--- In TekScopes@..., David <davidwhess@...> wrote:

I thought your measurement of TP1876 at the output of the z-axis
amplifier was way off?

Having been stymied from producing a clean scan of what the z-axis
waverforms should look like, I have my 7904 back together and am
prepairing to measure those test points and post them. As far as I
can tell, they redrafted the schematics but the circuits are almost
identical with no significant differences.

I can probably measure the heater current on mine with my own current
probe. I will look into it.

Maybe it is time to verify that the CRT accelleration voltage is
really there. Someone might have a suggestion for an easy way to test
for its presence without measuring it directly.

On Thu, 12 Jul 2012 18:02:12 -0000, "keithostertag"
<keitho@...> wrote:

Still trying to confirm whether the CRT is good or not, or why there's no activity from it.

Here is a photo of the current through the conductor to pin 1 to the CRT, which is one side of the (6.3V) heater:



Does this seem reasonable? Running about 22KHz, but I didn't realize it would be a square wave... with the current probe set to 10mA/mV, this calculates to about 215mA AC p-p, right? Is this normal/reasonable for a CRT heater? I don't see anywhere in the manual that indicates what it should be. One of you guys will have the experience to know if it is within the ball-park of normal operations.

I also looked at pins 2,3, and 4 of the CRT. None of those show any current using my current probe (with no scope input). Shouldn't pin 2 (the 3KV cathode) show some current? (measure -2950V with my Fluke and HV probe).

Basically at this point I am struggling to find out why there is no CRT activity (no BF, no readout, no trace, no dot). So far, the tests points I've looked at on the z-axis board seem within tolerances, though I can't go very far into the calibration check list without a trace. Same with the vertical and horizontal deflection inputs.

Any suggestions as to how to troubleshoot this would be greatly appreciated.

Thanks,
Keith Ostertag

--- In TekScopes@..., David <davidwhess@...> wrote:

I thought your measurement of TP1876 at the output of the z-axis
amplifier was way off?

Having been stymied from producing a clean scan of what the z-axis
waverforms should look like, I have my 7904 back together and am
prepairing to measure those test points and post them. As far as I
can tell, they redrafted the schematics but the circuits are almost
identical with no significant differences.

I can probably measure the heater current on mine with my own current
probe. I will look into it.

Maybe it is time to verify that the CRT accelleration voltage is
really there. Someone might have a suggestion for an easy way to test
for its presence without measuring it directly.

On Thu, 12 Jul 2012 18:02:12 -0000, "keithostertag"
<keitho@...> wrote:

Still trying to confirm whether the CRT is good or not, or why there's no activity from it.

Here is a photo of the current through the conductor to pin 1 to the CRT, which is one side of the (6.3V) heater:



Does this seem reasonable? Running about 22KHz, but I didn't realize it would be a square wave... with the current probe set to 10mA/mV, this calculates to about 215mA AC p-p, right? Is this normal/reasonable for a CRT heater? I don't see anywhere in the manual that indicates what it should be. One of you guys will have the experience to know if it is within the ball-park of normal operations.

I also looked at pins 2,3, and 4 of the CRT. None of those show any current using my current probe (with no scope input). Shouldn't pin 2 (the 3KV cathode) show some current? (measure -2950V with my Fluke and HV probe).

Basically at this point I am struggling to find out why there is no CRT activity (no BF, no readout, no trace, no dot). So far, the tests points I've looked at on the z-axis board seem within tolerances, though I can't go very far into the calibration check list without a trace. Same with the vertical and horizontal deflection inputs.

Any suggestions as to how to troubleshoot this would be greatly appreciated.

Thanks,
Keith Ostertag

On Tue, Jul 10, 2012 at 8:43 PM, Rob <rgwood@...> wrote:

Thanks guys on the impromptu training on the 7854. I had thought to be
helpful but I should have checked for similarities first before posting. At
least it is good to hear that if/when I finally get one of those my
experience in the other 7000's won't be a total waste. the readout is
basically the same on all of the other scopes I have. Anyway, my hope is I
did not confuse the original poster in my exuberance to finally have a
chance of helping for a change *smile*.

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of David
Sent: Tuesday, July 10, 2012 10:14 AM
To: TekScopes@...
Subject: Re: [TekScopes] Re: 7854: Excessive stored trace brightness.

The readout acquire uses the same ICs although it is encoded to binary and
processed by the microprocessor before being displayed.

I left out checking for the time slot pulse in my post. If it was missing,
then there could be short/open or U2320 (155-0017-00) which is another
custom Tektronix readout could be bad.

On Tue, 10 Jul 2012 13:13:23 -0000, "Albert" <aodiversen@...>
wrote:

Sure, though readout acquire, as viewed from the plugins, is still the old

method. Missing units in readout could be caused by a fault during the
corresponding time slot TS-9. I would first of all check for the presence of
the -15V pulses at the main interface connectors, contacts B39. All 4 plugin
positions have the B39 contacts in common so all should show the TS-9 pulse.

Albert

--- In TekScopes@..., "David C. Partridge"

<david.partridge@...> wrote:

The readout in the 7854 is radically different - it is part of one of the

logic boards.

Dave
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On
Behalf Of Rob
Sent: 10 July 2012 02:49
To: TekScopes@...
Subject: RE: [TekScopes] 7854: Excessive stored trace brightness.

P.S. All the numbers above are for a 7904. I assume they are the same

in a 7854.

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--- In TekScopes@..., "dutchbosstard" <childwhereugo@...> wrote:

thanks morris. I am going to try and buy the silver solder from stan's parts shop. I might also try and buy the cover clamps from there also since there is a minimum $10 order.

will I need to use flux with this tektronix silver solder, or is it already flux-cored? All the soldering I have done has always been with 60/40 flux cored solder, so I have never used flux and solder separately. If I do need to use flux, which kind should I use with this kind of solder?

As far as the fan goes, couldnt I just cut the wires and after I take it apart, soak it if necessary, and re-lube it, reconnect it back using these insulated male/female disconnect connectors from home depot? I know it would probably look tacky, but couldn't this possibly be better than having to solder/unsolder, especially if i ever need to pull the fan out again? Or do I just need to suck it up and stop being a pansy about soldering? haha.

this is what I had in mind if i were to just cut the wires:



let me know what you think, I am still going to try and buy about 15-20 feet of silver solder, in case I ever need it.

also since im not gonna be able to power on the scope until I get that fan taken care of, I did find V799, did some reading and looked up the datasheet, checked it with my multimeter and it measured zero ohms between pins 3&4 and 2&7. pin 5 is the plate, and i'm not sure if i could check it's resistance.

let me know what you think,

-Robby

--- In TekScopes@..., "Morris" <vilgotch@> wrote:

Hi again Robbie,

In answer to your questions, firstly no, you don't have to soak the bearings if you can get them turning. I have found that a lot of gunk collects there in some scopes if they were used in a dusty environment so I just like to give them a good clean. If 3-in-one works then go with it.

Tek solder would be ideal if you can get it. If it appears cheaply on ebay then so much the better.

The easiest way to check the sensing diode is to see if it lights up. Checking the filament pins with an ohmmeter will work but it should be obvious by inspection. Note that those tubes have an internal spring contact that shorts across the diode (anode to one side of filament) if and when the filament burns out. That's a fail safe mechanism to make sure the regulated heater voltage fails low.

It's good that you have the A type newer timebases. They can be a bit finicky to get going but hopefully the tunnel diodes in them are OK. We'll see once you've got through the preparatory stuff.

Let us know how you get on,

Morris


--- In TekScopes@..., "dutchbosstard" <childwhereugo@> wrote:

first I would like to say thank you for the very clear advice.

I have been slowly going through the manual since the day i got the scope, but i definitely need to read it thoroughly instead of just kind of skimming it. Yes, i did read the part in the manual about running it with all plug-ins installed. If anyone would like to know, I believe my scope may be a 1967 model, since there is a little information diagram on the bottom of the power supply that has written that it was inspected in '67. It also has the newer 21A and 22A time bases, and the vertical plugins that came with it are the type 53/54K and the type M 4 trace plugin. I do not know the name of the style of screw-in connector, not a BNC. they look like these:




can someone give me the name for those things? i guess i should be happy that the 2 probes that came with the scope have the same strange looking connector. the timebases have BNC connectors.

as far as the fans go, would it really be necessary to soak them in diesel fuel, if i happen to get em turning after disassembly? I know that electric motors and generators often use oil-lite bearings, i've never heard of the bearings losing their oil, but then again I dont know much about oil-lite other than it feels strange, looks strange, and has an interesting smell to it. However, if i cannot get the 555 fan to get turn nicely after taking it apart, i will surely follow your advice word for word.

as far as solder goes, I did indeed read where it says in the power supply to use the silver bearing solder. what I am confused on is: is this solder flux cored, or do i need to solder it with external flux (ive only ever soldered with 60/40 flux cored solder) or does this specific solder need flux? my last solder question is, should I buy this tektronix solder off of ebay?



as far as V799, the thermonic diode, I just did a little reading about it online, could i look up the datasheet to find the pins, remove it and measure the resistance of the filament to make sure its not blown that way?

thanks,

Robby


--- In TekScopes@..., "Morris" <vilgotch@> wrote:

Hi,

Let me add some comments from an experienced Tek scope (including a 555 scoposaurus) restorer to the excellent advice you have had so far:

I gather you are not experienced with vacuum tube equipment although you have worked with high voltage before. I assume you know how to be careful around gutsy power supplies, there's more than enough juice in the 555 to kill you.

At this stage you have had the scope running after a fashion so you can probably assume that the CRT is OK, you know the time delay relay works, no electrolytics have blown up, no smoke got released and the power supplies are at least producing enough to a give you a green flash. That's all very encouraging.

What I would do now is to stop and read the manual thoroughly so you become familiar with what's there, where the test points are and how the thing works. Then I would give it as thorough a clean as possible as has been discussed. The next thing to do before anything else is to get the fan working. The best way to do that is to remove it altogether which involves unsoldering the leads from the tagstrip, taking careful note of where to reconnect them. If there is no little roll of silver solder with the scope you need to go and get some - the commercially available silver bearing solder stuff is not exactly the same as the Tek solder but is preferable to ordinary 60/40 which should not be used.

Taking the fan motor apart is pretty straightforward, just make sure you record where everything goes so you can reassemble it. The bearings can be soaked in thin oil (such as 3-in-1), diesel fuel or kerosene to clean all the gunk off and then lubed with something thicker. Car engine oil is probably OK. Once it spins freely, you can put it back. Eventually you might do the same for the fan in the power supply but for now just put some oil into the oil holes on the bearings.

Once both fans are running you can run the scope again and check the LV power supply voltages at the test points. Start with the -150 which is the master reference for everything else. You don't need to measure the HV just yet but make sure the heater voltages are right. The heater supply is regulated using V799 in the power supply, a special thermal sensing diode type 2AS15A. If it's failed with an open filament then the heater voltage will be low to pretty well all the tubes in the scope. If V799's not lighting up you will need to suspend all operations until you can find a replacement (plenty available on eBay).

Incidentally I missed whether you mentioned which timebase & vertical plugins are installed. Please let us know. Don't try to run the scope without plugins.

Once you've done all that, get back to the brains trust here and I'm sure you will get excellent advice on how to proceed further.

Good Luck!!

Morris

--- In TekScopes@..., "dutchbosstard" <childwhereugo@> wrote:

so yesterday i got real brave and decided to power the scope up. the power supply had the proper 5 amp fuse, but the heater supply had an 8 amp fuse instead of the 7 amp one. i checked the fan in the power supply and i tried turning it by hand and it seemed to spin pretty well, but the larger fan in the 555 was harder to turn, and i also had to remove its dust screen since the dust screen was pressed in, preventing the fan's movement. i powered it on with all the covers off and the PSU fan came on right away, but i noticed that the 555's fan wasnt powering on. all the tubes started to glow and i heard a relay click and then i started fiddling trying to find a beam. i rotated both of the horizontal display knobs and i couldnt get a trace, but every time i turned the know, a trace would appear for a slit second. both beams did this. after the scope had teen turned on for a whole minute, i decided to shut the thing off since the fan in the 555 didnt come off. the fan in the PSU box also had originally started rotating rather slow, but kept gaining speed until after about 30 seconds it started rotating extremely fast.

now this might be a dumb question, but could I have damaged anything by powering it on with a 8amp heater supply fuse instead of the listed 7amp? and also, is there any difference between a "slo-blow" fuse and a "time-delay" fuse?

also, what should i do about the fan in the 555? should i disconnect it and try to power it up with 115v on its own?

--- In TekScopes@..., "mickeyaslam" <mickeyaslam@...> wrote:

I checked the no load voltages according to repair manual and most of the power rails are not powering up. For example 25v power rails show only 4.8v or so. Only good power rails was 5V and yes pin one and three on J6 were shorted as suggested in the manual. I also hear the hissing sound from the main transformer for low voltage power rails. It is located on the side of the PCB and it is the biggest transformer of all the other ones.

--- In TekScopes@..., David <davidwhess@> wrote:

My first thought was capacitors.

How did you narrow down the cause to the LV power supply module?

On Wed, 11 Jul 2012 13:44:50 -0000, "mickeyaslam"
<mickeyaslam@> wrote:

I have a TDS684A scope which refuses to turn ON, instead when power button is pressed it tries to power ON but shuts off right away and then it get stuck in half second ON half second OFF loop. I have narrowed down the cause to be LV power supply module. I have replaced all the electrolytic caps on the power supply but no change. All the power diodes and MOSFET seems to be working fine.

Any help in the right direction will be greatly appreciated. Even better if someone has schematic for power supply module.

thanks'

mickey

--- In TekScopes@..., "Rob" <rgwood@...> wrote:

It is a bit more complicated than just the ions and what is left after
evaporation/boiling on soft water vs. hard, etc. I don't want to get to
technical nor argumentative. However soft water via ion exchange is better
than hard water (because it rinses better). However it is not as good as RO
or distilled, etc.

So yes soft water does imply conductivity as the ions are simply swapped for
different. Soft does however leave less gunk around after washing and
rinsing than a hard water alternative (solubility of the ions is the
driver... calcium in particular has a negative solubility) even though it is
simply different ions as others have already said/pointed out.

Bottom line I would not use hard water, I would consider soft water in a
pinch but would prefer RO or distilled. I assume after all that soaps of
some kind are involved so rinsing ability is likely key.

All that said, I have refrained from using water as I do not have good
drying methods at my disposal. In addition, it still just seams "wrong"
somehow to me to mix water and electronics (especially socketed, etc.)...

Rob
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of John Griessen
Sent: Wednesday, July 11, 2012 6:04 PM
To: TekScopes@...
Subject: Re: [TekScopes] Notes about washing Tektronix Oscillosopes

On 07/11/2012 04:58 PM, David wrote:

Softened
water was an improvement for washing PC boards but we still rinsed in
distilled water or water from reverse osmosis.

Ah, so...

ion exchange (water softener system) does imply conductive/salty as I was
thinking.


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I don't yet have a working differential plugin.

Thanks,
Keith Ostertag

--- In TekScopes@..., "w6vy" <w6vy@...> wrote:

Thanks for all the replies. Haven't found anything locally on craigslist but I'll put a want in on the West Coast 40 Meter swap net and see what I can come up with. I'm watching a couple on eBay.

Bob

--- In TekScopes@..., "Steve" <ditter2@> wrote:

--- In TekScopes@..., "w6vy" <w6vy@> wrote:

What is a reasonable price to pay for a 465B in good condition - with probes and manual?

Thanks
Bob

They routinely go for $100-$120 at hamfests in the pacific northwest. (475/475A go for about $200). You willget a better price at a hamefest of craiglist, as on e-bay you are competing with everyone in the world.

- Steve

--- In TekScopes@..., "Steve" <ditter2@...> wrote:

--- In TekScopes@..., "w6vy" <w6vy@> wrote:

What is a reasonable price to pay for a 465B in good condition - with probes and manual?

Thanks
Bob

They routinely go for $100-$120 at hamfests in the pacific northwest. (475/475A go for about $200). You willget a better price at a hamefest of craiglist, as on e-bay you are competing with everyone in the world.

- Steve

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of Rob
Sent: Wednesday, July 11, 2012 7:01 PM
To: TekScopes@...
Subject: RE: [TekScopes] Notes about washing Tektronix Oscillosopes

It is a bit more complicated than just the ions and what is left after
evaporation/boiling on soft water vs. hard, etc. I don't want to get to
technical nor argumentative. However soft water via ion exchange is better
than hard water (because it rinses better). However it is not as good as RO
or distilled, etc.

So yes soft water does imply conductivity as the ions are simply swapped for
different. Soft does however leave less gunk around after washing and
rinsing than a hard water alternative (solubility of the ions is the
driver... calcium in particular has a negative solubility) even though it is
simply different ions as others have already said/pointed out.

Bottom line I would not use hard water, I would consider soft water in a
pinch but would prefer RO or distilled. I assume after all that soaps of
some kind are involved so rinsing ability is likely key.

All that said, I have refrained from using water as I do not have good
drying methods at my disposal. In addition, it still just seams "wrong"
somehow to me to mix water and electronics (especially socketed, etc.)...

Rob
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of John Griessen
Sent: Wednesday, July 11, 2012 6:04 PM
To: TekScopes@...
Subject: Re: [TekScopes] Notes about washing Tektronix Oscillosopes

On 07/11/2012 04:58 PM, David wrote:

Softened
water was an improvement for washing PC boards but we still rinsed in
distilled water or water from reverse osmosis.

Ah, so...

ion exchange (water softener system) does imply conductive/salty as I was
thinking.


------------------------------------

Yahoo! Groups Links






------------------------------------

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-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of John Griessen
Sent: Wednesday, July 11, 2012 6:04 PM
To: TekScopes@...
Subject: Re: [TekScopes] Notes about washing Tektronix Oscillosopes

On 07/11/2012 04:58 PM, David wrote:

Softened
water was an improvement for washing PC boards but we still rinsed in
distilled water or water from reverse osmosis.

Ah, so...

ion exchange (water softener system) does imply conductive/salty as I was
thinking.


------------------------------------

Yahoo! Groups Links