Tektronix 465B Oscilloscope Restoration

[tjg79]

Hello Forum,

I picked up a Tek 465B off eBay that powers up but no display. I intend to fully restore this scope. I've got the instruction manual and the troubleshooting manual, but I'm not completely familiar with this scope yet.

What do I need to do to complete remove any residual charge from this scope so that it's safe to work on?

The issues that I can see with minimal inspection and testing, besides no display, are as follows:

B(DLY'D) Trigger BNC Connector - slightly damaged
B(DLY'D) Trigger Level Knob, part # 366-1280-00 - missing
B(DLY'D) Trigger Source Lever - loose push/pull rod mechanical connection
X10 MAG Switch, part # 260-1208-00 - catches intermittently, feels worn out
Focus Potentiometer, part # 311-0075-00 - won't turn
CH1 & CH2 Volts/Division Knobs - no illumination
Position Knob/Potentiometer - very stiff
Holdoff Knob/Potentiometer - very loose with slight wobble
Air Filter - missing

Voltage Measurements:
+110 Volts - +108.8 Volts
+5 Volts - +4.12 Volts
+55 Volts - +54.9 Volts
+15 Volts - +14.95 Volts
-8 Volts - +0.78 Volts
 
I'm seeking recommendations and opinions on how to proceed.

Regards

[NilByMouth]

I had the same voltage measurement on the -8v rail on my 465 (not B). It was down to a faulty bridge rectifier. I was advised to chop away the body of it before desoldering it - saves taking the board off. Fit the new one 5mm above the board and bend it over so you can solder the legs.

Chances are you'll have capacitors failing - if not now, some time in the future. A lot of people re-cap at least the power supplies.

[PaulAm]

You need to check the ripple on the power supply testpoints.  I'd bet a donut the filter cap on the -8V supply is toast.  Maybe the +5 as well.

[tjg79]

Thanks for the replies guys.

I think I'm going to completely disassemble and do a full recap of the electrolytic caps as well considering the age of the instrument.

Is there anything else that should be replaced as preventive maintenance?

Does anyone know how to completely discharge this instrument so that I don't fry myself?

Regards

[PaulAm]

Can't hurt to replace all the PS electrolytics.  There was a recent thread where someone posted gerbers for an adapter for a standard snap cap to that wierd pinout.  They make a very nice repair.

Here's the thread:
https://www.eevblog.com/forum/testgear/tektronix-76037613-repairs/

You'll really want to use those boards.  Replacement caps will leak in 15-20 years and destroy whatever board they're mounted on.  They will not last as long as the originals.

I'm on the fence about tantalums.  There have been reports of them going bad, but I haven't personally seen it (and I've gone through a half dozen or so series 400 scopes).  If it's good and it's voltage rating is conservative and not near the rail voltage; I'd leave it in there.   Things got a lot worse on the 2400 series.  Don't touch anything on the timing board unless you have a demonstrated fault.

Clean all of the attenuator contacts with the recommended Tek procedure - get a little piece of copy paper, soak it in IPA and draw it through the closed contact.  Don't bend the tiny forks.  They use the same contacts on the timing board and you could clean those if you have access to it.

You can use regular contact cleaner (a drop at a time) on the function switches; just don't spray it around.

Most of the controls will clean up with some exercise.

You can use a dowel to fix the bnc, which is probably easier than replacing it.

There might be other problems, but you'll need to fix the power supplies first and do a functional check.  Before you get too deep, check the filament continuity on the CRT.   You didn't mention if you got any glow on the CRT and a dead crt is a major road block.  Could be the HV supply, could be the LV supply (-8V seems pretty critical), could be the crt, but you won't be able to tell without testing it.

It's easy to damage the main board pulling out caps or bridges, so have the proper equipment and exercise care.  The caps have 3 ground pins and one center pin.

[tjg79]

Can't hurt to replace all the PS electrolytics.  There was a recent thread where someone posted gerbers for an adapter for a standard snap cap to that wierd pinout.  They make a very nice repair.

Here's the thread:
https://www.eevblog.com/forum/testgear/tektronix-76037613-repairs/

You'll really want to use those boards.  Replacement caps will leak in 15-20 years and destroy whatever board they're mounted on.  They will not last as long as the originals.

Those cap boards are an elegant replacement. I haven't removed anything yet, so I don't know what my cap pin-outs look like. Where do you get the cap boards? Must you have them made? I haven't selected replacement caps yet, so buying the boards now may be putting the cart before the horse. I'm going to have to study this solution. I like it.

That thread link has a lot of good information. I was surprised at the number of resistors that were replaced for being out of tolerance. I'm going to follow that example and check all my devices one board at a time. Thanks for posting that very informative thread link. 

[tjg79]

I'm on the fence about tantalums.  There have been reports of them going bad, but I haven't personally seen it (and I've gone through a half dozen or so series 400 scopes).  If it's good and it's voltage rating is conservative and not near the rail voltage; I'd leave it in there.   Things got a lot worse on the 2400 series.  Don't touch anything on the timing board unless you have a demonstrated fault.

On just about everything I've read pertaining to these scopes, there're always comments about failed tantalums. I'll look at all of them and make a decision based on what I see and measure. Is it good practice just to replace them all due to their age?

Regards

[tjg79]

Clean all of the attenuator contacts with the recommended Tek procedure - get a little piece of copy paper, soak it in IPA and draw it through the closed contact.  Don't bend the tiny forks.  They use the same contacts on the timing board and you could clean those if you have access to it.

You can use regular contact cleaner (a drop at a time) on the function switches; just don't spray it around.

Most of the controls will clean up with some exercise.

I've read mixed information about cleaning switches with DeoxIT products. D100 is pure cleaner from what I understand and D5 has a residual lubricant. There's also a DeoxIT Fader F-Series that's supposedly is a good lubricant for contact switches. Some guys claim it's the best and some guys say it will ruin the switches and require frequent cleaning. I don't know what is the best solution for cleaning these Tek switches and potentiometers. Also, I've read some debate about using no-residue contact cleaner vice IPA. Perhaps just working the switches and the pots is the safest solution and if it's not broke, don't fix it.

[tautech]

Normal precautions apply re charged PSU caps but the EHT PDA lead should be treated with extra caution.
Often one can work around it and for other than a complete disassemble there is little need to disconnect it.
IF you do, an earthed screwdriver (to chassis) can be carefully slipped under the grommet where it connects to the CRT to discharge it.

I'm on the fence about tantalums.  There have been reports of them going bad, but I haven't personally seen it (and I've gone through a half dozen or so series 400 scopes).  If it's good and it's voltage rating is conservative and not near the rail voltage; I'd leave it in there.   Things got a lot worse on the 2400 series.  Don't touch anything on the timing board unless you have a demonstrated fault.

On just about everything I've read pertaining to these scopes, there're always comments about failed tantalums. I'll look at all of them and make a decision based on what I see and measure. Is it good practice just to replace them all due to their age?

Regards

Your call. 

IF you had the whole scope apart....for the few dollars they might cost it would be cheap insurance. Be sure to select replacements with as high voltage ratings as possible. Good rule of thumb for bead Tant's is twice the working voltage.

[tjg79]

There might be other problems, but you'll need to fix the power supplies first and do a functional check.  Before you get too deep, check the filament continuity on the CRT.   You didn't mention if you got any glow on the CRT and a dead crt is a major road block.  Could be the HV supply, could be the LV supply (-8V seems pretty critical), could be the crt, but you won't be able to tell without testing it.

It's easy to damage the main board pulling out caps or bridges, so have the proper equipment and exercise care.  The caps have 3 ground pins and one center pin.

I don't recall seeing any glow from the CRT. The illumination worked well. I'll check the CRT filament continuity to see if I need to scrounge up a CRT. I knew that this could be a CRT problem when I bought it, but with all the other issues, I'm hoping now that the CRT is good. Are there any other checks for the CRT besides filament continuity? I'm not familiar with this CRT, because I haven't seen one up close uninstalled. Where are the filament continuity check points located? Is there access with the CRT installed and the scope fully assembled?

The focus potentiometer is frozen. I suspect it suffered a surge and welded. It's located in the HV section of the main board. I've ordered a replacement, but I'll check the power supply before I install it so it won't repeat.

Regards

[NilByMouth]

Normal precautions apply re charged PSU caps but the EHT PDA lead should be treated with extra caution.
Often one can work around it and for other than a complete disassemble there is little need to disconnect it.
IF you do, an earthed screwdriver (to chassis) can be carefully slipped under the grommet where it connects to the CRT to discharge it.

I understood that you shouldn't break the seal on the cap on the CRT itself. i.e. To discharge it, you unplug the HT connection where it's joined to the multiplier and earth that (being careful not to earth it through yourself). See:

[tautech]

Normal precautions apply re charged PSU caps but the EHT PDA lead should be treated with extra caution.
Often one can work around it and for other than a complete disassemble there is little need to disconnect it.
IF you do, an earthed screwdriver (to chassis) can be carefully slipped under the grommet where it connects to the CRT to discharge it.

I understood that you shouldn't break the seal on the cap on the CRT itself. i.e. To discharge it, you unplug the HT connection where it's joined to the multiplier and earth that (being careful not to earth it through yourself).

You can only do that if the PDA lead is not potted into the multiplier.....many PDA leads are and then under the PDA grommet is the only option for discharge.

[NilByMouth]

You can only do that if the PDA lead is not potted into the multiplier.....many PDA leads are and then under the PDA grommet is the only option for discharge.

Yes, but this is the 465B which has a similar connector to what's shown in the video.

[PaulAm]

If you run the scope in a darkened room with the cabinet off, you might be able to see the filament glow on the crt.  If you have to check it, you need to pull the socket off the tube and check the pins.

No glow doesn't mean the crt is bad, the HV supply which also provides the heater supply might be dead.  CRTs do go bad, but a bad transistor in the HV supply is more likely.

I suppose you could use a clamp on current meter as well, but the cathode and filament run about -2450V or so relative to ground so you want to be VERY CAREFUL if you do that.

Before doing a wholesale rework, I'd get it at least partially working first, then do things in stages.  Much easier to catch a mistake that way.

[Addicted2AnalogTek]

If you do need measurements from a 465 type (154-0731-00) CRT tube, I happen to have one that I know is good sitting on a shelf.

Also, buy several bottles of 91% isopropyl alcohol and possibly some small camel hair paintbrushes from an art or hardware store. The IPA is a universal cleaner for these scopes and the brushes will help you get into hard to reach places.  IPA soaked printer paper is still the preferred method for cleaning gold finger contacts, but you will need to disassemble the scope almost entirely to get to them all.  I like to put a tiny amount of deoxit gold on the contacts to ensure good conduction in the future, but plenty of people choose not to do so.

As for stuck x10 switch or any like it, shoot some deoxit d5, IPA, or contact cleaner into the switch and operate it multiple times.  that should get it working again.    I've also had pots stick before, but not on any scopes - mostly the older AB style ones on 106 square wave gens and similar.  I just turned them shaft up, put a few drops of deoxit on the shaft and let it soak in, then operated it a bunch until it loosened. Sometimes I had to take mini slip joint pliers and gently pull/push the shaft while turning to get them to free up.   Turn the holdoff pot all the way CCW and leave it for now, you don't need it.
Also, don't bother with cosmetic replacements like plastic knobs until you get the circuitry figured out and working.

As for tantalum caps.. I bought quite a pile of them and usually just replace them regardless.  There's one guy that started a 485 repair a bit ago and chose to replace all the radial tantalums with Nichicon PW series.   If you have another scope, a function gen, and some basic cables/fittings, you can make a quite effective ESR tester that can be used in-circuit. 


I tested new caps against the existing ones, but you can also use datasheet info.  With that setup, higher uF caps such as PSU caps will be hard to distinguish as being bad until you get them out of circuit and test them at higher voltages, but it's a great method for testing the tantalums and other small caps above 1uf and below 100uf or so.

[tjg79]

If you do need measurements from a 465 type (154-0731-00) CRT tube, I happen to have one that I know is good sitting on a shelf.

Do you know which pins check the filament? Is there a minimal disassembly to get access?

Since I've got no indication of a display, even in dark room, and an obvious problem with the -8V rail, I'm going to start with the power supply. But, I would like to know if the CRT filament is good.

[Addicted2AnalogTek]

If you do need measurements from a 465 type (154-0731-00) CRT tube, I happen to have one that I know is good sitting on a shelf.

Do you know which pins check the filament? Is there a minimal disassembly to get access?

Since I've got no indication of a display, even in dark room, and an obvious problem with the -8V rail, I'm going to start with the power supply. But, I would like to know if the CRT filament is good.

I'm not sure which pins are which.  The steps to gain access to the CRT rear is in the maintenance section of the 465 manual.  I'm not sure if it's also in the 465B manual, but I would assume so.  All that needs to be done is removal of the rear plastic piece and then removal of the metal can that covers the CRT tube socket/CRT pins.

[Addicted2AnalogTek]

The two pins that connect to the rear-most part of the CRT internals are the two directly below the index pin, and it measures 12 ohms across them.

Before you get too far into things, it would help immensely for you to read the "Theory of Operation" section of the manual and reference the schematics in the process. Take your time doing so...  This is the advice I was given (and didn't follow) which would have saved me a lot of time and trouble. Now I ALWAYS read them.

[uncle_bob]

Hi

The filament can fail in two ways. One is to go open circuit. That's fairly easy to check with a DVM. The other way it can "fail" is to loose emissions. The purpose of the filament is to get nice and hot to generate a cloud of electrons around it. The rest of the tube works to blast those electrons towards the front of the tube. The filament is coated with "stuff' to help this happen. Eventually the magic gets into the "not so much" category. If the scope spent 30 years on a bench powered on .... be careful of this.

Next thing to watch for is phosphor burn on the tube. If the same guy that left it on for 30 years also left the trace running the whole time, the phosphors in the middle of the screen got a major workout. Because of this it's not going to work as well as the region to either side.

If the tube has a problem, the "easy fix" is (unfortunately) to buy another scope caracas. You can generally get the whole thing (not working) for roughly the same price as a tube (no way to prove it works). Yes this is why people accumulate piles of semi-dead scopes as part of the rebuild process.

Get things going to the point you can evaluate the tube and go from there. If you have to buy another carcass, it may have subassemblies that are in better or worse shape than this one. Far better to have them all in front of you before you spend a lot of time (and money) rebuilding things.

When you do get to the rebuild stage, that's an *old* scope (though nowhere near as old as I am). Plan on replacing all of the electrolytic caps in the beast. Don't bother with the track down this and track down that stuff. Get a batch of parts and replace them wholesale. You want the scope to work for another 10 or 20 years. You do *not* want to be tearing into it every year or two.

Bob

[tjg79]

The two pins that connect to the rear-most part of the CRT internals are the two directly below the index pin, and it measures 12 ohms across them.

Before you get too far into things, it would help immensely for you to read the "Theory of Operation" section of the manual and reference the schematics in the process. Take your time doing so...  This is the advice I was given (and didn't follow) which would have saved me a lot of time and trouble. Now I ALWAYS read them.

I've been reading sections of the manual, but I've got to go through it from front to back. I haven't disassembled anything yet, other than remove the cover for inspection and voltage measurements, because I haven't read the manual completely and digested it yet.

Thanks for the ohm measurement. I'll check mine when I start disassembly. That may be a while, because I've got to read the manual a few times and I have a lot of research to do on replacement caps. I plan to replace all the electrolytic and tantalums. It's been my experience that finding exact replacements for the large caps is not likely. So, the best available replacement caps have to be determined and those caps will likely need the boards described above, because the number of ground leads and lead spacing will likely be very different from the originals.

Thanks for all the info. 

[tjg79]

Hi

The filament can fail in two ways. One is to go open circuit. That's fairly easy to check with a DVM. The other way it can "fail" is to loose emissions. The purpose of the filament is to get nice and hot to generate a cloud of electrons around it. The rest of the tube works to blast those electrons towards the front of the tube. The filament is coated with "stuff' to help this happen. Eventually the magic gets into the "not so much" category. If the scope spent 30 years on a bench powered on .... be careful of this.

Next thing to watch for is phosphor burn on the tube. If the same guy that left it on for 30 years also left the trace running the whole time, the phosphors in the middle of the screen got a major workout. Because of this it's not going to work as well as the region to either side.

If the tube has a problem, the "easy fix" is (unfortunately) to buy another scope caracas. You can generally get the whole thing (not working) for roughly the same price as a tube (no way to prove it works). Yes this is why people accumulate piles of semi-dead scopes as part of the rebuild process.

Get things going to the point you can evaluate the tube and go from there. If you have to buy another carcass, it may have subassemblies that are in better or worse shape than this one. Far better to have them all in front of you before you spend a lot of time (and money) rebuilding things.

When you do get to the rebuild stage, that's an *old* scope (though nowhere near as old as I am). Plan on replacing all of the electrolytic caps in the beast. Don't bother with the track down this and track down that stuff. Get a batch of parts and replace them wholesale. You want the scope to work for another 10 or 20 years. You do *not* want to be tearing into it every year or two.

Bob

Thanks Bob. I plan to replace all the electrolytic and tantalum caps, and other devices as requried. I bought this "no display" scope, total price with shipping, for less than a replacement CRT. From some of the prices I see for replacement knobs, it's probably a better deal to just buy another non-functioning scope for parts. I don't see any indications that the CRT is burnt, but I haven't tested the filament yet either.

I think the power supply needs to be fully checked and restored, before going any deeper into other issues.

I haven't found one yet, but does anyone know of another 465B recap that has the BOM listed? It's always more efficient to check what others have done than to start from scratch. For these types of projects, I usually create a spreadsheet with what the service manual specifies, what's installed, and what the replacement will be. Although, from reading that other thread, I was enlightened by the number of resistors that were replaced, because they were out of tolerance. I would think the resistors should be able to be accurately tested measured while in circuit, because I don't want to have to remove all them for testing.

[uncle_bob]

I was enlightened by the number of resistors that were replaced, because they were out of tolerance. I would think the resistors should be able to be accurately tested measured while in circuit, because I don't want to have to remove all them for testing.

Hi

Be careful when you start looking at resistors. Not every resistor is critical in terms of value. A 5% resistor that is at +6% probably works perfectly well in 99.9% of the circuits out there. In some cases (logic pull up comes to mind) it may do just fine if it's at 2X the original value. Are there resistors that matter a whole lot? Sure there are. Your attenuator (input range select) has a bunch of critical parts in it. An extra 1% on some of those is a 1% hit to the accuracy of the scope.

====

Start shopping now for another 465 (or two). That's not to say you buy the first one that comes up. You have one. The trick is to buy the next one cheaper or higher value (= known good tube). You may have to wait a month or a year before the magic buy comes along. It is a bit of a pain to keep watching eBay (and other sources) forever and ever. Unless you want to spend a fortune on this, it is the right thing to do. The first fancy part you need to buy in a hurry will likely cost you more than a cheap full scope.

Bob

[Addicted2AnalogTek]

Here's a heads up with these older Tek scopes with socketed components.... I have purchased a few with "non working CRT"s.. and not one of them had a bad CRT.   With every one of them I was able to get something to display simply by cleaning all the switch contacts and wiggling/resetting all of the socketed components - of course in addition to replacing any obviously bad capacitors.  Of course this will be limited to only if the power supply is at least partially functioning. 
The majority of the power supply problems that I have had were due to filter caps, tantalums, and bad zener diodes with the oddball half-dying rectifier.

Also, when looking for parts scopes, don't forget about the 468. Aside from storage, it's the same as the 465B. The 465 will also have most of the parts you might need also.

[NilByMouth]

From some of the prices I see for replacement knobs, it's probably a better deal to just buy another non-functioning scope for parts. I don't see any indications that the CRT is burnt, but I haven't tested the filament yet either.

At least you're in the right country. Tek scopes and parts are far easier to come by and cheaper in the States. Here in the UK, it's more of a challenge.

[tjg79]

The two pins that connect to the rear-most part of the CRT internals are the two directly below the index pin, and it measures 12 ohms across them.

I'm not sure which pins your are referring to. It's easy access to the CRT pins from the rear of the scope. I see 14 pins with a key on the center stud. If you number the pins 1 to 14, clockwise from the center stud key, which two pins are the filament?

EDIT: OK, after some study of the instruction manual, I found the CRT Circuit diagram. It appears that 10 of the 14 CRT pins are used and the pins are numbered clockwise from the center stud index key. It appears pins 1 & 14 are the filament, the pins on either side of the index key, and I measure 12 Ohms continuity across these two pins. So, I suspect my CRT filament is good for continuity. As for the filament coating condition, that remains to be determined. Although it can't be known for sure, but I don't see indications that this scope sat on a bench powered for years at a time. I'm optimistic about the condition of the CRT.

Also, there is no voltage across CRT pins 1 & 14 with power on, so it's not likely there would be a display. I think that's good news, because it implies the problem is elsewhere.

Per the instruction manual, one item of test equipment I don't have is a variable autotransformer.