Test Equipment Anonymous (TEA) group therapy thread

[med6753]

Americans can't handle more than two Si Units at once without suffering mental overload.

So capacitors are 1000000uF and 15000pF

Go choke on a biscuit. 

[bd139]

Oooh biscuits. There's a good idea 

[factory]

A few days ago I said I wasn't going to look at the faulty display board from the 5248M counter till I had fixed all the other problems, but playing spot the difference with the readout board from the 5245L and trying that one, I realised the difference is in the neon/photo resistor based decoder section (the board from the 5245L only displays 3,4 & 5). 


Noticing the corrosion on the tube socket I thought I would have a look inside the decoder block to see if it was in the same condition, maybe it needed cleaning to stop the random glow (from all the digits) from the number readout bulb.
How wrong I was, unfortunately damp has got inside the block & eaten away some of the traces on the photo-resistor plate and this plate is the main difference in this display board between the 5248 & the 5245 models.

Before & after cleaning with IPA,



Looks like I'm stuck with only 7 usable digits unless/until I can find a replacement. 

Nearly everyone blames the neons for faults with these display boards, but in this case it was the photo-resistor & decades of neglect in a damp shed.


David

[bd139]

That's interesting. What does the photoresistor do in that assembly?

[AVGresponding]

I think the main confusion with using mF is that rather than milli-Farad, it used to be used to mean micro-Farad.

[bd139]

Yep.

µF -> alt+m on macOS FTW

[AVGresponding]

That's interesting. What does the photoresistor do in that assembly?

Brightness/intensity feedback for the neon tubes?

[factory]

No Comment

Amazing, is that a Fluke 123 with a working battery? 

David

[factory]

That's interesting. What does the photoresistor do in that assembly?

Brightness/intensity feedback for the neon tubes?

It's the decoder for converting the binary from those pairs of transistors to decimal for the number display bulb. I need to have a better look the paper 5248 & 5245 manuals to see why they needed to use a different decoder plate.

David

[bd139]

That's interesting. What does the photoresistor do in that assembly?

Brightness/intensity feedback for the neon tubes?

It's the decoder for converting the binary from those pairs of transistors to decimal for the number display bulb.

David

That's quite neat. Considerably cheaper than throwing more transistors at it at the time as well!

I remember someone telling me that when I worked for an MoD contractor that they had two guys full time reducing transistor count in discrete circuits in the early 1960s to cut production costs.

[tggzzz]

I think the main confusion with using mF is that rather than milli-Farad, it used to be used to mean micro-Farad.

And capacitance was measured in Jars. 1Jar = 1111pF, apparently.

BTW, µ is altgr-m in other Unices such as Linux, not just bastardised BSDs such as macOS

[bd139]

BTW, µ is altgr-m in other Unices such as Linux, not just bastardised BSDs such as macOS

https://www.opengroup.org/openbrand/certificates/1212p.pdf 

I've got to say, the ambiguity between the whole pF and uF scales on circuit diagrams has pissed me off for years, especially when you see someone specify obviously an electrolytic capacitor with "1000" so you have to reverse engineer what it's used for before you can determine if it's 1nF or 1mF 

[AVGresponding]

That's interesting. What does the photoresistor do in that assembly?

Brightness/intensity feedback for the neon tubes?

It's the decoder for converting the binary from those pairs of transistors to decimal for the number display bulb. I need to have a better look the paper 5248 & 5245 manuals to see why they needed to use a different decoder plate.

David

An analog binary to to decimal decoder? I'd have to draw that out to get my head around it properly.

The colour balance in the pics makes it a little tricky for us to play along with your spot the difference, the only things I can see are,
1. The 1W or so resistor on its own, 47k on the 5245 board and 10 or 100 ohms? on the 5248 board Grid bias resistor? I don't know enough about VT tech to make a good guess.
2. The four pairs of diodes with their anodes tied to connection 5 on the card edge on the 5245, on the 5248 are an older design and I'd want to check if the polarity markings make sense.
3. The colour coding on the 1-10 outputs from the decoder to the readout tubes is different. Is this because the coding is random and just a way for the assembly tech to make sure terminal 1 goes to pin 1, or is it because the pinout is different?

Given the output side is going to be effectively a ten output exclusive on-off switch, if the pinouts are wrong you're likely to get a scrambled version of what it should display, but without a complete failure to display anything.

[AVGresponding]

I think the main confusion with using mF is that rather than milli-Farad, it used to be used to mean micro-Farad.

And capacitance was measured in Jars. 1Jar = 1111pF, apparently.

Interesting. I guess that means that at one point there was a Standard Leyden Jar used as the base for the unit.

[Cerebus]

"nF" is foreign to me. So is "mF". But hey, at least I did graduate from "uuF" to "pF". 


And this is a resistor.   

You call that a resistor? This is a resistor:

[Cerebus]

Oooh biscuits. There's a good idea 

Only he didn't "biscuit", he meant "scone" or "scone".  Bloody Americans!

[Zucca]

Yep.

µF -> alt+m on macOS FTW

Also on German Keyboard, and also ²³  or the ° of  °C... or ô. That's why I believe the German layout is the best, and you can do italian  è é accents too.

[bd139]

The HP 5245L service manual is an interesting read. The neons are used for bit memories as well as decoding in the counter!

Edit: when I look back at that I think of all the pain of worn out neons 

Money shot from the schematics. To be clear the bit memory is used elsewhere by the looks, not in the final drivers.

Edit 2: transistors are 2n404a's which in ~1965 were $3 a pop approx. That's $24.80 each these days. So each display bit cost $50 today potentially  . When a decoder IC appeared on the market at $50 a go you can see the sort of scary cost savings the ICs landing had.

And here I am sitting on a machine with 1TiB of solid state storage 

[Robert763]

A few days ago I said I wasn't going to look at the faulty display board from the 5248M counter till I had fixed all the other problems, but playing spot the difference with the readout board from the 5245L and trying that one, I realised the difference is in the neon/photo resistor based decoder section (the board from the 5245L only displays 3,4 & 5). 


Noticing the corrosion on the tube socket I thought I would have a look inside the decoder block to see if it was in the same condition, maybe it needed cleaning to stop the random glow (from all the digits) from the number readout bulb.
How wrong I was, unfortunately damp has got inside the block & eaten away some of the traces on the photo-resistor plate and this plate is the main difference in this display board between the 5248 & the 5245 models.

Before & after cleaning with IPA,



Looks like I'm stuck with only 7 usable digits unless/until I can find a replacement. 

Nearly everyone blames the neons for faults with these display boards, but in this case it was the photo-resistor & decades of neglect in a damp shed.


David

Hmm, would a plate from a lower decade from a 5245 work? At leat it will do 0-9.

[Cerebus]

Yep.

µF -> alt+m on macOS FTW

Also on German Keyboard, and also ²³  or the ° of  °C... or ô. That's why I believe the German layout is the best, and you can do italian  è é accents too.

The coolest thing in this regard about using macOS is that if you hold down the key for a letter that frequently takes an accent or that has an alternative form you get a little popup where you're typing that shows all the alternatives and you can pick one with the mouse or the arrow keys.

So hold S and you get ß, ś and š, O will give you ô, ö, ò, ó, œ, ø, ō and õ, and so on. Simplicity itself and you don't have to remember the option-key versions unless you want to, or have frequent recourse to greek letters commonly used as symbols such as Ω, µ, π and so on which don't have a 'hold and wait for it to pop up' version.

There are floating accent keys too, but other than option-u for umlauts I haven't learned any of the others because the pop-up trick is so convenient. The Germans, not Motörhead, have to take the blame for me learning where the umlaut key is and that option-s produces a scharfes S  - ß.

The pop-up trick means forgoing auto-repeat for alphanumeric keys, but how often does one use that? You still get auto-repeat on - and =, the ones that you might actually use.

Using it is so little effort, that's why you'll almost always see me use the strictly correct "rôle" or "dæmon" rather than the lazy versions

[factory]

That's interesting. What does the photoresistor do in that assembly?

Brightness/intensity feedback for the neon tubes?

It's the decoder for converting the binary from those pairs of transistors to decimal for the number display bulb. I need to have a better look the paper 5248 & 5245 manuals to see why they needed to use a different decoder plate.

David

An analog binary to to decimal decoder? I'd have to draw that out to get my head around it properly.

The colour balance in the pics makes it a little tricky for us to play along with your spot the difference, the only things I can see are,
1. The 1W or so resistor on its own, 47k on the 5245 board and 10 or 100 ohms? on the 5248 board Grid bias resistor? I don't know enough about VT tech to make a good guess.
2. The four pairs of diodes with their anodes tied to connection 5 on the card edge on the 5245, on the 5248 are an older design and I'd want to check if the polarity markings make sense.
3. The colour coding on the 1-10 outputs from the decoder to the readout tubes is different. Is this because the coding is random and just a way for the assembly tech to make sure terminal 1 goes to pin 1, or is it because the pinout is different?

Given the output side is going to be effectively a ten output exclusive on-off switch, if the pinouts are wrong you're likely to get a scrambled version of what it should display, but without a complete failure to display anything.

Apologies for the difficulty in seeing the colours, reading the resistors on the newer board isn't helped the random orientation, both boards use silicon transistors (the earlier boards use germanium).

1). The board from the 5245L is about 10 years younger, hence the smaller sized diodes.

2). The markings on 47k resistor on the older board have worn off, just a little bit left underneath, it measured just over 50k.

3). You spotted the difference in the wiring for the tube socket, this is exactly as shown in the two manuals, will see if I can add some pictures of the code from the paper manuals, the PDF's I have are shite.

David

[mansaxel]

Americans can't handle more than two Si Units at once without suffering mental overload.

So capacitors are 1000000uF and 15000pF

If the english-speaking world hadn't been so hostile to character sets containing glyphs they don't very often use, they could actually use the proper term, i. e. µF. Greek characters written properly is like using RPN calculators, a coming of age thing 

The Swedish Professional keyboard mapping on OS X is actually quite sciency; I can reach most EE-useful symbols, like ∏, Ω and µ (Pi, Omega, micro) with just one modifier.

But they will never be as beautiful as if rendered in T_EX.

[factory]

Looks like I'm stuck with only 7 usable digits unless/until I can find a replacement. 

Nearly everyone blames the neons for faults with these display boards, but in this case it was the photo-resistor & decades of neglect in a damp shed.


David

Hmm, would a plate from a lower decade from a 5245 work? At leat it will do 0-9.

I first need to have a look at the manuals to determine why the 5245L board only displayed three out of ten digits.

David

[mansaxel]

Yep.

µF -> alt+m on macOS FTW

Also on German Keyboard, and also ²³  or the ° of  °C... or ô. That's why I believe the German layout is the best, and you can do italian  è é accents too.

But Q W E R T Z 

[mansaxel]

Using it is so little effort, that's why you'll almost always see me use the strictly correct "rôle" or "dæmon" rather than the lazy versions

I make sure to do that too, and to add the ¨ to o in "coöperate" just to make sure nobody ever mistakes me for a Trump voter...


It is a little known fact that extended character sets are illegal in the Bible Belt.  (just kidding)