All the goodies you have , and lacking the " good set of cables ;) Thanks again John

@Thesignalpath

8 жыл бұрын

+KD0CAC :( I know. I will get some.

@BruceNitroxpro

5 жыл бұрын

@@Thesignalpath, Did you ever get those good cables and is there another video to make this a series? You are a lucky fellow to have such fine tools. If you do, would you please update this Show More writeup to include a link to the new video? Thank you so much.

I like how the instrument yielded before your skills and started to work, rather than getting torn to bits :) Thanks man!

Not boring at all! I've repaired a few things by employing the very special technique you showcased in this video :) Right after cycling the power! Looking forward to the other repairs.

Thanks for another great video! Not boring at all; I always enjoy simply lifting a IC from its socket and pushing it back in for a complete fix (simpleton me!). I vote for an upgrade video too!

Great video, as usual. Don’t forget to put the shorting bars between Output and Sense terminals.

Great video and don't break for the sake of repair. I saw that their might be a dicky solder joint on the bent lead of a resistor. It's by the orange cap @ time 8:58 can't see the part number. You might want to go through it and check for cold solder joints. Looking at it zoomed in it looks like R222 is a cold joint. Look forward to the next video, Cheers.

LOL! It's only us electronic nerds who get disappointed if something we have bought is working:-) Thanks for an interesting video:-)

Interesting unit. Nice to see you posting more. Love your videos. Thanks.

Thanks Shahriar! I'm a novice to electronics/circuits and I enjoy your channel.

I would find it very interesting if you were able to take an old ebay instrument and reverse engineer to upgrade/hack it to use modern components and do a characterization on the difference. Any, improvements, worth upgrading, difficulty, costs, fun challenge? Anyhow, I love watching your troubleshoot and repair videos, thanks! Cool cat too. :)

man i love your videos,its 4am and i havnt slept yet but i cant stop watching :)

@Thesignalpath

8 жыл бұрын

+massivewangman Thank you.

I love this style of buttons, I've got Datron rack-mounting multimeter with very similarly looking ones, it seems they're the Metrologists Choice (TM) ;)

3 minutes in and you already fixed? that must be a new record!

The cat was like "Fuck this unit, it doesn't even have current sense... I'm out of here!!!"...... By the way, you have enough equipment :) You'll run out of space if you keep acquiring. Not to mention that it will be PAIN IN THE ASS to move somewhere else with all those equipment you got... NIGHTMARE!

@thekaduu

8 жыл бұрын

+thekaduu Awesome video, nonetheless.

What a nice gear! I think we fight for that on the Ebay:)

I would put dexoit on the switches and board connector pins. I use a little squeeze bottle applicator as the spray can goes everywhere.

Man I wish I had your lab equipment.

Excellent tour , also is it easy enough to repair the HPIB on one of these units , and do you need it to be operational in order to use the unit itself ? Thanks please let me know..

happy new year to you and "pooch"

@Thesignalpath

8 жыл бұрын

+Amy Marie Thank you, and Pooch says meow!

You mention possibly upgrading the reference. Maybe try a cheap GPS unit with an Arduino, or some other MCU. I like PICs. You can source Atomic Clock accuracy, for about a $30 budget. Don't forget to purchase the amplified type antenna.

👍👍

Perhaps the next video should be on the characterisation of a standard cat ;)

What a great company name

@Arek_R.

8 жыл бұрын

+tHaH4x0r Valllahahlahahalahahllah

Would foamed polyethylene make for good low absorption cables? Something like LMR-195 (UF variant if you want to bend easily 8) ), either with adapters, or broken out to banana plugs? Maybe an additional shield to stop stray voltages?

Excellent job. By the way, can you give me some advice to fix the problem from Valhalla 4600? The problem is that the LED screen can only display "+1" when the power button is turned on.

Excellent Video series! Retired Engineer here in SW Florida and have greatly enjoyed your videos. I too buy older instruments from eBay to flesh out my work bench and some need repair. Thanks... Lloyd - WA9NLA

Don't replace the reference, original one in your standard is aged and old. So it's likely to be much more stable than fresh LM399. Only suitable upgrade would be LTZ1000-module, but that would set you back ~300$ or more due to resistor requirements. Nice box btw. If you have any data or schematics, please share. As Valhalla stuff known for obscure service manuals and lack of many details of their units. And no, its not boring. You actually rushed it, as when doing such a calibrations, correct tongue angle and patience adjusting knobs is a must. Life ain't quick at ppm-precision levels! P.S. Cats vid approved.

"Lab Cat"!

At 4:30 you said MC68000 (64-pin DIP). You probably meant to say MC6800 (40-pin DIP).

Nice instrument!! Those series caps look like a modern-ish repair. I wonder if the noisy looking output at the LSB might be due to more failed caps. I'd have expected a much more stable output. Did you put it on the scope? Reverse engineering the current output would make a great series. Always love the repair videos, even the easy ones. Thanks!

@Thesignalpath

8 жыл бұрын

+Keenan Tims I will check the caps. I also wondered about the noise.

@lowcurrent

8 жыл бұрын

+The Signal Path Blog The LM399 has a peak-to-peak noise of about 1ppm

@CKOD

8 жыл бұрын

+The Signal Path Blog Think some of the caps might have went leaky (electrically) making the output charge slower, causing the nuisance tripping you were experiencing?

@gilgameshismist

8 жыл бұрын

+The Signal Path Blog Whoohoo, another detective story! :D

@absurdengineering

Жыл бұрын

Interestingly enough, the clicking happens when the DC link voltage is too high relative to requirements of the output stage. The DC link is fed from a transformer whose primary is phase-controlled by a pre-regulator. The DC link is kept about 200V above the output voltage. Whenever the output is turned off, or the output voltage is lowered by large steps - especially at the 1200V range - the relay kicks in whenever the DC link is say 250-300V higher than the output voltage. The relay bypasses a couple of bleed capacitors to speed up DC link discharge. When that relay is active for too long, the CPU turns off the output. The relay itself is passively controlled but IIRC monitored by the CPU. Overall, I find some design decisions worthy of improvement. The ppms in those precision resistors demand better treatment! :)

Please review the cat.

Great video! Question to you though, isn't the Keithley max voltage input only 350V? I am confused as to why would you measure 1000V on this meter as it wouldn't be accurate? Anyway, keep them coming!! Also in my opinion the cable used should be shorter to avoid any voltage drop at lower voltage...

@Thesignalpath

8 жыл бұрын

+Kris TheTrader The Keithley can measure to 1000V. Why do you think it is limited?

@kristhetrader5029

8 жыл бұрын

+The Signal Path Blog OK you are absolutely right! Sorry, Thought max input voltage was 700V, but that's only for AC! Thanks for clarifying...

@ciprianwinerElectronicManiac

8 жыл бұрын

+Kris TheTrader What voltage drop? There is basically bugger all current flowing trough them so there should be next to zero voltage drop.

@kristhetrader5029

8 жыл бұрын

+ciprianwiner You are right, the Keithley DM7510 has got 10M input impedance in DC1000V range, at 1000V is only 0.1mA, so voltage drop is negligible if you use a decent cable, even if it's 3 feet long like in this case. Thanks..

@PyroShim

8 жыл бұрын

+The Signal Path Blog It says 350V peak between the sense terminals of the meter.

I think kitty wants a look too

Look at C211 closer at 09:08: That one and the smaller ones next to it do not look too healthy tbh. The gray sleeves should look like the ones on the right 47µF/450V. It also looks like the rubber on the plus pole of C211 is about to push outwards. They definetly look iffy.

Will you actually use this instrument in practice? What I mean is that, if you calibrate it with the Keithley, doesn't that make the Keithley the 'single point of truth' standard in your lab?

@Thesignalpath

8 жыл бұрын

+jjensen2492 The voltage standard can now be used as a transfer calibrated instrument. I don't know what you mean by "Whats the point buying a voltage standard when having a meter capable of doing the work, use it as a standard." How can I use my multimeter to for example test another multimeter?

@Thesignalpath

8 жыл бұрын

+jjensen2492 That would take a very long time! There is a reason why these instruments are made.

You mentioned this unit uses PWM as DAC. Does it use one single PWM or 2 or 3 ? What are the frequency (ies) it uses? I was making the math, and if it is a single PWM, the freq would need to be pretty hi (120MHz) to have decent performance. My guess is that is has at least 2 PWM, at around 12bit each, where filtered output of one is "divided"" by 4000 and then add to first.

@InssiAjaton

6 жыл бұрын

Ivan Kocher - As far as I recall, the PWM does only the last 2 or 3 digits. The other ones are done by relay switching. A summing amplifier combines them into the final output

@absurdengineering

Жыл бұрын

There are two PWMs, at a ratio of about 4 orders of magnitude to each other in terms of step size. The PWM DAC generates between 0V and 7V. The relays then configure the feedback divider network for the output amplifier. These units can be reworked into quite a bit better specs. The key parts are precision resistors and the relays. BTW, the relays can still be bought new from DigiKey! The series capacitors after the HV rectifier are not the best idea, since their balancing resistors dissipate quite a bit when at 1000V. I’ve modified my unit by replacing those series caps with 16x0.56u in parallel, rated 2kV, and got rid of the balancing resistors, but had to lower the bleed resistors used to discharge those capacitors. The relay clicking after going from higher to lower voltages is the discharge of the capacitors. It’s not super intelligent but does the job. The unit doesn’t have much in the way of self diagnostics, so e.g. most problems in the HV ranges just result in that one non-latching relay clicking away. The common failure modes of this unit are the shorted failure of the pre-regulator, causing overheating of the mosfet balancing resistor string. The 450V capacitor string balancing resistors get over their power ratings as well at full voltage - there’s about 1400V across them when output is at 1200V. When the pre-regulator fails there can be easily 1500V on the smoothing cap string. Several things can and IMHO should be improved to use this unit for long-term: lowering internal dissipation, a better ground plane, more logical physical arrangement of resistors in the feedback string and in the PWM filter, improvements in filter to lower the noise and improve settling time, and a better MCU + WizNet module for Ethernet. I’m in the process of doing all that. Will share results in a couple months when everything is put back together. With an additional null-meter ADC and a different feedback resistor string, there would only need to be two ultra-stable precision resistors whose ratio would then be used to calibrate all the other resistors like Fluke calibrators do it. I’m also investigating that. Overall, the architecture of this unit is very DIY friendly, and begs for improvements. This beautiful beast can do much better. Overall, with lower dissipation with modern components, it could all fit into a much smaller enclosure without any thermal issues and with no fan still. It’s also easy to adapt as an ad-hoc Kelvin-Varley divider by feeding the reference voltage externally. The firmware needs mods to support it, but there isn’t much of it.

"I'm a genius" this always leads to it not working again shortly after. lol

Either Genius, or the device got scared being about poked inside!

HOW many amps at 1200

آقا تعمیرات تو دنیای شما خیلی ساده انجام میشه من خیلی بدشانسم نمیدونم چرا نون تو خون میزنم تا یه چیزی تعمیر شه

long tracks like horse racing

First! woohoo.