Author Topic: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser  (Read 22060 times)

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Offline EEVblog

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EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« on: September 20, 2013, 02:22:27 pm »
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: http://bit.ly/1aScAWJ

« Last Edit: September 21, 2013, 12:30:21 am by EEVblog »
 

Offline firewalker

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #1 on: September 20, 2013, 02:42:31 pm »
Maybe you should move the deflection (Yoke) coils back and forth to see if it changes anything.

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Offline firewalker

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #2 on: September 20, 2013, 02:47:10 pm »
What type of signal goes in the monitor? Maybe you could replace it with an LCD.

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Offline obsoletemac

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #3 on: September 20, 2013, 02:51:48 pm »
I saw a 68440 (DMA), a 68901 (MFP) and a 68000 (CPU), but I didn't see what the rest of the big chips were. Are there any hi-res photos of the processor board somewhere?

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Offline EEVblog

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #4 on: September 20, 2013, 02:54:44 pm »
Maybe you should move the deflection (Yoke) coils back and forth to see if it changes anything.

I gave it little shove and it seemed snug. But of course it's the only real explanation for the rounded edges, so I need to go back in and get more medieval.
 

Offline EEVblog

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #5 on: September 20, 2013, 02:55:42 pm »
I saw a 68440 (DMA), a 68901 (MFP) and a 68000 (CPU), but I didn't see what the rest of the big chips were. Are there any hi-res photos of the processor board somewhere?

I got some pics I'll upload, but didn't take the board out so they aren't that great.
 

Offline AlfBaz

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #6 on: September 20, 2013, 03:40:08 pm »
What type of signal goes in the monitor? Maybe you could replace it with an LCD.
According to wiki vga was introduced in 87 and the DSA had an 88 copyright so it may well be one of the earlier CGA or EGA types although the 16 way ribbon seems to suggest vga. It shouldn't be to hard to find the horizontal or vertical sync signals if it is. The biggest problem would be finding a small square lcd
 

Offline free_electron

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #7 on: September 20, 2013, 03:52:00 pm »
what a coincidence... That's the one that was on ebay a couple of weeks ago for 100$ ? works but no screen...

i got the 35665 that was on ebay at the same time. same problem. screen. machine works fine. paid 150$ for it.

The screens are MDA compatible. basically 4 wire TTL ( 0 -5 volt )
hsync , vsync and 2 bits. 1 bit tels you black or white. the other bit tells you full intensity or half intensity.

It is the same format as used by the old hercules graphics cards. 9 pin TTL MDA interface.
It should be possible to make a small cpld to create clock signal under control of the hsync and vsync and drive a stupid lcd panel with em. just hardwaire the bits for the lcd so you have two line : black , half white and full white

tft's are progressive scanned left to right top to bottom. so it shoudl be possible to do.

i got the some schematics for these machines as well as the firmware (and the 'keys')

This machine is basically a spectrum analyzer form DC to 150KHz ... but it has large dynamic range.

that filter is actually conductive... reduces emi from the monitor...

the rounded edges are probably because you didn't push the deflection coils all the way forward. the beam can't make the turn to hit the corners because the magnetic field is too much backwards.

when you loosened the screw the yoke probably slid backwards a bit. loosen the clamp and push the yoke all the way to the front of the tube. that should solve it.

as for storing it : get  a wire rack (metro cart) on wheels. they fit perfectly.
« Last Edit: September 20, 2013, 04:23:02 pm by free_electron »
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Offline M0BSW

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #8 on: September 20, 2013, 04:34:49 pm »
I remember years ago when  as a boy I used to help out in a TV repair shop, they used to move the deflection yoke, when they had a bad edge spot on a screen, on rental Tv's. Just remember that high voltage  when your in there, it could have a terminal effect on your health.
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Offline firehopper

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #9 on: September 20, 2013, 04:45:06 pm »
or it was dropped and the mask thats in the tube (if it has one) shifted and that is causing shadows in the corners.
 

Offline jahonen

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #10 on: September 20, 2013, 04:50:59 pm »
or it was dropped and the mask thats in the tube (if it has one) shifted and that is causing shadows in the corners.

That can be often diagnosed by wiggling the tube and listening if there is something loose inside the tube. For color tubes, if the mask is loose, the colors are usually totally screwed permanently. Loose mask could be felt when moving a manual energized degaussing coil near the screen.

Monochrome tubes IIRC don't have mask as such but perhaps there is something else loose inside, some HV electrode or so which now shadows the beam.

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Offline Rasz

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #11 on: September 20, 2013, 05:26:03 pm »
102 kHz? my question is why even bother?

It goes back to using closed source magic black boxes with buttons that do stuff (mostly if you pony up for license) instead of frontend + matlab/octave.
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Offline kcozens

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #12 on: September 20, 2013, 06:14:58 pm »
Mmm... 68000 CPU.  Beauty!  :-+ :-+  How did you manage to acquire this big beast, Dave?

The 68000 CPU and the 68901 DMAC both had a suffix of P10 so a reasonable guess is that the chips are being run at 10MHz. The other big chip seen is the 68440 multifunction peripheral chip. This chip was mentioned in the results of the built-in tests.
 

Offline free_electron

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #13 on: September 20, 2013, 06:16:58 pm »
 monochrome tube don't have a mask. the yoke is too far back.
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Offline nitro2k01

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #14 on: September 20, 2013, 07:31:27 pm »
Even though Dave's instinct turned out to be a winner, I was banging my head to the screen at about 7:05 when he took off the cover plate on the back side. On the bottom PCB there are what for all the world looks like power rail indicators. Waste a few seconds to plug in the damn cord in and see if they all light up! A good first approximation without having to poke those hooks.

I would presume the cover in front of the screen is for ESD discharge. Back in the CRT days, they were a common accessory for office workers sitting in front of the computer all day, to prevent getting you face all red. (Usually attached as a separate panel in front of the screen, with a ground lead going to the back of the computer chassis.) For test equipment like this, I'm assuming the reason is rather to prevent ESD damage or disturbances in the measurement.
« Last Edit: September 20, 2013, 07:34:42 pm by nitro2k01 »
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Offline Salas

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #15 on: September 20, 2013, 08:19:16 pm »
Good find. Maybe make a video showing the 1/f and wide noise signatures of various semis comparing them to claimed spec. 8)
 

Online PA0PBZ

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #16 on: September 20, 2013, 08:34:06 pm »
monochrome tube don't have a mask. the yoke is too far back.

Exactly. that is the only explanation for the corners not displaying. Loosen the yoke and push it to the front.
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Offline free_electron

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #17 on: September 20, 2013, 09:08:32 pm »
or disturbances in the measurement.
correct. that cover will be conductive and grounded throught he frontpanel and chassis.
removes the electric field caused by the scanning of the picture tube. prevents the scanning to show up in the measurement. ( these screens scan around 18Khz i believe. old MDA graphics standard )
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Offline N2IXK

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #18 on: September 20, 2013, 10:45:37 pm »
Great video!  Don't you love scoring a neat and exotic piece of gear cheap because of an easy fix like that? :) More videos like this!

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. Proper 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, shift the yoke, and knock the socket board loose. Glad to see that the tube didn't get necked, 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.
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Offline EEgalitarian512

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #19 on: September 20, 2013, 11:20:05 pm »
It is possible that the unit was mounted in a rack. The rack may have been accidentally dropped on its back during a move by a moving crew. Also, damaged equipment isn't always referred to "Qualified Personnel". The person who looked at it may have played with it a little - and not knowing how to repair it, marked it as "salvage". Just my 2 cents worth. John
 

Offline RupertGo

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #20 on: September 21, 2013, 01:33:05 am »
Great video - love those huge Moto chips and the fields of 74 series logic.

I spent some time in the 80s writing video code for a device that had a very non-standard CRT display (Pandora, a portable Sinclair ZX Spectrum with a flat screen that never saw the light of day.)  Never had the proper screen hardware to work with, so to simulate that, I had a 12" monochrome composite input Zenith monitor, which I bodged by sliding the deflection yoke back from the tube shoulder and fudging the scan waveform geometries through judicious application of various passives to the driver circuitry. A background of TV repair summer jobs as a school kid helped there...

But I never saw the same sort of blank areas as this unit showed. I don't think it's going to be a simple yoke adjustment; I suspect that whatever trauma unseated the tube socket and dislodged the magnets also mucked up the electron gun assembly within the tube. It would be illuminating (ho ho) to arrange to get a full raster on the screen and see what the shape of the shadowed area is. I suspect, though, that to return this thing to full spec would need a new tube, and that it's probably not worth doing unless you can find a replacement for very little money or hassle.

The vintage TV restoration people have good sources of old CRTs, and can sometimes also rebuild damaged tubes... but that's probably not appropriate with this unit unless you want something that's aesthetically perfect for collection appeal.
 

Offline victor

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #21 on: September 21, 2013, 03:13:13 am »

When I saw the board disconnected, the first thing I thought:
Oh no, someone tried to repair it, it didn't work and just put it toghether quickly and put it on eBay (as is).


I really like how straightforward is the front panel, I like the layout, everything symmetrical and aligned.


I hate when the do buttons like up and down sideways or left right vertically like
▲ ▼
or




Is too much to ask for this:
◄ ►


or
   ▲
◄   ►
   ▼
« Last Edit: September 21, 2013, 03:19:51 am by victor »
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Offline N2IXK

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #22 on: September 21, 2013, 03:38:30 am »
Unfortunately, rebuilding CRTs is already pretty much a "lost art". The last US rebuilder (Hawkeye Picture Tube) shut down a couple years ago, and RACS in France is in the final stages of doing so themselves.  Into at least the mid to late 1980s, there was at least one CRT rebuilder in any decent sized metro area, until the advent of the disposable TV sets, making a whole new set cheaper than putting a rebuilt CRT in the old one. the replacement market started to evaporate, then LCDs came along and finished the industry off.

http://www.tvtechnology.com/feature-box/0124/last-lone-wolf-crt-rebuilder-closing/206279

Rebuilding gear from both Hawkeye and RACS has been acquired by the Early Television Foundation, who are hoping to keep a minimum capability alive (at least for collectible TV type CRTs) as long as raw materials are available. As CRT manufacture dwindled, the suppliers of parts like electron guns, cathode coatings, and phosphors went away, as well.

The Chinese (Chunghwa Picture Tubes) may still be producing a handful of types but US manufacturers like Clinton Electronics and Video Display Corp. got out of the business years ago. Philips shuttered their TV and oscilloscope CRT production recently, as well. About the only US manufacturer still operating is Lexel Imaging Systems, who only do boutique types for military avionics, projection displays for flight simulators,  and similar high-$ niche markets.

There is still some old stock of replacement data display tubes available from places like Richardson Electronics, but limited to stock on hand in most cases. If you still use a CRT-based instrument, you may want to buy a spare tube while they are still available. The CRT industry died VERY quickly as LCDs took over. Kind of sad in a way. In 10-15 years you will be hard pressed to find people who have ever worked on CRT displays.

« Last Edit: September 21, 2013, 03:42:30 am by N2IXK »
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Offline jh15

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #23 on: September 21, 2013, 04:47:29 am »
Hey! I'll still be around that long...

Agree about the yoke position, remember to tilt it up with your hand as you push it forward so the funnel of the yoke will defiantly be against the bell of the tube.

     I think that is more likely than a damaged gun assembly, although I've seen stranger things.

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Offline Zad

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Re: EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser
« Reply #24 on: September 21, 2013, 05:16:45 am »
If it isn't the scan coil assembly that has got pushed back, I would check your voltages. Both on the tube base PCB and the scan coils. Low voltages can give some odd symptoms on CRTs. The fact that you had to wind up the brightness is possibly an indication that a voltage is possibly low somewhere.


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