Topics

2465B - Weak Readout Intensity


flanneltuba@...
 

Hi Folks -

I have a 2465B that I have been laboring over for a couple weeks, and have made great progress on from its initial condition, which was pretty sad—flickering speckles where the display readout should be and no visible traces. I bought it as a project, so was expecting some work, but I'm stumped on one last problem. After recapping the power supply, replacing the leaky electrolytics on the A5 board, replacing two resistors in the DAC voltage divider circuit, replacing a 74HCT00 on A5 that seemed twitchy when hit with freeze spray, programming a new Dallas NVRAM from the intact image of the original, which was thankfully still valid, and then finally running through the CAL 08 CRT adjustments, I am left with a basically working scope but one with a very dim Readout.

The main sweep trace(s) intensity is also a bit on the low side, though not nearly as dim. Increasing the intensity control beyond about half way simply causes the trace to stray out of focus rather than bringing the intensity all the way up to what would be considered "bright".

I have tried swapping U950 with one from a working 2465 with no change. I have crawled meticulously over the DAC circuit and double and triple checked all discrete parts and PCB traces, so I'm feeling fairly confident that this circuit is working, at least inasmuch as I can tell from my level of expertise, which is certainly well below anything resembling an expert, but certainly in the realm of capable and knowledgable. I have also gone through the A9 CRT power supply and DC restorer, for any obvious signs of problems or vastly incorrect voltages and found none to speak of, though I did not have the means to check the -1900v on the cathode, since I don't have a HV probe/meter.

I'm, hoping my windy description might ring familiar with one of you here, or that you might have some suggestions of where next I might next check.

Thanks in advance for any thoughts and advice.

- Scott


Chuck Harris
 

I would say that you need a new CRT. I have replaced several
in my customer's scopes that behaved the same way.

-Chuck Harris

flanneltuba@... wrote:

Hi Folks -

I have a 2465B that I have been laboring over for a couple weeks, and have made great progress on from its initial condition, which was pretty sad—flickering speckles where the display readout should be and no visible traces. I bought it as a project, so was expecting some work, but I'm stumped on one last problem. After recapping the power supply, replacing the leaky electrolytics on the A5 board, replacing two resistors in the DAC voltage divider circuit, replacing a 74HCT00 on A5 that seemed twitchy when hit with freeze spray, programming a new Dallas NVRAM from the intact image of the original, which was thankfully still valid, and then finally running through the CAL 08 CRT adjustments, I am left with a basically working scope but one with a very dim Readout.

The main sweep trace(s) intensity is also a bit on the low side, though not nearly as dim. Increasing the intensity control beyond about half way simply causes the trace to stray out of focus rather than bringing the intensity all the way up to what would be considered "bright".

I have tried swapping U950 with one from a working 2465 with no change. I have crawled meticulously over the DAC circuit and double and triple checked all discrete parts and PCB traces, so I'm feeling fairly confident that this circuit is working, at least inasmuch as I can tell from my level of expertise, which is certainly well below anything resembling an expert, but certainly in the realm of capable and knowledgable. I have also gone through the A9 CRT power supply and DC restorer, for any obvious signs of problems or vastly incorrect voltages and found none to speak of, though I did not have the means to check the -1900v on the cathode, since I don't have a HV probe/meter.

I'm, hoping my windy description might ring familiar with one of you here, or that you might have some suggestions of where next I might next check.

Thanks in advance for any thoughts and advice.

- Scott




flanneltuba@...
 

Thanks Chuck.

That was the sort of conclusion I was dreading. I do have a perfectly good 2465 (no suffix) with what I believe is the same CRT. It pains me though to pull a CRT out of an otherwise healthy scope just to prove that the subject unit has a weak CRT. I suppose it's that or roll the dice and buy a CRT off of EBay. There's a seller from Israel offering 154-0850-01 CRTs for $67, shipping included. "Very Good Working Condition." I'll admit to being a little apprehensive about buying parts from overseas.

One other thought: In the good old CRT television days, (were those the good old days?) one could often perk up a sagging CRT by bumping up the filament voltage on the heater. Sounds like something of a fool's errand for a tek scope of this sort, and more effort than it could possibly be worth, but I would be interested in knowing if anyone's ever given it a try.

Thanks,

- Scott


John Griessen
 

On 1/20/20 7:51 PM, flanneltuba@... wrote:
There's a seller from Israel offering 154-0850-01 CRTs for $67, shipping included. "Very Good Working Condition." I'll admit to being a little apprehensive about buying parts from overseas.
I would talk to the seller and tell them that you will immediately test it and ask for money back if not working. If they still want to sell to you, don't worry.
Ebay really takes care of buyers more than sellers, so all you have to do is make it plausible with photos and
they return your money.


toby@...
 

On 2020-01-20 8:51 PM, flanneltuba@... wrote:
Thanks Chuck.

That was the sort of conclusion I was dreading. I do have a perfectly good 2465 (no suffix) with what I believe is the same CRT. It pains me though to pull a CRT out of an otherwise healthy scope just to prove that the subject unit has a weak CRT. I suppose it's that or roll the dice and buy a CRT off of EBay. There's a seller from Israel offering 154-0850-01 CRTs for $67, shipping included. "Very Good Working Condition." I'll admit to being a little apprehensive about buying parts from overseas.
Israel has a lot of surplus tech. I'd go for it, it's probably fine.

The real no-go are Chinese ICs that purport to be US brands.

But then you CAN get good US surplus chips via Eastern Europe. So...

--T


One other thought: In the good old CRT television days, (were those the good old days?) one could often perk up a sagging CRT by bumping up the filament voltage on the heater. Sounds like something of a fool's errand for a tek scope of this sort, and more effort than it could possibly be worth, but I would be interested in knowing if anyone's ever given it a try.

Thanks,

- Scott



Jean-Paul
 

Scott:

A photo would be helpful.

Before a CRT replacement,RE A5 leaky SMD lytic issue,possibly the DAC and REF area have hidden damage, inner layers PCB, vias, etc.

Need to throughly inspect and clean the PCB and replace all R, C and trimpots in any corrosion affected areas.

CRT replacement is a long job and afterwards a complete CAL proceedure is required. Not for the faint of heart!

For TEK CRTs and other spares, the trusted sources are all overseas from USA: All will respond to emailed questions re shipping, warranty, etc!
Especially Condor Audio has long experience and papers on 2465 rework, caps etc. They are most generous to give advise!

Condor Audio, Tel-Aviv, Isreal
Sphere Research BC, Canada
Qservice Greece


CRTs occasionally appear on epay NIB, just add a search.


Good Luck!

Jon


Chuck Harris
 

If you do decide to go with an ebay seller, pay
particular attention that all of the wires, plugs,
and cables come with the CRT. Most scrappers think
the wires and cables are unimportant, and snip them
off close to the bottle.

You don't want a CRT like that.

Dinos in Greece sells an honest CRT. He knows what
they are for, and tests them before sending them out
to you. Several of the Israel sellers do as well.

You are probably going to spend closer to $150 all told.

The CRTs are slightly different between the 2465 and
the 2465A/B. They will interchange, but the changes
were made for a reason.

-Chuck Harris

flanneltuba@... wrote:

Thanks Chuck.

That was the sort of conclusion I was dreading. I do have a perfectly good 2465 (no suffix) with what I believe is the same CRT. It pains me though to pull a CRT out of an otherwise healthy scope just to prove that the subject unit has a weak CRT. I suppose it's that or roll the dice and buy a CRT off of EBay. There's a seller from Israel offering 154-0850-01 CRTs for $67, shipping included. "Very Good Working Condition." I'll admit to being a little apprehensive about buying parts from overseas.

One other thought: In the good old CRT television days, (were those the good old days?) one could often perk up a sagging CRT by bumping up the filament voltage on the heater. Sounds like something of a fool's errand for a tek scope of this sort, and more effort than it could possibly be worth, but I would be interested in knowing if anyone's ever given it a try.

Thanks,

- Scott




Bruce Atwood
 

When I was servicing TV's (mid 60's!) we carried, in our tube caddy tiny auto-transformers that would, for most BW tubes plug inline with the socket and boost the heater voltage by a volt or so. For Color tubes you would have to do a couple of cuts and splices. It was always the red gun. We also had a " Cathode Rejuvenator " Which would basically draw and arc between G1 and the cathode, the theory being that you could get a new oxide surface on the cathode. When it worked it was great, when it went bad the CRT was dead. There are several rejuvinators on ebay. If you are resigned to buying a new tube it might be worth it. The other trick, which is truly bold, is to whack the neck against your hand. Here the theory is that you might be able to move the cathode to the side, exposing and unused section of the oxide. Definitely wear leather gloves and a full face shield.


good luck

On 1/20/2020 8:51 PM, flanneltuba@...<mailto:flanneltuba@...> wrote:

Thanks Chuck.

That was the sort of conclusion I was dreading. I do have a perfectly good 2465 (no suffix) with what I believe is the same CRT. It pains me though to pull a CRT out of an otherwise healthy scope just to prove that the subject unit has a weak CRT. I suppose it's that or roll the dice and buy a CRT off of EBay. There's a seller from Israel offering 154-0850-01 CRTs for $67, shipping included. "Very Good Working Condition." I'll admit to being a little apprehensive about buying parts from overseas.

One other thought: In the good old CRT television days, (were those the good old days?) one could often perk up a sagging CRT by bumping up the filament voltage on the heater. Sounds like something of a fool's errand for a tek scope of this sort, and more effort than it could possibly be worth, but I would be interested in knowing if anyone's ever given it a try.

Thanks,

- Scott



.



--
Bruce Atwood PhD
Department of Astronomy
The Ohio State University
100 West 18th Ave., Room 4055
Columbus, OH 43210

Phone 614.314.0189
FAX 614.292.2928


flanneltuba@...
 

Thanks for all the responses on this. I suppose, since this is a "project" scope, and I don't really need it working in any particular time frame or to any particular level of calibration accuracy, ordering a replacement CRT might just be within the parameters of the job description.

I am quite curious about your comment Chuck, regarding the subtle differences between the 2465A/B CRT and the 2465 (no suffix) part. Assuming the differences are slight and perhaps only affect the edge parameters of its performance, the difference might well be lost on me, for the purposes I would use this scope for, which are admittedly pretty pedestrian—in the hobbyist/weekend tinkerer realm for the most part.

A friend suggested I just sell this scope on eBay, and pass its troubles on down the line. Some part of me just can't bring myself to do that. Partly because I've just put $100 worth of new parts into it, and 15 hours of bench time, but mostly I just refuse to stick some poor unsuspecting "next guy" with a bummer. So I trudge on. Deeper into the never ending 2465B project. My wife's mystified, of course, siting quite accurately, "but you must have 10 other oscilloscopes. Why do you bother?" Sound familiar to anyone here? Why climb Mt Everest?

So, being well aware of the challenge of trying to calibrate one of these high strung thoroughbreds, I march on. That said, I would be interested in any references to how to pull of the calibration without having the specialized test equipment spelled out in the manual. I do have a fair amount of decent test equipment. Calibrated signal generators, 5 ½ digit VOM, several other 80-90's vintage Tek scopes, voltage standards, and an ovenized time base frequency counter. All from the last century, but top-shelf stuff in its day. If someone can point me to a nice tutorial or web site that might help me decipher how to substitute standard bench gear of this sort for the specialized magic Tektronix gear site in the manual, I'd be grateful. Perhaps that question might better be asked in a separate thread, as it does stray from the original topic. No sure of the rules of decorum here on TekScopes Forum. I'm something of a newcomer.

- Scott


Chuck Harris
 

Hi Scott,

Visually, there are two big differences:

1) the early uses a red and black wire to drive the trace
rotation coil. The later uses a shielded wire.
2) The early has no ground point for the aquadag coating
around the funnel section. The later has a pad just
for that purpose.

Other differences I have seen are magnets on the neck that
align the beam so it goes through some of the masking
elements.

I have tried putting plain model CRT's in B scopes, and not
had good luck. I am not sure why, as the schematics and
voltages seem the same.

What I have seen is the focus point being very nearly fully
CW, and strange distortions in areas on the screen. I was
probably unlucky enough to try to sub a bad CRT for a worse
CRT...I don't know.

There are plenty of CRT's available, get the right one from
a good source. As I said earlier, Dinos in Greece is Aces.

-Chuck Harris

OBTW, if SWIMBO asks why you need all those scopes, ask her
why she needs all those shoes. Be sure to protect your head!

flanneltuba@... wrote:

Thanks for all the responses on this. I suppose, since this is a "project" scope, and I don't really need it working in any particular time frame or to any particular level of calibration accuracy, ordering a replacement CRT might just be within the parameters of the job description.

I am quite curious about your comment Chuck, regarding the subtle differences between the 2465A/B CRT and the 2465 (no suffix) part. Assuming the differences are slight and perhaps only affect the edge parameters of its performance, the difference might well be lost on me, for the purposes I would use this scope for, which are admittedly pretty pedestrian—in the hobbyist/weekend tinkerer realm for the most part.

A friend suggested I just sell this scope on eBay, and pass its troubles on down the line. Some part of me just can't bring myself to do that. Partly because I've just put $100 worth of new parts into it, and 15 hours of bench time, but mostly I just refuse to stick some poor unsuspecting "next guy" with a bummer. So I trudge on. Deeper into the never ending 2465B project. My wife's mystified, of course, siting quite accurately, "but you must have 10 other oscilloscopes. Why do you bother?" Sound familiar to anyone here? Why climb Mt Everest?

So, being well aware of the challenge of trying to calibrate one of these high strung thoroughbreds, I march on. That said, I would be interested in any references to how to pull of the calibration without having the specialized test equipment spelled out in the manual. I do have a fair amount of decent test equipment. Calibrated signal generators, 5 ½ digit VOM, several other 80-90's vintage Tek scopes, voltage standards, and an ovenized time base frequency counter. All from the last century, but top-shelf stuff in its day. If someone can point me to a nice tutorial or web site that might help me decipher how to substitute standard bench gear of this sort for the specialized magic Tektronix gear site in the manual, I'd be grateful. Perhaps that question might better be asked in a separate thread, as it does stray from the original topic. No sure of the rules of decorum here on TekScopes Forum. I'm something of a newcomer.

- Scott




satbeginner
 

Just a thought: if you tweak the Grid Bias setting on the side, do you see any change in intensity?


 

If anyone needs a jug for a 2465B I have one here in Kenilworth, UK. It had good intensity when I removed it from a 2430A with bad CCDs.

Postage to US may be prohibitive tho'

D.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of satbeginner
Sent: 22 January 2020 07:58
To: TekScopes@groups.io
Subject: Re: [TekScopes] 2465B - Weak Readout Intensity

Just a thought: if you tweak the Grid Bias setting on the side, do you see any change in intensity?


victor.silva
 

I have not had good luck buying stuff from Israel. I can think of about ten items I've bought and all of them I wish I could have changed my mind.
The only reason I can think why, is possibly all the good stuff is snapped up by technicians in country and the bottom of the barrel trash is what's left for ebay.

--Victor


Lawrance A. Schneider
 

For others of the unwashed (myself included) thank you for not passing on a problem!!
+++++++
Further: That said, I would be interested in any references to how to pull of the calibration without having the specialized test equipment spelled out in the manual.
+++++++
I strongly agree! I have NO OTHER specialized test equipment! I have a functioning (not calibrated) HP3312A generator, a HP E3630A power supply for which I just replaced the 10 digit ADC, Fluke 87 V, 121GW dmm and a Rigol 1054Z. That is it!!! I do not have a means of copying the Dallas EPROM as I have no eprom reader! I've taken the scope to the university and compared readings with some of their calibrated equipment ; so far EVRYTHING is within 0.5%. I feel blessed. I love my 2465BDM. Equally, I'm desperate to keep it in good working order. BUT HOW!! A tutorial would be most welcome!

Thank you, larry


tekscopegroup@...
 

I am sure there is a mountain of good info here in this group about how to fix and care for a 2465x, but not sure this has been compiled as a tutorial per se. For something close to that I would direct you to a long time thread over at EEVblog which deals exclusively with 2465 restorations and there are many interesting stories, experiences and information bits. Even tough it was started back in 2011 it is pretty much to this day still being updated, specially by new 2465 owners in need of advice. I found this thread while still doing research and way before even ordering my own 2465B off ebay, about a year and change ago. I ended up reading this thread from start to finish (back then it was about 47 pages, now its at 66 pages) and after doing so had the confidence that I could mostly tackle whatever the restoration job would end up needing and after a few weeks of looking at available options went ahead and got a scope. Of course it was nice and reassuring to still get occasional and very useful input from this group as well during the repair/restoration process. This EEVblog thread has become over time sort of a reference must read specially for any new/potential 2465x owners & enthusiasts.

If you feel like doing some serious reading go to:
Topic: Tektronix 2465B oscilloscope teardown (Read 419051 times)
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/

Or you can start from the most recent posts and go backwards, but I think it really paid off to read them all in sequence if you really want to get your feet wet. Quite a few of the members over there are also members of this group so you will definitively see some crossover info as well.


satbeginner
 

Been there, done that, for both my 2465, my 2465A, my 2465Adm, both my 2465B's and my 2467B....

But with respect to the original posting: "weak read out".
Did you try tweaking the Grid Bias?


flanneltuba@...
 

Regarding the adjustment of the Grid Bias, the answer is, yes. I can get a marginal increase in overall intensity from both the sweep trace and the readout characters by maxing out the Grid Bias. Alas the increase is only just enough to make the scope usable in low lighting settings. In a bright room, the readout is not discernible, and the sweep is just a bit too washed out to be useful.

There was another responder who asked if I could post a picture or two. I'm afraid I am not certain how to do that here, short of posting URL's to pictures hosted elsewhere. Is there a way to upload pics directly to the forum here?

Thanks,

- Scott


Lawrance A. Schneider
 

Thank you, larry


satbeginner
 

The 2465x uses what I call a "fly by wire" control system.

The settings from the front panel are just digital values counting up or down depending on the setting the user wants, and this is done per setting.

These digital values are available on the outputs of a register.
From there a DA converter converts the value (one at the time) into an analog value.
This analog value is redirected to the proper part of the scope using an analogue one to many switch.

All this happens in a continuous cycle, if I recall correctly there are 8 values in a round robin style.

To make a particular setting "constant" a sample and hold circuit is used.
Each individual setting has its own sample and hold circuit.
Depending on the function within the scope there is some level shifting done as well.

The sample and hold circuits are build using a simple opamp circuit.
The output of the analog switch charges a capacitor, and the high input impedance of the opamp keeps it at the presented level.
The opamp shifts the level depending on what the functionality needs.

I have seen these sample capacitors go bad as well as the opamps. (TLO72???)

I recommend checking these as well.

I'm not at home now, so I can not give you the partnumbers in the schematic right now.


tekscopegroup@...
 

On Thu, Jan 23, 2020 at 07:58 PM, Lawrance A. Schneider wrote:
Thank you, larry
You are welcomed Larry, hope that EEVBlog thread helps you out, as it has for many people so far.