A1 board removal? WAS Re: 'splitting' A2 and A3 PCBs when recapping Tek 2465


Jon Nicoll
 

Hi all - a follow on question re. recapping my Tek 2465; it might be better to start a new topic but I thought I'd stick with this one...

I've done all the boards now except the main one A1. Are there any guides around on demounting this board? It's a big board and I'd like to do it right... starting perhaps with how to disconnect the long plastic ng mains switch 'bar', perhaps...

Oh, and a separate question: the 'cat eye' end part of that bar has failed on my scope. It's purely mechanical, I think, and not important, but are they fixable?

Thanks, Jon N


Jean-Paul
 

Jon: Why do you want to remove A1?

1/ The A1 removal is risky and complex, i have never heard of this. Most recapping is on the PSU and A5 control bd for SMD lytics that leak, in 2465B.

2/ There are no caps or parts on A1 that need to be replaced if it is working OK.

3/ The on/off button is an IEE Schadow, you can find the caps on epay ...but usually a simple disassembly and fooling with it can fix the "eye"

Bon chance,

Jon


Jon Nicoll
 

Hi Jean-Paul

Well .. I *have* heard of people doing this, but you are certainly right that it is a way down the list. Menahem Yached's 'original' article on the web discusses recapping the small caps on A1, and the kit of parts I bought from him includes caps for this. I am sure he can defend himself here if he feels the need...

I could be persuaded not to do this ;-). Since posting the question I have found the right page in the service manual. The steps seem fairly straightforward, although I do have some questions:

- do you have to remove the front panel etc., as the instructions suggest?
- are the four Channel input BNCs 'tide; to the A1 board, and come out with it?

Anyway, that's the background. Thanks for the info on the 'Schadow', I will take a look at that.

Regards, Jon N


Jon Nicoll
 

PS: I see that it is "ITT Schadow". Thanks ;-)


Jean-Paul
 

Jon, removal of the front panel is not trivial and the input BNCs are part of the attenuators, can be damaged

"If it ain't broke don't fix it"

I have never done recapping on A1.

Have you done a calibration yet?

Jon


Jon Nicoll
 

Hi Jean-Paul

I haven't done a calibration - the 'scope is still in pieces...

Here's part of the (very long!) EEVblog on TEK repair which does include recapping the A1 board FWIW:

https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg589478/#msg589478

Regards, Jon


Mark Vincent
 

Jon,

I recapped the A1 board and replaced a few resistors that were underrated in wattage and the two 39meg carbons that were well out of tolerance. I know the two 39meg resistors are in the B version. The caps I used are Nichicon ULD 47mfd 25V types. I did add a heatsink to the horizontal output. I did not mind taking the time to do the work. I now know the parts I put in are new. Electrolytics that old should be replaced. You do what you want with yours.

Mark


Jon Nicoll
 

Thanks for the encouragement Mark! as I say, I could be dissuaded from doing this, but I am trying to determine the risk and difficulty:

- do I *have* to remove the front panel in order to do this? it looks to me that if I remove the cables & connectors, and the 13/14 screws, that it would just come out (I'd have to disconnect from the HV supply board as well)

I hadn't heard about the 39Meg and other possible resistor replacements on the A1 board, thanks. I'll look into those

I am still musing about doing anything with U800; I know it is a controversial topic...


Jean-Paul
 

Jon, please read all notes re U800, touching the screws or adding a heatsink can cause damage.

The lyttics that get old and dry are in PSU, not A1

Chuck Harris and Dennis are great authoritys on controversial points.

Bon Chance

Jon


Ozan
 

On Wed, Jun 23, 2021 at 11:18 AM, Jon Nicoll wrote:

- do I *have* to remove the front panel in order to do this? it looks to me
that if I remove the cables & connectors, and the 13/14 screws, that it would
just come out (I'd have to disconnect from the HV supply board as well)
--
Construction of 2465 looks similar to 2467B. Front panel covers the screws that connect attenuators to the front chassis.

Service manual has the steps for properly removing A1 board, I recommend following it rather than the EEVblog steps (you can use EEVblog pictures as a visual reference). Only difference I recommend is in step 6 not to pull the knobs below the screen but slide them off with the bezel. Although it seems possible to remove them if you are careful, it is very easy to break the plastic lips that hold them in place. This link shows pictures to explain it better:
https://groups.io/g/TekScopes/album?id=259435

Ozan


 

Heat the knobs with a hair drier on high before pulling them and they won't break.

On 6/23/2021 4:56 PM, Ozan wrote:
On Wed, Jun 23, 2021 at 11:18 AM, Jon Nicoll wrote:
- do I *have* to remove the front panel in order to do this? it looks to me
that if I remove the cables & connectors, and the 13/14 screws, that it would
just come out (I'd have to disconnect from the HV supply board as well)
--
Construction of 2465 looks similar to 2467B. Front panel covers the screws that connect attenuators to the front chassis.

Service manual has the steps for properly removing A1 board, I recommend following it rather than the EEVblog steps (you can use EEVblog pictures as a visual reference). Only difference I recommend is in step 6 not to pull the knobs below the screen but slide them off with the bezel. Although it seems possible to remove them if you are careful, it is very easy to break the plastic lips that hold them in place. This link shows pictures to explain it better:
https://groups.io/g/TekScopes/album?id=259435

Ozan






--
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On Wed, Jun 23, 2021 at 10:56 PM, Ozan wrote:


Service manual has the steps for properly removing A1 board, I recommend
following it rather than the EEVblog steps (you can use EEVblog pictures as a
visual reference). Only difference I recommend is in step 6 not to pull the
knobs below the screen but slide them off with the bezel. Although it seems
possible to remove them if you are careful, it is very easy to break the
plastic lips that hold them in place. This link shows pictures to explain it
better:
I think it's important to be aware that by removing the bezel without first pulling the knobs individually, as Ozan recommends, the coupling pieces carrying the knobs are removed from the pot axes. That way, the knobs themselves are in no danger of breaking.

Raymond


 

It's quite simple to remove the A1 - it just looks difficult, even though it is time consuming.
Do it once, do it right.

Unsolder the wires at each of the BNC connectors (Do not remove the BNC connectors from the chassis);
Remove (very gently) the 2 small wire connectors at the CRT (through the hole in the PCB);
Be ready to hold the delay cable under the PCB, without unravelling it.
That's all there is to it.

Expect a significant improvement in the sharpness of the waveform traces, after the A1 overhaul.

Menahem


Jon Nicoll
 

Hi Menahem

Thanks ... I guess it is just the CH3 and CH4 BNC wires you are talking about desoldering?

I know about the (4, I thought - 2 pairs?) of wires going to the CRT, I have some small pliers or tweezers for that.

I'm not 100% sure about the delay cable but I will look for some photos beforehand.

If that is everything, and I don't need to remove the front, then I will give it a go...

Jon N


Jon Nicoll
 

Well, that wasn't too bad - removing the A1 board that is.

Menahem, I have no idea what you meant about not removing the BNC connectors from the chassis (unless you meant the ones at the rear?)

Anyway, removing the front panel assembly was a lot easier than I expected; I hadn't realised it was just a push fit into the chassis aperture. And that gave me access to the six screws which hold the front BNSs to the main casting.

Replacing the A1 caps will be pretty easy I guess. I am a bit nervous about refitting but I am sure a little patience will go a long way.

Cheers, Jon N


Dennis Fernandez
 

where is the link? I need to change an attenuator.

Dennis N4KPI


Dennis Fernandez
 

sorry i read down further and found it in another post.


Jon Nicoll
 

Well, Success!

I went ahead and removed the A1 board, and replaced all the Caps. I've been slowly putting everything back together for the past week or so, including gluing up the fan mandrel that (like many others) broke on removal.

I rather tentatively powered the 'scope up today and ... got a weird readout screen and no main trace.

I powered down rather gloomily, but checked my work and found that I had misfitted one of the IDC connectors from the front panel. Corrected that and ... things are looking good!

I will probably post a photo or two after I have cleaned up the case a bit and fitted the scope back in it.

One thing ... now that it is working again, I am reminded that one of the front panel LEDs doesn't work (Channel 1 input mode 'DC' indicator). I assume it would not be much of a job to fix that? Any pointers to replacements etc.?

Oh, I had (only!) one screw left over ... one of the short 1/4-inch Torx screws. Not sure where that might have come from, I'm toying with stripping it down a bit one more time to find out..

Cheers from the UK, Jon N


 

Well done!