Author Topic: EEVblog #538 - HP35670A DSA Repair - Part 2 (Read 28979 times)

EEVblog · « **on:** October 22, 2013, 08:55:33 pm »

Part 2 of the HP 35670A Dynamic Signal Analyser repair.

vaualbus · « **Reply #1 on:** October 22, 2013, 09:36:05 pm »

could also not the the ADC it's self but some other circuitary.
I'm repearing an TDS540 that just for only a memory chip, failed in acquisition and proc interface.
So sometime just only a litle thingh can create thousend of errors.

ANd the most important thingh If you not connect the intra board coaxial cable of course some of? self tests failed....
(and the source is not connect to the board).......

xenocide702 · « **Reply #2 on:** October 22, 2013, 10:08:38 pm »

At around 20:10 when you were poking around the input jacks, did the LED flash in response to you touching it, or was that just coincidence?

EEVblog · « **Reply #3 on:** October 22, 2013, 10:52:56 pm »

Quote from: vaualbus on October 22, 2013, 09:36:05 pm

ANd the most important thingh If you not connect the intra board coaxial cable of course some of? self tests failed....

No, that's not it.

edwardcurrentclamps · « **Reply #4 on:** October 22, 2013, 11:14:24 pm »

My comment won't help much, but I have to admit that I can't wait for you to fix it. I'm also happy that I actually didn't buy it. Would have gone way beyond my knowledge!!! The 70 pages you refer to in the videos were quite intimidating to me. Being able to see you fixing it though is AMAZING!!!!!!

*Don't stop when you're tired, stop when you're done!*

Thanks

Rasz · « **Reply #5 on:** October 22, 2013, 11:33:31 pm »

maybe swap i2c eprom with a fresh blank one
and try to read the old one in the programmer

is it cpld or an fpga?

edpalmer42 · « **Reply #6 on:** October 23, 2013, 12:15:27 am »

When the original power supply failed, it must have spiked the voltage fairly high to take out the reverse diode and the regulators. If that high voltage passed through the shorted diode, it could have taken out lots of things.

You checked for chips that were getting too warm, but what about chips that weren't getting warm at all? Is the unit's power drain reasonably close to it's spec?

Do those boards use any kind of picofuses (i.e. soldered in fuses)?

Ed

c4757p · « **Reply #7 on:** October 23, 2013, 12:38:55 am »

I've a bad feeling about the I2C failure.... you're seeing activity on the bus, but are there responses, or just the processor calling out to a dead chip? I'd really worry that something which can take out a digital-only chip like the I2C cal ROM can take out a whole shitload of other stuff as well

It seems a shame that such an expensive piece of equipment wasn't better protected against failure. That power supply should be packed with an army of OVP crowbars...

EEVblog · « **Reply #8 on:** October 23, 2013, 02:18:55 am »

Comparison of Vimeo vs Youtube as I saw it.

scopeman · « **Reply #9 on:** October 23, 2013, 02:42:48 am »

Dave,

Are there any separate analog reference IC chips on the board (+ and - ref)?

Maybe something to look at. I would love to come to Sidney and help you fix it but it would be a long swim from Virginia!

Maybe some HP engineers or techs that worked on this thing will pop in to help or maybe just wait for another one with a different problem to show up on ebay.

Sam

EEVblog · « **Reply #10 on:** October 23, 2013, 02:44:21 am »

Quote from: scopeman on October 23, 2013, 02:42:48 am

Maybe some HP engineers or techs that worked on this thing will pop in to help or maybe just wait for another one with a different problem to show up on ebay.

Well, I haven't even started troubleshooting this yet really. I've only gotten as far as the PSU stuff.

AlfBaz · « **Reply #11 on:** October 23, 2013, 03:32:56 am »

I wouldn't give up hope on the asic just yet. Its most likely the troublesome -15V rail is solely for analogue stuff and if the analogue stuff fails to provide cal signals to the asic the unit's best guess is an asic failure

EEVblog · « **Reply #12 on:** October 23, 2013, 04:00:11 am »

Quote from: AlfBaz on October 23, 2013, 03:32:56 am

I wouldn't give up hope on the asic just yet.

I'm not even close to giving up on the ASIC yet. I haven't even looked into it, it's more likely than not, not the ASIC chip itself.

EEVblog · « **Reply #13 on:** October 23, 2013, 04:45:46 am »

Quote from: wilfred on October 23, 2013, 04:12:10 am

The example you gave below Dave isn't really sharp enough for me to easily pick a difference.

Look at the Lemo connector on the right hand side outside the chassis. Huge difference IMO.
And it's cleary visible in real time video. The outline of my head for example is very blocky on the Vimeo one, and smooth on the Youtube one.

bktemp · « **Reply #14 on:** October 23, 2013, 06:35:14 am »

I don't think that the power supply created a huge spike when it died:
As it looks like all voltage rails are generated from the same SMPS and there are no post regulators. Those LM3x7 and LM7xxx regulators have a SOA protection and will not die until the input voltage goes above >35V. This is about double the normal voltage. If the power supply had supplied double the nominal output voltage, some digital circuit on the 5V rail would also be dead. My guess is, the negative rail simply failed to output any voltage. The still working positive supplies would then have pulled the negative rail positive and killed the regulators and the diode. Putting a negative voltage (positive for negative regulators) into the output is something voltage regulators don't like at all and tend to fail quiete easily. This missing voltage could have killed some analog parts too.

HamiltonHipster · « **Reply #15 on:** October 23, 2013, 09:20:51 am »

Good video Dave!

Should have met you at Electronex, seriously kicking myself now

I have a Marshall B150 Guitar-Bass amplifier sitting on my bench at the moment. I turn it on and all it does is make loud scratchy noises. First thing i did was measure the negative voltage regulator, Lm7915, it was passing straight 20 odd volts to all the analog front end op-amps.

Of course, a big clue leading me to the regulator was the green corrosion spewing out the top of its package. Replacing it didn't fix anything, however...

Looking forward to part 3! :B

Fryguy · « **Reply #16 on:** October 23, 2013, 11:01:33 am »

Did the 19+ volts on the negative rail get through to the analog circuits ? That may have killed some of the analog chips - e.g. many op-amps are rated at +/- 15V max for operation and +/- 18V as an absolute maximum afaik .

kizzap · « **Reply #17 on:** October 23, 2013, 11:45:53 am »

Quote from: Fryguy on October 23, 2013, 11:01:33 am

Did the 19+ volts on the negative rail get through to the analog circuits ? That may have killed some of the analog chips - e.g. many op-amps are rated at +/- 15V max for operation and +/- 18V as an absolute maximum afaik .

most op-amps are specced as +/-18 Volts, being 36 Volts between rails, -19 to 15 volts is only 34 volts, so there is a chance that the op-amps are still fine. That said, it would pay to check them all out.

MauriceS · « **Reply #18 on:** October 23, 2013, 02:04:47 pm »

That is assuming the root cause was not massive overvoltage. The current (kinda working) PSU has 19V, but what was the voltage causing the regulators to pop? They are also speced somewhere in the 30v range usually - so that could have been just -30v or more on the negative bus alone.
But...

Then one would kinda expect one or more tantalums to have died a fiery death. But time to check the opamps i guess.

Winston · « **Reply #19 on:** October 23, 2013, 02:32:50 pm »

I would think HP would design a power supply or make sure a subcontractor would provide a power supply that wouldn't damage an entire unit if it failed. I wonder if the original power supply was taken out by a lightning strike.

tocsa120ls · « **Reply #20 on:** October 23, 2013, 03:41:39 pm »

Quote from: Winston on October 23, 2013, 02:32:50 pm

I wonder if the original power supply was taken out by a lightning strike.

A $20k unit plugged into an unprotected socket... seeing that my sub-1k gear is on a UPS, this thought makes me cringe.

Dave, making some progress there! Even less errors than the first time! Can't wait for a little I2C diagnostics

kaushleshchandel · « **Reply #21 on:** October 23, 2013, 04:16:58 pm »

Great video again! This is giving be some confidence to buy "Broken" "As is" "For repair" stuff from ebay.

There's a guy who has Datron 9000. And it's not working. And he is ready to sell it to me for $1000.

If you succeed, I may go for buying it and trying to repair it.

Kirill · « **Reply #22 on:** October 23, 2013, 04:31:37 pm »

Quote from: kaushleshchandel on October 23, 2013, 04:16:58 pm

If you succeed, I may go for buying it and trying to repair it.

Dave's success or failure doesn't mean a thing for other cases. Byuing a "for parts or repair" device may end up just repacing a blown fuse as well as literally rebuilding the device from scratch within an existing case. It always is like a state lottery. The only difference is sometimes you can actually win.

iXod · « **Reply #23 on:** October 23, 2013, 05:50:28 pm »

My intuitive sense is that the high-V failure of the PS killed not only the regs but also some critical logic components, prob. some unobtainium array stuff.

But that isn't to say that I wouldn't enjoy another vid to confirm this.

Keep up the great troubleshooting. It help give courage to others who might not have thought to tackle such a project.

"The outcome is really secondary."

Cheers!

holozip · « **Reply #24 on:** October 23, 2013, 06:02:27 pm »

I'm loving these video's where you get your hands dirty and try and mend stuff - just being able to observe the approach someone takes to troubleshooting is really valuable info; I can't wait to see if you manage to resurrect it.

Good luck!


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Author Topic: EEVblog #538 - HP35670A DSA Repair - Part 2 (Read 28979 times)

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