Tektronix 465B Oscilloscope Restoration

[Addicted2AnalogTek]

Bob,

W2AEW has a few vids where he makes/uses a simple fast rise pulse generator for TDR and such, which he specifies as being approx 2ns risetime... but what about pulling off something around 250ps risetime?  Is the best bet for that still a tunnel diode pulser, or piece of gear such as the 109 or 110 pulse gen?  I'm in need of something for 485 cal.
(apologies for the slightly off topic question)

[tjg79]

I'm rather surprised nobody has linked in this useful Tektronix document...

http://sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

I mentioned it in my first post. It's a very useful document. Thanks for posting the link for others.

[uncle_bob]

Bob,

W2AEW has a few vids where he makes/uses a simple fast rise pulse generator for TDR and such, which he specifies as being approx 2ns risetime... but what about pulling off something around 250ps risetime?  Is the best bet for that still a tunnel diode pulser, or piece of gear such as the 109 or 110 pulse gen?  I'm in need of something for 485 cal.
(apologies for the slightly off topic question)

Hi

Once you get below about 500 ps, you are into dedicated circuits. You are also into bandwidths that take a bit of care design wise. A tunnel diode or an avalanche pulser are the only things that come to mind quickly.

Bob

[tjg79]

Is there a way to distinguish the tantalum caps from the other electrolytic caps in the 465B Service Instruction Manual?

If there is, I don't see it yet.

[MrSlack]

There isn't a way really. Technically the NSN doesn't specify any more than CAPACITOR, FIXED ELECTROLYTIC which means that any part with that NSN or spec should really be fungible. Makes technical inventory easy for big corporations and armed forces etc.

TBH it doesn't matter. Just pick a close part. C4303 blew on mine. 3uF 150v tant axial. Replaced with 4.7uF 150v electrolytic axial. Problem solved. Modern alu electrolytics are much more reliable and cheaper than the original part. I think I was quoted ~ £35 for a replacement identical cap from an inventory stockist versus £2 from RS for 5. If you want to restore original parts, it's going to cost a lot.

There are however supplier codes on the right side of the BOM and vendor but it's difficult to isolate a specific single part 35 years later. But YMMV by looking for patterns as they tend to buy all electrolytics from one vendor and tants from another or the part numbers are different format.

[uncle_bob]

Hi

I would very much *not* recommend a wholesale replacement of tantalum caps with aluminum electrolytic caps. There are some very significant impedance differences between them at RF. They have gotten a lot better over the last 40 years, but they are not a perfect substitute. You need to look at were they are in the circuit and pick where you make a substitution.

Bob

[tjg79]

There isn't a way really. Technically the NSN doesn't specify any more than CAPACITOR, FIXED ELECTROLYTIC which means that any part with that NSN or spec should really be fungible. Makes technical inventory easy for big corporations and armed forces etc.

TBH it doesn't matter. Just pick a close part. C4303 blew on mine. 3uF 150v tant axial. Replaced with 4.7uF 150v electrolytic axial. Problem solved. Modern alu electrolytics are much more reliable and cheaper than the original part. I think I was quoted ~ £35 for a replacement identical cap from an inventory stockist versus £2 from RS for 5. If you want to restore original parts, it's going to cost a lot.

There are however supplier codes on the right side of the BOM and vendor but it's difficult to isolate a specific single part 35 years later. But YMMV by looking for patterns as they tend to buy all electrolytics from one vendor and tants from another or the part numbers are different format.

I've pretty much ruled out using original new old stock (NOS) electrolytic caps. Some are available, but when I inquired about their date of manufacture, they're at least 20 years old. I don't think these types of "original" parts are a good replacement choice today.

So, I intend to identify recently manufactured electrolytic cap replacements that match the original specs and design as closely as possible.

As for identifying the tantalums, it will have to be visually. I was hoping that it could have been done from the Service Instruction Manual, because I haven't disassembled anything yet.

[tjg79]

Hi

I would very much *not* recommend a wholesale replacement of tantalum caps with aluminum electrolytic caps. There are some very significant impedance differences between them at RF. They have gotten a lot better over the last 40 years, but they are not a perfect substitute. You need to look at were they are in the circuit and pick where you make a substitution.

Bob

That's my concern about wholesale tantalum cap replacement. I would think that although they may "work," you might have some calibration issues if you don't consider the original cap design and characteristics when researching replacements. The Service Instruction Manual cap description of capacitance, tolerance and voltage rating doesn't give a full and adequate description of the engineering requirements. So, I intend to replace electrolytic tantalums with electrolytic tantalums.

[MrSlack]

Hi

I would very much *not* recommend a wholesale replacement of tantalum caps with aluminum electrolytic caps. There are some very significant impedance differences between them at RF. They have gotten a lot better over the last 40 years, but they are not a perfect substitute. You need to look at were they are in the circuit and pick where you make a substitution.

Bob

You're right they're not a perfect substitute but the device will most likely function within specifications afterwards. I've seen many substitutions in production RF kit (military comms) that people would consider horrible but don't cause any functional impairment.

You have to make a trade off really.

[tjg79]

I've got another 465B with what appears to be a broken CH 2 Volts/Div VAR switch. The switch passes through the detent and the detent isn't very strong. Also, the Uncal lamp doesn't illuminate when the knob is moved from the detent.

The Service Instruction Manual indicates this Volts/Div & VAR knob/switch assembly is complex. From looking at the diagram, I'm not sure what parts likely need to be replaced.

Does anyone have any experience with this knob/switch assembly and have an idea what likely needs to be replaced?

Regards

[Addicted2AnalogTek]

I've got another 465B with what appears to be a broken CH 2 Volts/Div VAR switch. The switch passes through the detent and the detent isn't very strong. Also, the Uncal lamp doesn't illuminate when the knob is moved from the detent.

The Service Instruction Manual indicates this Volts/Div & VAR knob/switch assembly is complex. From looking at the diagram, I'm not sure what parts likely need to be replaced.

Does anyone have any experience with this knob/switch assembly and have an idea what likely needs to be replaced?

Regards

I have a 454A that has the same issue with both CH1 and CH2. Although I have not even powered it on to see the extent of their demise.  I assume I will need to replace or attempt to rebuilt the pot/switch assembly on both of them.

A suggestion for that 3uf 150V 109D tantalum, which I actually used a few times -  There is a seller which has 3.6uf 125V wet tantalums which will run you $20 for 2.   That's as close as I have found to the original. 

[tjg79]

I've got another 465B with what appears to be a broken CH 2 Volts/Div VAR switch. The switch passes through the detent and the detent isn't very strong. Also, the Uncal lamp doesn't illuminate when the knob is moved from the detent.

The Service Instruction Manual indicates this Volts/Div & VAR knob/switch assembly is complex. From looking at the diagram, I'm not sure what parts likely need to be replaced.

Does anyone have any experience with this knob/switch assembly and have an idea what likely needs to be replaced?

Regards

I have a 454A that has the same issue with both CH1 and CH2. Although I have not even powered it on to see the extent of their demise.  I assume I will need to replace or attempt to rebuilt the pot/switch assembly on both of them.

A suggestion for that 3uf 150V 109D tantalum, which I actually used a few times -  There is a seller which has 3.6uf 125V wet tantalums which will run you $20 for 2.   That's as close as I have found to the original.

Well, my CH 2 Volts/Div VAR switch isn't as big a deal as I thought. I can see the VAR switch behind the Volts/Div switch assembly. It's only $14 to $19.00 for a NOS switch plus shipping. At least the switch appears to be available. It's likely the same type of deal on your 454A.

[tjg79]

My two trigger level/slope switches, 311-1192-00, have a mechanical problem with the slope part of the switch. The switch doesn't turn easily and feels as thought it's gummed up inside. A replacement switch is a difficult to find part. One electronics parts company has them, but their asking price is $60/each. I think it's odd that both switches would exhibit the same condition. Perhaps it's an indication that the scope was dropped or something fell on these protruding switches.

Has anyone had any luck cleaning this switch? Can it be disassembled?

Regards

[Addicted2AnalogTek]

My two trigger level/slope switches, 311-1192-00, have a mechanical problem with the slope part of the switch. The switch doesn't turn easily and feels as thought it's gummed up inside. A replacement switch is a difficult to find part. One electronics parts company has them, but their asking price is $60/each. I think it's odd that both switches would exhibit the same condition. Perhaps it's an indication that the scope was dropped or something fell on these protruding switches.

Has anyone had any luck cleaning this switch? Can it be disassembled?

Regards

I wouldn't attempt disassembly, but if you look closely you will notice that there are two holes around the perimeter of the body.  If you sucked up some deoxit or cleaner in a hypo needle you could shoot it in there and soak/clean it.

[tjg79]

My two trigger level/slope switches, 311-1192-00, have a mechanical problem with the slope part of the switch. The switch doesn't turn easily and feels as thought it's gummed up inside. A replacement switch is a difficult to find part. One electronics parts company has them, but their asking price is $60/each. I think it's odd that both switches would exhibit the same condition. Perhaps it's an indication that the scope was dropped or something fell on these protruding switches.

Has anyone had any luck cleaning this switch? Can it be disassembled?

Regards

I wouldn't attempt disassembly, but if you look closely you will notice that there are two holes around the perimeter of the body.  If you sucked up some deoxit or cleaner in a hypo needle you could shoot it in there and soak/clean it.

I suppose that's the best first approach. If cleaning the switch through the two holes with DeOxit doesn't improve the performance, I will attempt to disassemble if for no other reason than to perform an autopsy. I might even be able to fix it.

[Addicted2AnalogTek]

If you aren't able to clean or fix it, you may be able to find a replacement on ebay**(for a reasonable price)**.  I continuously surf the tektronix stuff and have often seen the part under "4XX trigger switch, trigger level control, trigger slope switch.." etc. (where XX is the corresponding numbers for any of these 400 series scopes - they all have the same part for the trigger level/slope).  If I come across any more I will link them here for you.

[tjg79]

I received my order of replacement bridge rectifiers, 152-0556-00, for the -8V rail. The spec is 2.5A 50V per the service manual. I received one that had the Tek part number, but the rest were MDA970G1 4A 50V.

The original acted like a fuse. Perhaps it protected something down circuit. I suspect the -8V rail filter cap failed and took the bridge rectifier.

What's the best choice for the replacement? Does it make a difference?

Regards 

[Addicted2AnalogTek]

The ones I have been using are the MDA970G1's.   I think we may have the same supplier, actually.    My 465 manual specifies MDA960-1, though.  They can be had off of ebay...... for almost $30.00 each. haha

I trust Tim's inventory to be the correct replacement parts - and I've not yet had any issues with the MDA970G1's.   I actually remember reading somewhere in an old Tek engineers documents that the MDA970's are an upgraded replacement part.

[tjg79]

He indicated that the Tek 152-0556-00 crossed to SDA10271K, which is what the SM indicates, MDA970G1, and KBL005-B at various times from Tek.

The MDA970G1 and KBL005-B are 4A 50V bridge rectifiers. I think the SDA10274K is a 2.5A 50V bridge rectifier.

Perhaps it makes no difference.

[Chris56000]

Hi!

One very important question .... who shrunk all the type in the paper copy of 465B manual since the last time I had it open? That (judging from the bookmark used) was some time in the 1990's ... I seem to have become very used to scans since then.

I don't know about shrinking text, but I certainly do know about shrinking circuit and layout diagrams! That one linked on "Opweb.de" has been scanned with only about a quarter of each layout and schematic page uploaded as well as at least four of them completely missing!

However, the download isn't totally useless, as it contains four official Tek 465B Manual Amendment Sheets that are very useful, and not, as far as I'm aware, available elsewhere separately for download!

Worse, the supply of original 465B paper copies is starting to get scarce, and US sellers are beginning to ask silly postage prices for them – does it REALLY cost over £200 to ship a 300 page A4/8½" × 11" manual package from the US over here?!

I may be wrong about this but didn't Tek supply TWO copies of the Service Instruction Manual with every new piece of gear ordered from them at one time in the 1970s/1980s?

I'd to buy mine from Artek in the end then still had aggro downloading from their FTP, it was emailed to me in the end!

Chris Williams

[George Edmonds]

Hi

There is a good clean scan of the 465B manual on the Tektronix UK web site. it also free.

George G6HIG Dover UK