HP54600B with spike problem with and without signal - Page 1
Forum section: electronics / repair

author: sacha
author_rank: Contributor
timestamp: April 15, 2024, 09:56:06 pm
content: Hi, I have a problem with my HP 54600B which at startup generates many spurious signals on the signal it displays. I couldn't find the manual with the diagrams. I wonder if any of you have the manual for this oscilloscope and if you have ever seen this defect. Thank youI also ask if it is possible to reset the error you see. Thank you all

author: Runco990
author_rank: Frequent Contributor
timestamp: April 15, 2024, 11:05:18 pm
content: I'd check the power supply first. They are known to leak capacitors quietly underneath where you don't see it.Also once the scope warms up, run the self-calibration and see if it clears, as old capacitors get a little better as they heat up.Check visually for discolored tantalums on the main board.I've been buying these scopes and fixing them for many years. Not much goes wrong with them. Usually a capacitor on the display, causing a compressed image, leaking capacitors in the power supply, sometimes a burnt tantalum, a dead NVRAM that holds the calibration settings.... aaand dirty controls. Whew!Measure for AC ripple and correct voltages on the power supply connector.There are really no schematics for these as far as I know. I think someone drew out the power supply and the display board, but not the main board. Noise is likely power related anyway, as the main board is pretty bullet proof.

author: sacha
author_rank: Contributor
timestamp: April 16, 2024, 04:30:28 am
content: Hi, thank you for the reply, in fact as soon as I turn it on the signal is very dirty and after about 15 minutes it disappears on its own. I tried to check the voltages coming out of the power supply but I didn't see any ripple and the voltage is around 5.10Volts. However, I noticed that if I cool the U33 the spikes return, perhaps it could be this integrated circuit or the timing of the signals is incorrect

author: iMo
author_rank: Super Contributor
timestamp: April 16, 2024, 05:20:37 am
content: The U33 is a standard cmos sram (32kB). It could be a solder joint gets crappy. What will happen if you press a little bit on its package?

author: sacha
author_rank: Contributor
timestamp: April 16, 2024, 06:48:38 pm
content: Hi, thanks for your reply, actually the soldering all seems fine, I also tried using a pin to move the U33's feet but everything seems well soldered.

author: sacha
author_rank: Contributor
timestamp: April 16, 2024, 07:00:06 pm
content: This is what it looks like just turned on and with no input signals

author: sacha
author_rank: Contributor
timestamp: April 16, 2024, 07:09:16 pm
content: This is what it looks like after 15 minutes of being turned on and with no input signals.If you notice the error you see it went away because I pressed the erase button.

author: Runco990
author_rank: Frequent Contributor
timestamp: April 16, 2024, 10:51:05 pm
content: Oh... that's not good. Get out the freeze spray and see if you can find the part. There is usually little luck fixing the main boards on these.....Nothing to loose.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 17, 2024, 02:16:09 am
content: Maybe probe clocks if you can. That could be due to marginal timing and (parallel) bits being read out of order, for example.Supplies are a good bet, as timings and performance in general depend upon them. Electrolytic capacitor ESR varies with temperature, particularly towards end-of-life. That's one supply checked, but I don't know how many that thing uses, and I would guess there are more to go. You might also need to check local supplies, in case some sections or chips are supplied by RC filters for example, and there may also be toasted or marginal tantalums, stuff like that.IC timing constraints also vary with temperature. Presumably something else is responsible for the timing failure -- it would be very strange for any given chip to fail by developing poor timing -- but perhaps something at the start of the timing chain, or bus mastering, or etc., is doing it.Tim

author: sacha
author_rank: Contributor
timestamp: April 17, 2024, 05:54:55 am
content: Hi, thanks for the reply, it should be the clock generator if I'm not mistaken. I don't have the scheme and I go by intuition

author: iMo
author_rank: Super Contributor
timestamp: April 17, 2024, 06:32:56 am
content: As written above - try to cool down the chips, go chip by chip (start with the U33), perhaps you will be lucky.Perhaps a single drop of IPA (isopropylalcohol) on the chip will be enough, it cools it down a little bit.

author: xavier60
author_rank: Super Contributor
timestamp: April 17, 2024, 07:08:38 am
content: Or preheat something before the DSO switched on.

author: MathWizard
author_rank: Super Contributor
timestamp: April 17, 2024, 11:42:31 am
content: The PCB looks pretty cool, it reminds me how small the circuits I work on have been.

author: sacha
author_rank: Contributor
timestamp: April 17, 2024, 08:55:55 pm
content: Hello everyone, Today I cooled the parts and I realized that if I cool U25 or U33 together or one at a time the spikes come back, it seems strange to me that both are defective. and if when they are hot and the spikes have disappeared I turn off the oscilloscope and turn it back on immediately the spikes return as if the integrated circuits were cold. If when the spikes are present I connect the oscilloscope probe (x10) to pin 20 of U33 the spikes disappear.

author: Runco990
author_rank: Frequent Contributor
timestamp: April 17, 2024, 09:15:40 pm
content: If there is NO ripple on the power rails and all voltages are in spec, I'd change that IC, as it is pretty simple and RAM does go bad.

author: sacha
author_rank: Contributor
timestamp: April 17, 2024, 09:31:52 pm
content: Hi, So is U33 worth trying as the first ic to change? But how is it possible that even if I only cool U25 the spikes still come back?Are HP spare parts available in your area?Thanks for the reply

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 17, 2024, 10:06:44 pm
content: Can you scope the pins?Also wonder if the logic levels are indeterminate. Could be heat shifts both the output level / drive strength, and the input threshold, and both happen to work when warm, but they diverge when cold. That could explain why the ASIC is affected.Decayed transistors could happen, or corroded pins/bondwires (can be microscopic, inside the package). And the RAM array itself, and readout, are very precise and can age too, maybe in terms of increased access time (before stable), maybe data corruption.Tim

author: sacha
author_rank: Contributor
timestamp: April 18, 2024, 09:13:38 pm
content: Hi, I agree with everything you wrote, I tried checking the U33 (ram) address input and data input/output levels, but found no apparent defects. I will try to change U33( Ram) with a faster one.Can any of you tell me if the 1SL7-0001 ic is available in any stores?Thank you.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2024, 03:01:02 am
content: The 1SL7- is an HP proprietary ASIC; it's basically only going to be available as replacement, or salvage from other boards. (All the more reason to make sure everything is fine first..!)Tim

author: sacha
author_rank: Contributor
timestamp: April 20, 2024, 08:07:34 pm
content: Hi T3sl4co1l , if you give me an email or Telegram address I will send you the sequence of waveforms that I see on all the pins of the RAM, I can't send them here because they are too heavy.On Telegram you can find me as: Shacawhile my email address is: conduel@libero.it

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 20, 2024, 10:23:52 pm
content: How are they "too heavy"? Scope screenshots should be a couple 10 kB each, easily attached to a post. Photos rather than screenshots, low 100s k maybe. Do you not have an image adjustment app?Tim

author: sacha
author_rank: Contributor
timestamp: April 21, 2024, 04:20:46 am
content: Hi Tim, I made two videos where on the first you see from pins 1 to 14 and on the second you see from pins 15 to 28. I only have two hands but it's the fastest method I know. I created two files that I can send to your inbox or on a social network such as Telegram. I don't rescale or compress them so as not to lose video quality.sorry for the late reply but I was asleep :-)

author: iMo
author_rank: Super Contributor
timestamp: April 21, 2024, 07:13:18 am
content: Without a schematics would be your effort pretty laborious.. Simpler way might be to focus yourself on the components in the area you have already identified. The temperature dependent problem could be caused by any part there, incl. ceramic and tantalum capacitors.Cool down the area and heat up locally the parts, one by one, or vice versa.. You should be able to identify the part. Some YT bloggers do repairs of everything equipped with infrared camera and cooling spray only, sometimes they use resistance meter

author: fmashockie
author_rank: Frequent Contributor
timestamp: April 21, 2024, 12:10:41 pm
content: Quote from: sacha on April 21, 2024, 04:20:46 amWhy not just make a YouTube account? You can post your videos there and just add a link to it here. That way many EEV blog users can view them so you can get more feedback. Also, can you capture the waveforms on your scope, save them, and then take a photo with your phone? Unless of course they are hard to trigger on, then taking a video is a good way to go.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 21, 2024, 12:43:58 pm
content: Anyway, main thing was to inspect the rising/falling edges, preferably those coming from or going to the RAM; so, a trigger on /OE, /WR would be relevant, also general signal quality, and timing if you can tell if there's anything funky going on over a longer time scale.This is more of an interactive process that isn't really something that's going to work well back-and-forth on the forum I'm afraid... I would encourage more learning about how these systems work generally, and how to test and debug them, or if that's too much bother, just replace the chip(s) and see if that improves it.Tim

author: sacha
author_rank: Contributor
timestamp: April 21, 2024, 02:05:31 pm
content: Thanks Tim, you're giving me a lot of advice to think about, in any case I think the best way is to try to understand the cause before intervening with the removal of the components. At the moment I only have the new Ram available. As soon as I can I will take measurements using OE/WR as trigger. I wonder what changes in the reading when using pin 20 (S) as the trigger of this memory?these are the links to the videos on youtubeI don't know if they can be useful because I didn't use the trigger on the pins recommended by Timhttps://youtube.com/shorts/J2vYJLIUjlc?feature=sharehttps://youtube.com/shorts/Ifw9fT1vDFY?feature=sharebelow you can see my latest little one who arrived today :-)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 22, 2024, 02:53:36 am
content: Looks nice and periodic, but who knows what the edges are doing.To clarify: you need a range under 100ns/div at least, to even begin to resolve the edges. A 100MHz scope may not be sufficient to resolve it, either.Tim

author: sacha
author_rank: Contributor
timestamp: April 22, 2024, 08:49:38 pm
content: Hi, I made the measurements with the trigger on pin 22 and I see clean signals on the rising and falling edges. But on pin 20 I see this signal.https://www.youtube.com/shorts/3bgqQN2jaMc

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 23, 2024, 03:28:55 am
content: The other pins look fine, sharp rise, no wobblies?Whatever's driving (or not) might be open-collector/drain style, and the waveform is normal; it only matters how long, and when, /S is below threshold, and the rise might not matter. You'll have to trace back the source and see what type of driving pin it is. It is definitely not a normal waveform for a CMOS driving pin.Tim

author: sacha
author_rank: Contributor
timestamp: April 23, 2024, 05:50:42 am
content: I don't see those noises on the address pins or even on the in/out pins. I'll try to understand where that signal is coming fromthe photos you see were taken on pins 9 and 11 of the memory

author: iMo
author_rank: Super Contributor
timestamp: April 23, 2024, 07:35:29 am
content: First tell us what are the voltages of your signals, it should be 5V aprox. Next pls indicate the names of the pins (instead of numbers), like DQ4, /WR, /CS, /OE, A11 when you talking the U33 for example.The ramp on your last shot is suspicious. The U33 memory is 85ns access time (so the system clock in that part of system will not be higher than 10-12MHz), afaik, so you should see all signals well on your 100MHz scope.When you see such a slow ramp you may try (as a test or a quick workaround) to wire a 1k pullup (against the 5V) on that signal, sometimes it may help.PS: in order to look at the memory sigs you may, for example, to trigger your scope on the /CS or /WR or /OE edges (on the channel1) and look at all other signals (channel2), one by one.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 23, 2024, 12:39:35 pm
content: I'm guessing it's 2V/div, 5V supply, and the ramps are open bus (with weak pull-ups, but nothing reading during so it doesn't matter). But this would be a good place to have multiple channels showing the strobe signals.Another tweak that may be diagnostic: loading the signal (particularly the suspicious pin) with a resistor of say 1k, down to even a couple hundred ohms, pulling to VDD or GND, or with a capacitor of some 10s of pF, and see how much is necessary to cause data corruption. Most likely, all the other signals will be well-behaved (tolerant down to, say, 200 ohm or so, or up to 30pF or more), and the suspect signal fails with much less (or in the pull-up case, potentially improves). You will see the effect of these loads on the scope trace.Tim

author: sacha
author_rank: Contributor
timestamp: April 23, 2024, 07:07:06 pm
content: Thanks for the replies, your help is very important in finding the cause of this fault. all the tests done refer to U33 which is powered by 5V. All the signals we see are around 5vpp. I used the video number in reference to the pins of U33, photos or video 1 = pin1, etc.... For the images you see I used the OE pin (22) as the trigger. And the suspicious shape is seen on the CE pin (20). During the tests I noticed that by touching only pin 20 with the oscilloscope probe the spikes attenuate. and I see that my probe set x10 puts 15 pf in parallel on pin 20. I will do as you said to put resistive loads on +5V and 0V and see what happens.Opening a similar oscilloscope I realized that it has a RAM with a lower access time (70nS) I could try to replace U33 with a lower access time than the current 85nS.The photo I posted describes the Memory I saw on the second Oscilloscope, the same but with U33 with an access time of 70 nSThanks again, I'll let you know as soon as I've tested it.

author: sacha
author_rank: Contributor
timestamp: April 23, 2024, 07:19:36 pm
content: I attach what I found online as schematics for this HP 54600B

author: sacha
author_rank: Contributor
timestamp: April 23, 2024, 07:21:10 pm
content: I attach what I found online as schematics for this HP 54600BI apologize, but I couldn't find the complete manual

author: fmashockie
author_rank: Frequent Contributor
timestamp: April 24, 2024, 01:00:00 pm
content: Another general recommendation: you should join the HP/Agilent/Keysight test equipment group on Groups.io. It is a group for discussing HP/Agilent/Keysight equipment.

author: sacha
author_rank: Contributor
timestamp: April 25, 2024, 01:07:53 pm
content: This scheme is also very similar to the 54600b

author: sacha
author_rank: Contributor
timestamp: April 25, 2024, 01:11:12 pm
content: Hi fmashockie,Sorry but I can't see the page, try sending me the link.

author: fmashockie
author_rank: Frequent Contributor
timestamp: April 28, 2024, 09:22:21 am
content: It is a private group so you have to request an invite, but you should at least be able to search through chat/forum history before getting approved. And then you can make posts of your own.https://groups.io/g/HP-Agilent-Keysight-equipment

author: sacha
author_rank: Contributor
timestamp: April 29, 2024, 05:41:05 am
content: Hi fmashockie,Thanks, I'll try to ask.

author: sacha
author_rank: Contributor
timestamp: May 07, 2024, 07:37:22 pm
content: Hi everyone, I solved it by replacing U33 and with a small capacitor on pin 20.

author: fmashockie
author_rank: Frequent Contributor
timestamp: May 12, 2024, 03:23:35 pm
content: Glad you fixed it! Might be helpful to change the subject of your first post to include 'fixed' or 'solved' in the title to help others with a similar issue.

author: sacha
author_rank: Contributor
timestamp: May 14, 2024, 07:36:45 pm
content: Hi fmashockie, thanks for your clarification, in reality it is not fully functional yet because I also have channel 1 which is not precise on the reading on the ranges from 1 volt /division upwards. As soon as possible I will add the other components that I find faulty.