No.141 - Matrix MCR-5200 LCR Meter Repair - Follow-Up
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- เผยแพร่เมื่อ 8 ก.พ. 2025
- A follow-up to my Matrix MCR-5200 repair, in this video I test out the crystal on breadboard and suggest how it generated a USB Flash Drive symptom.
Part 1 video = • No.139 - Matrix MCR-52...
Part 2 video = • No.140 - Matrix MCR-52...
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Very good of you to follow up and test that crystal. That really puts the last nail in that one.
I think the manufactures should acknowledge the work you've done on the meter. Thanks for the follow up Ian.
Excellent demo, Ian. You was right when you told it's extremely rare that a xtal fail. Several years ago, I had the same problem which drove me crazy. Finally, it was one xtal...maybe internally broken. Was a very difficult fault, because the machine was a Sony PCM3348 digital audio 48 track recorder (in my own studio). Thanks again for all your efforts and excellent explanations and clarifications.
I was hoping you were gonna do this. Thanx.👍
Thanks for the follow up. I don't think that I would have ever guessed that it was the crystal. I can just about get my head around the crystal causing a stall when the USB stick was plugged in. Possibly the software selects the internal on chip oscillator at the start but switches to the crystal oscillator when it detects the USB stick so that the clock is accurate enough. If the clock switch fails it could the stall. Though I can't explain the the random lock ups.
USB requires a clock tolerance of 0.5%, outside of that it won't be reliable.
Very nice to see the actual fault condition. Thank you Ian!
Nice little test rig matey. The meter repair videos have been fabulous. cheers.
The USB interface is implemented as part of the microprocessor. The clock speed for basic USB functionality is 12MHz. I'd bet that if you measured the frequency of the bad crystal, it would also be out of spec. The USB device has it's own crystal of course and if they're too far out of agreement, the protocol can't sync. It's a shame that this locks up the CPU, but this is a story I won't forget for the future. Very subtle but specific symptoms.
Appreciate the follow up, makes me wonder how many things I've written off due to bad xtals. I kinda thought they either work or they don't.
A faulty cristal ... I would not have put a penny on this one. As always it's good to learn something. Awesome vid ! Cheers from Belgium Iam
I have been keeping a stock of 74AC14s. They are fast, work from 2-6V, and can source or sink 20mA so they can directly drive a LED with the appropriate series resistor.
I was thinking, doesnt everyone have these around?
USB needs a internal clock in the processor, so it probably adds a load to the internal PLL's & deviders, The logic level's aren't even reached. Feels good you persisted on the meter's fault finding.
That was a difficult one! But you nailed it 👍
The 74VHCU04 unbuffered inverter is essentially providing a “raw” N/P channel totem pole directly to the I/O leads. Thus this single stage inverter has lower gain and is more readily biased to operate in its analog region to produce more perfect sine waves through the crystal. At higher frequencies one U04 buffer stage may be sufficient, but at lower frequencies more than one series buffer stage may be necessary to attain the output buffer gain comparable to a standard logic gate.
A Schmidt trigger is the worst choice for a resonator based oscillator and will needlessly induce jitter. A properly driven resonator will produce beautiful sine waves that swoop through the zero crossing noise free; it just needs amplification to extreme clipping.
good follow thru thx
We all know this is "FM". Thanks Ian!
I suspect heat damage to the xtal. Maybe the person that did the through hole assembly, held the iron on in too long. Great video series, as always.
Weird fault mode for sure, not would I have guessed at all.
It would be interesting to see a VNA scan of that crystal to get more info on what is actually wrong with it.
Hi. A VNA sweep should be very interesting but from scope results you can guess that xtal insertion losses are incredibily high causing a low amplitude oscillation. Regards from Italy.
I found this repair thread because I was looking for information on this particular LSR meter. I'm in the market for a meter and wanted to know how you're liking this meter and if you would recommend it? Anything you don't like about it? I loved the videos and you have earned my sub. Thanks!
I like it!…..haven’t found any smoking’ gun that renders any huge problems. It’s my go to LCR meter on the workbench.
@@IanScottJohnston Great! Just what I needed to hear... now how to hide the purchase from the wife???🤔😅
Very interesting follow up, would be possible to bisect the crystal open and check if it is a mechanical failure or it's some sort of material deterioration or maybe oxidation? Thanks again for the great content :) .
What a weird fault. It would be interesting to put the crystal in a network analyzer. I guess you’ll see a weak resonance. Then open it up under a microscope and see if it has a crack or a delaminated connection. I volunteer for either…
Might try and measure its ESR compared to a good one also.
That it crashed looks like the internal clock buffering was barely able to make the processor work, and when you plug in the USB device a transmission gate is turned on, that allows the clock to be applied to a part of the processor associated with USB, that till then had been basically powered onn and disconnected from the internal clock and data and address buses, waiting for the interrupt that comes when the USB device is inserted, and applies a sink or source to the data lines, triggering an internal flag that the processor uses to enable the USB system, and load the USB handling code. The extra load on the clock probably is what caused parts of the clock system to not trigger, you probably had this before where the threshold would dip after the chip got warm, and then it would fail to clock parts of the processor, leading to the lock up. Had that years ago with a clock oscillator, turned the crystal around and it worked again. You might want to try that as well and see if the amplitude changes.
Your knowledge never fails to amaze me :D
I wonder if you see a difference in the ESR between the faulty and the good crystals.
Not the glue. Thanks Ian.
that's a new one for me
i wonder if it measures out of spec in any other way?
Maybe too low an amplitude for the USB hardware to work; it usually uses a PLL to multiply the 12MHz to 48MHz and that may have had problems with the weak clock
Is the faulty crystal running at the correct frequency? Just wondered if it was off far enough to cause unexpected/unhandled USB timing errors.
It's weird that the data lines to the USB were toggling. So it's not like the crystal just failed when the USB got plugged in. Maybe the USB circuitry caused the crystal to be switched in somehow that then made it where the CPU could not longer get a PLL, or it was trying to talk to the USB and fell into a software bug, because who'd expect to have the crystal suddenly no longer have enough oomph to power the chip plus the USB circuitry. This might make sense given when you unplug it, the software stays broken and doesn't 'heal' itself. Though how that ties into the situation where the CPU just randomly quits updating the screen without USB intervention is a puzzler.
Could you measure the esr of that crystal and a good one? That would be interesting
It would not surprise me if the crystal may be overdriven in the original circuit potentially damaging the crystal over time. The crystal manufacturers do specify a maximum drive level in uW/mW, but that’s rarely considered and connected directly to the IC without a series drive resistor. Physically smaller the crystal are more likely to be overdriven.
Possibly, just a bit surprising that this is a brand new LCR meter with this fault out of the box. Could also be cheap xtals and maybe damaged via the ultrasonic cleaning.
Its a large HC49 crystal, not going to be an issue.
@@jaro6985 Actually, it’s a truncated one that withstands less power. Check your data sheets.
@@ChrisSmith-tc4df I don't see any spec for LPC2478 for drive strength though, maybe you'd have to measure it.
Could this have been tested in circuit?
is the frequency of the bad crystal spot on? I had a repair instance where the frequency was off on a crystal. the unit would work fine, but the associated remote control wouldn't work as the timing was off just enough to cause an issue.
11.999610 MHz on the Racal-Dana 1991
When you think that the frequency is maintained by the mechanical properties of the crystal its a wounder they work at all. Was they crystal still on the correct frequency, as the meter would work at any old frequency. But I expected that the timings for the usb bus are quite tight and could fall foul of them locking up on coms retries
The only way you would know that the frequency was out was by measuring a known capacitor value. As it would still measure a value but it would be out of specification. Crystal's in old radios were known for either getting lazy or intermittent.
What would happen if you amplify the output from the second stage with transistors? Will that make the output strong again?
Yes, you could very easily add a Schmitt Trigger (40106) on the end there to get it back to full 5v operation. Despite being weak the freq. appears spot on.
..Any date codes anywhere?.. I.E. Covid parts shortage allowing out of spec parts to escape the dumpster?
Ahhh. I see the date on the start up screen indicates software version 1.8.1. #2017.8....so that sets likely max age...
...Also serial no is 662024 - 06052 (6'28" in part 1 video) which seems to indicate 6th June 2024. This sets likely min age....
...Any dates on components?
EDIT ... I see early 2023 date codes at 17'14" in part1.... Guess that puts component manufacture around the middle of the Covid parts supply chaos.
The original Ram IC is 2315, so 15th week 2023.
wow, that could have been a needle in a haystack.
Yeah, I think it was ticking strong enough for basic operation anymore and it pooped its pants.
great to know the crystal was definately at fault 🙂
This Cristal test circuit schematics give me please
Bet that crystal has a high ESR, that's why it oscillates so weak 😋
Probably a different circuit which loads it less might improve the output.
it's ALWAYS a crystal 🙄. New shirt coming up
Might be the start of something!
That is a weird one, in my 50 years of electronics I have not seen that one. A completly failed xtal... sure but not this
Measures 11.999610 MHz on the Racal-Dana 1991, so I suspect the ESR of the Xtal has gone through the roof.