Need Schematic for Tektronix 432 Scope

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EPA III
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Need Schematic for Tektronix 432 Scope

Post by EPA III » Thu Apr 23, 2009 11:07 pm

My Tektronix 432 has gone black. I had a manual, but can not find it. Anyone have or know where I can find a set of schematics and layout drawings for this scope? And, yes I know it is old so please don't make fun of it.
Paul A.

Robert Reed
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Re: Need Schematic for Tektronix 432 Scope

Post by Robert Reed » Fri Apr 24, 2009 7:33 am

Have you tried BAMA (Boat Anchors Manual Assn.) yet? Just google up BAMA on search engine and they list many older quality instrument manuals for free download. Since they have a pretty impressive list there is a good chance you will find it. These are complete service manuals and some are upwards of 300 pages.

Dean Huster
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Re: Need Schematic for Tektronix 432 Scope

Post by Dean Huster » Fri Apr 24, 2009 2:03 pm

If you're having trouble finding a manual for the 432, try hunting for one for the 434. Infinitely more 434s were made than 432s. The main difference is in the 434's split-screen, bi-stable storage circuitry. The vertical amps and timebase are virtually the same. I'm sorry you have to work with the 432 as it was quite the boner in the Tektronix stable. A few years ago, I wrote up the following article on the 434/432 which might be of interest. Heed that part about the back casting screws!

Dean


Article:


Hints and Kinks for the 434

The 434 (and the non-storage 432) has to be one of the worst mechanical designs to ever come out of the hallowed halls of Beaverton. It is this model that made me form the opinion that all Tek mechanical engineer "interns" should spend two years in the field to see what works and what doesn't work. They only look at what's cute or what works on the assembly line. They don't see what happens a year or two later when a scope needs repair. They need to see that. Here are the problems to look out for.

With the exception of units that I've had in for service before, I have yet to get a 434 into the Service Center that did not have some of the screws that hold the rear casting in place either be loose or out of their holes altogether. And the screw that is the worst for this hides under the little cover that's over the fuse holder. If this screw comes loose (and I have had several instruments that have had this happen), it can play merry hell with the line voltage inside that little enclosed box. Whenever you work on a 434, ALWAYS WITHOUT FAIL use a good, solid #2 Posidriv screwdriver to tighten the rear casting screws, especially the one that hides inside the fuse compartment. Don't be afraid of stripping these screws out or breaking them off – they have a 10-32 thread and are quite robust. Crank those puppies down with everything you have. I doubt that even Arnold "I'll be bok" Schwarzenegger could damage these screw interfaces. A smart person might even remove each screw and add some Loctite or epoxy to keep them in place. Of course, the epoxy will make removal of that rear casting impossible, but .....

What is the most common failure in a 434? It's the knob skirt lamps. What are some of the hardest components to replace in a 434? The knob skirt lamps, of course. To replace these little puppies, you have to remove the vertical amplifier board which means unsoldering a bunch of wires, disconnecting some connectors, removing a third of the front panel knobs and pushbuttons, removing extension shafts, etc. and then remove a bunch of little 3-48 brass screws that hold the vertical amplifier board to the chassis. Then you have to unsolder the lamps which risks melting down the lamp housings. I recommend that if you have to replace these lamps, replace them with high-brightness LEDs, either yellow or white. On the main circuit boards, there are series resistors that limit lamp current that you can replace to get the right value for the LED current limiting you need. You can use even higher values for these resistors if your high-brightness LEDs are too blinding.

Next most common failure? Intermittent attenuator and vertical amplifier gain switches. Pull the vertical board (see above), clean the switches.

Unlike most Tek scopes that switch vertical sensitivity by switching four attenuators in and out of a 5mv/div front end, the 432/434 only uses two X10 attenuators and does gain switching for the 1-2-5 sequencing. This causes the trace thickness to vary in a 1-2-5-10-20-50 sequence and the trace position (balance) to shift also in a 1-2-5-10-20-50 sequence. And because of this method of switching the vertical gain, you'll find that gains may eventually be off. You have to replace some low-value (below 10 ohm or even below 1 ohm) 5% tolerance resistors. Getting to these resistors on that vertical board is difficult. Measuring their actual values to see if they've shifted is also difficult without using a Kelvin resistance measuring setup.

If you have to pull the vertical board (or the horizontal board), here's a hint. Don't remove the little red "VAR" knobs. Instead, loosen the setscrew at the coupler- or pot-end of the shaft and pull the knob and shaft out as one unit. Much easier and one-less small, loose part to deal with. And you'll have to pull the metal or fiberglass extension shaft anyway. Might as well leave the knob in place since it makes it easier to reinstall with the knob in the correct position.

The power supplies in serial numbers below B500000 are high-efficiency, but use discrete components rather than Tek's infamous single IC controller. They're bears to troubleshoot. Absolute bears. So if you insist on buying a used 434, consider rejecting one below that serial number unless it's a steal.

Tek made a big mistake when they designed the 434 when they decided to use the PCB mounting screws they did. Every other Tek portable uses steel 4-40 screws with captive washers to hold PCBs in place. Not in the 434. It uses brass 3-48 screws. They have captive washers, but they don't stick to a magnetic screwdriver and they have to go into some out-of-the-way places. So, of course, they fall off the driver or out of your fingers and get lodged in some pretty nasty places in the instrument. It might be an excellent excuse to drill out the board holes (#32 drill bit) and retap the chassis for 4-40 screws (#43 tap drill bit). Of course, you have to check to make sure than any plated-through holes are not critical for grounding – I've not checked for that little wrinkle myself, so be careful there.
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

Robert Reed
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Re: Need Schematic for Tektronix 432 Scope

Post by Robert Reed » Sun Apr 26, 2009 3:40 pm

Dean
A little off topic, but not off subject - After reading that excellent reply above, I was pondering another Tek problem (or at least so I have heard). A couple of years ago I purchased a Tek 2465 300 Mhz scope and thus far am tickled pink with it as it seems to represent the best of both the digital and analog worlds. Before I purchased this scope I did a liittle internet detective work on it and it seems the horizontal ( X-axis) output chip going defective was a common problem with this series. The chip name escapes me at the moment, but was of small scale integration consisting of the amplifier and four interface circuits built into it for various source inputs. The scary thing is that these chips are unobtainable now. First Manu sold company to another fab house. The new fab house discontinued production on these after a year or so due the the limited market for that chip.
This impressed me so much that I almost didn't buy the scope. Do you have any experience or thoughts on tis tentative problem?
PS - My scope still works fine, but I still have nightmares :shock:

Dean Huster
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Re: Need Schematic for Tektronix 432 Scope

Post by Dean Huster » Sun Apr 26, 2009 7:40 pm

Robert, if the Tek P/N on the chip is 156-xxxx-xx, it's from an outside source; if 155-xxxx-xx, it's a Tek-made chip, not uncommon with vertical output amplifiers and other specialty circuitry such as switching supplies, preamps, vertical switching, trigger control, etc. The 2465 came out about the same time I left Tek for teaching, so I have absolutely no experience with the model. Tek used to support its products for something like 12 years after last appearing in the catalog (they extended that support for the 453 and 454), but over the past 20 years, have been making long warranties (3 years vs. only 1) and limiting post-production support. I think that's because technology turns over so quickly these days and they have to keep up and even more so the fact that Tek's most-feared competitor is Tek -- their older equipment that keeps going like the Energizer bunny. They had a devil of a time selling the new stuff of the 1990s when the "new" 400-series portables and the 7000-series lab scopes were hitting the surplus market for pennies on the dollar back when N&V was primarily a classified ad tabloid and had lots of wonderful deals. Who wanted to buy a new $20,000 scope when you could have a fantastic 500 MHz 7904 completely loaded with plug-ins for $500 and lots of fantastic specialty plug-ins like logic analyzers and spectrum analyzers available at similar prices? Anyway, you'll probably have to rely upon a "hangar queen" for replacement parts like that horizontal output amp.

Ah, well. Back to our original topic, the 432. And by the way, other than the maintenance problems, I really liked the 434. Such a light-weight (in pounds) scope, 25 MHz, split screen storage, really fine feel and simple controls. Although it didn't have delayed sweep, it was a nice little blue box.

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

EPA III
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Joined: Tue Aug 17, 2004 1:01 am
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Re: Need Schematic for Tektronix 432 Scope

Post by EPA III » Thu Apr 30, 2009 11:48 pm

Robert,

Much thanks for the web site. Great resource. I am having a bit of trouble downloading the manual, but at least they do have it. Thanks again,

Robert Reed wrote:Have you tried BAMA (Boat Anchors Manual Assn.) yet? Just google up BAMA on search engine and they list many older quality instrument manuals for free download. Since they have a pretty impressive list there is a good chance you will find it. These are complete service manuals and some are upwards of 300 pages.

And, thank you Dean for the excellent information. I could not agree with you more about electronic design engineers needing more training (whip and chair) in mechanical design.
Paul A.

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