UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 27th Jun 2013, 1:02 pm   #21
maninashed
Rest in Peace
 
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
Default Re: Tektronix 465B Scope - Some problems.

David, the bridge rectifiers in the scope are rated at 2A, find one that will physically fit (cpc) it doesn't matter if its higher rated, just dont go below. Again be careful desoldering, the pads lift very easily. I can't see what your D83 is set to, but some of those traces definitely look suspect. Ignore any low level hf hash at this stage and get the psu right, otherwise you'll be chasing your tail.
Bill
maninashed is offline  
Old 27th Jun 2013, 2:57 pm   #22
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

Hello Bill,

Thanks for the info on the bridges, saves me having to wait for the manuals to arrive.

Yes the traces Im sure are showing some problems, for certain the first one relating to the -8V supply, definitely not right.
I think the scope was set to 5mS, at least that 's what the switch says now.

The PSU's are my priority now. Changing the bridges is going to be fun I think.

Dave.
davidgem1406 is offline  
Old 28th Jun 2013, 11:22 pm   #23
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

I have replacement bridges now, I picked 4A @ 200V devices as they may have an easier life than 2A devices. I now have to hope they will fit the PCB holes.

The first thing I did was to take pictures of all the boards showing the wire connections. Then I dropped the pictures into a CAD package and added wire colour labels to all the connection points. Other pictures will be taken along the way.

Well I knew this was going to be some awkward job to say the least. Gaining enough room to work is not easy.

I first removed the Right hand scan board. That gave room to get at 2 bridges, but not the -8V or the +15V. The transformer was in the way of those.

To allow the transformer to move, taking it out is not an option, the screen plate on the CRT side of the metal work has to be removed to gain access to the lower screw holding the transformer bracket, that just involves the removal of 1 nut.
After removing the screen plate I found the lower bolt was welded into the main metalwork so removing the nut from the transformer side was all that was needed there.

The 2 rear bracket mounting screws needed to be removed so that meant removing the outside rear plate to get at the screws. In turn that meant removing the AC supply cable.
Once the transformer mounting rear screws were removed the transformer would move but the mounting bracket was getting in the way so had to come off.
The bracket was removed from the transformer.
Mounted on the bracket is a thermal trip that requires the wires to be un-solderd and removed. That was done and the bracket removed.

Although there is more room now it is not really enough to work comfortably so maybe 2 of the other smoothing capacitors will have to be removed, not a good idea unless really necessary.

At the moment I have had enough for today so will try to remove the bridges tomorrow, maybe!

Dave
davidgem1406 is offline  
Old 28th Jun 2013, 11:32 pm   #24
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: Tektronix 465B Scope - Some problems.

It's good practice to avoid working on the CRT magnetic screen. Stressing them or knocking them can cause them to become slightly magnetised. Mostly trace rotation and shift controls fixes the effect, but it's best avoided. They were annealed after they were made.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 29th Jun 2013, 1:08 am   #25
maninashed
Rest in Peace
 
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
Default Re: Tektronix 465B Scope - Some problems.

David, working on these scopes is not easy. It takes time and patience. Don't lose will, because it will be worth it when fixed. I know to my cost, what it entails. Just make sure you have components that will physically fit without strenuous bending etc. Try and do the repair so you can test it without complete reassembly. Once you are satisfied with the results, leave it on soak test, till you are happy its fixed. Then reassemble properly.
Bill
maninashed is offline  
Old 29th Jun 2013, 2:58 pm   #26
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

Hi David (Radio Wrangler)

It is nothing to do with the CRT screening. Maybe screening plate is the wrong name to call it, it is just a flat steel plate with a coating on one side that looks to be grey paint. The plate is fixed to the aluminium chassis between the transformer and the CRT held in place by 1 nut. Maybe it is transformer screening.

Hi Bill,

Yes it sure is not an easy item to work on.

I'm looking at the possibility of using either a junior hacksaw or a tile saw to cut the bridges into 4 parts so as to be able to remove 1 leg at a time. That would definitely make the job very much easier.

Trying to test without complete assembly is probably not an option as the transformer will have to be refitted and that will need the bracket fitted and wiring reconnected.
I will look to see if it is possible to safely leave the transformer lose, but any doubt about that will mean full reassembly.

I now have 6800uf 35V capacitor that arrived this morning.

I will be back with the results.

Dave.
davidgem1406 is offline  
Old 29th Jun 2013, 8:54 pm   #27
maninashed
Rest in Peace
 
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
Default Re: Tektronix 465B Scope - Some problems.

Dave, I've found the best way to remove those bridge rectifiers, is firstly DONT try and de-solder. Then mechanically waggle the the component until the legs fatigue. You may not have much room to waggle them, but its worked for me 100%. Saves an awful lot of dismantling. With a de-solder station the remnants of the legs will just get sucked up, but you will have to be careful to extract them. Sounds crude, but it does work. If you have pre-heated the pads, don't try this method!! they will break loose. When re-fitting the new components leave a little more leg free from the pcb so you can bend it towards the pcb. If it ever goes again, its then easy to replace. (But that's up to you!)
Bill

Last edited by maninashed; 29th Jun 2013 at 9:22 pm.
maninashed is offline  
Old 29th Jun 2013, 11:45 pm   #28
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

Hi Bill,

Well I did try cutting through one with both a junior hacksaw and a tile saw blade, that was just hard going that stuff is really hard, blunts the junior blade quite quickly.

I then came up with another option. I used a very large pair of side cutters, the sort that cuts 10mm cable with ease, and cut the encapsulation away in largish pieces. It just tends to shatter under pressure.
That just left the wire ends to remove, dead easy then just heat the wire and out it comes, one by one and all removed.

I have replaced 3 of the bridges, all fitted on long wires now and turned flattish because of the restrictions in the available height when the cabinet is fitted.
No worry to remove and replace if needed in the future.

I have now refitted the transformer and mounting bracket, the mounting bracket is also used to ground the scan board.

Before I refit the scan board im fitting and IEC socket in place of the fixed supply cable, much better. I don,t like fixed supply leads anyway.

I have added 2 pictures 1 of the transformer moved, the other of the three bridges when replaced.

I have to make a confession. When I removed the 5000uf capacitor I later found that the PCB through plating to one of the connections came away stuck to one of the terminals.
As this is a double sided board it was in fact quite easy to repair.
I took a crimp ferule (bootlace ferule) of such a size that it would be a tight fit in the PCB hole.
With a fine triangular file I cut of a short length off the ferule that was just long enough to protrude above the level of the pads on either side, something like 0.5mm.
This was then pressed into the hole until it protruded through the other side and finally soldered into place, without filling the hole.
A very easy and permanent fix to the problem.

Dave
Attached Thumbnails
Click image for larger version

Name:	Dscf0596.jpg
Views:	322
Size:	44.7 KB
ID:	81358   Click image for larger version

Name:	Dscf0597.jpg
Views:	294
Size:	71.2 KB
ID:	81359  
davidgem1406 is offline  
Old 1st Jul 2013, 8:52 pm   #29
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

I have now fully reassembled the unit.

First I ran it with the replacement 6800uf capacitor fitted and noted the results from the -8V rail.
Next I removed that capacitor and put the original 5000uf in place, the results were identical so I shall now fit the original back. I see no point in replacing it.

I feel the traces are still much the same as they were first off, may be a marginal improvement but nothing significant.

When I first attempted to take measurements for the power rails I found there was a lot of HF stuff on the rails. This I found was all being picked up by the Tek scope and showed on the power rails. Maybe these scopes are rather sensitive to picking up stray signals without their cabinet in place.
I then had to turn of everything else that was not needed to make the tests, the PC was the biggest culprit and just turning it off was not the answer it had to be unplugged as the PSU was still putting out a lot of rubbish.
I was left with the Telequipment scope and a DVM in use.

Here are the latest results but the problem still exists.

The power supply voltages are all good with -8.01V, +5.00V, 14.90V, 55.10V and 110.50V

The power rails were checked with the Telequipment scope:

-8V rail was at 2mV to 3mV of HF rubbish but clean of 50Hz. The scope was set to a speed of 0.5mS per division. (Image_A1)

+5V rail The same result as the -8V rail.

+15V rail 1.5mV to 2mV of HF appears clean from 50Hz (Image_A2)

+55V rail 4mV of ripple plus HF scope scan speed set to 10mS per division (Image_A3)

+110V rail 15mV saw tooth at 100Hz +HF on top scope scan speed set to 10mS per division (Image_A4)
I am not sure if this 110V rail is stabilised or not.

Basically that is as far as I can go for now until the service information arrives.

Dave.
Attached Thumbnails
Click image for larger version

Name:	Image_A1.jpg
Views:	168
Size:	37.6 KB
ID:	81436   Click image for larger version

Name:	Image_A2.jpg
Views:	147
Size:	31.3 KB
ID:	81437   Click image for larger version

Name:	Image_A3.jpg
Views:	139
Size:	29.9 KB
ID:	81438   Click image for larger version

Name:	Image_A4.jpg
Views:	156
Size:	32.4 KB
ID:	81439  
davidgem1406 is offline  
Old 1st Jul 2013, 9:28 pm   #30
maninashed
Rest in Peace
 
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
Default Re: Tektronix 465B Scope - Some problems.

Dave, ripple on the psu rails should be as follows 110v at TP 1518 20mv, 55v @ TP1536 4mv, 15v @ TP1548 2mv, 5v @ TP1558 2mv, -8v @ TP 1568 2mv. All rails except 110v are derived from the 55v rail and that should be between 54.72 and 55.27v. Placing the instrument back in its case will cut down on radiated interference especially from the eht oscillator. The 110v rail is regulated.
Just as a wild card, check the operation of the scope when using the delayed timebase and see if this is functioning correctly.
Bill
maninashed is offline  
Old 1st Jul 2013, 11:19 pm   #31
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

Hi Bill,

Thanks for that info.
If I am at the correct test points then the figures look correct for ripple. It is just the HF sitting on top of everything.
I cant tell if I'm on the correct test points as they are not marked and the relevant board drawing is missing.
The points I am using are on the large board underneath and placed between the rectifier bridges etc. and the EHT section.

Ignoring the HF on the rails the only one i find questionable is the 110V rail with its 15mV of sawtooth. That's the one bridge rectifier I did not replace.

I will give the delay time base a try, just have to rack my brains on that as its a long time since I needed to use one.

Thanks
Dave.
davidgem1406 is offline  
Old 2nd Jul 2013, 7:28 am   #32
maninashed
Rest in Peace
 
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
Default Re: Tektronix 465B Scope - Some problems.

The TPs are all on the main board underneath, small raised loop connectors, the voltage is printed close by. Use the psu ground tag on the same board for probe ground. Make sure you haven't got a big noisy florescent light on over your bench, or worse still energy saving florescent bulbs, they radiate a lot of interference which a high bandwidth scope will pick up. Also, leave the scope operating for an hour or more to get fully warmed up, just to see if the problem improves or gets worse.
Bill
maninashed is offline  
Old 2nd Jul 2013, 9:53 am   #33
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Tektronix 465B Scope - Some problems.

Have you checked the EHT?
PJL is offline  
Old 2nd Jul 2013, 10:25 am   #34
maninashed
Rest in Peace
 
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
Default Re: Tektronix 465B Scope - Some problems.

PJL, low eht will tend to give a blurred or wide trace, but it wont display interference such as this. Its important to rule out the simpler things first and once he knows that they are correct, then proceed to the next stage. Its difficult when the instrument isn't in front of you, these are a complex scope and this fault could be due to a number of different causes. The -2450v cathode supply will be on the check-list.
Bill
maninashed is offline  
Old 2nd Jul 2013, 2:01 pm   #35
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

Hi PJL,

The EHT, or rather the cathode voltage will be checked, the final anode I cant check as I have no means to do that.


Hi Bill,

Yes those are the test points I have been using.

I do have 1 energy saving lamp here but on or off the scope display is the same.

I did run the delay timebase and it does seem to be working, although when there are 4 traces on screen it somewhat messy, doesn't seem to be enough room for them all.

Whilst doing that I noted that the trigger was very difficult to obtain a stationary wave form, especially with 2 traces and both with inputs.
Also if the traces are moved towards each other then it will blank out both traces.

I have just been playing and I found that the delay timebase seems to be running permanently.
At the moment I have the call square wave into channel A, no signal to channel B.The horizontal speed is at 1mS, horizontal display alternate selected.
Vertical mode is both channels on and alternate selected.
The display lock steady with some flicker being in alternate mode. Both traces are undulating at what looks to be 50Hz.

The delay timebase is set to source normal, coupling at AC. Delay time at zero.
To me that says the delay timebase is off, maybe I am interpreting the meaning of normal wrongly!
However turning the trigger level pot will turn the delay timebase on with the B intensity and trace separation working.

Maybe it is a case of the delay timebase is always working when alternate is selected? Anyway it is fully functional.
The only way to stop it is to set the horizontal display to A.

Maybe this is all correct but I will have to check with the manual.

I will have to put it all back into the cabinet and then see what the traces are like. Some of the 50Hz seems to be pick-up as without any signal to the vertical inputs some 2mV to 3mV can be seen. Switching the inputs to ground reduces the 50Hz.

Dave.
davidgem1406 is offline  
Old 3rd Jul 2013, 10:51 am   #36
dave cox
Nonode
 
dave cox's Avatar
 
Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,059
Default Re: Tektronix 465B Scope - Some problems.

According to the results you posted, and the spec that Bill posted, your PSU seems OK. One failure mode I've seen that can cause interference pick-up is when one half of a differential signalling system goes AWOL - in this scenario its quite possible that the circuit can appear to work but with poor rejection and linearity. I haven't looked at the schematic but I wouldn't be surprised if your scope uses the same in both vertical and horizontal amplifiers.

dc
dave cox is offline  
Old 3rd Jul 2013, 12:54 pm   #37
maninashed
Rest in Peace
 
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
Default Re: Tektronix 465B Scope - Some problems.

Dave, can you post a pic of your front panel, so I can see your controls. I have a 465 and 475, but not the 'B' version. I know they are similar, but there will be some serious modification within. I want to be able to assimilate your results and duplicate where possible.
Both timebases should not be running continually, you should be able to switch off the B timebase.
Just use one channel input for now, and keep it simple. We need to identify to source of the problem
Bill
maninashed is offline  
Old 3rd Jul 2013, 3:00 pm   #38
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

Hi Bill,

I have found that the way to switch the delay timebase off is to set the horizontal display to A and not on Alternate.

All 4 rectifier bridges have now been changed, just for good measure really.

I have found that a lot of the 50Hz stuff, if not all, is definitely pick-up.

Today I checked for 50Hz again but had the Tek lifted up away from the bench surface.
The settings used were:

Time: 5mS/Div
Trigger mode: Normal
Trigger source: Line

An input of 50Hz sine wave to channel 1

There appears to be no discernible 50Hz on the traces, just the HF stuff. (Image_B1)

Image of Front Panel for Bill (Image_B2) If you need a high resolution image you can magnify just send me a PM with your Email and I will send one.

Now found that channel 1 switch is dodgy on 1V, 2V and 5V positions

Dave
Attached Thumbnails
Click image for larger version

Name:	Image_B1.jpg
Views:	176
Size:	34.5 KB
ID:	81527   Click image for larger version

Name:	Image_B2.jpg
Views:	166
Size:	71.8 KB
ID:	81528  
davidgem1406 is offline  
Old 3rd Jul 2013, 8:54 pm   #39
davidgem1406
Heptode
 
davidgem1406's Avatar
 
Join Date: Feb 2011
Location: Sheerness, Kent, UK.
Posts: 936
Default Re: Tektronix 465B Scope - Some problems.

I was looking at things earlier this evening and thought I would look at the focus control to see what may be found.
First removing the EHT cover to gain access but nothing really could be seen, so another item to await the arrival of the manuals.
I suspect the voltage on the focus control will be to high to look at on a scope!

Whilst the cover was of I checked the -2500 line for the CRT cathode supply. That was OK at a little below -2500.

I have added some pictures showing the effect of the focus control on the CRT spot. (Image_2A shows the pot at full A/C, Image_2B at full C/W and Image_2C the best focus obtainable)

Dave.
Attached Thumbnails
Click image for larger version

Name:	Image_2A.jpg
Views:	159
Size:	37.5 KB
ID:	81537   Click image for larger version

Name:	Image_2B.jpg
Views:	182
Size:	32.0 KB
ID:	81538   Click image for larger version

Name:	Image_2C.jpg
Views:	150
Size:	36.4 KB
ID:	81539  
davidgem1406 is offline  
Old 3rd Jul 2013, 9:04 pm   #40
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: Tektronix 465B Scope - Some problems.

Can you use your second scope to look at the voltages on the deflection plates with a stationary, centred dot (low intensity) showing on the faulty scope.

This should give a definite indication of whether you're chasing noise/ripple or whether the CRT isn't focusing.

I've put my 465B on and I'll leave it for half an hour and duplicate your focus pot position photos, then post them.

Have you tried adjusting the astigmatism pot right by the focus knob?

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 12:32 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.