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On 12/1/2014 4:27 PM, Bert Haskins bhaskins@... [TekScopes] wrote:

My very high mileage 465B seems to have lost it's legendary braggability.
It looks like something is pulling the -8 line positive to the point
where the
safety diode CR4515 turns on.
The strange thing is that this is random, and it may or may not have the
problem
upon powerup and it may run seconds or minutes before shutting down.
Don't ya just love intermittents ?

Has anyone run into this one before?

////////////////

While babysitting this, I did my trick of wiping the case and pouch with
spray can tire cleaner with the usual almost amazing results.

Swapping U4206 (the opamp) restored the -8V and my 465B lives again.
I hope!!, with intermittents it's hard to be sure.
Note to the other poster:
When the -8 supply is down, it's shuts off just about everything else.

-- Bert

The

Thanks to everyone who has emailed the list with suggestions for me to try
to cure my ailing scope. I have a copy of the service manual and have taken
a look at the various schematics. To say I'm intimated is an
understatement. Just looking at the voltages coming out of this unit scares
me. I am just starting out on this electronics hobby path, and spend my
time playing with low voltage DC circuits. To be honest, I'm not even sure
how to go about checking the voltage within the unit, and forget about
techniques to determine ripple on the supply. I have trouble really
understanding what is going on in a typical RC circuit, and that's just
running off a nine-volt battery. I'm afraid this one is over my head. It's
a shame as I really like the scope, and I'm finally in a position with my
family life that I can start fiddling with it. The scope had been in
storage for about a year as I focused on my family and work.

Again, thanks to everyone who gave some practical suggestions. I will file
them away. And if I can't find someone who has experience with these scopes
and who can take a look at it, then, one day, when I feel more confident
playing with high-voltage equipment, I might drag it out and see about
repairing it.

OK, back to my lurking status.

Kevin

Give Talon Electronics a buzz. George is an old-timer that understands TVs - and they will have your service manual, in PDF form. The B series were among the last Zenith sets made.


Talon is also the place to go for the old degaussing thermistors used in CRT televisions, glad I found them before buying on eBay.


Taylor

Hi Kevin

Before you do anything, check your power supply voltages for correct voltages AND ripple. I have repaired hundreds of 4xx scopes, some with your problems, and almost all of them had severe ripple on one of the supplies. If your scope has been stored for a while, that's by far, the most likely problem.

Keep us posted and good luck. Tad WA1FQO

Hello,


My 2465A starts up with a TEST 04 FAIL 02 diagnostic error. I understand that this has something to do with a calibration value at is limit. Is there a way to find out which calibration is involved?
And more generally, is there somekind of map available that shows the relation between the calibration location in memory (locations 00 to FFas shown in routine EXER 02) and the calibration values? In other words which memory location is related to which calibration?


Regards,


Jos, PA0JOZ

This seems reasonable:
TEKTRONIX 2465A / 2467 SERVICE MANUAL



TEKTRONIX 2465A / 2467 SERVICE MANUAL US $45.00 Used in Business & Industrial, Electrical & Test Equipment, Test Equipment



View on www.ebay.com
Preview by Yahoo

Ed;

You are right about the horizontal deflection circuitry in many of the late generation CRT TVs. The government was pushing for greater efficiency of electronic equipment to reduce power demands on the electric power industry. Most of them changed to LV power supplies that eliminated large power transformers and in turn used the horizontal deflection/HV power supply section as a switching power supply and added multiple secondary windings on the flyback transformer to derive other voltages to supply circuits in the rest of the set. Many sets had remote controls that remained on after the set was turned off and the push was there to reduce that to a flea-power level in the standby mode.

Those late generation CRT TVs can be a real bear to work on. Most of the manufacturers recommended using an isolation transformer with voltage step-down/up capability to aid in troubleshooting and provide some additional protection against electrical shock.

CRTs can hold HV for days and weeks when the set is turned off. There is a recommended way to discharge the CRT HV for each type set before servicing HV circuitry. If someone is not educated in how to safely do this, an appropriate service technician should be called. Many CRTs use a HV to achieve proper focus and that voltage can be around 4-5KV too. CRT screen grid voltages can be around 800-1.5KV. There are many locations in CRT type sets that can give a nasty shock.

One thing about changing from a CRT based set to a modern flat screen set is the difference in the aspect ratio versus the size of images on the new sets. We changed from a 32" CRT set to a flat screen LCD type years ago and found that we had to go up to a 42" wide LCD set to achieve images that had the same size vertical display as the old CRT unit. Count on up-sizing about 31 to 32% in order to still see things the same apparent size on the screen.

Joe
KC5LY

On 12/02/2014 10:10 PM, Jim Popwell jpopwell@... [TekScopes] wrote:

Siggi’s right… get the proper manual….artek’s are very good….
read the manual…. Tek has been very very good about teaching you HOW it works and then letting you trouble shoot it. The 465b is a very good scope to work on. take the feet off of the back and the two center screws and then carefully slide the whole cover off. LOOK!….. study the manual and see where things are and where the dangers are and where to make your test measurements. most of the 465 has individual transistors making things a lot easier to test. from the look of your video 1/2 of the horizontal amp is not working. first just for fun…wiggle any of the transistors on the horz bd that are in sockets…. you could get lucky…. then as Siggi suggested, check your power supply voltages. go slow and read as you go..you’ll get done…there is plenty of help here…


jim

Yeah, and it's been a while since we've had a good troubleshooting thread. I learn from all of them!

Mark

Siggi’s right… get the proper manual….artek’s are very good….
read the manual…. Tek has been very very good about teaching you HOW it works and then letting you trouble shoot it. The 465b is a very good scope to work on. take the feet off of the back and the two center screws and then carefully slide the whole cover off. LOOK!….. study the manual and see where things are and where the dangers are and where to make your test measurements. most of the 465 has individual transistors making things a lot easier to test. from the look of your video 1/2 of the horizontal amp is not working. first just for fun…wiggle any of the transistors on the horz bd that are in sockets…. you could get lucky…. then as Siggi suggested, check your power supply voltages. go slow and read as you go..you’ll get done…there is plenty of help here…


jim

On Dec 2, 2014, at 6:44 PM, siggi@... [TekScopes] <TekScopes@...> wrote:

One more thing. It appears Artek Manuals have three different 465 scans for different serial ranges < <>>. You may want to buy the one that matches your scope's serial number (on the front of the scope, I believe). Dave's scans are going to be better quality than the free one on bama, and OCR-ed too.

Feel free to shoot questions and observations as you go, someone may notice trouble you miss in the heat of the moment. In addition to tinkerers like me, there are real-life experts hanging out here, but they seem to reserve themselves for the tougher problems :).


Have fun,
Siggi

[Non-text portions of this message have been removed]

One more thing. It appears Artek Manuals have three different 465 scans for different serial ranges < >. You may want to buy the one that matches your scope's serial number (on the front of the scope, I believe). Dave's scans are going to be better quality than the free one on bama, and OCR-ed too.

Feel free to shoot questions and observations as you go, someone may notice trouble you miss in the heat of the moment. In addition to tinkerers like me, there are real-life experts hanging out here, but they seem to reserve themselves for the tougher problems :).


Have fun,
Siggi

I just took a quick peek at the horizontal deflection circuit schematics. Doesn't look too frightening, first step would be to check the DC supplies. A common failure is failing or drooping supplies. Horizontal seems to use 110V, 55V, 5V and -8V. Measure the DC level, and if you have a decent DMM, measure AC for signs of ripple too. If those check out, it's to the DC levels in the schematic to see where those are at.
You'll probably be closer to a cause with that already.


Good luck,
Siggi

Hey Kevin,

Welcome to the group. Start by grabbing the sevice manual, which can be found online. Here < > is one place. Give it a read, take a deep breath, then dive in to diagnosis and repair. These old service manuals are amazing.
Now, I don't have a scope from this era myself, but I understand the transistors may be socketed. This may help as it's easy to pull them out for testing, and to swap them around.
Do you have access to a second scope for troubleshooting?


Siggi

Hi,

I think this is the easy part, you need a restore CD and a new compatable harddisk. But one should suspect another problem "hiding" behind the missing/crashed harddisk , a bad acquisition board or CPU board. It happened to med once when I bought a LTA715 with a 1 Ghz DSO module TLA7E2, bad harddisk, was easy to restore but the expensive part was a bad DSO module!

Problem:


1. When you push it in (calibration position), value indication on led display remain on.
2. In this position any of the constant values (for example FAST 2.0), still affect the reference frequency.
3. Also when you push and keep it full in, the “8.8” diagnostic led display no lit. It go off.


Solution in my case:


1. I replace both U110 and U115. Those are two logic ic's, 74LS00 and 74LS02.
2. After that you need to readjust the “variable timing center control” R145, to center the range.


I hope this help someone with the same problem.

Gary Robert Bosworth grbosworth@... [TekScopes] wrote:

Rich:

I never worked on TVs, but numerous disimilar problems are usually
associated with the power supply which supplies all the different circuit
parts. I am surprised you cannot get a schematic from Howard Sams
publishing.

Use the chassis number to look for a manual. There are quite a few free service manual sites for consumer electronics. news:sci.elecronics.repair is a good place to ask for help with a TV set. If you don't have a Usenet server, you can reach it through Google Groups:

The 454 is old enough that contact oxidation is a problem. The transistors are
socketed and odd problems like a missing channel may be due to a poor contact.
I've fixed more than one scope of that vintage simply be reseating the transistors.

I have a 454 on my desk that I refurbed earlier this year. I really like being able
to read the controls without having to dig up a magnifier; it's my scope of choice
for when I need a quick look at something.

--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@... | Unix & Windows

Maybe it looks more promising if you know that the 454 contains no Tek-made ICs. See also


Finding the fault in the second channel must be much easier than finding the fault in the HV unit. The fault can't be that far from the "entrance" and you can compare voltages/signals of both chanels. With some luck you only have to clean a switch!

Albert

Yes, that thing must be a real beast to handle and to work on. First, be aware that it can kill you if you screw up - there's the HV dangers, plus some or all of the circuitry may not be isolated from the AC line, and the CRT can implode like a bomb if fractured. If you're not familiar with working on TVs, it may be best to let it go and get a new type to replace it.

The change in horizontal scan size with brightness indicates that the high voltage (around 27 kV for a big set like this) and H deflection (which comes from the same circuitry) are changing too much, so it is probably overloaded. Sometimes the entire TV power comes from the horizontal system too, which acts as the power supply, HV supply, and H deflection.

Since it is worst when cold, but is capable of working for a little while, I'd guess that there's a lot of dust and grime all over the HV circuitry and CRT, causing excessive leakage and overloading the HV. Depending on your local climate and humidity, this can be relieved a bit after it warms up, which could explain the startup symptoms. This is actually the best scenario - if it's not that, then there's a component failure that may be a PITA to diagnose and repair.

The HV in the set makes it an excellent electrostatic dust precipitator, so over time everything around it will become laden with filth. The first and easiest step is to clean it out as much as possible with minimal contact. With the set unplugged, and off for a while, try to blow out the dust with compressed air (and do it outdoors if possible). Always wear safety goggles when working on it, and a dust mask during cleaning, and avoid direct contact between the air nozzle and any part - a short piece of plastic tubing over the nozzle end will serve as a cushion and spacer to help avoid banging on anything.

Then try it again after cleaning, and see if it is improved. If the grime doesn't come off readily, or the symptoms don't change, then you'll have to get in deeper, with more risks. Please report back the results, and people here will give more advice on how to safely work on it up close, especially regarding discharging the HV before getting in there for more thorough cleaning or diagnosis.

Good luck.

Ed

I would say you have a number of bad capacitors. Check the caps in the power supply, around the flyback, and in the vertical circuit with an ESR meter if you have one. If you want to keep the TV, stop using it until it's fixed because it's just a matter of time until something else fails.

It sure sounds like a power supply problem, maybe a high esr capacitor?

But if it were me, I would just replace it with a LED LCD flat screen new TV and let the savings on the electric bill pay for the credit charge. Now days, you can get >36 inch LCD sets for ~~ $100 or so. Maybe even better just after Xmas.


Tom