replies interleaved:
On 2/12/2022 10:56 AM, Tim K4SHF wrote:
It appears my thread was inappropiately hijacked but I'm still here.
Happens lots.
I slipped the cover off the DM44 yesterday and now the issue has entered muddy waters.
Someone else has been in there with a solder iron so now it may no longer be a natural failure but may have issues induced by someone else. I checked with the guy I got it from, all he had done was some passive probing of voltage levels. I believe he may have gotten it at a hamfest....
Hamfest stuff could be very good, or not.
Is there a table somewhere that indicates what I should see at each testpoint, like voltage/signal/resistance? I've just gotten into the schematics area of the manual I downloaded (the gentleman with the hard copy has not gotten back to me yet).
If you have a reasonably scanned copy, Tektronix generally showed you waveforms and voltage levels within the schematic section.? It could be a separate table of waveforms, or they could be in the schematic itself.? There should also be a note that shows you what the appropriate control settings happen to be and what the input waveform/voltage should be.? While you may or may not get detailed waveforms, the "theory of operation" is always good to read, as is the test verification procedure.? Those should be in the manual. Tektronix either did an operation & service manual or separate ones, depending on the equipment.
All those little blue, chiclet components, are those a film ceramic type? I haven't had a chance to work on anything this new for quite a long time and I have issues identifying components so far.
Hard to say what those are, with just that explanation.
However:
If you can ID them by position, then that allows you to cross reference them to the parts list and schematic.? If you have a copier/printer, a printout of the parts positioning page and the schematic are very useful to have.? These sound like standard components, not surface mount.? Surface mount parts (in later equipment), have tabs for connections.? Those tabs are soldered directly on the board.? Tektronix gradually switched over to the surface mount parts in later equipment.
If the part on the schematic is either indicated as a polarized capacitor (+ marked), or the rating is roughly 1 uf or greater, or if there is a voltage rating on the part, then just by the schematic it's likely to be an electrolytic capacitor.
Tantalum electrolytics, depending on voltage in the circuit and part rating, are at times prone to failure.? Tektronix (per manufacturer's instructions!) used, say, a 16 volt part on a 15 volt line.? Turns out the manufacturer was wrong.? 16 volts is too low, and should have been 25 or 35 volt rating.? These parts can often fail shorted, which either drags down a filtered (small resistor in series that may not survive the exercise) or unfiltered line.? Depending on the supply design, such a direct short can shut down the power supply in the equipment.
Tektronix did have a few "this is what the part looks like" sections as well.
The manuals are generally quite good at helping you out.
Harvey
Comments appreciated!
Tim
