyone any idea which might be
the dodgy one(s)?

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Roger
Evans via Groups.Io
Sent: 22 May 2019 16:44
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7B92A time-base plug-in odd behaviour
On my 7B92A, the microswitch near the front panel is connected by a single
wire to P911 on the interface board. P911 is to be found on schematic <4>,
'Delaying Sweep', near the top right >corner. It is marked as going to R334 on
schematic <3> and the switch is marked as S490. S800 on 'Horizontal Logic',
schematic <7> is marked with 'pull for alt, push for delay' and is surely the
second switch on that shaft, it connects through to the Readout board.
I noticed while investigating my 7B92A that the whte plastic 'cotton reel'
that activates the microswitch didn't seem to be an entirely tight fit on the
shaft but settled down happily after a few >iterations. I hadn't noticed any
odd behaviour when it is operating in the mainframe.

Regards,
Roger



Re: Isolation???

dnmeeks
 

Using the two-probe method that Mike suggested is the usual way of making a
differential measurement (when expensive diff probes are not available, or
when the voltages are too high for them).

One thing I wanted to add, is you can simply connect the probes' grounds
together WITHOUT connecting them to chassis ground or anything else. That is
also a common technique.

Good luck -

Dan

Re: 497P owners-- bad RADIAL lead through-hole tantalum caps!

Miguel Work
 

https://nepp.nasa.gov/files/29192/NEPP-TR-2018-Teverovsky-T22-Capacitors-TN52048.pdf

-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Chuck Harris
Enviado el: viernes, 24 de mayo de 2019 17:45
Para: TekScopes@groups.io
Asunto: Re: [TekScopes] 497P owners-- bad RADIAL lead through-hole tantalum caps!

That type of capacitor is a wet slug tantalum capacitor, and it uses sulfuric acid as its electrolyte. Over time, the positive lead gets etched away, and the acid leaks out. Lots are starting to fail these days... more will in the future.

Wet slug tantalum capacitors are used because they have very high voltage ratings for their size... much higher than dry slug tantalum capacitors. They also can be very small in size for their voltage and capacitance. You will often find them in sub microfarad values, at relatively high voltages, so don't be fooled.

You can recognize this type of capacitor, as the metal case is silver plated, with usually a mossy silver color, and the positive terminal will have a weld, or a ball on it right next to the case insulator. The case insulator is usually teflon. The weld/ball joint is there to separate the internal tantalum terminal from the more easily soldered tinned copper, or copper clad steel, wire.

There is another type of capacitor that looks similar to the wet tantalum, but is actually a hermetically sealed dry tantalum slug capacitor. This type has a steel colored case, a glass insulator that is soldered into the tinned steel case, and may or may not have a ball on the positive wire. The clue is the glass insulator, and the color of the case.

Hermetically sealed dry slug tantalum capacitors are space rated, and will last about forever, if you don't reverse their polarity, or exceed their rated voltage rating. I don't believe I have ever found one to be bad in 40 years of messing with this stuff.

One you should consider replacing (wet slug), the other you should keep (hermetic dry slug).

-Chuck Harris

radioconnection@... wrote:

During trouble shooting, I've found several bad 50 uF at 25 VDC radial lead (not SMD!) on the first few boards I pulled for inspection.
All of those caps showed severe leakage and many had open leads due to
corrosion. If you own a 497P it might be worth inspecting the first
few plug in boards (LO driver, Preselector driver, etc.) to see if
your version has these caps (photo posted in library.) Serial number
of unit with bad caps is B020199 version 9.7--late production run. I



Re: Isolation???

 

Hi Harvey,
Regarding Mike Harmon's need for a way to measure a signal common mode without a true differential amplifier:

The devil is in the details. Amplifier design involves a variety of compromises which the end user would normally not be aware provided they used the amplifier as it was designed to be used. One of the things to be aware of with the vertical amplifiers Tek designs is their limited off-screen range. As long as the signals being displayed are on the screen or within a few divisions off screen they are in their linear range. But when you exceed that range the amplifier will saturate. You will not see this since it will be off screen. But the effect of this saturation is to slow down the recovery time of the signal considerably.

Tek lists the "Overdrive Recovery Time" in its specifications for each vertical amplifier. For instance the Overdrive Recovery Time for the 7A26 as 0.1mSec or less. Depending on what you are measuring that can be significant. As a general rule as long as the trace is on screen you don't have to worry about overdriving slowing or distorting the signal.

How successful you will be using one of Tek's general purpose dual trace plugins (7A12, 7A18, 7A18A, 7A24, 7A26) as a "poor-man's" differential amplifier will depend on attention to these details:
1) Both probe's must have exactly the same attenuation. The probes should be as closely matched as possible and be adjusted so their attenuation is the same.
2) The gain of each channel should be adjusted to be the same.
3) The signal coming to each channel must be attenuated the same amount by setting each Volts/Div knob the same if possible.
4) Each signal (by itself) should not go off screen at any point
5) The combined Add of CH1 to CH2 Inverted should not go off screen at any point.
6) The probe ground leads should be left floating. This may result in picking up a lot of 60Hz AC.

How much of a DC offset the vertical amplifier can handle between channels is not specified. The maximum each channel can take is for a 7A26 is 250VDC but that may only be under certain conditions.

Dennis Tillman W7PF

-----Original Message-----
From: Harvey White, Sent: Thursday, May 23, 2019 7:47 PM

On 5/23/2019 10:07 PM, Mike Harmon wrote:
I'm working on an old Motorola power supply. One of the adjustment steps says to connect a scope between the positive DC output terminal and a +41V test point inside the power supply, and look at the waveform. I have a 7904A with 7A26 vertical plugins. The problem is that whichever point I connect the common probe lead to is going to be taken to chassis (earth) ground! I'm not comfortable with lifting the scope chassis above ground by disconnecting the ground wire at the AC input.
What's immediately jumping out at me is that you have a 7904A with a 7A26. You can put a scope probe on channel 1 to the positive DC output, and the scope probe from channel 2 on the 41v test point. Set channel 2 to invert, then the display mode on the plugin to "ADD".

The 41 volts should be within the common mode range of the 7A26, but a quick look at the manual will tell you for what ranges.

Very standard way of measuring a differential voltage.

A 7A22 or a 7A13 has a built in differential voltage capability, so you wouldn't necessarily need the DC voltage, but with the 7A26, you should be just fine.

Harvey
--
Dennis Tillman W7PF
TekScopes Moderator

Re: 497P frequency counter question? How to turn on?

Steve Wiseman
 

On Thu, 23 May 2019 at 11:45, <radioconnection@...> wrote:

Well, two odd things. The switches are set for a 497P. I didn't fully
understand how the counter works. It apparently is enabled in this
particular 497P, regardless of the fact that the switches are set for the
correct model.
Bear in mind that the DIP-switches may well not actually work. Despite you
moving the lever, the metal gubbins inside may not move. This can become
confusing when debugging - check voltages, rather than relying on switch
positions.

Steve-the-bitter.

Re: 7904 excessive shadow/flare

 

Hi Max,
The expansion mesh was an engineering compromise which had significant drawbacks but all the alternatives had worse drawbacks.
Tek scopes were always known for their razor sharp trace. When the 7000 series was being designed it became apparent that the high frequencies the scope had to attain were going to require a new breakthrough if the length of the CRTs were going to be reasonable. The result was the expansion mesh which, unfortunately traded the super sharp trace for higher bandwidth.

An alternative is available however. The 7104 does not use the expansion mesh. It uses a box lens so the trace is finer. It also has the Micro Channel Plate which improved the brightness of the trace so much it was now possible to see a single 300pSec pulse in normal room light at 200pSec/Div sweep speed.

You need to get yourself a 7104. There is so much more it can do than a 7904.

Dennis Tillman W7PF

-----Original Message-----
From: unclebanjoman, Sent: Friday, May 24, 2019 6:21 AM

O.K.! Thanks to everyone for the comprehensive answers, very instructive to me!

Undoubtedly the driving circuits of the 7904 and 7804 CRTs are completely different and this could partly explain the different behavior regarding the halo / flare effect.
Over time I will get used to the remarkable brilliance of my new 7904 (and his associated halo /flares) which, moreover, is really in excellent condition and after careful calibration it matches perfectly the manual's specifications.

My 7904 has serial number B269718; reading the manufacture date of a pair of TI SNxxxx ICs, it should be from 1979.

If another 7904 to be repaired happens to me, I will be curious to observe the halo / flare effect, whether it is identical or not. I will let you know if the case.

Thanks again,
Max
--
Dennis Tillman W7PF
TekScopes Moderator

Re: 465B Attenuator servicing

Adrian
 

Hi Colin,

Yes you can, the Pro Power IPA is good I get 400ml spray cans from Farnell (or Element14 or whatever they want to be called today) or CPC (who are also Farnell) sometimes have offers on 10 packs of it. Farnell is around 3.75 GBP/can at 10 off I think.

Apart from the convenience I also work on the principal that if the pressure hasn't got out then the H2O has not got in!

I buy 25L bulk cans for the board washer on ebay where a bit of water is not an issue.

Adrian

On 5/24/2019 12:41 PM, Colin Herbert via Groups.Io wrote:
OK, so the existence of spray-can IPA is new to me. Perhaps I should see if
I can get it in the UK

2715 frequency counter problem

Jeff Woolsey
 

What with all this talk about frequency counters in spectrum analyzers,
it's probably time to address the problem my 2715 is having.

I find I can no longer count the center frequency, failing with

FREQ NORM SUGGESTED (1ST LO)

and when I try to do the reference frequency normalization
[UTIL][5][5][1][1] with an external 10MHz, that fails as well.  Trying
to use last norm or default values doesn't "fail", but I still can't
count center frequencies.  This used to work.

Running a full normalization finishes (eventually), but doesn't cure the
problem either. REF FREQ NORM still FAILed.

Advice?

--
Jeff Woolsey {{woolsey,jlw}@jlw,first.last@{gmail,jlw}}.com
Nature abhors straight antennas, clean lenses, and empty storage.
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel. -Crow on solitaire

494P problems - ROM and 1st LO

Sparky99
 

Hi everyone,

Some years ago I purchased a 494P needing repair and now finally have some time this weekend to investigate the faults. On power up it returns ROM 1 test failure. Pushing a button then completes the boot up process and the instrument appears to function in most modes, however decreasing the frequency span below 5MHz produces a 1st LO tuning failure, which is then replaced by Frequency control failure after a minute or so or when the frequency span is further reduced.

Unfortunately I don't have the extender cards (or manual), and before investing in these just wondered if anyone has any thoughts as to the best places to investigate for these errors (I'm not sure if these are separate problem, or a single problem which is associated with both the ROM and LO failures.)

Thanks for any thoughts.

Julian

Re: Latest firmware for TDS210 and TDS2CM?

 

On Fri, May 24, 2019 at 04:57 PM, Jared Cabot wrote:


it had the earthing recall fix already done too, so it was post recall as well.
That was done on TDS210 below B049400 and TDS220 below B041060.
If your S/N is lower than that and has the P/S MOD sticker the main board has been replaced to the newer version.
This was not a recall but it was done on extended warranty if one or more BNC connector had become loose.

/Håkan

Re: 7904 excessive shadow/flare

unclebanjoman
 

Thank you for your explanation Dennis. Very instructive!
I take this opportunity to inform you that a few weeks ago I sent you an e-mail regarding the repair of my 7854 smps (finished with success), but I have not received a reply.
Maybe it was lost due to an antispam or blacklisted?

Thanks again,
Max

Re: 494P problems - ROM and 1st LO

John Miles
 

Some years ago I purchased a 494P needing repair and now finally have some
time this weekend to investigate the faults. On power up it returns ROM 1 test
failure. Pushing a button then completes the boot up process and the
instrument appears to function in most modes, however decreasing the
frequency span below 5MHz produces a 1st LO tuning failure, which is then
replaced by Frequency control failure after a minute or so or when the
frequency span is further reduced.

Unfortunately I don't have the extender cards (or manual), and before investing
in these just wondered if anyone has any thoughts as to the best places to
investigate for these errors (I'm not sure if these are separate problem, or a
single problem which is associated with both the ROM and LO failures.)
I'd want to straighten out the ROM test failure before even thinking about any further troubleshooting. Trouble is, the original 494 models had mask programmed ROMs, all of them soldered in place from what I've seen, and I don't think they have ever been archived.

I would suggest checking ko4bb.com, but the ROM images no longer seem to be stored alongside the manual files. All I see for the 494 is a note (ROM_images.txt) that says "Firmware version info and ROM images are in 3_ROM_Images." There is no "3_ROM_Images" directory on the site, and the "Tek roms" folder under "01_Rom_images_and_drivers" is empty.

Didier, any input on how to navigate this apparent change in the directory structure?

Meantime, it's never a bad idea to have a look at the usual suspects, supply rail voltages and capacitors. Service volume 1 contains some troubleshooting guidance on the first LO failure, so it's a logical place to continue looking once the firmware has been ruled out.

Re: the caps ...

During trouble shooting, I've found several bad 50 uF at 25 VDC radial lead (not
SMD!) on the first few boards I pulled for inspection.
All of those caps showed severe leakage and many had open leads due to
corrosion. If you own a 497P it might be worth inspecting
the first few plug in boards (LO driver, Preselector driver, etc.) to see if your
version has these caps (photo posted in library.)
Serial number of unit with bad caps is B020199 version 9.7--late production run.
To be precise, those aren't radial-lead capacitors, they are axial-lead parts (think of an 'axle' with wheels mounted on the ends of the component leads.) An ESR meter is helpful for checking them, but often bad ones can simply be spotted visually as in your case.

Radial tantalums are the epoxy-encapsulated spheroidal ones that are famous for failing shorted, especially in circuits with a lot of inrush current and/or insufficient voltage derating. Both the radial and axial parts are common trouble sources, but they are constructed very differently as Chuck says and they fail in very different ways. I've rarely seen shorted axial caps or open radial ones.

-- john, KE5FX

Re: OT: App that keeps track of "Or Best Offer" auctions on eBay to tell you what a seller will accept.

Kevin Oconnor
 

FWIW, and more OT, I sell frequently on eBay, but almost never in auction format. I will use BIN with or without offers. When eBay shifted to profit on final value with essentially free listing it made no sense to me to continue the uncertainty of auction format. I know what margins I need to make an acceptable profit. If you have no cost basis in an item an auction may be ok, otherwise you are either under or overpriced.
eBays current returns policy is also onerous. eBay is becoming like amazon in that they will let a customer return an item for any reason. The seller generally can’t fight it. If your customer pays the shipping costs, you will have to credit the final value, refund the shipping costs and pay the return shipping if you want the item back.
I have sold electronics where the buyer removed components and returned the item as defective. eBay won’t do anything.
I now sell a lot of items with free shipping. I build the costs into the pricing. I pay FVF on the total and figure that into my margins. Whether or not I offer a guarantee, the customer always has to pay the return shipping before a refund is issued. Customers think twice if there is a hard return cost.
On eBay you have zero clarity on best-offers which, in my experience, range from 100% to 25%.

Kevin

"Volts/Div" knob for Tek 2235 needed [ Tek part No : 366-2148-01]

donald collie
 

I only really need the clear plastic skirt on this knob [minimum], or two
complete knobs [maximum], as I can probably repair the other one, which has
a cracked skirt. Willing to pay for these. Probably also used on other 22xx
types.
Also : I replaced the chopper MOSFET in the psu with a NZ$1-60 generic
type. It gets very hot to my way of thinking - too hot to hold your finger
on the heatsink near it- does anyone know if an exact replacement is
necessary - perhaps a faster type with lower losses. The MOSFET`s molex
socket shows signs of being quite hot over some time [browning]
Thankyou in anticipation for your
reply.........................................................Donald ZL4GX