EEVblog #523 - REPAIR: HP 35660A Dynamic Signal Analyser - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: September 20, 2013, 02:22:27 pm
content: 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

author: firewalker
author_rank: Super Contributor
timestamp: September 20, 2013, 02:42:31 pm
content: Maybe you should move the deflection (Yoke) coils back and forth to see if it changes anything.Alexander.

author: firewalker
author_rank: Super Contributor
timestamp: September 20, 2013, 02:47:10 pm
content: What type of signal goes in the monitor? Maybe you could replace it with an LCD.Alexander.

author: obsoletemac
author_rank: Newbie
timestamp: September 20, 2013, 02:51:48 pm
content: 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?//c

author: EEVblog
author_rank: Unknown
timestamp: September 20, 2013, 02:54:44 pm
content: Quote from: firewalker on September 20, 2013, 02:42:31 pmI 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.

author: EEVblog
author_rank: Unknown
timestamp: September 20, 2013, 02:55:42 pm
content: Quote from: obsoletemac on September 20, 2013, 02:51:48 pmI got some pics I'll upload, but didn't take the board out so they aren't that great.

author: AlfBaz
author_rank: Super Contributor
timestamp: September 20, 2013, 03:40:08 pm
content: Quote from: firewalker on September 20, 2013, 02:47:10 pmAccording 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 smallsquarelcd

author: free_electron
author_rank: Super Contributor
timestamp: September 20, 2013, 03:52:00 pm
content: 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 whitetft'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.

author: M0BSW
author_rank: Frequent Contributor
timestamp: September 20, 2013, 04:34:49 pm
content: 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.

author: firehopper
author_rank: Frequent Contributor
timestamp: September 20, 2013, 04:45:06 pm
content: or it was dropped and the mask thats in the tube (if it has one) shifted and that is causing shadows in the corners.

author: jahonen
author_rank: Super Contributor
timestamp: September 20, 2013, 04:50:59 pm
content: Quote from: firehopper on September 20, 2013, 04:45:06 pmThat 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.Regards,Janne

author: Rasz
author_rank: Super Contributor
timestamp: September 20, 2013, 05:26:03 pm
content: 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.

author: kcozens
author_rank: Contributor
timestamp: September 20, 2013, 06:14:58 pm
content: 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.

author: free_electron
author_rank: Super Contributor
timestamp: September 20, 2013, 06:16:58 pm
content: monochrome tube don't have a mask. the yoke is too far back.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: September 20, 2013, 07:31:27 pm
content: 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.

author: Salas
author_rank: Frequent Contributor
timestamp: September 20, 2013, 08:19:16 pm
content: Good find. Maybe make a video showing the 1/f and wide noise signatures of various semis comparing them to claimed spec.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2013, 08:34:06 pm
content: Quote from: free_electron on September 20, 2013, 06:16:58 pmExactly. that is the only explanation for the corners not displaying. Loosen the yoke and push it to the front.

author: free_electron
author_rank: Super Contributor
timestamp: September 20, 2013, 09:08:32 pm
content: Quote from: nitro2k01 on September 20, 2013, 07:31:27 pmcorrect. 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 )

author: N2IXK
author_rank: Frequent Contributor
timestamp: September 20, 2013, 10:45:37 pm
content: 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.

author: EEgalitarian512
author_rank: Contributor
timestamp: September 20, 2013, 11:20:05 pm
content: 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

author: RupertGo
author_rank: Regular Contributor
timestamp: September 21, 2013, 01:33:05 am
content: 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.

author: victor
author_rank: Regular Contributor
timestamp: September 21, 2013, 03:13:13 am
content: 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▲◄ ►▼

author: N2IXK
author_rank: Frequent Contributor
timestamp: September 21, 2013, 03:38:30 am
content: 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/206279Rebuilding 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.

author: jh15
author_rank: Frequent Contributor
timestamp: September 21, 2013, 04:47:29 am
content: 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.Now this old man goes back to his 3d printer and Raspberry PI/Bluetooth projects.

author: Zad
author_rank: Super Contributor
timestamp: September 21, 2013, 05:16:45 am
content: 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.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: September 21, 2013, 09:27:00 am
content: Oh, I forgot to mention this. When you put a metallic screwdriver in the width adjust hole, it disturbed the adjustment, as expected. But I noticed that this made the image more narrow. You could possibly use this to your advantage. First adjust the coil to produce the minimum width, then permanently put some long metallic object in the hole, which will narrow down the image a small bit more. Then fix this object to the case with some semi-permanent method, such as a small dab of hot snot.

author: SeanB
author_rank: Super Contributor
timestamp: September 21, 2013, 09:39:49 am
content: If you want a tube I can post you one, complete in the box with the rest of the monitor. Orange and not green, but it still works well, and you just transplant it complete with the yoke, it will either plug straight in or just match the colours. Might have a few slight screen burns on it but otherwise working. Going to be expensive to airmail, but sea will take about 8 weeks to do it. I had more but had a clean up last month and tossed all the dozen or so CGA monitors that were still around. Still have one EGA one left up on a shelf though

author: G7PSK
author_rank: Super Contributor
timestamp: September 21, 2013, 10:19:28 am
content: I think that to pull the picture back to shape you need a key to rotate each of those magnets in the cage around the CRT.They are there top counter balance the earths and other magnetic fields. I can remember fiddling with them in the past you turn one and the picture distorts one way then you have to turn another to pull that and so on until the picture comes right. A real PTA. That unit had quite a shock to knock the gun connector board off as well as those PM's probably moved the yoke back as well on the other hand it could have been subjected to high levels of vibration over a period of time such as in an aircraft or truck.

author: PChi
author_rank: Frequent Contributor
timestamp: September 21, 2013, 10:22:30 am
content: I always thought that Hewlett Packkard had let the metal work quality slip with the HP35660A. When I picked up the unit to move it my fingers didn't like the sharp corners on the box. I always assumed that it was primarily designed to be rack mounted.I'd say the box is of some use because (if I remember correctly) it goes down to near DC (input can be DC coupled) that a PC sound card wont do. Also the absolute levels are known without requiring a calibration oscillator and procedure.It also has a 16 bit A/D so better dynamic range than an Oscilloscpe and possibly better than actual PC performance.From memory I was under the impression that the noise performance of the input amplifier was nothing special.

author: Ketturi
author_rank: Regular Contributor
timestamp: September 21, 2013, 11:28:16 am
content: Dave you poked CRT with plastic black (ESD one I presume) adjustment tool! Last time I did that I got pretty nasty bite from high voltage discharge.

author: EEVblog
author_rank: Unknown
timestamp: September 21, 2013, 12:07:07 pm
content: Quote from: PChi on September 21, 2013, 10:22:30 amNo, it's not. You aren't going to be measuring leading 1/f noise with it.

author: Salas
author_rank: Frequent Contributor
timestamp: September 21, 2013, 12:44:15 pm
content: Quote from: PChi on September 21, 2013, 10:22:30 amJust looked in it. It is quoted as -130dBV/SQRT(HZ) from 160Hz to 1.28kHz and -140 from 1.28-102.4k.That will translate to a 5k5 Ohm en in the first case. I.e. no better than 9.54 nVrtHz performance in that band.Surely no good to characterize ultra low noise semis with low frequency 1/f corner with this HP DSA model.Still good for checking non ULNA preamps, average NF quoted BJTs and JFETs, Zeners, chip regulators, etc.

author: EEVblog
author_rank: Unknown
timestamp: September 21, 2013, 01:01:41 pm
content: Quote from: Salas on September 21, 2013, 12:44:15 pmYep, not the best, but still good for tons of uses.I was just thinking that it might be possible to upgrade it with modern really schmick opamps. The service manual does not have a BOM, so no idea what opamps are used.I presume it would be mostly driven by the opamps, and the FET input stage is unlikely to dominate.

author: Psi
author_rank: Super Contributor
timestamp: September 21, 2013, 01:01:55 pm
content: Quote from: EEgalitarian512 on September 20, 2013, 11:20:05 pmThat's the best explanation so far.It would provide enough force to move the yoke and knock the board off while leaving the case undamaged.

author: EEVblog
author_rank: Unknown
timestamp: September 21, 2013, 01:10:30 pm
content: BTW, I can confirm it was the yoke moved slightly back on the neck, I wasn't rough enough the first time.Followup video has been uploaded and will be released tomorrow.Image is now just fine.

author: Salas
author_rank: Frequent Contributor
timestamp: September 21, 2013, 01:12:30 pm
content: Quote from: EEVblog on September 21, 2013, 01:01:41 pmThe head amp will dominate the SNR as long as its gain isn't less than 1/3 the total closed loop gain of the input preamp's stages.Surely worth looking at its gain structure in the service manual and decide where the upgrade will likely be most effective.

author: EEVblog
author_rank: Unknown
timestamp: September 21, 2013, 01:23:28 pm
content: Quote from: Salas on September 21, 2013, 01:12:30 pmYeah, need to check. IIRC the FET input stage is just a buffer.

author: Salas
author_rank: Frequent Contributor
timestamp: September 21, 2013, 02:00:45 pm
content: Quote from: EEVblog on September 21, 2013, 01:23:28 pmThey combine a FET source follower with a bipolar input op-amp just for high input impedance then?In that case that op-amp's noise spec will dominate the whole preamp's spec as long as it does a good portion of the total gain.There are enough low noise op-amps these days to choose. The AD797 can hit 1nVrtHz at 100Hz for instance.

author: bktemp
author_rank: Super Contributor
timestamp: September 21, 2013, 02:54:43 pm
content: Quote from: Psi on September 21, 2013, 01:01:55 pmIf the device really got a hard hit, it would be a good idea to check the power supply. Large capacitors and the transformer are heavy parts and can easily be ripped of the board like in this device:Even if it still works, there could be bad solder connections which will lead to arcing and slowly destroy semiconductors. I have seen such failures a few times in TV sets an PC monitors around the heavy flyback transformers where broken solder joints destroyed the horizontal output transistor due to voltage spikes.

author: envisionelec
author_rank: Frequent Contributor
timestamp: September 21, 2013, 04:43:10 pm
content: I maintain that it was a sustained vibration incident rather than a blow to the chassis. The metalwork would be damaged internally which would be evidenced by difficulty of access such as sliding the monitor out or removing the lid.

author: RupertGo
author_rank: Regular Contributor
timestamp: September 21, 2013, 10:56:10 pm
content: Quote from: EEVblog on September 21, 2013, 01:10:30 pmAh, fabulous. One of the occasions it's really good to be proved wrong.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 22, 2013, 01:24:56 am
content: Might it be possible to replace the CRT module with a composite LCD?

author: M0BSW
author_rank: Frequent Contributor
timestamp: September 22, 2013, 07:05:15 am
content: I enjoyed both video's repair and explanation

author: free_electron
author_rank: Super Contributor
timestamp: September 22, 2013, 07:35:40 am
content: I am working on replacing the tube with an lcd.There is a company that offers replacements. The monitor in the analyser (matsushita) was very popular in cnc machines. There is a someone that sells a 400$ lcd monitor that is compatible with this matsushita one.I am trying to get an lcd panel to run.I have a panel from an infiniium scope. This is bstandard tft panel (not with lvds but with normal inputs)Basically the lcd panel has 24 bit for color. A hsync , vsync and a clock.Driving such a panel is easy. Assert both hsync and vsync to set the picel cursor top left. Apply data on the rgb bus and give a clock pulse. When you reach end of the first line you give a hsync to move to the next line. (Hsync without vsync means move to next line. Is both are asserted it means reset to top left)I will wire the rgb data to fixed values and use the msb of r,g and b to select full or half brightness.I think a small cpld could do the work. Hsync and vsync come out of the graphics card of the machine.The itemsity bit and blankin also , so those will drive the rgb.A local clock oscillator in the cpld will provide the pixel clock. I need to set the speed of that oscillator in such a way that it provides avout 720 pulses between hsyncs. ( these screens are mda 720x400 i believe)The panels i have are 800x600 so it should work perfectly.It'll take me some time to build it. I'll post results.

author: EEVblog
author_rank: Unknown
timestamp: September 22, 2013, 07:44:01 am
content: Quote from: Salas on September 21, 2013, 02:00:45 pmYep, looks like it.I need to get back in there and see what parts are used.Would also be awesome if the opamp was socketed, but of course it won't be.

author: Salas
author_rank: Frequent Contributor
timestamp: September 22, 2013, 05:04:41 pm
content: Quote from: EEVblog on September 22, 2013, 07:44:01 amDoes it have the ADC resolution and Y scale options on the screen display to support a possible 100dB+ SNR spec upgrade in the analogue domain?

author: mmagin
author_rank: Frequent Contributor
timestamp: April 04, 2017, 03:31:41 am
content: For my amusement, I recently got one of these for "parts or not working", though it didn't power up nor show a display when I got it. Things that needed repair:Did some CRT rejuvination (alahttp://www.ke5fx.com/crt.html) and turned up/adjusted the CRT's controlsHad vignetting also! Loosened the clamp and slid the yoke forward and tilted it to level, very gently tightened the clampReplaced a front panel BNC that was dented upSince the particular BNC connector is no longer in production, I bought the whole front BNC board on ebay and replaced it. Good thing too, one of the old MOVs was toasty, they mean what they say about floating only +/-4V to groundI think the floppy may still be non-functional, and I haven't had a chance to check any of the calibration aside from running the self-test/self-cal stuff. Too bad the only scan of the service manual out there is incomplete, and too bad I don't have much space for boatanchors :/

author: Pezo
author_rank: Newbie
timestamp: November 04, 2023, 01:54:26 pm
content: Dave,did you by any chance keep a copy of that service manual around that you could upload somewhere? The link doesn't work any more, and I could only find a broken copy of it that is incomplete and seems to have several other manuals mixed in...Thanks, Peter