Tektronix 465B repair

[bd139]

Ok so the aforementioned Tektronix 465B arrived and as expected it doesn't work. The best kind of purchase!

Initial power up assumption was that the HT fuse was popped and the tant on the HT oscillator was short. This turned out to be incorrect. Sticking it in X-Y mode and cranking up the intensity shows some glow off the top of the screen but there is no sweep. This usually suggests power rail problem somewhere but alas those are all pretty good too.

Current assumption is that one or more of the amplifiers is dragging the beam away. I will, later, measure the deflection voltages across the amplifiers and see if they respond to change in X-Y mode. If they do not or are unbalanced, I'll disconnect the deflection plate wires and isolate that amplifier and see if the other one and the HT works. If both are disconnected and nothing improved I'll assume that there's an HT or tube problem to contend with.

Anyway first picture...

20230928_080724723_iOS.jpg

[Zenith]

There's nothing like getting your teeth into a good oscilloscope fix.

My current one is a 100MHz Hitachi V1050F. It had an intermittent 5V supply problem, eventually traced to a dry joint, a host of problems caused by dirty switches and Y channel 1 has a frequency response which drops off too low.

A lot of Hitachi scopes have much the same Y amps with factory selected components to make the bandwidth match the model number. Putting a small capacitor across one of these makes the frequency response nearly right. I'm mulling over whether to be satisfied with a solder side bodge or to take out the board, power it from a bench PSU, and investigate that filter with factory selected values properly.

V1050F is one of the earlier models. It's a bit chunky but it is a genuine 100MHz scope with a dual timebase.

I'll write up a proper description with piccies when it's done.

[bd139]

Indeed there isn't. Interested to see your write up!

Well I was bored on a Zoom call so I managed to get the vertical back and working. Stuck it in X-Y and poked the delay line with a DMM and moved the vertical around looking for differential signal. There was only half of one. Wiggling the transistors around in sockets did the job and I now have full vertical and horizontal control.

It doesn't sweep or trigger properly though. One for the next round!

[tggzzz]

It doesn't sweep or trigger properly though. One for the next round!

That sounds very familiar See some of my other posts!

[MED6753]

Chris, if you need any measurement data let me know.

[bd139]

Chris, if you need any measurement data let me know.

Thank you kindly

[bd139]

It doesn't sweep or trigger properly though. One for the next round!

That sounds very familiar See some of my other posts!

Yes it does indeed. I will bear them in mind if I get stuck but I like going into problems with zero assumptions as the indication of this thread is that mine were wrong!

[tggzzz]

It doesn't sweep or trigger properly though. One for the next round!

That sounds very familiar See some of my other posts!

Yes it does indeed. I will bear them in mind if I get stuck but I like going into problems with zero assumptions as the indication of this thread is that mine were wrong!

Yeah!

FWIW, I failed to locate the problem by looking at waveforms around the sweep/trigger loop. I finally located the problem by measuring the voltages on transistor terminals, eventually discovering that a V_CE~=0 even though V_BE indicated the transistor should not be conducting. (N.B. that tilde looks like a minus when previewed?!)

[Zenith]

Wiggling the transistors around in sockets did the job and I now have full vertical and horizontal control.

It doesn't sweep or trigger properly though. One for the next round!

I'm of two minds as to whether the transistors in sockets in 400 series Tek scopes are a good or bad thing. I've never had them cause any problems with bad contacts but I've always been suspicious of them. OTOH, they have sometimes made fault finding and repair easier.

Approach it systematically, and if you find you are getting nowhere with a fault, leave it for a bit. After a few days and with a different perspective you may well find the problem obvious.

[bd139]

Ok further debugging has found the unfortunate cause of the problem. I suspected this was the RC network of R7272 and C7273 doing it (open C7273) as the voltage on AUTO RC was wrong (0 instead of 5.2V). While poking around I touched U7375 with my finger and got singed. It's running red hot. The 5V rail is slightly sagging at 4.81 volts and this appears to be the culprit. If I pull it out it and power it up it goes to 5.02 volts. So nearly all the current is going into the trigger IC which is clearly not happy! Have checked the socket for shorts and there are none so I think this is a duff IC.

I will contemplate what to do next over the next few days.

[MED6753]

Ok further debugging has found the unfortunate cause of the problem. I suspected this was the RC network of R7272 and C7273 doing it (open C7273) as the voltage on AUTO RC was wrong (0 instead of 5.2V). While poking around I touched U7375 with my finger and got singed. It's running red hot. The 5V rail is slightly sagging at 4.81 volts and this appears to be the culprit. If I pull it out it and power it up it goes to 5.02 volts. So nearly all the current is going into the trigger IC which is clearly not happy! Have checked the socket for shorts and there are none so I think this is a duff IC.

I will contemplate what to do next over the next few days.

If you can't find one locally I may have one in my parts stash which you could have for cost of shipping only.

[bd139]

Ok further debugging has found the unfortunate cause of the problem. I suspected this was the RC network of R7272 and C7273 doing it (open C7273) as the voltage on AUTO RC was wrong (0 instead of 5.2V). While poking around I touched U7375 with my finger and got singed. It's running red hot. The 5V rail is slightly sagging at 4.81 volts and this appears to be the culprit. If I pull it out it and power it up it goes to 5.02 volts. So nearly all the current is going into the trigger IC which is clearly not happy! Have checked the socket for shorts and there are none so I think this is a duff IC.

I will contemplate what to do next over the next few days.

If you can't find one locally I may have one in my parts stash which you could have for cost of shipping only.

Thanks for the offer. I'm contemplating what to do at the moment and will let you know.

The outcome is one of:

1) Go argh and wonder why I bought another 465B

2) Accept your gracious offer

3) Buy all the 465B's that come up on eBay and surround myself with a wall of scopes.

[MED6753]

U7375 is P/N 155-0049-00. Turns out older 465 has U870 which is the same P/N.

I have a scrap 465B and 465 so I'm pretty certain I have one. They are in my storage unit so I'd have to verify.

Let me know.

Edit.....go with choice 3. I did.

[Cubdriver]

Thanks for the offer. I'm contemplating what to do at the moment and will let you know.

The outcome is one of:

1) Go argh and wonder why I bought another 465B

2) Accept your gracious offer

3) Buy all the 465B's that come up on eBay and surround myself with a wall of scopes.

Go with choice three, but don't limit yourself to 465Bs - variety is the spice of life, and there are just so many different types! Duplicate the Freqq's wall-o-counters, but with wigglescopes...

-Pat

[tggzzz]

Thanks for the offer. I'm contemplating what to do at the moment and will let you know.

The outcome is one of:

1) Go argh and wonder why I bought another 465B

2) Accept your gracious offer

3) Buy all the 465B's that come up on eBay and surround myself with a wall of scopes.

Go with choice three, but don't limit yourself to 465Bs - variety is the spice of life, and there are just so many different types! Duplicate the Freqq's wall-o-counters, but with wigglescopes...

-Pat

Quite.

Everybody needs a 485 for its 50ohm input. Helps if the user can do mental arithmetic, rather than relying on cursor readout

[Cerebus]

3) Buy all the 465B's that come up on eBay and surround myself with a wall of scopes.

... wear Kleenex boxes on your feet and start storing all your urine.

[nixiefreqq]

i should not be a model to be emulated.

my sickness should be a cautionary tale.

how did you know about the jars of urine.....did med rat me out?

[Cubdriver]

Quite.

Everybody needs a 485 for its 50ohm input. Helps if the user can do mental arithmetic, rather than relying on cursor readout

Extra points if you snag one with P-11 phosphor.



-Pat

[Cubdriver]

i should not be a model to be emulated.

my sickness should be a cautionary tale.

how did you know about the jars of urine.....did med rat me out?

Jars beat using Depends!! At least you don’t marinate in it.

-Pat

[tggzzz]

Quite.

Everybody needs a 485 for its 50ohm input. Helps if the user can do mental arithmetic, rather than relying on cursor readout

Extra points if you snag one with P-11 phosphor.



-Pat

As far as I am concerned , P11 is the normal phosphor. I had forgotten that a 485 I sold had the uninteresting green phosphor.

Currently got three 485s, one on the bench, one parts mule, and one waiting for me to have a look at it.

Might get another parts mule, if nobody else picks it up in the next couple.of weeks.

[Cubdriver]

Picked that one up a few months ago; haven’t yet gone through it other than to turn it on and confirm it at least partially works, as seen there. Seems that at a minimum the trace mode switches are going to need some cleaning.

-Pat

[tggzzz]

Picked that one up a few months ago; haven’t yet gone through it other than to turn it on and confirm it at least partially works, as seen there. Seems that at a minimum the trace mode switches are going to need some cleaning.

When working they are delightful, and have the main position on my bench.

Replace C911 and a couple of other 15V tants on a 13V rail, before they You Know What. More details at the Other Place; I'm off to bed

[tautech]

Extra points if you snag one with P-11 phosphor.

Speaking of such I have this interesting phosphor chart in my archives.

crt_phosphor_research.zip

[teadmin]

How the fuck do I attach a 200kb pdf ?

Zip it and attach the zip file.

[Cubdriver]

Picked that one up a few months ago; haven’t yet gone through it other than to turn it on and confirm it at least partially works, as seen there. Seems that at a minimum the trace mode switches are going to need some cleaning.

When working they are delightful, and have the main position on my bench.

Replace C911 and a couple of other 15V tants on a 13V rail, before they You Know What. More details at the Other Place; I'm off to bed

Appreciate the tip; will make that a priority when I dig into it. Don't want matches lighting off inside! Just ordered a manual for it from our favorite wallet depletion site.

-Pat