Test Equipment Anonymous (TEA) group therapy thread

[Vince]

For all the Metrix crazies: have a few GX5000's left. If you're interested, PM me.

No you don't  ! I don't see them in your ebay shop !! 

... that means they are not ready for sale... that means they are broken ! 

Mine is too but there is no service manual for it anywhere  ! Contacted Metrix directly and they said "yeah we remember that one, but have no info on it as we outsourced its R&D, we didn't design it ourselves ". Bummer 

Actually like new, in a carry bag. With manual (user, not service). But there are quite of a few of those on eBay, I'd rather wait a bit 

Oh since you have several and they work fine... maybe you could help me if you have 5 minutes.

Here is a video showing the problem with mine.  I set the instrument to outùput a repetitve signal, so it acts as a square wave generator. I set it to 10MHz (100ns period), with 50% duty cycle.
Problem is that the frequency of the output signal appears to be very unstable. In the video I measure the frequency using two different counters, and they agree with one another : the frequency is very unstable and jumps all over the place, by tens of Hertz, even a few hundreds of Herts at times.  Could you do the same experiment and tell me if the output(s) on yours  is stable at 10MHz ?

I assume there must be a programmable PLL in these that fails to lock ?!...... 
Without a service manual, will be fun trying to diagnose it 

[Vince]

Spec a MX 52 just popped up today here ! 

https://www.leboncoin.fr/bricolage/2102250385.htm

90 Euros, seller might an offer but still a bit pricey.... plus if you zoom on the LCD window, looks like there is a big scratch in the top left corner, and not too sure either about the condition aof the 4 window corners...  so, no, that won't be the one for me....

[Ice-Tea]

Like so?

[factory]

Spotted a couple of old Racal frequency counters on eBay.

There is this 520 - https://www.ebay.co.uk/itm/384663905868   - This is the version with individual lamps in a vertical column.    Starting bid is £20.

Racal 836   6 digit ***** ****  30MHz  -- https://www.ebay.co.uk/itm/324991526216  BIN at £150.  No thank you.

I know nothing about the sellers or the

I won't be bidding or making offers on either one.   

The former is the first frequency counter I ever used.
From memory, it topped out around 10MHz.

The SA520 is only good for 300kHz and the SA535 1.2MHz. 

I picked up a 520 for about £15 a few years ago, not found a 535 yet (but missed plenty on evilbay), have a 540 too with problems, all of these are riddled with very unreliable Ge transistors.
Still looking for the 540 & 505A manual, preferably from a seller that isn't an Indian scammer, been there, been done. 

And the 836 is too much money IMO too. Apart from a couple of tant beads  feeding the probe socket & the 60mA HT fuse wire rotting away, it's been very reliable. Counter logic is 74 series with 10 driver transistors for the tubes, pdf circuit diagrams can be obtained on the UKVRR forum. I should point out that the seller has no connection with a UKVRR forum member of the same name.

David

[Vince]

Like so?

Wow thanks a lot for the video !! 

So yours exhibits the very same problem, except 10 times worse : frequency is jumping around by the kHz rather than tens or hundreds on mine.

So... maybe that means it's normal and my unit works just fine ?!  Being a pulse generator, it's not meant / expected to have any kind of stability in frequency when used in continuous mode ?
Must be that... OK cool, so if it's normal, that's one less TE that needs fixing, great ! 

Thanks for your help ! 

[Atomillo]

Final exams end in two days. The subject I've already passed with midterms and lab grades, so today I took it easy.

Was doing a quick scroll through eBay when I found out a Keithley 181 Nanovoltmeter with input cable that had caught my eye before new years but had dismissed due to high price as well as being busy studying

A look to my healthy finances due to Christmas and my unhealthy lack of nanovoltmeters (as well as my growing interest in low level voltage measurements) convinced to pull the trigger.

Tomorrow I will be printing the service manuals, schematic, etc... as well as more material regarding nanovolt measurents. Suddenly that exam doesn't seem quite that important...

[factory]

I've also bought some Soviet 74188 clones to try & fix the second 5340A control board (according to the manual there are four in total, two of which are on the control board), still waiting for them to arrive.
Earlier this week I got the rare opportunity to work in the lab for a day, while I was there I had a read of the manual for the Expro 60/80 programmer & it will read/write the 74188, but knowing my luck the ancient PC that it is part of, will be dead/emit smoke/or HDD corrupted by now. 

David

I'm going to use National Semi DM8577s.  I found a few NOS parts.    They are read compatible with the '188 but do not program the same way. 

I have no idea about programming the Soviet clones.  Presumably they program like the TI 74188??

If my device works (that is a bigif)  I will have a couple of partly populated PCBs  available at cost.  (about $20 + shipping)    There are still some DM8577s on eBay. . .

While I have a TI 74 series databook including the 74188, I can't find much for the K155RE3, in this blog archive someone did get one programmed with 74188 selected in the programmer they used, if you keep reading they also mention they often needed to program more than one of the originals back when they were common.
https://www.mail-archive.com/search?l=cctalk@classiccmp.org&q=subject:%22Programming+Bipolar+PROMs%22&o=newest&f=1

As for the DM8577, I'm avoiding ancient Nat Semi/TI parts, the Soviet clones should be a bit newer. Strange how the Nat Semi parts on ePay-UK are marked as both DM8577N & DM74188AN if they can't be programmed the same way. 

David

[Kosmic]

Has anyone ever tried this style of test clips (accidentally spotted on eBay while looking for something else)? Any good?

Yep got 2 sets of those. Quality is ok and they are working well. Not like some other micrograbber I ordered.

Couple of pictures of the one I got.

Best one on the left, worst one on the right.






They all have a male connector compatible with a standard female header.

[Ice-Tea]

Like so?

Wow thanks a lot for the video !! 

So yours exhibits the very same problem, except 10 times worse : frequency is jumping around by the kHz rather than tens or hundreds on mine.

So... maybe that means it's normal and my unit works just fine ?!  Being a pulse generator, it's not meant / expected to have any kind of stability in frequency when used in continuous mode ?
Must be that... OK cool, so if it's normal, that's one less TE that needs fixing, great ! 

Thanks for your help ! 

Well sure seems like that

[Vince]

Thanks for that again ! 

So even an HP does it... "problem" solved then... there is no problem at all, looks like I was naïve  / clueless and it was only my expectations for the instrument that were set too high !

That's cool then because since there is no service manual for this thing, I didn't hold much chance of success on that one !

[Robert763]

Try setting the width a bit lower. You have not allowed anytime for the transitions and it may be confusing the unit.

[factory]

....snip....

I would have made a close-up picture of the screen to prove I am not lying about frequency and signal amplitude. Sadly just before doing that, I tried fiddling with the adapter to see if I could shove it in a bit more to make sure the trace does not go unstable right as I am trying to photograph it and... as I was grabbing the adapter, I got ZAPPED !!! Yes this generator tried to kill me !!! 
So no close-up picture for you sorry... instead I immediately pulled the plug !

Checked with the DMM for resistance between the two line terminals in the power socket, and chassis/enclosure.... no short, got 5Mohms and slowly climbing.

So I am not touching this generator for now ! 

Think I will retrofit an IEC power socket hidden at the back (to not ruin the looks of the face plate), and get myself a life saving earth connection....

Will look at the schematic of the generator to see if there is maybe some failing cap that could explain the mishap...

Catching up still......

Looking at your previous posts on the Metrix 920, it seems to have two capacitors to ground (aka the case) and looking at the back of the mains inlet there are two dubious looking capacitors on the sides of the inductors, I would be amazed if these weren't wax paper deathtraps/smoke bombs.
And the DMM will be of no use here, you need a proper DC insulation tester at 250V or 500V to check them, but probably best to just change them for some class Y rated capacitors anyway.





David

[Andrew_Debbie]

As for the DM8577, I'm avoiding ancient Nat Semi/TI parts, the Soviet clones should be a bit newer. Strange how the Nat Semi parts on ePay-UK are marked as both DM8577N & DM74188AN if they can't be programmed the same way. 

David

I was nearly caught out by that.   The ones I have are factory marked DM74188AN   DM8577N.   I was initially using the TI Databook.  I have one around here somewhere and it was easier to find on the web.   Mostly because I was curious, I did an extensive search and found the DM8577N in a National book.   Much to my horror, they are "Pin Compatible"  but very different internally.

[Vince]

....snip....

I would have made a close-up picture of the screen to prove I am not lying about frequency and signal amplitude. Sadly just before doing that, I tried fiddling with the adapter to see if I could shove it in a bit more to make sure the trace does not go unstable right as I am trying to photograph it and... as I was grabbing the adapter, I got ZAPPED !!! Yes this generator tried to kill me !!! 
So no close-up picture for you sorry... instead I immediately pulled the plug !

Checked with the DMM for resistance between the two line terminals in the power socket, and chassis/enclosure.... no short, got 5Mohms and slowly climbing.

So I am not touching this generator for now ! 

Think I will retrofit an IEC power socket hidden at the back (to not ruin the looks of the face plate), and get myself a life saving earth connection....

Will look at the schematic of the generator to see if there is maybe some failing cap that could explain the mishap...

Catching up still......

Looking at your previous posts on the Metrix 920, it seems to have two capacitors to ground (aka the case) and looking at the back of the mains inlet there are two dubious looking capacitors on the sides of the inductors, I would be amazed if these weren't wax paper deathtraps/smoke bombs.
And the DMM will be of no use here, you need a proper DC insulation tester at 250V or 500V to check them, but probably best to just change them for some class Y rated capacitors anyway.





David

Thanks for doing my work Dave ! 

Just looked C11 and C12 in the parts list... they are indeed paper caps ! They are 10nF 10%. 

Will replace them of course !

Will keep the old caps so I can test them later for fun and educational purposes...

Hell I could cobble a crude tester together easily I guess !

After all these caps are simply subject to mains AC ! So all I need to test them in a relevant manner, is to connect the to mains and measure the leakage current, eh ?

Just need to put a series resistor to limit the current to a safe value, I don't know, less than 500mA, since my Metrix meter has a 500mA current range / fuse.

Will open up the generator in the coming days, if I can sort out this problem right now, why wait... there are enough things to do and fix in this lab for me not to post pone repairs I can do quickly and easily !

[factory]

Still catching up....

Extra picture for page 4440...
https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3934442/#msg3934442

Pictures were taken in 2013, finally got round to editing & posting them. 

David

[Vince]

Try setting the width a bit lower. You have not allowed anytime for the transitions and it may be confusing the unit.

Not sure what you mean ? 10MHz, 100ns period, pulse 50ns wide so 50% duty cycle, 50ns "off" time... isn't that plenty enough to "recover" ?!
Unit can do 50MHz to boot, so a period down to 20ns. So at 100ns I am really not pushing it 

Anyway, just tried it. 20% duty cycle this time, so 20ns pulse and 80ns off.

Result is exactly the same, no better or worse, status quo.

But it was my first good excuse to use my shiny new coax cables and adapters ! 
Boy it's so nice to have all the cables and adapters you need at your disposal, in a just few seconds everything is connected up properly like a pro, no more scope probes banana adapters and bits of wires hanging ! I am a pro now ! 

However I have a new problem now... looks like my Metrix Nixie counter has a problem with its LF / 1Meg input ! Signal is only 10MHz so it can take it no problem. However it would not register / count anything at all, only zeros on the Nixies, even though I have good signal amplitude, 5Vpp unloaded, and no matter how I fiddled with the input "sensitivty" pot/control. Plus, when I connect the counter, I can see on the scope that the signal goes haywire. Big drop in amplitude + it becomes completely out of shape, looking like a wiggly triangle, no more a rectangular pulse at all !  If I use the HF / 50R input instead, all is well.
So, the LF front-end has a problem.... some more repairs in the queue !
This counter is not easy to work on I fear, very compact in there. It's not going to be fun I think...   

[factory]

As for the DM8577, I'm avoiding ancient Nat Semi/TI parts, the Soviet clones should be a bit newer. Strange how the Nat Semi parts on ePay-UK are marked as both DM8577N & DM74188AN if they can't be programmed the same way. 

David

I was nearly caught out by that.   The ones I have are factory marked DM74188AN   DM8577N.   I was initially using the TI Databook.  I have one around here somewhere and it was easier to find on the web.   Mostly because I was curious, I did an extensive search and found the DM8577N in a National book.   Much to my horror, they are "Pin Compatible"  but very different internally.

They are awful, they even put the 74188 first, wonder how many got wasted by folks programming them as 74188 instead of 8577 over the years. 

David

[factory]

....snip....

I would have made a close-up picture of the screen to prove I am not lying about frequency and signal amplitude. Sadly just before doing that, I tried fiddling with the adapter to see if I could shove it in a bit more to make sure the trace does not go unstable right as I am trying to photograph it and... as I was grabbing the adapter, I got ZAPPED !!! Yes this generator tried to kill me !!! 
So no close-up picture for you sorry... instead I immediately pulled the plug !

Checked with the DMM for resistance between the two line terminals in the power socket, and chassis/enclosure.... no short, got 5Mohms and slowly climbing.

So I am not touching this generator for now ! 

Think I will retrofit an IEC power socket hidden at the back (to not ruin the looks of the face plate), and get myself a life saving earth connection....

Will look at the schematic of the generator to see if there is maybe some failing cap that could explain the mishap...

Catching up still......

Looking at your previous posts on the Metrix 920, it seems to have two capacitors to ground (aka the case) and looking at the back of the mains inlet there are two dubious looking capacitors on the sides of the inductors, I would be amazed if these weren't wax paper deathtraps/smoke bombs.
And the DMM will be of no use here, you need a proper DC insulation tester at 250V or 500V to check them, but probably best to just change them for some class Y rated capacitors anyway.





David

Thanks for doing my work Dave ! 

Just looked C11 and C12 in the parts list... they are indeed paper caps ! They are 10nF 10%. 

Will replace them of course !

Will keep the old caps so I can test them later for fun and educational purposes...

Hell I could cobble a crude tester together easily I guess !

After all these caps are simply subject to mains AC ! So all I need to test them in a relevant manner, is to connect the to mains and measure the leakage current, eh ?

Just need to put a series resistor to limit the current to a safe value, I don't know, less than 500mA, since my Metrix meter has a 500mA current range / fuse.

Will open up the generator in the coming days, if I can sort out this problem right now, why wait... there are enough things to do and fix in this lab for me not to post pone repairs I can do quickly and easily !

I'm surprized no one else commented on this, all too busy criticising the RF connector. 

Also does the Metrix TV related gen you have, also have these two cRapacitors on the mains inlet?

David

[factory]

Tidied these away into the component drawer units bought from work, was surprized to see what RS used for the filling inside the wee boxes. 



David

[mansaxel]

I just post this here, a small Swedish reading lesson!

[Neper]

What are ΩF?

[Vince]

Also does the Metrix TV related gen you have, also have these two cRapacitors on the mains inlet?

David

That would be my " Wobuloscope " ! Type 232.

Yes now you talk about it / remind me, you are right, this one also scared me a bit... never got zapped proper, but it was more like a frequent suspicious  "tickling" feeling I got when touching anything on the front panel....

Just looked at the schematic. I can't see any cap as such, I mean not stand alone discrete components. However the schematic none the less show what "looks" liek caps anyway, but that might integrated into the coils "assemblies"  ? Looking at my old pics of these coils, I indeed can't see any cap nearby....

So if the "cap" is built into the coil assemblies, that's gonna be tricky to fix ! Would need to see if they can be taken apart, if so, find a way to "disable" this "cap", then add new good ones soldered externally.
Or if I can't do that, maybe see if I can isolate the coils from the chassis with a plastic washer or something. That would achieve the same thing I guess.

[Vince]

Tidied these away into the component drawer units bought from work, was surprized to see what RS used for the filling inside the wee boxes. 



David

It's TTL it doesn't care, it's tough ! 

Those little card board boxes with custom printing look adorable, I am sure someone would pay a good bit to have these in his collection ! 

[Saskia]

Just had a quick glance at the Bram Stoker Dracula pinball.

Mains fuse (the one in the house) blows immediately when plugging in and switching the power on.

Transformer looks and smells ok.
Hmm.

Power distribution and EMI filter box:
There is a MOV and an NTC. Line in going to one input of an EMI filter (Corcom 5VK1), other line input going to a fuse and to the other input of the Corcom EMI filter.
Across those inputs there is a MOV. Between Fuse and input there is an NTC.

Output of the EMI filter goes to the main transformer which is hooked up via a rather large and bulky Molex connector.
I unhooked the transformer and plugged the thing in.  Mains fuse blows immediately.
Detached the MOV. Tried to measure it (no continuity)
Measured resistance across the EMI filter inputs (5 Ohms, is that not a bit low ? TBH I would expect something in the MOhms range ...)

Need to check a different pinball for comparison. But at this stage I would replace MOV, NTC and EMI filter. and retry.

[factory]

Try setting the width a bit lower. You have not allowed anytime for the transitions and it may be confusing the unit.

Not sure what you mean ? 10MHz, 100ns period, pulse 50ns wide so 50% duty cycle, 50ns "off" time... isn't that plenty enough to "recover" ?!
Unit can do 50MHz to boot, so a period down to 20ns. So at 100ns I am really not pushing it 

Anyway, just tried it. 20% duty cycle this time, so 20ns pulse and 80ns off.

Result is exactly the same, no better or worse, status quo.

But it was my first good excuse to use my shiny new coax cables and adapters ! 
Boy it's so nice to have all the cables and adapters you need at your disposal, in a just few seconds everything is connected up properly like a pro, no more scope probes banana adapters and bits of wires hanging ! I am a pro now ! 

However I have a new problem now... looks like my Metrix Nixie counter has a problem with its LF / 1Meg input ! Signal is only 10MHz so it can take it no problem. However it would not register / count anything at all, only zeros on the Nixies, even though I have good signal amplitude, 5Vpp unloaded, and no matter how I fiddled with the input "sensitivty" pot/control. Plus, when I connect the counter, I can see on the scope that the signal goes haywire. Big drop in amplitude + it becomes completely out of shape, looking like a wiggly triangle, no more a rectangular pulse at all !  If I use the HF / 50R input instead, all is well.
So, the LF front-end has a problem.... some more repairs in the queue !
This counter is not easy to work on I fear, very compact in there. It's not going to be fun I think...   

I would try another signal source, as maybe it can't detect the narrow pulse on the low frequency input? , I know some of the old counters I've got can be a bit fussy on the input signal.

David