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Re: yet more 465M musings, and the evil 434
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Miroslav Pokorni
We are all seating here praising Tektronix superior designs and at the same
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time listing lousy design practices. I think where we are going wrong is thinking of old tube scopes, which really were superior designs, and criticizing practices found in post 500 series. At this forum I hear of problems with various portables; at the present I own only 7000 series, so that is only family that I can say something about and that is not flattery, it is downright bad, especially when it comes to using digital components. I have seen things that rawest rookie would not do, like capacitive coupling to a clock of a counter without establishing DC level (found in S52), RC delay to plain TTL input using 680 Ohm resistor (in one of 7B plugs). All these things hobble along, but if IC is replaced with one from a different batch, as you would have in field or at the factory after few weeks, the circuit might not work. Even modules as shipped are operating with digital circuits robbed of its noise margin, not a goal of your designs for production, these are gentlemen amateurs playing at design. Personally, I did not notice 200 V electrolytic in 195 V circuit, but I did not work on power supply, yet. However, I noticed propensity for use of selected components, like selected 2N3904 for LED drivers. All these leaves an impression of design by rookies without adult supervision. Regards Miroslav Pokorni -----Original Message-----
From: walter2@... [mailto:walter2@...] Sent: Friday, August 10, 2001 9:20 AM To: TekScopes@... Subject: [TekScopes] yet more 465M musings, and the evil 434 One small thing to keep in mind, if your only experience with any scope is via the repair center, of COURSE they all seem broken. who sends in good ones to fix? The surplus ones showing up on ebay and elsewhere are all the ones that have been scrubbed for one reason or another, so it can be hard to see the good side of a product if you only ever see busted ones. Meanwhile, the 465M has no fan because for once, the power supply was correctly designed to dissipate the heat outside via the massive rear apron heatsink, what a concept! I hate fans in equipment, they blow dust and dirt everywhere, especially into the HV section, then fail. Tek seemed to have a real problem with heat management in most products, and there are many deflection transistors and Z axis transistors in the 7000 series that run far too hot, making the board eventually intermittent, or failing outright. we usually add some clip on heat sinks, and find life is greatly prolonged. two things always puzzled me about the generally superior Tek designs: if a part could be run to +100C, they did it, and if a supply was +195V, they used a 200VDC rating on the bypass cap. they could have used a bit of input from mil-derating tables, as these issues always came back to bite people over time. the 434: yes, this is an evil piece of hardware. the 1X / 10X panel lights for the vertical knob skirt (even after many mods) remain the worst piece of design in modern history. the scope virtually has to be disassembled to fix these lights, which burn out regularly. in the process, one is forced to notice all the other horrifying assembly problems. it works fine, it just better not ever fail, or all the available manpower in the western world has to be diverted to its repair for an extended period. I have to assume that people who liked Telequipment scopes liked the later Tek-inspred T900 series, not the earlier D series. I think the T900 stuff is great for low end work, and pretty rugged, they made their way into a lot of classrooms. The early Telequipment D series units are just frightening in every way. Still, people like what they are used to, so I suppose somebody must have bought those D-things in the Uk and fallen in love with them. all for now, walter ------------------------ Yahoo! Groups Sponsor To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... Your use of Yahoo! Groups is subject to |
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