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On Sat, Aug 10, 2019 at 09:19 AM, Gary Robert Bosworth wrote:

Please explain the solution. How does a fan interfere with the switching
power supply?
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On Fri, Aug 9, 2019 at 9:49 PM <[email protected]> wrote:

Happy ending: the problem was the fan wiring all along. I rearranged it
before I inserted the SMPS for the last time, and we have life.

The best way to explain it is probably a picture: /

Note that little tab? It was intermittently touching the chassis. This morning I made a neat sandwich of electrical tape to put underneath it and now the problem is solved.

Sean

Please explain the solution. How does a fan interfere with the switching
power supply?

--
Gary Robert Bosworth
grbosworth@...
Tel: 310-317-2247

On Fri, Aug 9, 2019 at 09:25 AM, Paul Amaranth wrote:

I haven't opened up a 577, but those are likely the typical Sprague capacitors
used by Tektronix in that era. They may still be good; I'd check them with a
good capacitor and esr meter before removing them.

If you need to replace them, the neatest repair is one I use in 4xx and 7K
scopes - use
a small carrier board to mate the footprint to a commonly available snapcap.
This
provides the jumpers that Tek used and the footprint for the new cap. Use
105C caps as replacements. You can find these on ebay and there are gerbers
floating
around if you want to send them to a board house yourself. You can also etch
them
yourself of course.

Some purists might restuff the cans with a new snapcap.

Paul

Paul,

I have become quite adept at re-stuffing cans with modern capacitors. I "restuffed" all the filter caps in my TYPE 576 power supply with modern caps. Having previously just replaced these large cans with modern caps, there is something about the "look" of those large cans that is satisfying, in a way that small and modern caps just cannot replicate. With me, it is not so much being a purist, just about scale, symmetry and general appearance that drives me to do this. I appreciate your insight and advice regarding this problem.


--
Michael Lynch
Dardanelle, AR

Cangratulations!? I like when stuff is easy.
Bob

Hi :

I have a 485 working after repair , but there are missing parts of fuse-holder p/n :352-0326-00, plastic.

Anyone can help ? I am locate in Hong Kong.

Regard
Tony Cheung
Aug 10 2019

Happy ending: the problem was the fan wiring all along. I rearranged it before I inserted the SMPS for the last time, and we have life.

This might work

I use to have half a dozen working tdr plugins with mix of pulse gens & samplers in imperial and metric.
Long gone on eBay, but do they count??
Kevin, KO3Y

Sent from kjo iPhone

It's the fan. If I pull on the power leads that go to the fa, the SMPS will start. Maybe something's rubbed up in there. Have to take a look.

So I had a considerable breakthrough. While I still don't know WHAT is shorting out, I have determined that there is no electrical problem as far as I can tell. It's mechanical. I "fixed" it with my tinkering...then it started clicking again when the SMPS module was reinstalled in the mainframe. Thinking something is pushing on something in there when the module is installed.

Yes, I have 7S11 and 7S12 plug-ins and two S-4 sampling heads, S-51 trigger countdown head, S-52 pulse generator head, and two S-53 trigger recognizer heads.? I'm sure others in the group have more extensive collections.Nice score with the S-42.? Several decades ago I had a CSA803 scope at work with at least one SD-24 sampling/TDR head.? I can't remember what we used for OE conversion, maybe just the fiber optic receivers themselves.? Kind of lost interest in F/O though.I find the 7S12 + 7S11 + S-4 combo very cumbersome to get to work properly.? Hard to even get a stable trace on the screen.? Maybe I'm doing something wrong?JimSent from my Verizon, Samsung Galaxy smartphone

It's a sampling head, not really a plugin, but plugs into a plugin, I guess. I was in such a rush to gloat I used the wrong terminology. I am being punished, the thing is shipping Fedex, I didn't even check that. I will be destroyed by the customs charges.
An expensive trinket to be sure. I have no fiber optics to plug into it.

Well, if that's your only plug-in, no.I do have the S-42 on my wish list, though.Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone

Most, if not all, of the boards have "harmonica connectors" for the supply input. When I am faced with this, I connect the ohmmeter at the PSU perhaps, and, noting the resistance, remove the connectors one-by-one, checking to see if the resistance reading jumps up a bit. If it does, you have likely found the board with the shorted cap. From there it is usually a simple matter to check the resistance across the caps on the board.
It usually is about this simple, especially on the 7000 series. It is also possible that the short is in the PSU proper, again, disconnecting it from the main scope should reveal the location.

oh yeah.



I am the king of rare and obscure plugins.

Prove me wrong! :)

On 8/9/19 5:47 PM, [email protected] wrote:

On Fri, Aug 9, 2019 at 03:39 PM, John Griessen wrote:

Can you rig a little current to flow through a resistance to be

mild like
20 milliamps total, then do you have a 6 or 7 digit voltmeter? Probing will
show dropping volts along power
rails until you get next to the offending tantalum cap, then not change much
if probing farther along than that...

Input it where?

Right where the 5V is made, at its SMPS source. or rectifier and caps, (I have not looked at a 7104 schematic today), and relative to a ground point that is the 5V return.

So, that way, as you probe along in the 5V loads, and/or hold up caps, one will be more of a short than the whole
and you will notice that lowness.

If you no longer suspect the 5V and switch, *DO* switch the return GND point also to be related to the new suspect.

On Fri, Aug 9, 2019 at 03:39 PM, John Griessen wrote:

On 8/9/19 4:42 PM, [email protected] wrote:

I believe the issue lies in either the +5V rail

Seems likely. Can you rig a little current to flow through a resistance to be
mild like
20 milliamps total, then do you have a 6 or 7 digit voltmeter? Probing will
show dropping volts along power
rails until you get next to the offending tantalum cap, then not change much
if probing farther along than that...

Input it where?

I've been poring over the schematics trying to map out in my head where everything is.

On 8/9/19 4:42 PM, [email protected] wrote:

I believe the issue lies in either the +5V rail

Seems likely. Can you rig a little current to flow through a resistance to be mild like
20 milliamps total, then do you have a 6 or 7 digit voltmeter? Probing will show dropping volts along power
rails until you get next to the offending tantalum cap, then not change much if probing farther along than that...

Hi all,

Scored a very nice condition 7104 and plugins at auction for a great price. Long story short it was working during the item viewing hours the day before the auction. Got it home this morning and it's clicking...anyway...

I believe the issue lies in either the +5V rail or the +/-15 V rails. However, specifically, the manual says the typical resistance for the +5V rail when everything is connected up is 0.005 Kohm. I'm measuring 3 ohms. Is there any chance that is a typo and it should be 0.050 Kohm and not 0.005 Kohm? It's the former for 7904 mainframes.

Here's my readings:

With the mainframe circuits connected:

+50 is at 1.82 kohm
+15 is at 73 ohm
+5 is at 3 ohm
-15 is at 84 ohm
-50 is at 4.494 kohm

With the mainframe circuits disconnected:

+50 is 9.28 kohm
+15 is 154 ohm
+5 is 7.53 kohm
-15 is 8.55 kohm
-50 is 30.2 kohm

Thanks,

Sean

Sadly, I don’t have anything to use as a pattern. The entire plastic part of the knob is gone. One of these days I will try that casting material, it sounds like it would do the trick if you had a pattern.

--
Michael Lynch
Dardanelle, AR