Tektronix 468

[synx508]

This Tektronix 468 with both service manual volumes and the operator's manual was unavoidable, at the rally. I was told that it had a bad timebase but what I wasn't told was that the person who reassembled it after deciding they couldn't fix the timebase had mangled one of the internal coaxial connectors rendering the horizontal output inoperative.
Once I'd bashed the connector back into shape the deflection was restored and on to the next problem, there was no triggering and no timebase activity at all. X-Y mode worked, so all was not lost. Power supply voltages seemed almost perfect.
I swapped the Tek ICs between the A and B timebases and this restored the A timebase and triggering, as expected the B timebase is inoperative.
The digital storage feature seems to work but there's a problem with the cursor knob, turning either way decreases the value, so the cursors roll off the bottom (V) or left (t) of the screen. Not very convenient. I'll stare at the schematic tomorrow to see if there could be an electronic reason for this but perhaps the switch is broken in some very strange way.
There are a few other problems, attenuators on channel 1 (again!), width of the trace seems inadequate and in non-storage mode at lower sweep rates the blanking is completely messed up, blanking beginning about a third of the way across the screen - again, not terribly convenient.
It looks stunning though, if you twist your head around a bit…

[tggzzz]

Overall I quite liked my 468, but not enough to prevent me flogging it.

The analogue part is a 465B, which is a good start.

The digitising part is slow but not based on a CCD sampler, thus avoiding slow sweep speed aliasing problems. Indeed, it even has an "envelope detect" mode that wouldn't reappear for several decades.

[Zenith]

On balance I'm glad I didn't spot that one. I did come away with a Tek 465 which is still in the car. I've been investigating a Wavetek function generator which came from there.

I always feel a sense of relief when those Peltola connectors fit back successfully. They look very easy to damage. I haven't wrecked one yet.

[tggzzz]

On balance I'm glad I didn't spot that one. I did come away with a Tek 465 which is still in the car. I've been investigating a Wavetek function generator which came from there.

I always feel a sense of relief when those Peltola connectors fit back successfully. They look very easy to damage. I haven't wrecked one yet.

I haven't had a problem with the Petolta connectors, mainly because they are open frame so you can see whether the solid core is entering the inner socket correctly. If that wasn't the case then it would be easy to push a bit too hard and terminally (ho ho) bend the solid core.

[Zenith]

I haven't had a problem with the Petolta connectors, mainly because they are open frame so you can see whether the solid core is entering the inner socket correctly. If that wasn't the case then it would be easy to push a bit too hard and terminally (ho ho) bend the solid core.

Peltola, definitely Peltola.

https://w140.com/tekwiki/wiki/Peltola_connector

I have peculiar difficulty remembering the name and have to look it up. I always want to call them Pelota connectors.

[tggzzz]

I haven't had a problem with the Petolta connectors, mainly because they are open frame so you can see whether the solid core is entering the inner socket correctly. If that wasn't the case then it would be easy to push a bit too hard and terminally (ho ho) bend the solid core.

Peltola, definitely Peltola.

https://w140.com/tekwiki/wiki/Peltola_connector

I have peculiar difficulty remembering the name and have to look it up. I always want to call them Pelota connectors.

I always call them Petolta; people seem to understand me

[synx508]

My plan to work on the HP 8405A changed and I had a closer look at the Tek 468's cursor control today.
I've identified the fault as the RC4151 V-F converter that turns the resistance change in the 10kΩ potentiometer into fine cursor movement. It's a form of A/D converter. I have found two sources of this part so should be able to repair it, meanwhile I spent money with the very well known overpriced ebay destroyer of test equipment for his collection of possibly broken 468 ICs, which sadly doesn't include the RC4151, but may get the B timebase working.
I wouldn't normally buy parts for this old junk but thorough searching of my box of dodgy old ICs (label on the box "SEMI CHAOS") turned up nothing. I clearly need to buy more busted up old test equipment without accidentally fully repairing it.

[Zenith]

I feel your pain. That 465 I bought for a tenner appears to work. It was only a lazy attempt to put it through its paces, but a proper probe on the calibrator produces a passable square wave in both channels. I haven't checked the delay sweep. It seems a shame to use it as a parts mule.

The Wavetek function generator works apart from the LCD display. It's a special COG display a bit like the displays on multimeters. It's had a ding which has wrecked part of it. I think the original is unobtainable and so now I'm trolling through my collection of displays, contemplating whether something can be pressed into service using a µcontroller. The ideal solution would be to find another Wavetek Model 21 for not much, obviously shot but with a good display, or trawl through a box of junk and find a couple of Wavetek spare displays for a quid each. Stranger things have happened. This is is the only Wavetek model 21 I can recall seeing at a rally.

I've identified the fault as the RC4151 V-F converter that turns the resistance change in the 10kΩ potentiometer into fine cursor movement. It's a form of A/D converter. I have found two sources of this part so should be able to repair it, meanwhile I spent money with the very well known overpriced ebay destroyer of test equipment for his collection of possibly broken 468 ICs, which sadly doesn't include the RC4151, but may get the B timebase working.

It is possible to use modern parts to replace things like that. It may not be a trip you want to take. I've never been drawn to 468s and a number of other Tek scopes, and for some reason HP scopes leave me cold.