Tektronix 465B Oscilloscope Restoration

[uncle_bob]

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?

Hi

I would read that as 1 and 14

edit:

After a long and dangerous journey into the dark recesses of the "library" ... Yes indeed, the manual page that shows the CRT schematic calls out the pins as numbers 1 and 14.

Bob

[Addicted2AnalogTek]

Yes, my apologies. I should have worded that better.   Pins 1 and 14 are indeed the ones I meant, and by "index pin" I meant "index key".  12 ohms is what I measured across those pins on that specific CRT, which I know definitely works quite well.  That 465 had gotten attenuator shafts damaged in shipping due to worthless packaging, so I parted it.

[uncle_bob]

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.

Bob

[Addicted2AnalogTek]

http://www.opweb.de/en/model.php?id=2650

[tjg79]

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 cleaned the X10 switch with a cotton swab and just IPA as best I could without any disassembly and it's working fine now. I think it could possibly be partially disassembled if it was disconnected from the push rod for a better cleaning. I'll look at that once I disassemble the scope. But, it is working 100% better now and has a good feel as well. I had looked up a replacement for that switch and the one I found, NOS, was $25.00 plus shipping. I thought that switch was too far gone for a rejuvenation with a simple cleaning, but I was wrong. Thanks for the suggestion.

[tjg79]

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.

Bob

I think it's the poor quality printing by Tektronix. My hard copies have shrunk as well. So, I'm using pdf copies, because I can override the shrinking text.

[Addicted2AnalogTek]

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.

Bob

Well that's interesting... I didn't know they did that.   I only have one paper manual, but have an old 454 manual and a 485 manual on the way. I'll try to keep that in mind from now on when buying paper manuals and always try to get the earlier (as long as still correct) manuals.    They still have fold-out diagrams though, right??

[uncle_bob]

Hi

Yup, the still have fold outs and nice tabs to let you find the sections in the manual. I would *swear* that the print was easier to read 20 years ago ....

It couldn't possibly be *me* could it ? .....

There are indeed some advantages to a scan over a "real printed manual".

Bob

[tjg79]

The instruction manual lists four signal generator type instruments for calibration; Calibration Generator, Sine-wave Generator, Time-Mark Generator, and Low Frequency Generator. Also indicated are Tektronix examples for these various signal generators.

Is there an accepted signal generator from another manufacturer that does all these functions in one unit? If so, what's the model number.

Regards

[Addicted2AnalogTek]

A good start:

[Addicted2AnalogTek]

I doubt you're all that close to Morgantown WV, but if you are or if you feel it's worth the trip sometime, I could help you out with calibrating your scope.  I have all of the equipment.

[tjg79]

I doubt you're all that close to Morgantown WV, but if you are or if you feel it's worth the trip sometime, I could help you out with calibrating your scope.  I have all of the equipment.

Thanks, but you're only 8 hours/450 miles round trip away from Occoquan, VA.

I'll eventually acquire the signal generators, because it's more convenient and they are useful to have. I was just wondering what others use to calibrate these scopes and if there was an all-in-one model signal generator that met all the Tek requirements.

I've got another 465B that's working, but it likely needs to be tweaked, because I don't know anything about the previous calibration. 

[tjg79]

I haven't pulled any of the physically large capacitors off the A4 Interface board yet, so I don't know what the existing capacitor lead configuration, pin-outs, or A4 trace/hole spacing look like, and I'm not sure that the gerber files for the capacitor adapter boards posted on the Tektronix 7603/7613 Repairs thread will be applicable for the 465B A4 Interface board. So, I suspect I'll likely have to create capacitor adapter board gerber files for this 465B recap project.

Does anyone have recommendations for a free download type PCB Cad/gerber file software program?

I see a few when I do a Google search, but I haven't studied any of them in sufficient detail to determine which is the best choice. I was wondering if anyone here has first hand experience with any of the freeware packages?

 

[MrSlack]

I've just recapped one of my 465B's. I've literally just soldered the new caps in place on extended leads with some heatshrink around the exposed legs. The caps are much smaller now so I've spaced them with 4mm thick plastikard and cable tied them. You don't need to do anything fancy to replace the bases; just check the PSU schematic in the service manual and make sure the caps are rated correctly and connected to the right rails. The old bases were for mechanical stability which isn't an issue if your capacitors weigh 1/3 the amount.

Used Vishay Sprague 105oC low ESR devices to replace.

Then again I want to use my scope, not build a museum piece so it depends what you want out of it.

Before you do that though, check the rails for ripple. If they are in spec and the voltages on the test points on the A4 board are fine then don't bother changing anything yet. If it's not done too many hours the caps are probably fine still then. I've seen Sprague caps from 1968 that are still fine and in spec!

[tjg79]

I've just recapped one of my 465B's. I've literally just soldered the new caps in place on extended leads with some heatshrink around the exposed legs. The caps are much smaller now so I've spaced them with 4mm thick plastikard and cable tied them. You don't need to do anything fancy to replace the bases; just check the PSU schematic in the service manual and make sure the caps are rated correctly and connected to the right rails. The old bases were for mechanical stability which isn't an issue if your capacitors weigh 1/3 the amount.

Used Vishay Sprague 105oC low ESR devices to replace.

Then again I want to use my scope, not build a museum piece so it depends what you want out of it.

Before you do that though, check the rails for ripple. If they are in spec and the voltages on the test points on the A4 board are fine then don't bother changing anything yet. If it's not done too many hours the caps are probably fine still then. I've seen Sprague caps from 1968 that are still fine and in spec!

I like the look of the capacitor adapter boards. And, I'm not in a hurry to get this "no display" scope up and running. The 465B instruction manual indicates to look at the power supply circuit first for "no display" condition. My rails are not in spec.

I've got to get the rails in spec before I check for ripple. My +5V and -8V have problems. Once I get the rail voltage issues resolved, I'll resolve any rail ripple issues. I think that once I replace the device or devices, if any, that are causing the rail voltage issues, the recap of all electrolytic and tantalum caps will resolve any ripple issues.

Do you have the Bill of Materials (BOM) for your 465B recap? Is so, can you post it?

Regards

[MrSlack]

Check the 55v rail first as others are derived from that or referenced against it. I had a blown tant on that which killed all the other rails. That nearly killed all the ripple just replacing that (that was RS 108-5507). See my thread here on progress on my two 465B's: https://www.eevblog.com/forum/repair/sick-tektronix-465b/ - you can see a fine view of the sick tant on there.

I don't have the full BOM on me at the moment as I deleted that RS receipt unfortunately.

[tjg79]

My +55 volt is in spec.

Your blown tant, as with many others I've read about, is the reason why I'm replacing all my tants.

[MrSlack]

In that case, ESR meter. Cheap Chinese transistor tester units are good enough. Dot replace them until you've isolated them as the cause though as circuit loading on the regulator output can also cause these symptoms.

[tjg79]

I've got a Peak Electronic Design, LTD Atlas ESR+ Model ESR70. I think a recap resolves a lot of issues with nearly four decade old electronics.

I'm going to fully disassemble and check all the devices. This is a restoration project and I don't want to have to go back in a year or two later.

I'll isolate the power supply from the other boards until I have rail voltage and ripple in spec.

[NilByMouth]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

[tjg79]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

Did you have a "no display" condition as well?

[NilByMouth]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

Did you have a "no display" condition as well?

Yes. I bought it as a non-worker. The 1.25 inch fuse on the power supply board had blown. I replaced that and it worked for half an hour then no trace. I still need to go over it with an ESR meter to check the caps, but it's working again fine with a new bridge rectifier on the -8V rail.

[tjg79]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

Did you have a "no display" condition as well?

Yes. I bought it as a non-worker. The 1.25 inch fuse on the power supply board had blown. I replaced that and it worked for half an hour then no trace. I still need to go over it with an ESR meter to check the caps, but it's working again fine with a new bridge rectifier on the -8V rail.

Are your electrolytic caps original?

The ESR meter is very helpful to locate a bad cap, but with 40 year old electronics, I think any cap can go bad at any time. Also, although old caps may have a relatively good ESR measurement, in general, the ESR readings of old caps don't compared favorably to new caps. There are exceptions, because amazingly, some caps seem to not show their age. To avoid having to repeat the troubleshooting routine, I'm going to replace all the caps that usually cause trouble with age. Those are the electrolytic and tantalum caps.

[NilByMouth]

Are your electrolytic caps original?

The ESR meter is very helpful to locate a bad cap, but with 40 year old electronics, I think any cap can go bad at any time. Also, although old caps may have a relatively good ESR measurement, in general, the ESR readings of old caps don't compared favorably to new caps. There are exceptions, because amazingly, some caps seem to not show their age. To avoid having to repeat the troubleshooting routine, I'm going to replace all the caps that usually cause trouble with age. Those are the electrolytic and tantalum caps.

Yes, they are most likely all original. If I was going to use the scope in anger, I probably would replace them all. I will probably get around to recapping all of my old scopes (I have 8 Tek scopes and currently only use my Siglent DSO).

[tjg79]

I checked the power supply's five large filter caps with my ESR meter. The filter cap on the -8V rail, C4419, tests bad as open. The instruction manual describes this cap as: Cap., FXD, ELCTLT: 5000UF, +100-0%, 25V. The Tektronix part number is 290-0571-00.

The power supply circuit's unregulated -8V tests as +0.52 volts near the bridge rectifier, CR4411.

I'm not sure if those test results indicate that both the filter cap and bridge rectifier are bad or just the filter cap.

I checked Mouser Electronics for replacement filter caps and I don't see any that match the specs for these caps as described in the instruction manual. That's usually the case for these types of caps in vintage electronics.

I can get a NOS 290-0571-00 from Sphere Research Corporation, but they are pricey with shipping and I'd rather replace with a new modern cap if I can find one that's a good fit per the specs.

Does anyone have a recommendation for the power supply filter caps replacements?