Test Equipment Anonymous (TEA) group therapy thread

[factory]

Mini 212, round 4.

snip....

And here's an example of the documentation not matching the board. The trace routing to R141. Those 2 orange tants. One is a 1uf/35V, the other is a 1uf/50V. I'm not sure which one is which and there's a 50% chance of getting it wrong resulting in smoke. So I'll wait until assembled and powered up then measure voltage on each. In the meantime changing out the other tants on this board. The main board is still to do and I have to figure out how to get access to the solder side.

Same problem with most hp TE, the available manual rarely covers the revision you are working on.

I know you've already sorted that board while I was stuck at work, but I noticed it looked similar to the one in the Tek 214 at work, the available manual shows a similar layout, but the upper tant  is not fitted.
Also the lower tant seemed to show 1-35 (1uF 35V?) when you zoom in on your picture. 

David

[Neper]

On the risk of being stupid, what's the point of 1 µF tantals (or 1 µF electrolytics) anyway, nowadays? Why not just use a simple Wima instead?

[ch_scr]

On the risk of being stupid, what's the point of 1 µF tantals (or 1 µF electrolytics) anyway, nowadays? Why not just use a simple Wima instead?

It's vintage TE, and people usually want it to be restored faithfully.
I'm usually all for the upgrade, as the part sits inside and the TE looks the same from the outside - but more often than not there is fierce opposition to modify the beloved...

[Neper]

Ok, that's understandable. Then again, I certainly wouldn't want to restore an old radio using tar/paper capacitors.

[ch_scr]

Ok, that's understandable. Then again, I certainly wouldn't want to restore an old radio using tar/paper capacitors.

I think there is a personal "line" of how much "true-to-original" the restored item should be.
The obvious example is the ship of theseus were every piece of wood in the ship had been replaced at one point
and it still counts as the same ship -
but if you built a new metal ship that "just" looks the same - thats a different ship...

[Robert763]

On the risk of being stupid, what's the point of 1 µF tantals (or 1 µF electrolytics) anyway, nowadays? Why not just use a simple Wima instead?

Apart from "keeping it original" a 1uF Tantalum is not the same as a 1uF wet electrolytic or 1uF film or 1uF ceramic. The impedance at different frequencies, dissipation factor, temperature and voltage coefficents can all differ.
In many cases it makes no difference, but in some it does. In old  TE we may not know why a particular type and value was chosen. Even "simple" things like power supply decupling can be critical  with he wrong type causing instability. This may only be apparent at certian voltages or loads.

[ch_scr]

On the risk of being stupid, what's the point of 1 µF tantals (or 1 µF electrolytics) anyway, nowadays? Why not just use a simple Wima instead?

Apart from "keeping it original" a 1uF Tantalum is not the same as a 1uF wet electrolytic or 1uF film or 1uF ceramic. The impedance at different frequencies, dissipation factor, temperature and voltage coefficents can all differ.
In many cases it makes no difference, but in some it does. In old  TE we may not know why a particular type and value was chosen. Even "simple" things like power supply decupling can be critical with the wrong type causing instability. This may only be apparent at certian voltages or loads.

True words! In other circumstances, say feedback capacitance in a power supply where a 1uF electrolytic might have been used because it was a lot smaller and cheaper than foil caps at the time, and leakage of a new 'lytic was deemed "good enough" a foil cap might be an valid upgrade nowadays.
As usual, the answer is "it depends" and YMMV - if in doubt go (close to) original, I guess?

[med6753]

I will play around with capacitor values, but not types, where appropriate. For example, 40uf and 50uf electrolytics used to be common. The 40uf may get 39uf or 47uf. The 50uf will get 47uf. Tolerances are great enough that it makes no difference. Also, 100uf tants are insanely expensive and usually in short supply. Two cheaper 47uf tants in parallel take care of that.   

[Saskia]

building new computer for daughter.

I don't have a fitting PSU yet.
But I found an i5-8400 and some RAM and I still got the not-so-expensive board from Reichelt.
And somewhere I still have a Streacom case floating around.

This may seem like overkill, but she's my daughter.

Note the jimmy-rigged PSU gizmo.

[ch_scr]

Part 2 of the Apollo comms teardown from curious marc is out 

[Saskia]

here it eees:

[BU508A]

The gate 2 goes to the potentiometer to set gain. The gate 1 is internally biased on BF1005 
And while connecting it directly (as in DC-wise) to something (say between the "parallel" fet's) is not recommended by the datasheet, I hoped the part-to-part variation (on the internal biasing) would be small enough for it to work (and it seems to).
The alternative - dc-decoupling each gate 1 individually from the input line - took too much space and parts for my liking.
So rest easy, it is not floating. In fact, I also used this kind of fet on the active probe - too bad none of these are in production anymore  ! The only dual gate fet I could find (on a distributor) was also NRND and without the internal bias - maybe this kind is more expensive to manufacture, and DG-MOS out of (mass production) use in general?

Just found on ebay 40 BF1005 for EUR 5.55 + EUR 1.60 for shipping.
Let's see, if I'll tinker with them one day.   

https://www.ebay.de/itm/144237270383

[BU508A]

here it eees:

Saskia (to daughter): "Here it is."

Daughter: "Oh, look mum, no a computer!"

SCNR   

[Neomys Sapiens]

The gate 2 goes to the potentiometer to set gain. The gate 1 is internally biased on BF1005 
And while connecting it directly (as in DC-wise) to something (say between the "parallel" fet's) is not recommended by the datasheet, I hoped the part-to-part variation (on the internal biasing) would be small enough for it to work (and it seems to).
The alternative - dc-decoupling each gate 1 individually from the input line - took too much space and parts for my liking.
So rest easy, it is not floating. In fact, I also used this kind of fet on the active probe - too bad none of these are in production anymore  ! The only dual gate fet I could find (on a distributor) was also NRND and without the internal bias - maybe this kind is more expensive to manufacture, and DG-MOS out of (mass production) use in general?

Just found on ebay 40 BF1005 for EUR 5.55 + EUR 1.60 for shipping.
Let's see, if I'll tinker with them one day.   

https://www.ebay.de/itm/144237270383

I bought some parts from Hoefler Elektronik. (still ongoing)
Among those is a bag of unknown Harris 4-pin devices in TO-72. We'll see what it is and what's the f_t of them. If they age DG-fets, I could share.

[beanflying]

Eeewww not YEW ok price to go with your 'new' Avo @Brumby  eBay auction: #124937836970

look like a missing battery cover too.

[cyclin_al]

Yeaaaah... that post was more aboot delivering a terrible pun than it was aboot advising papa smurf on how to fix a Tek... That would be like telling your octogen-stripper how to suck... eggs. 

mnem
And now I get to repeat said terrible pun...   

You keep mentioning that stripper. Do you require a refresher re-post? 

I can assist with a smurf-licking dragon. 

Should I choke you with my tits ?
(You were asking for this, sorry)

Death by motorboating? Sounds.....nevermind. 

I am not sure I needed to learn that term....

A good day is a day when you learn something new???   

[cyclin_al]

*currently gusseting a bedframe for my son*

Just put a bottle jack under it and be done ... that is what I did.

Although I do have my bedframe in the garage from a previous lifetime (before kid, before marriage), but her antiques count more ...

[vk6zgo]

You are a day late and a dollar short. 

My mantra.....ALWAYS read ahead before responding. 

I read your post about those components earlier and I wouldn't insult your intelligence by even recommending that ... 

I'm not insulted nor offended. I knew the Captain Obvious's would come out of the woodwork and I would have to explain my motivation.

To someone who had to repair a lot of stuff over the years, always with time pressure, your motivation seemed a bit esoteric.

My rule was that of the three things:- Form, fit, & function, the most important was function,
Thus, equipment often had components of higher voltage rating & even, sometimes, of different type fitted as replacements, especially where the original was "unobtainium", or of inferior quality.

One Electrohome Pix monitor used, for some reason, a high voltage rated bipolar electrolytic  capacitor as part of a DC supply off an overwind on the EHT transformer.

As these things do, it died, so I looked up the catalogue for one of our usual suppliers, & was delighted to find they stocked the same value at that voltage rating.

They were much smaller, too, So, marvelling at the advance in technology, I fitted one.

The monitor "rustled up", everything looked good for about 5 seconds, then with a hissing sound from the new cap, the original fault returned------Yep! the originals were low ESR, the new one, not!

More chasing through catalogues, phoning, etc, revealed that low ESR BP caps in those ratings were not available in Oz!
Maybe in the GWN, where the EHome hailed from?

Anyhow, it ended up with a "Christmas tree" of polyester "greencaps", was returned to service.
Definitely looked uglier inside, but EHomes we pretty ugly, anyway----hardly Canada's finest product!

My view is that, even with "collector" type stuff, work performed over the years (like, maybe the 50v cap in your case), is as much part of the devices history as the original configuration, so fitting a higher voltage rated cap now is just as legitimate.

[0culus]

Type 547 is back to her feet...the replacement matched pair of vertical output transistors arrived today and now it's running the latest revision vertical amplifier circuit.

[Neomys Sapiens]

*currently gusseting a bedframe for my son*

Just put a bottle jack under it and be done ... that is what I did.

Although I do have my bedframe in the garage from a previous lifetime (before kid, before marriage), but her antiques count more ...

Those that haven't shagged a bed to tatters haven't truly lived?

[mansaxel]

*currently gusseting a bedframe for my son*

Just put a bottle jack under it and be done ... that is what I did.

Although I do have my bedframe in the garage from a previous lifetime (before kid, before marriage), but her antiques count more ...

Sounds like you need to upgrade in the Nixie counter dept.

[mansaxel]

My view is that, even with "collector" type stuff, work performed over the years (like, maybe the 50v cap in your case), is as much part of the devices history as the original configuration, so fitting a higher voltage rated cap now is just as legitimate.

Amen to that. My -hp- 6206b came with the milky neon power indicator, and it worked, sort of. It was intermittent, and had gotten a few bumps through the modification by GSP method. (Same went for entire meter, and it as a matter of fact was a shipper refund). I located a new replacement for the neon, same brand, same mounting hole and all, but clear instead of milky, and fitted it.  It is visible, it is in style, it works and performs as the old one, maybe slightly better.

If the supply had been repaired in service, (and you can argue that it has been, by me, because I run it as my primary single voltage source) there would have been such upgrades made.  So it is fine. Part of caring for a Really Useful Instrument.

If you disagree, there are batches of NOS RIFA X2 capacitors in the Bay. 

[BU508A]

This one is especially for Zucca:



 

SCNR

[Saskia]

Flat joke. Go stand in the corner. Face to the wall.

[BU508A]

Menno!

<grummel>