开云体育

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

Good day. I'm having some trouble with my beloved Tektronix 465B and I'm hoping some gurus on this list may be able to assist me. Let me first say that I am a fledgling electronics hobbyist and have little or no experience troubleshooting something as complex as this scope. I purchased the Tek 465B around 2012. When I purchased the scope, all was well. Now, a few years later and the scope is acting up. I had the scope in a closet for about a year. My first boy was born and I didn't have time to play with it. In any case, I just pulled out the scope this week and hooked it up to a signal generator as a test. The scope trace only fills part of the screen.Here is a link to a short youtube video I posted that shows the problem.




I contacted a friend who is a Tek expert who said the problem may be that half of the differential drive has failed. As I am completely new to this electronics game, I don't feel comfortable breaking into the scope and probing around. Maybe I will in a few years after I get more building and troubleshooting experience under my belt. So I thought I would reach out to this group to see if anyone here has had a similar experience and can guide me along the way, or if there are any businesses/hobbyists that I can send the scope for possible repair.


Thank you for any assistance. I look forward to hearing back.


Kevin

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. Best of luck to you. I had several brand new TVs go
intermittent recently. We would probably be better off without them.

Gary
On Dec 1, 2014 11:56 PM, "mechanic_2@... [TekScopes]" <
TekScopes@...> wrote:

Hello all,
I am having a problem with my Zenith 36" CRT TV. It goes into shutdown
mode. When it is cold I have to start it up over and over before it will
stay on. Also as the brightness of the screen varies the size of the
horizontal axes varies. When the size becomes very small the tv goes into
shutdown. I believe that it is dropping into low voltage shutdown.
Also the top of the screen is rolling over and it started about 2 months
ago. At first it was just a variation in the size of the horizontal axes
but it has been getting progressively worst. Up to last week it would stay
on once it was warmed up but now it is shutting down when the screen has a
lot of white space on it.
I know that without a schematic and a list of the voltages that it will be
impossible to fix it but what I am asking for is any thoughts or ideas of
where to look first. This thing is a monster and I will have to have a
friend come over and stay here for a while to help me move it.
Any thoughts and/or ideas?
Thanks,
rich!

Ronan,

I think you will find the 454 much easier to work on than a 485. The cover comes off easily, and many (not all) circuits can be accessed conveniently.

--John Gord

Does changing the brightness also change the focus of the picture? If so the CRT may be conducting too much due to improper bias of the control and screen grids.

Vertical fold-over can also be an indication of power supply problems. So is inadequate horizontal deflection. The first place to look is in the LV power supply. Look for any high wattage resistors that may have fractured solder underneath on the PC board where they are connected. The same can happen on power regulation transistors and ICs. This is a common problem with both tube type and solid state power supplies. The unit could also have electrolytic capacitors that have dried out enough to cause problems too. Many sets produce from the late 1960s onward have special parts that are safety related items and must be replaced with specific part types in order to maintain compliance with fire and other safety issues.

Some sets also had HV regulation circuits that would kick the set out of horizontal frequency lock to keep the HV from rising too high (and consequently cause X-rays from the CRT and HV components). That makes the set unwatchable of course. You did not describe that type problem though.

I would start with the LV power supply. There are still sources for schematics on TV sets, so find the one appropriate for your set first. Working on one without the schematic is a stab in the dark. The schematic will tell you what voltages to expect and what waveforms to expect in each circuit if you get a good manufacturer's schematic or a Sam's schematic.

Joe
KC5LY

Dave,
It is a B36A24Z.
Thanks,
rich!

Model number?

Hello all,
I am having a problem with my Zenith 36" CRT TV. It goes into shutdown mode. When it is cold I have to start it up over and over before it will stay on. Also as the brightness of the screen varies the size of the horizontal axes varies. When the size becomes very small the tv goes into shutdown. I believe that it is dropping into low voltage shutdown.
Also the top of the screen is rolling over and it started about 2 months ago. At first it was just a variation in the size of the horizontal axes but it has been getting progressively worst. Up to last week it would stay on once it was warmed up but now it is shutting down when the screen has a lot of white space on it.
I know that without a schematic and a list of the voltages that it will be impossible to fix it but what I am asking for is any thoughts or ideas of where to look first. This thing is a monster and I will have to have a friend come over and stay here for a while to help me move it.
Any thoughts and/or ideas?
Thanks,
rich!

Thanks for the encouragement - I agree generally, it is just that my primary focus is to use test equipment in service/design,rather than to spend inordinate time repairing it. Having said that I know I would love doing anything I felt was a challenge I could overcome!

If I could have found someone -- an expert on the 485 to take it on for a reasonable fee, I wouldn't mind so much compensating said person... however I DID get immense satisfaction I followed the Tek manual to isolate the problem; without that I would have given up a long time ago!


With the 454, it's no match for the 485, but at least it's a Tek analog scope with no apparent HV issue (yet).

Cheers,
Ronan/KB6NHQ

Ronan:

There is a great amount of satisfaction in successfully repairing high-tech
instrumentation. Some of my old equipment out-performs the latest
offerings. Often it is worth the trouble to do the repairs. Try not to
think of the disappointments.

Gary
On Dec 1, 2014 6:31 PM, "dudelucky583@... [TekScopes]" <
TekScopes@...> wrote:

Hello!


I've troubleshot my beloved 485, to the point I have to just let go -- I
must send it to my scrap heap (spare parts shed) -- with the help of the
service manual, I traced the problem to the -3KV cathode supply; once I got
into it and tore the scope apart to get to the "transformer board" (whoa
what a mess) -- I realized I might not have the time/patience to get it
back together, even if I could test the HV diodes, multiplier (for anode)
etc, "pot" my own multiplier, find a replacement, etc....


How much time should a person spend reviving a 485 when you can find them
on craigslist for $400 "calibrated"?


I used a digital scope (Rigol 50mhz) to easily capture that 485 startup
"balancing node" thingy, where actually the Rigol proved it's $300 value by
saving me a lot of headaches to capture that 20ms period after power up and
after the 6ms initial delay. It asked that I bend a pin on one of those
"comb" connectors, and if the scope powered up (sans HV), it was the
cathode supply short circuit (then I didn't find any obvious problem in the
HV in continuity checks I assume my DVM doesn't put enough volts out to
cause forward conduction).


So, if anyone has any "encouragement" on what I should / can do with the
485, that's appeareciated but by default I am "beyond mourning" -- I'll
just leave it for another day or when I need to steal parts to make a Ham
radio.


Yesterday I acquired a 454; it actually has one trace working (rough test)
and the other trace doesn't appear. Anyone know if this is a "known or
common issue"? SN 60101XX series, if that helps. I hope to avoid another
half day wasted ending in frustration as I don't have the parts nor
experience to know what parts to substitute, where to get oddities that
won't break my bank, etc.


I've not mustered the courage to crack the 454 open, I bought it from a
fellow HAM who knows what he's doing, I don't think repair attempts have
been like made.


I have one thread of me wanting a Tek analog scope back on my bench, I
know the Rigol has it's own plusses/minuses, but I have only so many years
to spin away on fixing stuff so I can do what I want to do ultimately
(building ham equipment and actually using it).


Thank you kindly!!!!!!!


Ronan/KB6NHQ
Meadow Vista, CA

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Hello!


I've troubleshot my beloved 485, to the point I have to just let go -- I must send it to my scrap heap (spare parts shed) -- with the help of the service manual, I traced the problem to the -3KV cathode supply; once I got into it and tore the scope apart to get to the "transformer board" (whoa what a mess) -- I realized I might not have the time/patience to get it back together, even if I could test the HV diodes, multiplier (for anode) etc, "pot" my own multiplier, find a replacement, etc....


How much time should a person spend reviving a 485 when you can find them on craigslist for $400 "calibrated"?


I used a digital scope (Rigol 50mhz) to easily capture that 485 startup "balancing node" thingy, where actually the Rigol proved it's $300 value by saving me a lot of headaches to capture that 20ms period after power up and after the 6ms initial delay. It asked that I bend a pin on one of those "comb" connectors, and if the scope powered up (sans HV), it was the cathode supply short circuit (then I didn't find any obvious problem in the HV in continuity checks I assume my DVM doesn't put enough volts out to cause forward conduction).


So, if anyone has any "encouragement" on what I should / can do with the 485, that's appeareciated but by default I am "beyond mourning" -- I'll just leave it for another day or when I need to steal parts to make a Ham radio.


Yesterday I acquired a 454; it actually has one trace working (rough test) and the other trace doesn't appear. Anyone know if this is a "known or common issue"? SN 60101XX series, if that helps. I hope to avoid another half day wasted ending in frustration as I don't have the parts nor experience to know what parts to substitute, where to get oddities that won't break my bank, etc.


I've not mustered the courage to crack the 454 open, I bought it from a fellow HAM who knows what he's doing, I don't think repair attempts have been like made.


I have one thread of me wanting a Tek analog scope back on my bench, I know the Rigol has it's own plusses/minuses, but I have only so many years to spin away on fixing stuff so I can do what I want to do ultimately (building ham equipment and actually using it).


Thank you kindly!!!!!!!


Ronan/KB6NHQ
Meadow Vista, CA

My first guess is that the full wave bridge for the -8 volt supply is dying.
Replace it with the highest spec bridge that can be made to fit. The
lead wire size of the full wave bridge is the limitation as far as I know.
Bend the leads to adjust the spacing and then bend all of the leads to
lay the bridge over on an angle so you can do the soldering easily.
tom jobe...

Hank:

It is a slow pulsation as if it is a sinusoidal tied to the line
frequency. It does not flash bright and dull. The trace never completely
disappears. Someday I may find the time to go in with a scope probe to see
what is varying. It does not seem to be connected to any logic signal
phenomenon. Actually, I just wish it would go away. In the 1960's, I
worked in the test, calibration, and repair department at Systron-Donner.
After so many years of troubleshooting, I have little patience with
annoying aberations. Thanx for your interest in this current nightmare.

Gary
On Dec 1, 2014 2:48 PM, "HankC hankc918@... [TekScopes]" <
TekScopes@...> wrote:

Gary,
What kind of pulsating display does your 7904 have ?Is it worse at slower
sweep speeds ?If so, the readout may be in "Gated" mode.
HankC, Boston
WA1HOS

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