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Thanks, I did have that in mind. I don't think I have anything to worry about with my 555. It came from an estate sale and stunk so bad I had to keep it outside for a month. No question as to why the previous owner was SK! When I give it a bath, the rinse water will look like coffee. It does work to some degree, if it can stand that collection of toxins I doubt anything I might use on the cover is likely to be a problem. Combusted nicotine is horrible enough for equipment, I wonder what effects clouds of vape exhaust will have? It usually contains polyethylene glycol, which condenses on things and is hygroscopic. High voltage flashovers, anyone?

??? Bruce Gentry, KA2IVY

My DSA602A shut off by itself and clicks with power light flashes / will not start. If I disconnect A24 from power the DSA shows signs of life and appears to boot normally.

Before I go doing component level repair of A24. Does someone have a parts unit for sale or an A24 board they want to sell? I'm located in Michigan and someone local would be great but beggars can't be choosers.

Besides being a huge power hungry boat anchor, I love my DSA602A. It has been a fixture in my lab for years and a reliable final answer to many questions when troubleshooting.

With the standard 7603 type vented plastic cover over the heat sink, I estimate the case of the hottest TO-3 transistor (center top) reaches about 75 deg C rise over ambient, or about 115 C with 40 C maximum ambient. This appears to be the pass Q for the -15V supply. Assuming none of the six transistors dissipate more than 30W, this indicates maximum junction temp about 160 C, for high ambient normal operation with some nominal load - in this case a 7A18, 7A26, and 7B53A installed. At reasonable lab temp it should be around 125 C.

I picked the common 2N3055 as a representative example, with Max Tj 200 C and Rth J-C of 1.52 C/W, and it looks like there's a decent margin for normal conditions. Without some additional cooling, it will be toasty, but not too bad. Under fault conditions, a lot can change, but assuming the supplies use some degree of foldback current limiting, and the raw supplies collapse somewhat more with excessive loading, the dissipation in the Qs may be not too bad either. I'll be studying it and measuring a few things to see how it looks.

Ed

On Sun, Dec 15, 2024 at 06:30 PM, Gianni Becattini wrote:

in the 11403, I could not make it run, because I could not enable the trace

Touch Def Wfm in the top right corner of the display and select compartment (L, C or R).

/H?kan

The springs/washers don't press against the front panel but against the front the frame. The springs resemble the type where a plugin's board connects to other boards via pins/sockets and the spring goes between the two boards on the threaded mounting post. I suspect that's where they came from.

Thanks,
Barry - N4BUQ

Be careful with what ever you use as it will transfer to or interact with the instrument (e.g. paint, trim bits, knobs, etc.) that you are covering.

Reminds me of my A?C cover. I always heat it up in the direct sun before trying to put it on or fold it up. Helps some.

I would guess that someone added the springs to secure the front panel. I think that option 6 does not have any nuts to hold the panel firmly.

With all of the knobs removed, does the front panel rattle?

Clark

Hi,
I tried to use a 7000 vertical amp (a 7A19). In the 11302 it works perfectly, in the 11403, I could not make it run, because I could not enable the trace, not having the plug-in button. Today I should receive a DSA 602A, I will try also with it.

@be_moulton: in a book I am preparing, I am going to write a chapter about the DSA 602A, may I report your experience? I found it very interesting and it arrived exactly at the right moment...

Renaud,

The 50V supply should be within ,25V, 49,75 to 50,25V. The 475A schematic has more voltages listed at points in the power supply. Pins 2 and 3 of the IC should be 9V. Pin 1 should be 10,4V. Pin 8 should be 23V. Check the voltage across VR4122 to be 43V. The B of Q1424 and C of Q1432 should be 52V. The B of Q1426 should be 51,5V. See if there is a 20V drop across VR1423. Check (TP)105/160V to see what voltage it is. Check TP 50V unreg. If that and the 50V out are the same, CR1426 is suspect of being shorted. Cr1424 and CR1432 could be bad. I do not know if you tested the transistors in the 50V supply out of circuit or not. The series pass can be left in with Q1424 being removed to test the series pass. If C-E is shorted, the diode mentioned above is suspect. Get the 50V working first then see about the high voltage section.

David and Zen are correct. Normally a crackle sound is heard when the high voltage comes up at turn-on.

Mark

Definitely fascinating, Ed!
It would be great to see some picture of the process, should you have some; or, at least, the final product. If not, most of us would have to use our own imagination, which would make it even more fascinating...
Titi

A quick go - NO go testing of the high voltage sections would be to run the back of your hand near front of the tube. Of the hairs on the back of your hand stand up due to the static then you can assume HV is present. No static on the front of the CRT it can be assumed that the HV is missing.

Power needs to be on of course but the case covers can be in pace for this test. To increase the sensitivity of the test the implosion shield can be temporarily removed to expose the front glass.

Zen

I recently purchased a 7A18 with Option 6. For cleaning purposes, I removed the knobs and faceplate. When I removed the VOLTS/DIV knobs, each had a washer against the frame with a spring which pushes against the back side of the knob. I've never seen this arrangement and the manual doesn't show those parts. Was this ever included from the factory? I doubt it and figure that someone decided to add those but I'm not sure so thought I'd ask the group.

BTW, both VOLTS/DIV knobs and the small trigger selection knob are pretty badly broken. If anyone has some for sale, I'd be interested.

Thanks,
Barry - N4BUQ

Having spent some time trying to fix a 2756P analyzer, I can contribute
to the group some of my findings.

The analyzer had so many problems that I was close to giving up.
In many cases, troubleshooting had to be based on replacing suspicous
components that behaved strange as well as replacing most supply
bypass capacitors I could find without actually testing them
for value or ESR. It was a matter of saving time and working my way
board by board. After all, this analyzer is almost 35 years old
so I guess it could have passed its "best before" date long ago.

There were several Allen Bradley carbon resistors that had drifted
far beyond their designated resistance value. Both low ohmic resistors
used for supply bypass as well as high resistance types found
elsewhere.

A 4.7 MOhm was found to be 7M. A 10 MOhm was found to
be 14M. These resistors are found on the YIG/PLL boards.

Also the resistor locations given by John Miles, KE5FX was bad but
in my case I replaced them with 1% metal film types.

Note that there is one A-B resistor hidden underneath the large
R1040 (25 Ohm) on the 1st LO driver board.

C2072 (10nF) was replaced with 0.1uF.

In general: All ceramic thru-hole capacitors Y5V was
replaced with modern X7R or NP0 types (where applicable)

Some tantalum axial capacitors was found to be a bit leaky
and was replaced with aluminium types.

I did replace some OPAmps in the YIG/PLL circuitry,
replacing them with OP07 (and removing the 100pF frequency
compensation capacitors) but used sockets after unsoldering
and saving the removed OPAmps. If this contributed to the
analyzer performance I do not know but it drifted out of lock
before and together with the rest of the components that
was replaced stayed stable afterwards.

PSU was completely recapped but I remember a hint by a friend:
Replacing suspicous older electrolythic capacitors in power
supplys can result in shut-downs due to detected over current
transients caused by the modern types lower ESR. In the case
of the 2756, no such shut-down occurred however.

The temperature of the air from the rear vents was +65 celsius
or higher and the surface was getting hot to the touch.
I had previously drilled extra holes in the large case close
to and under the front panel. This time, I increased the
number of holes considerably and the air temperature went down
as well as the fan started running at a slower pace. I do not know if
Tektronix designed the instrument and its case to run that hot
as the original air vent intake area was even smaller but it seems strange
to me if that was the intent.

Ulf
SM6GXV

Hello David, thank you for your response. I did all the tests that Mark advised me below but without success. I think that the problem is with the HV module. Unfortunately, I do not have the equipment to measure voltages above 1000 v. Is there another way to check the HV module and the tube ? Thanks in advance for your reponse, PS

Hello Marc, Thank you very much for your response. I tested all the Zener diodes and transistors following the schematic but so far I have not found any faults. What is the max/min voltage accepted on the 50 v unreg? Thanks a lot, Renaud

Fascinating story Ed. It sounds like your hard work paid off. I did this kind of swap once with a 502, but it was very simple compared to yours. I basically just removed the front panel, turned the scope on its side, and bolted it back together with the RM502 panel in place.

Martin thank you. You reminded me of modifying 7000 series plugins to use in the 602. All that was required was to grind off the lug on the connector that positioned them in a 7000 series scope. Ver simple and the plugins were a lot cheaper. Some of the auto functions wouldn’t work with the 602 but didn’t present much of a problem, as I recall.

Totally agree. I have two DSA602s, unfortunately not the "A" version with the floppy, but thanks to digital photography thats not as bad.

Memory depth could be better, but the windowing capabilites are excellent when hunting events.

It seems that 7000-modules can be used as well. I never dared to try it.

Have repaired the memory bug on mines, since then very reliable. Excepte for some rare power failures where the scope suddenly switches off itself. Have seen that on another 602, too. Happens once or twice in a year, so no big deal until now, but I fear degrading capacitors somewhere buried deep inside.

Perfect tool in winter times, especially!

cheers
Martin

Thank you for your comments. The 502 Frankenscope. Is a hybrid. It was made from a 502. The three plugins are from a 561A. The connect directly to the two beams of the 502. Unfortunately it was never made operational. The chassis has no room for the power supplies necessary for operation. I am still working on that one! But it is a fun project anyway.