HP54600B with spike problem with and without signal

• HP54600B with spike problem with and without signal
  Posted by sacha on 15 Apr, 2024 21:56
• 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 you
  
  I also ask if it is possible to reset the error you see. Thank you all
  
  
  

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• #1 Reply
  Posted by Runco990 on 15 Apr, 2024 23:05
• 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.
• #2 Reply
  Posted by sacha on 16 Apr, 2024 04:30
• 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

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• #3 Reply
  Posted by iMo on 16 Apr, 2024 05:20
• 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?
• #4 Reply
  Posted by sacha on 16 Apr, 2024 18:48
• 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.
• #5 Reply
  Posted by sacha on 16 Apr, 2024 19:00
• This is what it looks like just turned on and with no input signals

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• #6 Reply
  Posted by sacha on 16 Apr, 2024 19:09
• 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.

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• #7 Reply
  Posted by Runco990 on 16 Apr, 2024 22:51
• 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.
• #8 Reply
  Posted by T3sl4co1l on 17 Apr, 2024 02:16
• 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
• #9 Reply
  Posted by sacha on 17 Apr, 2024 05:54
• 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

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• #10 Reply
  Posted by iMo on 17 Apr, 2024 06:32
• 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.
• #11 Reply
  Posted by xavier60 on 17 Apr, 2024 07:08
• Or preheat something before the DSO switched on.
• #12 Reply
  Posted by MathWizard on 17 Apr, 2024 11:42
• The PCB looks pretty cool, it reminds me how small the circuits I work on have been.
• #13 Reply
  Posted by sacha on 17 Apr, 2024 20:55
• 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.

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• #14 Reply
  Posted by Runco990 on 17 Apr, 2024 21:15
•  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.
• #15 Reply
  Posted by sacha on 17 Apr, 2024 21:31
•  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
• #16 Reply
  Posted by T3sl4co1l on 17 Apr, 2024 22:06
• 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
• #17 Reply
  Posted by sacha on 18 Apr, 2024 21:13
• 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.

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• #18 Reply
  Posted by T3sl4co1l on 19 Apr, 2024 03:01
• 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
• #19 Reply
  Posted by sacha on 20 Apr, 2024 20:07
• 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: Shaca
  while my email address is: conduel@libero.it
  
  
  
  
  
• #20 Reply
  Posted by T3sl4co1l on 20 Apr, 2024 22:23
• 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
• #21 Reply
  Posted by sacha on 21 Apr, 2024 04:20
• 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 :-)
• #22 Reply
  Posted by iMo on 21 Apr, 2024 07:13
• 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 
• #23 Reply
  Posted by fmashockie on 21 Apr, 2024 12:10
• Quote from: sacha on 21 Apr, 2024 04:20

  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 :-)
  

  
  Why 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. 
• #24 Reply
  Posted by T3sl4co1l on 21 Apr, 2024 12:43
• 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