Test Equipment Anonymous (TEA) : Discussion and Group Therapy Thread

[mnementh]

I hope he won't use it to measure the mains.

Well, I did take the precaution of giving him only a pair of 10X probes with it.

Sorry, I have to be boring and I know I'm teaching you how to suck eggs.

Posting a yootoob vid. Oh, the indignity!

Of course you are!

I don't need Dave to show me how to blow up a scope, gorramm it; I can do that just fine all by myself!

mnem

[tggzzz]

Well, I did take the precaution of giving him only a pair of 10X probes with it.

Sorry, I have to be boring and I know I'm teaching you how to suck eggs.

Posting a yootoob vid. Oh, the indignity!

Of course you are!

I don't need Dave to show me how to blow up a scope, gorramm it; I can do that just fine all by myself!

mnem

We know you know.

Does the inexperienced kid know?

[Zenith]

Obvious when you bear in mind that that the grounding lead on the probe is a direct connection to mains earth, but it could easily be done.

Another thing which has caught a few out is "live chassis" TVs and radios. No mains transformer, just direct to the rectifier for the valve HT and the heaters were in series with a dropper resistor. Some of the 1950s plugs weren't polarised and anyway, a polarised plug could be wired incorrectly, or the connections reversed. You could end up with the chassis at 240V AC. Normally it would be at mains Neutral, which could still be many volts above earth. The sensible way to work with them is through a 1:1 isolating transformer to give the mains supply. Contrary to what a lot believe, most variacs are auto transformers, not isolating transformers.

The last Tek 475 I picked up didn't power up. I checked its fuse, which was blown. I also checked the mains plug. The fuse in that was OK, but the earth lead was deliberately not connected (cut short with no bare wire left). So I wired it properly. I wondered if it had been done so they would have a floating scope - dodgy for a bench scope. It still blows its own fuse after a couple of seconds. I suspect a bad reservoir cap, or bridge rectifier. I suppose it might be one of the marginally voltage rated tants across the supply rails. I haven't looked at it properly. I'm adding a load of caps to the next order for Digikey.

[tggzzz]

Obvious when you bear in mind that that the grounding lead on the probe is a direct connection to mains earth, but it could easily be done

As a kid I thought earth and neutral were at the same potential.

Now I know better, including that I don't understand all the various types of mains electricity supplies.

Another thing which has caught a few out is "live chassis" TVs and radios. No mains transformer, just direct to the rectifier for the valve HT and the heaters were in series with a dropper resistor. Some of the 1950s plugs weren't polarised and anyway, a polarised plug could be wired incorrectly, or the connections reversed. You could end up with the chassis at 240V AC. Normally it would be at mains Neutral, which could still be many volts above earth. The sensible way to work with them is through a 1:1 isolating transformer to give the mains supply. Contrary to what a lot believe, most variacs are auto transformers, not isolating transformers.

The last Tek 475 I picked up didn't power up. I checked its fuse, which was blown. I also checked the mains plug. The fuse in that was OK, but the earth lead was deliberately not connected (cut short with no bare wire left). So I wired it properly. I wondered if it had been done so they would have a floating scope - dodgy for a bench scope. It still blows its own fuse after a couple of seconds. I suspect a bad reservoir cap, or bridge rectifier. I suppose it might be one of the marginally voltage rated tants across the supply rails. I haven't looked at it properly. I'm adding a load of caps to the next order for Digikey.

I doubt a tant would take out a fuse; I expect it would cause the SMPS to shutdown. IIRC there's a specific node in the PSU that indicates whether the LV rails are sufficiently "balanced". Imbalance prevents startup.

Hence I'd start at the big electrolytics near the power cable.

[Zenith]

There's a 50V tant across the 50V line. One of the tants has been replaced with a neat butt soldered in job. I'm inclined to replace all the ones in the PSU, but it's a lot of work

When I've seen tants fail spectacularly, they've gone red hot and smoked. I've seen a few which have exploded. I wouldn't put it past them to fail with a dead short. I suspect it's one of the reservoir caps which has failed S/C or fails S/C after a few seconds. I've had problems with them in the past. It might be a bridge rectifier acting strangely, although they rarely fail.

I hope it's just a PSU problem, rather than something more obscure and harder to fix. The second last 475 had a cap in the PSU which had gone O/C and caused terrible problems with ripple. When that was fixed with a bodge, (two 200V caps in parallel), the scope worked and the supply lines were as they should be.

[tggzzz]

There's a 50V tant across the 50V line. One of the tants has been replaced with a neat butt soldered in job. I'm inclined to replace all the ones in the PSU, but it's a lot of work

Sprague C1428? Spec is indeed 50V on a 50V line. Oops.

When I've seen tants fail spectacularly, they've gone red hot and smoked. I've seen a few which have exploded. I wouldn't put it past them to fail with a dead short. I suspect it's one of the reservoir caps which has failed S/C or fails S/C after a few seconds. I've had problems with them in the past. It might be a bridge rectifier acting strangely, although they rarely fail.

I hope it's just a PSU problem, rather than something more obscure and harder to fix. The second last 475 had a cap in the PSU which had gone O/C and caused terrible problems with ripple. When that was fixed with a bodge, (two 200V caps in parallel), the scope worked and the supply lines were as they should be.

I've seen them take out a series resistor (485, tant bead) and spew acid across tracks (1502, milspec axial tant).

The possibility of spontaneous rapid disassembly is one of the better reasons for wearing any form of glasses.

[Zenith]

I had a couple go up in smoke and destroy a couple of PSU transistors in a CRC Schlumberger sweeper. I replaced them with modern electrolytics. Racal counters are often full of them. They don't fail that often. If there's anything like high frequency, an electrolytic in parallel with a ceramic works. Mass replacement would be a pain and they seldom cause problems. My last experience of them was a couple of weeks back with a Fluke 8800A with PSU problems which seemed to be down to the tants. There were six and I changed the lot, as it was easy - unlike the Racal counters - and the power supply problems disappeared.

On another forum years ago tants were being discussed, and someone said he'd had one explode and bits of it were embedded in the wall. There are similar, rare, stories about big electrolytics in valve gear, which have been known to blow apart violently. In that case I believe you have electrolysis and then a hydrogen-oxygen explosion. Another problem with electrolytics is a failure where the electrolyte leaks out rapidly and destroys circuit tracks and component leads. When that happened to me I was told it was because of a manufacturing fault in the L.C.R brand capacitors.

[bd139]

I had one go short in a Racal 9915. The thing was an LC network on the main analogue ASIC and took out the L bit totally. Smoked it.

[Zenith]

In most cases it's not practical to change all the tants, just the failed ones or those known to cause problems. In particular those Racal counters can be a pig to replace components on. The parts are packed close together, the hole is only slightly larger than the lead and they bent the leads over at right angles. For the most part, the tants sit there working.

[bd139]

You should always snip them flush on the top and remove the leads from the bottom when doing rework. It's never worth fucking the board up.

When I did the mods on the 9915 I had to run it off a 10MHz OCXO I did that which can be seen here:

yHjQlz8.jpg

[Zenith]

I did cut them off flush and removed them from the bottom. It was still a mission. Getting at them to cut them off flush wasn't easy, and I have a pair of nice Lindstrom side cutters.

[25 CPS]

Calling Cubdriver... calling Cubdriver...

Been here all morning; everybody's pretty much gone. Did I walk right past and not recognize you?

mnem

What prizes did you come away with?

A few bits and bobs...

mnem
continued next post...

That's a nice pickup and a very kind thing to give that scope to that kid as a surprise gift. I hope he enjoys it. Do you know if he had anything to use it on, something he could safely probe to get a couple of interesting traces on the display?

[bd139]

I did cut them off flush and removed them from the bottom. It was still a mission. Getting at them to cut them off flush wasn't easy, and I have a pair of nice Lindstrom side cutters.

I don't bother cutting flush on the first hit. Quite easy after that and I have some crappy Xcelite cutters.

[Zenith]

That's a nice pickup and a very kind thing to give that scope to that kid as a surprise gift. I hope he enjoys it. Do you know if he had anything to use it on, something he could safely probe to get a couple of interesting traces on the display?

He could tinker together a relaxation oscillator using TTL or a 555 timer.

[tggzzz]

That's a nice pickup and a very kind thing to give that scope to that kid as a surprise gift. I hope he enjoys it. Do you know if he had anything to use it on, something he could safely probe to get a couple of interesting traces on the display?

He could tinker together a relaxation oscillator using TTL or a 555 timer.

The (modern equivalent of the) ICL8038 0-2MHz function generator has lots of twiddleability and the diode-shaped sine output is entertaining.

Or give him a bipolar TTL divide by 100/1000 circuit, and encourage him to understand which bits of the waveform are and aren't important. Not so effective with CMOS, though.

CMOS would have the advantage that it could be powered from a couple of cells, without any mains PSUs.

[Zenith]

I did cut them off flush and removed them from the bottom. It was still a mission. Getting at them to cut them off flush wasn't easy, and I have a pair of nice Lindstrom side cutters.

I don't bother cutting flush on the first hit. Quite easy after that and I have some crappy Xcelite cutters.

It depends where on the PCB. Some of it's fairly accessible, other parts, such as around the OM335 UHF hybrid, are very cramped.

[Zenith]

The (modern equivalent of the) ICL8038 0-2MHz function generator has lots of twiddleability and the diode-shaped sine output is entertaining.

Or give him a bipolar TTL divide by 100/1000 circuit, and encourage him to understand which bits of the waveform are and aren't important. Not so effective with CMOS, though.

XR2206 was another one. You can find function generators on ebay based on them for about £7. Sometimes they are sold as kits. I recall the sine wave has a pip at the peaks. Also on ebay are 8038 based ones for about the same price. I suspect they are based on Chinese copies of the original chips.

Maxim made their own souped up version of the 8038 which went up to 20MHz. I saw a few designs based on them, but they never pushed them to anything like 20MHz because they reckoned they were twitchy because of parasitics at that frequency. They weren't on the market for long and they were quite dear. Occasionally they turn up on ebay but they are very expensive.

There are loads of things the kid could put together which would be instructive, such as a multivibrator with a couple of transistors and other bits and pieces.

[Zenith]

CMOS would have the advantage that it could be powered from a couple of cells, without any mains PSUs.

CMOS doesn't use much power but can have unpleasant surprises for the unwary. Mucking about with batteries wears thin. He'll be looking for a nice little variable linear PSU next.

[nixiefreqq]

attached is a picture of asta and my ic-V8 2 meter transceiver.

seems my little radio has been in the news lately.

asta has not.

[25 CPS]

Unfortunately, I didn't get any pictures but one of my 34401A's got some running time lately when my friend and I finally had an afternoon to dig into that powered loudspeaker that died. The 7815 in the +15 rail failed so we installed a replacement hoping that was the extent of it but no luck. The replacement was fine until we reconnected everything and attempted to feed test tone into the speaker's input jack. We now think the fault may be on the preamp board. I suggested instead of smoking more 7815 regulators, we use an outboard power supply to power it up and that way we have we have the ability to monitor and limit current and see what's happening. This means either an HP 6623A or 6624A system power supply is going to be pressed into service to make the three voltages the preamp board needs. I don't know when this is going to happen though since both our work schedules are terrible.

I've also had a couple of equipment pickups recently.





I don't have any experience with Hameg gear but I have to admit the scope looks an interesting bit of kit. The built in component tester/curve tracer and the ability to invert either input make this look like it'll be a very capable XY display. The wealth of selections for triggering off video waveforms is interesting too but more academic since I don't do much with video at home other than watch it sometimes.

The two bay mainframe is an interesting pairing of equipment too. I would've expected a low distortion sine generator next to the distortion analyzer instead of a function generator. Maybe there was one and it was stored separately and swapped in when needed, and got separated from the test stand where the scope and mainframe were stacked on top of eachother when they were retired.



This Hewlett Packard 33E was available on Facebook Marketplace and had been price dropped down to $25 so I messaged the seller and arranged to pick it up after work. I'm really surprised nobody jumped on it at that price before I got to it but there wasn't any interest, apparently. The seller and I enjoyed a beautiful evening shooting the breeze outside until the sun started to go and I needed to head home.





From what I've been reading, it looks like the base unit Amber is Canada's answer to the Hewlett Packard 339A. It combines a low distortion signal generator plus distortion analyzer in the same box the way 339A does. The manual mentions the expansion unit on the top as one of the options that was available and states that it's designed to be handy for radio broadcast use but the book doesn't include a full manual for it, unfortunately. And the book it came with is the same revision level (Issue 9, 1988) that's available online. It does mention that the tip/ring/sleeve sockets are for Western Electric WE-310 type plugs and can be damaged by regular 1/4" TRS plugs so it looks like I have some shopping for connectors to do, but I'm eager to play with this one soon.

I'm not sure I'll be getting into any of this stuff much this weekend since I have a friend coming in to visit from out of town. This friend is an aspiring ham radio operator and has an associate's degree in Electrical Engineering but we may or may not do any workshop play with equipment.

[Zenith]

I've also had a couple of equipment pickups recently.





I don't have any experience with Hameg gear but I have to admit the scope looks an interesting bit of kit. The built in component tester/curve tracer and the ability to invert either input make this look like it'll be a very capable XY display. The wealth of selections for triggering off video waveforms is interesting too but more academic since I don't do much with video at home other than watch it sometimes.

I've got a Hameg HM 205-3 20MHz storage scope. It came from a swapmeet a couple of weeks back. It's quite clean and they wanted £5 for it, so I found myself buying it. It works as much as a quick check can show. The shaft of the channel 1 vertical shift is broken off and the knob is missing. I didn't spot that. The missing knob is a pain. I haven't worked out how to use the storage facility, but it appears to only work on three, not particularly useful, timebase ranges. I haven't had the cover off, but I guess it's generally similar to one of their straight 20MHz scopes sold at the same time.

A problem you are very likely to find is the 1000µF 35 Volt reservoir capacitors, which always seem to act up. They are 20mm high which makes tracking down replacements a little harder. You can get away with a 25mm high part, but it's a tight fit. There are smaller capacitors in the power supply, 10µF 40V from memory. These also play up and cause ripple on the supply lines at a few MHz. The PCBs are a lot of trouble to remove and replace, but you can replace the capacitors from the side. The smaller ones can require keyhole soldering and shields put in place to avoid damaging wires with the soldering iron. You can also cut apart the old cap with side cutters leaving the leads and solder the new part to the old leads. Messy, but it avoids a lot of work. Apart from that, those scopes suffer from dirty contacts and dry joints. The multi-position lever switches can be stiff but the plastic lever arrangement (which works a slide switch) can be lubricated from the front with PTFE dry lubricant, without removing the front panel. They get so stiff there seems a good chance of breaking off the levers when using them. Hameg manuals for the scopes are a bit superficial, and you may find that it doesn't exactly cover the version you have, and it doesn't have a set up procedure. Some language versions cover details missed out in the English version.

The TV triggering was from the days of analogue TV and is unlikely to be much use now, unless you are into vintage TV. Some people rave over the component tester and Hameg made a big deal of it. I've never found it very useful.

Generally, they are pretty good basic scopes.

The two bay mainframe is an interesting pairing of equipment too. I would've expected a low distortion sine generator next to the distortion analyzer instead of a function generator. Maybe there was one and it was stored separately and swapped in when needed, and got separated from the test stand where the scope and mainframe were stacked on top of eachother when they were retired.

There were whole range of instruments which would fit into the Hameg mainframes.

https://www.sm5cbw.se/hameg/hm80/index.htm

I almost never see them at swapmeets but they turn up all the time on ebay, especially with PSUs and function generators. They sell for far too much in my view.

I have a Hameg HM 8028 spectrum analyser in a home brew case. It works and has the strange BNC cable. I'm sure it was based on a CATV tuner. It is not a sophisticated instrument. I'd like to stumble across a mainframe with the HM8038 tracking generator for not too much.

This Hewlett Packard 33E was available on Facebook Marketplace and had been price dropped down to $25 so I messaged the seller and arranged to pick it up after work. I'm really surprised nobody jumped on it at that price before I got to it but there wasn't any interest, apparently. The seller and I enjoyed a beautiful evening shooting the breeze outside until the sun started to go and I needed to head home.





From what I've been reading, it looks like the base unit Amber is Canada's answer to the Hewlett Packard 339A. It combines a low distortion signal generator plus distortion analyzer in the same box the way 339A does. The manual mentions the expansion unit on the top as one of the options that was available and states that it's designed to be handy for radio broadcast use but the book doesn't include a full manual for it, unfortunately. And the book it came with is the same revision level (Issue 9, 1988) that's available online. It does mention that the tip/ring/sleeve sockets are for Western Electric WE-310 type plugs and can be damaged by regular 1/4" TRS plugs so it looks like I have some shopping for connectors to do, but I'm eager to play with this one soon.

I'm not sure I'll be getting into any of this stuff much this weekend since I have a friend coming in to visit from out of town. This friend is an aspiring ham radio operator and has an associate's degree in Electrical Engineering but we may or may not do any workshop play with equipment.

The Amber 3501 looks impressive. There were a few lesser known makers who produced very good low distortion sine wave generators and distortion meters. With a lot of this stuff the units aren't common and the manuals, even circuit diagrams, are unobtainable, even if you pay for them.

[AVGresponding]

In response to a question from someone on EEVBlog recently, I had cause to poke at my Metrix MX57-EX. It's a nice, well featured DMM, with a quirky design (I suspect "because French"), however the question, about the RS232 mode, had me discovering it's even more quirky than I first thought.

a_front.jpg

As you may or may not know, the "stand" on the back, isn't; it's actually the tool to open the front cover, where the battery, fuses, and, eventually, the IR comms is located.

not_a_stand.jpg

prybar.jpg

There's several layers of Ex protection to get through before you get to the battery, fuses, and IR. After you get the front cover off, there's a synthetic rubber seal, then a clear polycarbonate cover, held in place with a cap-head allen bolt.

prophylactic.jpg

to_cap_it_off.jpg

Finally you get to the gubbins. One does wonder just how you can possibly use the RS232 for anything other than downloading saved data, since you practically have to disassemble the meter to get to it.

hello_down_there.jpg

There's a nice label on the back that mentions how to access RS232 mode, something strangely absent from the manual, or at least the one I have found.

neat_cheat_sheet.jpg

The question from the EEVBlog member related to the RS232, which I was hitherto ignorant to the existence of. They are getting a BAT warning and loss of contrast in the LCD when activating it. I did a quick experiment with mine this morning to measure current draw and the low battery threshold and found it to be between roughly 2 and 6mA, depending on range/mode, and the same whether RS232 is active or not, and with a BAT warning when the terminal voltage falls below 7.95V, so it seems there may be a fault with their meter; corrosion, dry joint, partial short on a component in the RS232 circuit, or something along those lines.

[25 CPS]

In response to a question from someone on EEVBlog recently, I had cause to poke at my Metrix MX57-EX. It's a nice, well featured DMM, with a quirky design (I suspect "because French"), however the question, about the RS232 mode, had me discovering it's even more quirky than I first thought.
a_front.jpg

That's interesting about the RS-232 on that meter.

As for EEVBlog, do you and the others here frequent it still? I haven't looked at it since the big blowup other than spot reading the occasional thread that comes up in Google results for equipment I've looked up.

[tggzzz]

As for EEVBlog, do you and the others here frequent it still? I haven't looked at it since the big blowup other than spot reading the occasional thread that comes up in Google results for equipment I've looked up.

Yes, and participate. No reason not to, since there are still some interesting conversations and the prat whose catch phrase is "would you agree that..." has been banned again.

Unfortunately he has just popped on TekScopes asking an off topic question and still not being able/willing to use gurgle. Makes me want to post the traditional usenet question when somebody asks a question they could easily answer themself, i.e. "What time is it?", But there's no way that poster would take a hint, or even a LART.

Oh well.

[MED6753]

As for EEVBlog, do you and the others here frequent it still? I haven't looked at it since the big blowup other than spot reading the occasional thread that comes up in Google results for equipment I've looked up.

Not everyday like I used to but I do browse it once in a while. And I do have some threads that are tagged, such as the 2465B Teardown, that I receive email notifications.

As far as the TE Anonymous thread if I have an interesting project I'll post it but don't generally engage in conversation unless someone has a question that I can answer.