Tektronix 465b oscilloscope CH1 & 2 issues

[Radio Surfer]

Hello,

Had a thought last night (doesn't happen very often) but it worked.

A Meccano imperial cranked spanner fits those awkward bolts behind the metal capacitor, the final removal once loosened by the spanner was with a pair of long nosed pliers. One less job to remove the capacitor. That looked a bit awkward to solder as not much room.

One small victory, but it pleased me.

Regards Richard

[MrBungle]

Great solution! Anything that makes it easier is a win.

[Radio Surfer]

Hello,

yes, just a little less work and errors I could make!

Once I've taken the Attenuator board and associated gubbins out to sort out the remaining 2 dodgy contacts (just 2 for all this work!) should I:

1) grease, with a light clear grease, the ratchet mechanism on the cam where there is a small metal spring pressing against a wheel to secure the volt/div wheel in its set position? There seems to be evidence of some lubrication stains running down inside. Although the manual does imply nothing is required.

2) do anything else, whilst dismantled. I don't want to do too much as I want to minimise the risk of me introducing a new problem. Things seem to be working subject to the switch contacts already mentioned. Equally, its a pain to dismantle, so really i'm looking for a " if you did one thing..." type preventative maintenance. Accepting that "one thing" might be replacing 50 capacitors, in which case I'll come back to it later once I've proven the scope works.

3) the fan has a metal mesh with about a 1/4" gap that presumambly a filter fitted. Any recommendations, or will almost any filter material do of suitable depth?

Many thanks for all the advice.

Regards,

Richard

[MrBungle]

I have never greased anything in there at all. I don’t think it’s necessary and may migrate to somewhere harmful.

Clean the vertical mode switches while you’re there. I just give them a squirt of switch cleaner.

On the fan forum member ColinTheAmpMan inherited my old 475A and had a solution for that. Probably worth dropping him a PM on the matter.

[ajgriff]

A few years ago I did some research regarding the air filter and came to the conclusion that the foam used in aquarium filters was a good option provided you can find something 6-8 mm thick and cut it to size. It fits on the outer surface of the aluminium grille ie, not between the grille and the fan blades.

The manual is pretty unhelpful on the subject but some earlier manuals for the big 500 series scopes describe washing their filters (big foam pads) and spraying them with light filter oil before refitting. Used sparingly the stuff supplied for car air filters should do the job if you wish to take a belt and braces approach.

It is important to use open cell foam so that air can flow freely in terms of cooling. Personally I wouldn't use scouring pads, as sometimes recommended, because they tend to 'shed' and I don't want green bits floating around the insides of my 465B.

Not having aquarium filter foam to hand I actually used a piece of anti-static foam that came with a static sensitive electronic device. It just happened to be about the right thickness. Didn't bother with the oil on the basis that my scope lives a pretty easy life in a relatively clean environment.

Alan

[Radio Surfer]

Thanks chaps,

I've just had a clear out over the past few months and one of the things to go was the aquarium and associated kit including filters. Never mind, just had a look at prices and only a few pounds for a small sheet. Other option might be PC filter which I have, very thin but I could pack round the edge with some foam/draught excluder to hold in place even as a temporary measure whilst I find something more permanent. I know what you mean about scouring pads, they do shed quite a bit. I use them to clean vintage Scalextric track, which is the recommended way, but then spend time picking the green bits out of the slot.

Just building myself up for the dismantling process. Not looking forward to it, but hopefully won't be too bad. But I need to sort those bottom contacts out. Ill take plenty of pictures and drawings. Not done one of these before, so fingers crossed.

Regards, Richard

[Goldie99]

The foam used in aquarium filters is called 'reticulated foam' - it's basically a PU foam, that's been post-treated to remove the cell 'windows', to maximise air- or fluid-flow.

Alan

[twizzle]

I didn't manage to read all the helpful replies posted here but in my experience just keep going at cleaning the contacts in the attenuator section, in particular the ones you haven't spotted yet. I have a Tek 468 that had exactly the same issues and the more I looked the more contacts I found. I used the method you're employing and eventually I got all voltage ranges to work. I nearly gave it up at one point but glad I persevered. Strips of j-cloth soaked in IPA, that's all. Good luck.

[Nymrod121]

Richard, I've some air filter media* left over from when I changed that on my 465 (having initially used green scouring pad, I reverted to conventional following the advice received here). I can send you some in the post f.o.c. if you'd care to PM me your address?
All the best
Guy

* ('Electruepart': FLT3940)

[Radio Surfer]

Hi Twizzle,

Thanks for the comment, I keep deferring the strip down, but I know which sets don't work as I've followed Mr Bungle's advice and the manual and using my multimeter can confirm when they are working. I also made a jumper wire to mimic the switches working to prove the scope would work and that i had just these 2 contacts to sort. There are underneath the attenuator boards one set is on channel 2 board I can just get at, but after 2 days no joy. There are 2 possibilities, the first is there is a raised blob of solder from a resistor lead that is keeping me from getting at the contact properly, the other (as i found on the top) is that the prongs of the fork style contacts are not coming down absolutely square and need a very slight "tweak". When I close the contact on a piece of paper, one side has resistance when I pull the paper, the other side doesn't. The other dodgy contacts are below channel 1 and they are hidden by channel 2's cam. I can't even see it let alone get anything close to clean it. It would be the 2 I can't get at which are the problem.

I did get one set working briefly only to find they failed the next day and cleaning this morning had no results.

I'll have one last go, but I suspect the very delicate contacts have lost some of their original spring, a bit like I have with age!


Here's to one more bash,

Regards,

Richard

[Radio Surfer]

Hi Guy,

Very kind I'll PM you now.

Regards, Richard.

[Nymrod121]

Hi Richard

Envelope on its way to you today. With luck, you should receive it first thing Thursday by means of earliest postal delivery (a.k.a. 'Tiree Dawn Porter' perhaps).

OK, OK, I'll get me coat ....

G.

[Radio Surfer]

Cheers Guy,

Postie will leave it on dining table as we don't have letter boxes here. Once he's got over the shock that a letter has arrived on the island.

Simples

Regards Richard

[Radio Surfer]

Ok,

So dismantling in progress. Section 5.14 gives me the basics of what to do, although I'm not sure which model the author was working on when he/she wrote it !

Anyway, what's the best way of disconnecting the push button extension shafts. I'm frightened of cracking the plastic as it my have dried out with age. The way I'm reading the manual, you insert a small screwdriver in the gap between the white shaft on the switch and the black extension arm and then twist gently the screwdriver to lever the 2 halves apart.

Any tips before the request comes in for a new extension arm?

Regards, Richard

[MrBungle]

You don't have to take the shafts off. They pull out with the attenuators. Only the main attenuator, vertical position and coupling knobs etc need to come off.

I managed to break the power switch arm on an HP 3478A last time I tried to do it so I wouldn't recommend undoing them at all

[Radio Surfer]

Thank you,

I won't risk it, I tried to ease the extension off, but it seemed too tight. I'll do as you advise.

Tomorrow we have a power outage most of the day to repair fallen power lines, not unusual for here. So that gives me an excuse to hopefully, strip the bits out, clean, test and get back together.

I'll report back when we have some power.

Regards. Richard

[Radio Surfer]

Morning,

The planned power outage has been postponed as the workforce couldn't get to the Isle, so I've been able to log back on.

The dismantling process fell at the first hurdle. The small grub screws in VAR/DIV are so rounded that there is no way they are coming out. I have used the correct allen key as per the manual (1/16") and the set I have are good quality barely used. Looking at most of these in the various knobs, most appear to have been "attacked" at some point in their life or overtightened when first fitted. I wasn't totally surpised and expected this to be an issue, they usually are whenever I come across them especially at this small size.

So any bright ideas? Some have said there is no need to dismantle, which I'd be delighted to, but how have you managed to get to the underside contacts of CH1 hidden by the Cam of CH2.

Thanks in advance

Regards, Richard

[MrBungle]

Oh fun! One of those ones! I've managed to get the rounded ones out before using a suitable Torx driver tapped in with a hammer. You need replacement grubs though.

I've never managed to clean them effectively without dismantling. Usually victory is very short lived.

[Radio Surfer]

As you say, such fun we had,

Yes, I've had another good look round and no way can you get to the underside contacts, and as you say some contacts that were fine yesterday are iffy again. It needs a really good clean, its not just a fleck of dust.

Are the grub screws readily available? I'll try your method, Ever tried drilling out it all else fails?

Regards, Richard

[ajgriff]

Do you have a small flexi-drive chuck and an electric drill with reverse action? If so, attacking this type of obstinate screw with a suitable bit will sometimes jar it free. Lack of room may negate this as an option of course.

Alan