HP 140T calibration - Page 1
Forum section: electronics / testgear

author: Floopy
author_rank: Regular Contributor
timestamp: June 18, 2018, 01:09:03 am
content: Hello,Don't know if this is considered "repair".I acquired an HP 140T. I ordered the plugins and they should arrive soon. In the meantime, I thought that I would make sure that the voltage rails are outputting what they should be doing.Here are the following voltages:-12.6V, 250V, -100V, 100V, and 2350VThe last one being on a separate board labeled High Voltage for obvious reasons. I tuned the -12.6V from 11.6V to -12.601V, the 100V from 95V to 100.07V, but for some reason the 250V would only go up to 248.77V and the -100V only to -93.7V. Same for the 2350V line would only go up to 2000V. That's how far the potentiometers would go.Is this normal? maybe it's because I don't have the plugins installed? Do I need to fix something?I took a picture of the low voltage board. Thankfully I had a high voltage probe on hand, although I should invest into an electricians screwdriver.Any other concerns I should be worried about?-Thanks

author: Floopy
author_rank: Regular Contributor
timestamp: June 18, 2018, 01:12:20 am
content: Forgot to add:One of the handles is cracked. Can I just take a propane torch some silver solder and fix it up?I think I can.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 18, 2018, 01:23:52 am
content: A good TIG welder should be able to fix you up.If you have the service manuals, the should tell you how to test the voltages. If not, the may be on-line now.I had the 141 with three plug-ins many years ago. One for KHz, one for 100MHz or so and one for 1.3ish GHz. I also had the GHz tracking generator for it. Mine had the analog storage tube. Have fun with it.

author: Floopy
author_rank: Regular Contributor
timestamp: June 18, 2018, 01:28:25 am
content: Quote from: joeqsmith on June 18, 2018, 01:23:52 amI only have a SMAW welder (Stick). I don't have access to any TIG welders anymore. I don't have the budget either.I do have the service manual and that's the voltages it said I had to be reading. Let me double check here in a minute.-have fun with it.I will?

author: Floopy
author_rank: Regular Contributor
timestamp: June 18, 2018, 01:32:29 am
content: Verified,

author: joeqsmith
author_rank: Super Contributor
timestamp: June 18, 2018, 10:48:44 am
content: Welder meaning a person who is skilled in the art of welding, in this case with a TIG. I was not suggesting you personally invest in a TIG.That's just a table. There should be a whole procedure for checking out the power supply.

author: Floopy
author_rank: Regular Contributor
timestamp: June 18, 2018, 02:04:48 pm
content: Quote from: joeqsmith on June 18, 2018, 10:48:44 amSorry, where I live a welder and a welder are said the same way and they mean different things. Ones a machine the other a skillful person.I can TIG weld well enough that it doesn't look like a chicken took a dump. I also edited the previous post to include the short section about checking voltages. The manual points out where I can find the right voltages . I'm quit surprised how much documentation there is for just a service manual.Manual:http://bama.edebris.com/manuals/hp/140t/

author: joeqsmith
author_rank: Super Contributor
timestamp: June 18, 2018, 11:43:50 pm
content: Quote from: Floopy on June 18, 2018, 02:04:48 pmQuote from: Floopy on June 18, 2018, 01:28:25 amYou said you don't own a TIG. Take it to someone who does and is skilled in using it.5-22 is preceded by 5-20 which the first sentence states "5-21. This procedure can be followed using either spectrum analyzer or oscilloscope plug-ins." Start with 5-20 then work through it. Jumping in the middle may not yield the correct results.

author: Floopy
author_rank: Regular Contributor
timestamp: June 19, 2018, 05:40:30 am
content: Quote from: joeqsmith on June 18, 2018, 11:43:50 pm-from the weight it's aluminum die cast. So TIG is the only way, unless I can find some fixing compound or something like that. I really wish I still had access to a shop.Anyway, according to the manual, it's the -100V supply that's throwing everything off. I just need to trace it through. I'm just afraid to plug in the modules with voltages all over the place. The manual says to test with them.

author: kirill_ka
author_rank: Frequent Contributor
timestamp: June 19, 2018, 11:14:44 am
content: Quote from: Floopy on June 19, 2018, 05:40:30 amFrom my experience with 141t, you should be able to get the correct voltages without plugins.You can try to swap power transistors to see if they are the problem.Also take a look at Veraxis' videos:

author: Floopy
author_rank: Regular Contributor
timestamp: June 19, 2018, 03:30:01 pm
content: Quote from: kirill_ka on June 19, 2018, 11:14:44 amThank you, I watched it yesterday after doing some searching. I need to find what is causing trouble on the -100V.

author: factory
author_rank: Super Contributor
timestamp: June 19, 2018, 07:59:39 pm
content: Firstly make sure you have the correct manual that covers the serial prefix of your 140T, they often made many changes over the years for instruments with a long production run like the 140 series.The manual I have downloaded says all the supplies are referenced to the -100V supply (exactly like the earlier 140A's I have), but looking at the power supply diagram the adjustment pot for the +100V isn't, not sure why (there must be a mistake somewhere with the manual).Anyway you should check all the voltages listed on the diagram for the -100V supply, to try & find out what has failed, once this supply rail is fixed you will probably find you need to re-adjust all the other rails that were referenced to this one.For the high voltage supply, did you verify the calibration of your high voltage probe using a known lower voltage? Also the HV probe could be loading down the HV supply if it's a low ohms per volt one.David

author: factory
author_rank: Super Contributor
timestamp: June 19, 2018, 08:10:36 pm
content: AlsoR473R467 (circled in picture) looks a bit discoloured in your picture, could it be open-circuit or dry jointed? It's in part of the -100V supply.Davidedited 26/8/18 to change error.

author: Floopy
author_rank: Regular Contributor
timestamp: June 19, 2018, 08:45:36 pm
content: Thank you! I forgot about the little guy. I'll test them later this week when I'm not buried in other work. Also, I'm pretty sure that the manual I have is correct for the serial number. I have one of the original models. It says "last calibrated: Sept 1970". The boards are exactly the same as the ones in the pictures.I checked the nuvistor and I didn't find any problem with it. That's how I know that the -2350V line is being affected by the -100V.Quote from: factory on June 19, 2018, 08:10:36 pmThe symptoms are what is described here.When I would wiggle the -100V I would get a direct response on the -2350V.I checked the fuse voltage and they seem normal.I just need more time to dig deeper.

author: Floopy
author_rank: Regular Contributor
timestamp: June 20, 2018, 03:59:17 pm
content: New question, the neon bulbs are poised to the point that they don't light anymore. I want to replace them. I only have NE2 bulbs, but the service manual says that I need NE2 and NE96.What's the difference? Does NE96 have a different break down voltage?

author: factory
author_rank: Super Contributor
timestamp: June 20, 2018, 06:00:17 pm
content: Quote from: Floopy on June 20, 2018, 03:59:17 pmThose neons NE2 (V606) & NE96 (V607, V608) are between the grid & cathode of the nuvistor & CRT, they will only light when the grid to cathode voltage is too high, usually I've only seen them only light during power up before the tube heaters have warmed up, do yours light briefly at power up?The NE96 has a higher breakdown voltage than the NE2.Also be very careful not to disturb them as the legs are made from copper plated steel, they tend to either snap off or fall off very easily if knocked, I even found one in the bottom of a parcel from a 140A scope I bought years ago (that was a very easy fix, it had stopped the timebase from running).I still think you should concentrate your fault finding with the -100V supply before worrying about the HV section.David

author: Floopy
author_rank: Regular Contributor
timestamp: June 21, 2018, 01:50:18 am
content: Quote from: factory on June 20, 2018, 06:00:17 pmYour right, they do light just before the CRT begins to light up. I thought that they where dead. I plugged in the modules to see if it would change the voltage in anyway and it didn't. I ended up blowing the fuses on the modules also. At least I verified that they worked. I've tested the power transistors and they are okay. I swapped them and the voltage is exactly the same.I measured the reference voltages that are given on the schematic. The ones outlined in blue mean they are different, the ones with a green check mark mean they are withing 0.2V of the marked voltage. I measured by touching the ground plane with the negative probe and the positive probe went where I was measuring. For some reason I forgot to write down the voltage I had for terminal 927. I will update it when I open it again. The markings of the side of the paper is the resistors that are heating up and discoloring the board. I'm really starting to get stumped on what might be producing the problem. Probably because I haven't worked as much with these kind of power supplies before.Sorry for all my mistakes, this is the first time I trouble shoot such a large and dangerous piece of equipment.EDIT: the One I forgot to write down (29V next to power transistor), is 62V+. That is not normal and I'm pretty sure I measured that right.

author: Floopy
author_rank: Regular Contributor
timestamp: June 21, 2018, 04:26:27 pm
content: I merged the two schematics in the service manual since they where overlapping.

author: factory
author_rank: Super Contributor
timestamp: June 21, 2018, 08:23:37 pm
content: Quote from: Floopy on June 21, 2018, 01:50:18 amOk your measured voltages for Q462 are;Collector 62VBase 1.2VEmitter 0.5VAs you have checked the series regulator (power) transistor is OK, I suspect Q462 is open circuit, you should be able to verify this out of circuit with the diode check on your DMM.As usual the manual only gives a HP in-house part number for it (1854-0022), it's probably a standard part but it will need looking up in the equivalent charts available on the web.I don't think you need to worry too much about resistors R467 & R473 (the discoloured ones) as they form a voltage divider across the +100V & -100V rails and the -20V is correct. You may wish to re-solder them if the joints look dry and if I've done my calculations correctly they only dissipate about 0.8W of heat between them.David

author: Floopy
author_rank: Regular Contributor
timestamp: June 23, 2018, 04:11:57 pm
content: Quote from: factory on June 21, 2018, 08:23:37 pmI de-soldered and it tested fine, NPN no shorts. Should I try replacing it anyway? I don't see who else could be causing problems. It seems that the wrong voltage is being applied to the base of the regulator and its' raising the voltage from 29V to 62V. I'm going to do a little more probing around and trace the voltage as it goes through. I'll test the reference voltages on the +100V and see if everything is normal.Thanks!

author: factory
author_rank: Super Contributor
timestamp: June 23, 2018, 07:54:14 pm
content: Quote from: Floopy on June 23, 2018, 04:11:57 pmIt won't be shorted as all the voltages measured for that transistor were different, but was either half of it open circuit? The only other part that could potently be open circuit is R465 (56k).David

author: Floopy
author_rank: Regular Contributor
timestamp: June 24, 2018, 01:50:30 am
content: I de-soldered both 1854-0022 transistors, (there where two) and swapped places. The outputs where almost exactly the same. I tested the 56K resistor and it was reading fine. The only voltage differences in the 100V+ circuit was the zener (CR445) was at 52.8V instead of 69.8V and the inputs at terminal 926 was 154V instead of 126V. I measured the "calibrator" voltage and it was extremely off the page. it was reading -0.5V instead of 1V and -4.5V instead of 10V. I tested the transistor and it had a base to emitter of 0.2. I un-soldered it and disconnected the resistor that was connecting to -100V (R493). No luck unfortunately, the output was just the same. I just need to dig deeper, I'm going to start trying to disconnect certain parts of the circuits and other boards to see what happens.

author: factory
author_rank: Super Contributor
timestamp: June 24, 2018, 12:58:54 pm
content: Unless there is a track break or bad connection in that area I'm not sure what else to suggest, I've had a quick look at the pictures of the power supply boards in mine, none of the adjustment pots are at the end stops, do they all actually change the output voltages when adjusted?The discoloured board around the resistors, mentioned earlier may indicate your 140T has had a lot of use, none of mine are like that.Also one of the manuals (140A 1967) mentions that the measured voltages on the circuit diagrams may vary depending on the plug-ins fitted, of course with no load (no plug-ins) that may explain the higher voltages before the regulator transistors.As for the calibrator, the outputs are a 1V & 10V peak to peak square wave at mains input frequency (i.e. 50Hz or 60Hz depending on country), did you use an oscilloscope to check this?The transistor Q490 is germanium type, they have a lower forward voltage than silicon types, but if it's reading 0.2V (base to emitter) both ways (out of circuit) then it's leaky.One important thing with the calibrator circuit, DO NOT measure the tunnel diode (CR490) with your DMM as they are very easy to destroy, they can also be damaged very easily with the heat of soldering.David

author: Floopy
author_rank: Regular Contributor
timestamp: June 25, 2018, 04:30:12 am
content: Well, never thought I would end up doing this.I ended up taking almost everything apart. Finally I had enough and I thought that if the potentiometer won't go farther, I will make it go farther. R470 is a resistor that is right before the regulating potentiometer. It's value is only 4320, I grabbed a similar resistor that was 5.9K and swapped the two. I could now regulate it to where I wanted it and I got all the other lines to where they needed to be. No problem anywhere. I plugged in the units and the fuses have not been blowing anymore (crossing fingers). I forgot to mention that they where blowing. I did not find anything odd after some testing. Is this a band-aid, or a real solution? I think it's fine now.Also the fan was not turning very fast at all. (maybe 2 RPM). Taking it out was a pain! Really! I oiled the shaft after a disassembly and now it's blowing enough air that I can feel it on the side vents.Anything else I should look for. Right now it looks really nice with everything setup

author: Floopy
author_rank: Regular Contributor
timestamp: June 25, 2018, 05:49:20 pm
content: Forgot to mention. I measured the 1V and the 10V, I didn't know it was a peak-to-peak voltage. It measured fine, the problem was my ignorance.

author: factory
author_rank: Super Contributor
timestamp: June 27, 2018, 08:06:45 pm
content: Quote from: Floopy on June 25, 2018, 04:30:12 amGood to hear you got it all working, it may be you've compensated for something has drifted slighty out of spec in the power supply.Here is the power supply board in my 140B, I think it may be the same type as yours, I will have to check the no-load voltage next time I use it (it's currently at the bottom of a stack of equipment), I've never done that before as I have plenty of the required scope plug-ins listed in the manual.David

author: Floopy
author_rank: Regular Contributor
timestamp: June 27, 2018, 10:18:05 pm
content: Thanks for all the help. That board looks almost exactly like mine with two differences. #1 the components are a bit different (that's expected) and #2 I don't have an ENIG plated board.You've been a great help!I just need to figure out how to use all the functions now.I'm still looking for a solution to the crack in the frame, but the essential is working. In total it cost me 140$, I think it's a good deal for a unit like this.

author: factory
author_rank: Super Contributor
timestamp: July 01, 2018, 09:42:22 pm
content: Quote from: Floopy on June 27, 2018, 10:18:05 pmHave a look at this thread for a possible solution to the cracked frame;https://www.eevblog.com/forum/testgear/hewlett-packard-740b-dc-standard-digital-voltmeter-(and-740a)/msg1419955/#msg1419955It's something I will be looking at doing since I have a lot of HP delivery victims here too.David

author: Floopy
author_rank: Regular Contributor
timestamp: July 06, 2018, 01:45:55 am
content: Funny,That instrument has the tag Brigham Young university, that's where I'm going, I asked the welding shop here and they said they could try and it might work, but could not guarantee the result. I'm still debating whether I should let them try tig welding it.Thank for the replyQuote from: factory on July 01, 2018, 09:42:22 pm

author: Floopy
author_rank: Regular Contributor
timestamp: August 19, 2018, 03:56:18 am
content: Quote from: factory on July 01, 2018, 09:42:22 pmWell hopefully your still around. I thought that what I had done was good enough. I haven't use it a lot this past few months because of other projects that were in the way and work. I wanted to see if a certain frequency I was emitting was going to show up on the analyzer, I was just going to do this for practice. The minute I saw the screen light up I knew something was wrong. The display had shrunk and there was a brighter than usual spot. For some reason the beam was overlapping! (see video)Back on the bench, opened it up again. I knew it wasn't the problem, but I thought I would check the voltage rails.81.3VSomething is deteriorating I don't know what! I haven't checked any of the caps for leakage or correct value. I have to check the schematic again.Anyway not the main problem, I'm guessing something is wrong inside the IF section of the analyzer. I need to look into it further. I found the manual and a block diagram. This one is going to be interesting.On the bright side, I got the crack repaired! The welding shop asked 50$ to get it repaired, I asked if I could just pay for the supplies and time on the welder, but they didn't want to. I ended up buying some aluminum brazing rods. I had some trouble at first, heating a large piece of aluminum takes longer than you would expect. I forgot to clean more than just the crack on one side and it bulge a little. It holds well, I got some 220 grit sand paper and finished up the frame. I have some before and after pictures.For a first time I don't think it looks too bad. I've only done copper pipping before.Things to consider next time:#1: hold the torch farther away from the work. It's easy to think that more flame will heat the work faster.#2: Clean the work area thoroughly before applying the heat. I did one side, but the other did not get as much cleaning.#3: put down the brazing rod before taking of the safety goggles. I have a nasty red spot on the side of my cheek now.I'll study the schematic, there's a lot more components in the IF section than in the power supply. I think that some component is dying slowly in the power supply.This is taking longer than I had anticipated, but there's a lot to learn in the process.

author: Floopy
author_rank: Regular Contributor
timestamp: August 19, 2018, 03:58:23 am
content: More pictures...

author: Floopy
author_rank: Regular Contributor
timestamp: August 19, 2018, 04:00:30 am
content: I noticed they are a bit blurry. Oops

author: factory
author_rank: Super Contributor
timestamp: August 21, 2018, 02:12:11 pm
content: Quote from: Floopy on August 19, 2018, 03:56:18 amI'm still here, it's quite easy to miss threads as there is more stuff to look at than I have spare time.Sounds like the same area of the power supply has gone wrong again, the shrinking display on the CRT could be linked to the -100V supply failing causing lower HV.Yes the modules look a nightmare to work on without the appropriate extenders & all the test gear in the manual.I can't get the video to work, it just comes up with a login page.The case repair looks good to me, I think I should have some practice on something that doesn't matter first, as I've only had a couple of hours training at work on copper pipe (for new work starting soon). I seem to remember the trainer mentioning you need to get the right brazing rods for the material and the some of the cheap ones weren't very good.David

author: Floopy
author_rank: Regular Contributor
timestamp: August 21, 2018, 04:07:03 pm
content: Oops, the link timed out early. The problem is not a shrinking display, but the signal is not being drawn correctly. I took individual pictures. I believe it is the IF section because it is the one who draws on the X axis. As you can see in the picture one spot is brighter than the rest of the display. As I move the wave form to the left it "wraps around" and goes to that spot. I've never seen a problem like this one. This one won't be easy to identify. I'm also going through every component and seeing if the values match the ones written in the schematic.I used these rodshttps://www.amazon.com/gp/product/B0000CBJGI/ref=oh_aui_detailpage_o02_s01?ie=UTF8&psc=1They worked well after I learned to use them.

author: kirill_ka
author_rank: Frequent Contributor
timestamp: August 21, 2018, 04:34:52 pm
content: Did you try manual sweep? Is it ok?

author: factory
author_rank: Super Contributor
timestamp: August 21, 2018, 06:10:54 pm
content: Quote from: Floopy on August 21, 2018, 04:07:03 pmBut the display does seem to have lost 20% of the horizontal in the same way that the -100V supply has gone down approx 20%. Can't really comment on the 8552B, as I only have the 8552A (still not tested).Will have to find a local supplier for the rods, amazon UK don't have them at sensible price (about 10x the price over here).David

author: Floopy
author_rank: Regular Contributor
timestamp: August 23, 2018, 03:39:27 pm
content: I did a thorough check of all components testing every single one of them. That included de-soldering one leg and checking for correct values. I found 4 resistors that where completely off value (28k instead of 40k!). I tested the diodes for forward voltage, but I don't know how to test the zener diodes for reverse voltages. I'm going to order a new set of capacitors just in case if changing the resistors does nothing. I'm getting tired of ordering a few parts and then finding out I need more. Where I live everything has to be bought online. Anyway, I'll be testing the bigger can capacitors.I used this technique of trouble shooting when I don't know what the problem is. I just go through every component and put a black dot on the ones I have already tested. It's tedious, but I am able to find out what values are off. The only problem is that it only checks the components when they are not running. It doesn't mean that when power is flowing through it, it will behave the same way.The hunt continues!

author: Floopy
author_rank: Regular Contributor
timestamp: August 23, 2018, 03:45:35 pm
content: I did forget to mention.Some of the light bulbs had burnt out in the IF section. I replaced them all and the ones that where too expensive to buy where replaced with LEDs with resistors. It looks nice now with all the lights turning on.I still can't believe that you can buy a replacement bulb on amazon for a 55 year old machine!

author: factory
author_rank: Super Contributor
timestamp: August 23, 2018, 08:29:09 pm
content: Quote from: Floopy on August 23, 2018, 03:39:27 pmI'm curious as to where the drifted resistors are in the circuits, are they related to the problems you've had?It's probably best to check to Zeners powered up in circuit for the correct voltage given on the diagrams (most will have a 5% tolerance, voltage reference ones may be better tolerance), they could also be tested out of circuit with an appropriate power supply &current limiting resistor(to limit to something like 5mA), but they can get easily damaged by removal (if glass) or from overcurrent. Equivalent types of Zener diodes don't always behave the same in circuit as the originals either.Quote from: Floopy on August 23, 2018, 03:45:35 pmWhich lamps were too expensive? Most are common types that will have used in lots of stuff until LED's became more commonly used.David

author: Floopy
author_rank: Regular Contributor
timestamp: August 24, 2018, 01:29:48 am
content: Quote from: factory on August 23, 2018, 08:29:09 pmI'll just grab my 100V bench power supply and do it! (I wish) or I could measure the voltage drop while it's running. I'll have to seeCM2107 (for CHICAGO MINIATURE / CML) I couldn't find them cheaper then 2.99$ for one. I needed two and that doesn't include the shipping.The other ones where 367 bulbs. I got those for .75$ a piece and free shipping.Question: do film capacitors work just as well as electrolytic. They seem to be the only kind you can buy that have a 200VDC rating. I probably won't replace them, but I would just like to know.I'll get a picture soon.

author: Floopy
author_rank: Regular Contributor
timestamp: August 24, 2018, 02:13:27 am
content: The components with the scribble and the lifted leg are off value. Mostly burnt ones. I will replace the resistor I had swapped thinking it would fix it.

author: factory
author_rank: Super Contributor
timestamp: August 26, 2018, 01:30:59 pm
content: Quote from: Floopy on August 24, 2018, 01:29:48 amI only mentioned other ways of testing the Zener as I collect old test gear, I have a few suitable power supplies & a decade resistance box for current limiting. But I would normally just check them in circuit with the DMM as it's quicker & easier, only if I suspect a problem might I check with something else.I've recently just acquired another suitable power supply (HP Harrison 6209A 300V) for the collection, I think it may need a bit of work and also the current control sacrificed itself to save the rest of the unit from damage during shipping.Another way of testing Zeners & other components is using my Heathkit curve tracer (with an X-Y scope), it has 0-40V & 0-200V supplies inside for testing.CML (now VCC) have discontinued the 2107 10V 40mA lamp, other brands are still available if you search for #2017 bulb/lamp. Or you could have tried the 12V version (#2174 lamp) for a longer life, with a slight reduction in brightness, Mouser have them at approx .68$ each. Having said that the LED conversion will probably outlast them too.https://www2.mouser.com/ProductDetail/JKL-Components/2174?qs=sGAEpiMZZMtj1PWpWL2%252bvDwicDUvKr1eMp%2f%252bXqB0Bog=Are the 200V rated capacitors your asking about the orange Sprague ones on the power supply circuit board? If yes these are good quality film ones and shouldn't need replacing.If not 200V is a non-standard voltage rating for capacitors these days and can be replaced with a higher voltage one eg. 250V.The other three capacitors (metal cased) are Tantalum ones, again they shouldn't need replacing unless they measured bad. Or are Sprague type 109D (wet Tantalum type), usually you can see those easily as they rot badly if they leak.Film capacitors are usually a lot bigger than electrolytic types for the same value/rating, so not usually practical to change them to film, ESR may be different too.Davidedit: Picture of some rotten Sprague 109D capacitors below for reference.

author: factory
author_rank: Super Contributor
timestamp: August 26, 2018, 02:08:13 pm
content: Quote from: Floopy on August 24, 2018, 02:13:27 amThose look like;R431, 49.9kR433, 100kR454, 22.1kR467, 30.1kThe first three are part of the adjustment resistor dividers for the +250V & +100V supplies and R467 is one I mentioned before (looked discoloured) in the -100V supply.Make sure that any replacements are similar physical size or they may overheat too, you may need to up the wattage when looking as 1/2W (from the manual) are usually far too small these days.David

author: Floopy
author_rank: Regular Contributor
timestamp: August 26, 2018, 05:12:16 pm
content: Quote from: factory on August 26, 2018, 02:08:13 pmWell darn, I hadn't thought about that when I order the parts on Thursday. They are all about half the size of the old ones. I'm still learning how to order the right components. Next time I'll place an order I'll make sure to buy different kinds. I'll use the ones I ordered just for testing purposes. Then I'll remove them.What's the difference between metal film and thin film resistors?

author: factory
author_rank: Super Contributor
timestamp: August 26, 2018, 09:18:41 pm
content: Quote from: Floopy on August 26, 2018, 05:12:16 pmIt seems very little for the ones you have ordered, the metal film usually have a round cross-section same as the old ones and the thin film types are usually flat on a piece of ceramic (but the data-sheet for the MBB type ordered says they are round metal film too).Here is the data-sheet for the SFR metal film resistors from your order,https://www.vishay.com/docs/28722/sfr16s25.pdfAnd the MBB metal (thin) film type,https://www.vishay.com/docs/28768/mb_vg06.pdfIf you keep them spaced off the board when testing it should prevent any board damage if they overheat.You may need to look for 1W or 2W to find similar size to the originals. Not sure why they specified 1% if they wanted values like 22.1K as it could be anywhere between 21.879 & 22.321, this should allow you to round the numbers off it you can't find the exact values at the higher wattage.David

author: Floopy
author_rank: Regular Contributor
timestamp: August 31, 2018, 07:44:37 pm
content: I finally found all the parts I needed. I tried getting them all from the same manufacturer, but in the end I had to diversify in between Xicon and Vishay. Unfortunately one item is back ordered. The shipment is suppose to come around Sept 12. For now I'll just put everything aside and hope that the parts can come quick, because I'm getting tired of waiting for parts.

author: Floopy
author_rank: Regular Contributor
timestamp: September 14, 2018, 05:13:13 am
content: Got the parts earlier than expected. The resistors are almost the same size as the old ones, but after hours of searching for the same brand with the right values I think I did what I could. After some soldering I turned it on. After some measuring and some tweaking every line came to their correct voltages. Even after waiting half an hour it was all staying within a .04% tolerance. Modules plug-in and all!Lets hope it stays that way...The display reverted back to normal. Maybe it was due to a bad voltage rail, only time will tell. I left it running for some time and after a while I turned it off and touched the resistors. They seem warm, but not burning. I will have to measure the temperature.I thought that I had taken a picture of the board after, but apparently I didn't. The new resistors are about 3/4 the size of the old ones. I also found that the analyzer works well with my pen plotter. The pen lift output will create a "break" in the paper. I guess I can call that the "save" feature. I'll take a picture of the final unit. I didn't replace the capacitors after all. Now I just need to find a VHF or UHF frequency generator to calibrate it.(I remembered that I had a 275V power supply and it had a limited current output at just 50 milliamps. )

author: factory
author_rank: Super Contributor
timestamp: September 16, 2018, 08:03:07 pm
content: Good to hear it's sorted, it's surprising the difference just one incorrect supply rail can cause, I thought I had all good power rails in a counter I'm repairing but completely missed the separate one for the oscillator (down 25% causing the main 5Mhz output to be too low to operate rest of the counter circuits).Your 275V 50mA power supply is more than enough to check Zener's if you wanted to, you would need to calculate the series resistor to prevent destroying them. The output capacitance is usually enough to short Zener's if you don't (been there done that at work, luckily it didn't matter as we had plenty of new ones).David

author: Floopy
author_rank: Regular Contributor
timestamp: September 17, 2018, 01:40:21 pm
content: I did all the calibration procedures this week on the RF section. I didn't do the ones on the IF section because I don't have a UHF generator. I will have to find one somewhere. For now it works well and I can see my local radio stations popping up on the screen.Hopefully I can say that I'm done for now.

author: Floopy
author_rank: Regular Contributor
timestamp: April 30, 2019, 01:08:17 am
content: It's me again!At this point I might just be talking to myself though. I don't know someone might find this useful. At least I've learned a lot.I've been quite happy with this boat anchor so far. I've only had to replace the fan because the unit was over heating and the thermal shutoff would turn on. Now it handles much better, but it is a bit noisier. I wish I could thank the engineers for putting easily available parts.I've got a new problem and this time it's with the display again. I noticed that it's shrunk. It's a bit smaller on the edges and when I try to adjust the horizontal gain it maxes out. I'm dig deeper into the service manual and see. In the mean time anyone have an idea of their head what it might be? I also noticed that the "scanning" light never comes on except a few times on power up then it turns off. Also when I start getting near 0-10Mhz the signal seems to be mirrored around some axis. Could all of these seem to be related.The display is showing a 833Mhz -30db signal.

author: 0culus
author_rank: Super Contributor
timestamp: April 30, 2019, 01:14:49 am
content: Capacitor going bad in the HV circuitry?

author: Floopy
author_rank: Regular Contributor
timestamp: April 30, 2019, 02:19:17 am
content: Quote from: 0culus on April 30, 2019, 01:14:49 amNow that I think about it I'm asking why I didn't check. I was blaming the RF section because it drives the display, maybe it's the display section.

author: 0culus
author_rank: Super Contributor
timestamp: April 30, 2019, 02:30:40 am
content: Quote from: Floopy on April 30, 2019, 02:19:17 amI would start there. From my (admittedly limited but increasing) knowledge of troubleshooting HP gear, my progression is always mechanical stuff first (contacts, pots, etc) first and then suspect anything that has contact with mains and then higher voltage circuits before suspecting any low voltage circuits. The former two will always be under more stress than anything on the low side.