EEVblog #523 – REPAIR: HP 35660A Dynamic Signal AnalyserPosted on September 21st, 2013 16 comments
Dave repairs a classic HP 35660A Dynamic Signal Analyser (DSA), and does a bit of a teardown with random commentary in the process.
Service Manual HERE
Oh Dave these are my favourite videos, love the trouble shooting and repairs, glad you kept well away from the bit that bites.
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Dave make shure that the coil assembly is pushed all the way to the back of the tube as this will limit the scanning area of the electron beam.
Good Stuff as always Hooch.
The magnets are for improving linearity at the corners.
To fix the “missing” display corners move the yoke to the front of the tube.
To remove the death spots You have to check if the coils are on right position. I think, due to serious hit, the coils were slided down too far on the neck and the neck board was pushed out. This also explain the fracture the holder of magnets, when they hit the metal shield around the coils.
If you want to know, these four magnets are used for geometry correction on the corners of the screen. When the grid looks non straight on particular corner You can use right magnet to adjust it just by turning it a bit.
Just after the retaining clamp there are two black rings. These magnet rings are used for center the picture on screen. But I think that You will not need to use them in further regulation.
Great video! Dont you love scoring a neat piece of gear cheap because of an easy fix like that?
I would suggest removing everything from the CRT neck (socket, deflection yoke, and edge/corner correction magnet assy), and reinstalling them after checking for mechanical damage.
The yoke generally gets installed tight up against the flared part of the CRT envelope, as far forward as it will slide. being a centimeter or so to far back will definitely cause “neck shadows” in the corner of the screen., where the electron beam hits the glass neck at the extreme edges of the raster.
The 4 magnets correct screen geometry (linearity and/or focus in the corners. The individual magnets are sealed in place with paint, so if you get the whole assembly seated back where it was (attached to the yoke, the mu-metal shield, or the CRT itself?) you should be pretty close for adjustment. Poprer adjustment will need a crosshatch test pattern, which the generator self test may be able to provide.
You can (carefully) set the yoke rotation with the unit powered, as long as you grap the insulated parts of the yoke, and watch your fingers.
Definitely looks like the unit took a hard shock front to back. Enough to bust the magnets loose, and knock the socket board loose. Glad to see that the tube didn’t get cracked, and looks good as far as brightness and phosphor burn.
Would be curious as to what the interface is between the display and the main bioard. TTL or analog video? Or some proprietary interconnect? Might be a candidate for an LCD conversion if the CRT goes out.
I’v repaired hundreds of these CRT-Units, almost driven by Motorolas famous CRT controller 6845.
This unit defenitely was dropped from high hight. Normally, the tube backplane sits very tightly and the deflection yokes are firmly fixed.
Did you find any scratches or deformations on the instruments housing?
I work in an research lab that studies hearing. We run on this thing.
I have one question. How the heck do you read the floppy disks on any modern computer. We have the same model you do and there is some code from HP to read the disks back but it does not seem to actually work.
Currently we use the GPIB interface which connects to a program we wrote on a PC.
Or even better is to replace the floppy drive with an floppy to usb emulator. Just google around and you will find it.
Dave, the reason I can’t use a USB floppy drive is that the formatting of the disks is fundamentally different from what a modern computer uses.
Reminds me of my time at Uni – we had a spectrum analyzer donated by someone in a research lab nearby because it didn’t work (they wanted a new one). So our tech’s opened it up and swiftly ‘fixted’ the problem and we all came out ahead.
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