Problem with Horizontal trace on Tektronix 465B

[Tedyp]

Hello,
I am asking for the "guru"s help and assistance...
I read all the posts on this forum about the similar problem. I have no horizontal trace, and I am trying to fix it myself, as it's my main apparatus - I can do nothing without it - out of work...:sad:
After opening the case, I've checked all the supply voltages, I found them OK (I couldn't check the HV).
I've found that one resistor is overheating and checked it. It is R4376. From one side (Right side) it shows me approx 54.5V, and from the other side - 0V. The problem is that after downloading the manual in .djvu form, I couldn't find it in any schematic. I know its value (953 Ohm), and it is OK, however is becoming very hot in less than a minute. I suppose (not sure) that this is the "area" to search - but I cannot find it anywhere. Any help please?
As I've mentioned, this is my main tool, and as a pensioner I cannot afford to purchase a better or newer one.
I've also uploaded the manual at this link: **broken link removed**
Thank you in advance for helping.
Sincerely,
Tedy

 

[BradtheRad]

Your photos show the horizontal sweep using only 1/5 of the screen.
Ordinarily it should be possible to adjust so that it starts at the extreme left, and travels to the extreme right.

Almost certainly some component has developed a low resistance, with two effects:

* drawing away current through the hot resistor

* causing your horizontal sweep to shrink.

One likely culprit to look for is a nearby transistor.

Can you adjust the width of trace to any degree?

Can you alter its position left/right?

 

[FvM]

There are some instruments with hard-to-get service manuals. Classical Tektronix instrumenst aren't among them! Tek465 schematics are definitely available at the internet, e.g. here https://bama.edebris.com/manuals/tek/

But it may take about quarter or half an hour to locate said R4376 in one of the pdf copies. Thus I suggest that you try to find a suitable handbook version among the available ones and refer to the respective page or post the extracted pdf page.

The manuals I know have a lot of expected voltage numbers in it. It would be reasonable if you check it beforehand.

 

[Tedyp]

Your photos show the horizontal sweep using only 1/5 of the screen.
Ordinarily it should be possible to adjust so that it starts at the extreme left, and travels to the extreme right.

Almost certainly some component has developed a low resistance, with two effects:

* drawing away current through the hot resistor

* causing your horizontal sweep to shrink.

One likely culprit to look for is a nearby transistor.

Can you adjust the width of trace to any degree?

Can you alter its position left/right?

Thank you for your answer BradtheRad,
I've tried again to find the the "thief" - I found a capacitor, probably a decoupling one, 0.1u/50V having a 2.2 Ohm Resistance. I found 2 through-hole caps 473, solder them in parallel, and the trace appeared!
I can adjust the trace vertically and horizontally. without problem.
However, a new problem arose: the trace shows me some ripple, a sinusoidal like signal which I can't get rid of it. Maybe is caused as the scope is still open and has no screening...
I'll check this, however, it shows signs of life. Thanks again.
Tedy

---------- Post added at 10:29 ---------- Previous post was at 10:26 ----------

There are some instruments with hard-to-get service manuals. Classical Tektronix instrumenst aren't among them! Tek465 schematics are definitely available at the internet, e.g. here https://bama.edebris.com/manuals/tek/

But it may take about quarter or half an hour to locate said R4376 in one of the pdf copies. Thus I suggest that you try to find a suitable handbook version among the available ones and refer to the respective page or post the extracted pdf page.

The manuals I know have a lot of expected voltage numbers in it. It would be reasonable if you check it beforehand.

Thank you for your answer FvM
The file I've d/lded is in a format new for me. Very useful, as you may zoom without losing any detail. I've tried to do a trick: I've converted it to a pdf, and used an OCR software and I've tried to locate this component. I had no success.
There is no way to find the main board schematics... without electronic schematic is just shooting in the air, and hoping to get a duck...
It is really strange, most of the boards appear - having the relevant schematics and components values, this one is missing, or...spending almost 2 hours, I cannot find it.
Thanks again,
Tedy

 

[Tedyp]

Hello again,
I am attaching a new display picture, explaining how it looks now. The "ripple" responds to all the adjustments, increasing and decreasing. Any idea(s)

 

[E-design]

Did you replace C4375?

The manual you downloaded seems to have ASSY 10 (Horizontal amplifier) circuit missing.
R4376 is on there.

With a scope of this age it is always a good idea to also measure the ripple on all the DC supplies (use a Fluke on AC setting).
I have seen a lot of Tek scopes with dried up electrolytics that can create very strange looking faults.

 

[Tedyp]

Did you replace C4375?

The manual you downloaded seems to have ASSY 10 (Horizontal amplifier) circuit missing.
R4376 is on there.

With a scope of this age it is always a good idea to also measure the ripple on all the DC supplies (use a Fluke on AC setting).
I have seen a lot of Tek scopes with dried up electrolytics that can create very strange looking faults.

Hello,
C4375 wast the first one to be replaced, as it had a value of 2.4 OHM!
I assumed that the problem is on the vertical amp now, however I haven't checked the PS ripple. As I don't have any idea the value of the AC do I have to expect I'll be thankful for assistance. I'll purchase in a few hours a large cap, something as 470uF / 100V, I'll put it in parallel with each capacitor on the PS. However, as far as I see, the ripple is changing (the amplitude) according to my hand proximity, looking as there is a missing ground somewhere.
The most confusing thing thing is that there is a button named "A Trig View" - it shows on the display without any ripple!
If you may have the link to a site where I could find the circuit INCLUDING the ASSY 10, I'll be very grateful.
Thank you.
Tedy

 

[Tedyp]

Well my friends, I think I fixed it...up to next time of course :smile:
I've learned 3 important things - and one of them I'll repeat in an additional thread, as I think it is very, important for all of us, and I hope it won't be moved or deleted.
1. Friendship and Good Will are some of most important things in the world. Thank to all the friends who assisted me, helped me and spent their precious time for me.
2. Never to give up - there is always a hope.
3. Never , but Never try to fix an oscilloscope near a fluorescent lamp! Even the ones so called "economical" bulbs. They "inject" such an electrical noise, that may drive you crazy!
After replacing the faulty C4375, (this was the only problem I had), I almost gave up, the ripple on the screen was more than "crazy". It had no rules, something randomly... As soon as I've turned off my "economical" bulb - it almost disappeared. After turning off 2 additional lamps on my desk - got a straight, ripple free trace. After assembling the scope (...screening) - it worked without any problems (so far... I am a pessimist...).
So, I wish to thank to everybody who assisted me!
Sincerely,
Tedy

P.S. Just in case that E-design or anyone may provide me the FULL manual (including the ASSY 10 (Horizontal Amp. circuit), I'll be very thankful.
Thanks in advance.

 

[BradtheRad]

Good going.

I spotted R4376 in a manual which I downloaded direct as a pdf. (I could not read the rar file.)

Link:

www.bama.edabris.com/download/tek/465b/465b.pdf

It's on page 249 (out of a 291 page manual).

The A4 interface board. A good tactic is to search among any and all resistors numbered in the 4000's.

It might be shown in a schematic as well.

 

[FvM]

I fixed it...up to next time of course

Very good.

I realized that the Tek465B manual from bama has only partial pages, and the basically good one from http://www.ko4bb.com/ is missing the said A10 schematic page. I did check this before, because I never needed to fix a 465B. Sorry for causing confusion.

 

[Tedyp]

I realized that the Tek465B manual from bama has only partial pages, and the basically good one from http://www.ko4bb.com/ is missing the said A10 schematic page. I did check this before, because I never needed to fix a 465B. Sorry for causing confusion.[/QUOTE]

Thank you FvM,
I've tried to d/l from every source I've found, including http://www.ko4bb.com/, but all of them have more or less the same manual, in different forms.
I've tried to find the CIRCUIT DIAGRAM including the H_Amp, I am sure it exists somewhere, as E-design uploaded a part of it. Up to now, I had no success, I've d/led 20-30 pdfs - no way to find it...
Sincerely,
Tedy

 

[Tedyp]

Just for the members information, and just in case - there is a site which sells complete schematics for almost any oscilloscope.
Here is the link:https://artekmedia.com/

 

[E-design]

I scanned the page from my own personal library of Tek manuals.

Unfortunately the pages are a bit faded. This is the best scan out of several attempts.

 

[Chris56000]

Hi!

I'll be purchasing a full original paper manual this weekend when I'm lollified and when I receive it I'll upload Circuit Diagram 10 for the Horizontal Amplifier, the component layout drawing for the A9 assembly and the parts list/circuit description as this section seems to be a common cause of failure in this series of scopes!

I've got a Mustek A3 scanner so I should be able to make a reasonable job of it!

I've also purchased a 465B for myself in (allegedly!) excellent condition to replace the Metrix one, so I'll add my findings with it as well as the diagrams!

Chris Williams

 

[Chris56000]

Hi!

Are these any use to everyone? It doesn't look like there's an A9 assembly in the instrument so it looks like the poster who mentioned it made a typo!!!

The Horizontal Amplifier Circuitry is actually a part of the main A4 Interface Board Assembly - the 'scope I'm waiting for in the post hasn't come yet and I've not found the drawing showing the A4 board yet - I'm not sure Tek actually illustrated it in full - I think they only did bits of it!!!

Chris Williams

PS! I have got the full manuals these pages were from but I'm not sure what the upload limit on this forum is!!!