Test Equipment Anonymous (TEA) group therapy thread

[TERRA Operative]

I used some rubber mounts for the fans in mine too, helps a lot with noise. Digikey part no. EAR1058-ND (Manufacturer part no. F-331-C8012)
Use 4 per fan and cut them shorter once all installed to keep it neat.

[factory]

A question for those with the Peak DCA75 component tester, does anyone else have trouble with it testing 1N82x series reference Zeners? Mine fails to detect some of them, but these do test OK with the curve tracing software, note both the firmware & software are up to date.

David

[ch_scr]

Interesting plot, with some "soft" knees (pink, blue) and the others with a "sharp kink" (teal, brown, red). Are they different types / manufacturers?
The DCA75 supposedly tests them with 5mA where they all are far into the "steep" region, not sure what's going wrong 

[factory]

Yes a selection of different makes of 1N827, some from the stock I bought from work, the others from a batch of 20 from ePay (those were two different types too), from a seller with ex mil parts, one of the batch of 20 is testing at 1.6V too (i.e. dead). The curve tracing was a quick check to prove the parts were OK, maybe I could do some better plots of the different types here. Oddly the Peak DCA75 no longer makes any sound, since the V23 firmware update was installed.

I remember some fakes we had at work, TC was terrible, cleaning the paint off revealed they were a cheapo 6V2 Zener, I would like to retest those if I can find them, as I now know the 1N82x series TC parts have a reverse connected diode in the package, they only test one way, this may be confusing the Peak, as it doesn't actually know they are Zeners, it detects them as a diode at approx 6.2V.

Need to do more testing tomorrow, as I actually need to fit a replacement 1N821 in the Harrison 6209A PSU, it's not the main problem with that supply which has a strange oscillating output, as I mentioned previously here.

David

[TERRA Operative]

I have a DCA75, but none of those diodes unfortunately.

[Brumby]

Bidding wars.  Do people bid more than once?  The highest bidder only pays the second highest bid.  So increasing the bid multiple times should have no advantage over putting in the highest price one is okay with paying just once.

Good Morning 44kgk1lkf6u, I agree and I enter the absolute highest I would pay and let Ebay increase the bids for me automatically.  If the price increases beyond what I would pay, then I was not meant to have it.  The last minute bidding wars make no sense at all.

This is one possibility. But humans are not rational, they tend to increase their bid, if someone outbids them. Therefor it is an advantage to bid the last second what you want to bid. So no one can increase anymore what he just bidded. ebay likes if you bid early - this drives the prices up. Eg. there is a bid of $100. You set $300. The first bidder increases and stops at $290, you pay $291. Else if you bid last moment, the first bidder can't increase his offer anymore. You pay $101 - or what others think what it is worth without seeing your bid.

There is some art in the bidding process on eBay.  There are a small number of basic bidding behaviours which can be encountered - and if you are properly prepared, you can improve your chances for a good result.  This is not a guarantee by any means, but you won't be any worse off if you do it right and you might just score a bargain.

[m k]

I'd say that real bargain is possible only when you find an item others have not found.
All other cases you value the item more, so it's a conditional bargain.

Best possible situation is when seller doesn't know what they are selling and use misleading name.
Then your job is just spot the revealing picture.

[factory]

I have a DCA75, but none of those diodes unfortunately.

Guess it's just me that works on old DVMs & PSUs that use these, modern stuff must use reference ICs instead.

Some more testing with various temperature compensated Zeners from the 1N82x series, there is a regular 6.2V BZX79 series Zener for comparison, which have a much sharper knee than the TC Zeners.



As for the 6209A PSU, I found a 1N754 6.8V non TC Zener fitted* where it should be a 6.2V device. I've fitted one of the black 1N821, voltage is still a little high at 6.4V, needs further investigation, once I've fixed the main problem, of output oscillation at very low frequency, it doesn't go to zero either.

*I say fitted, only one lead was soldered by the previous user/owner/repairer.

Edit: The above Zener measured at 6.4V was perfectly OK, the +/-0.3V tolerance in the manual is the same as the spec for a 1N821, working while tired convinced me otherwise.



P.S. SCR part of the 6209A might be OK, if I remove Q21 (SCR gate drive) I can stop the output oscillation and actually get zero output. Of course I gave it a check with another Peak tester. Need to move on to the voltage regulator part, which involves that TO-3 Bendix power trannystor and a few other Germanium parts, the only silicon trannystors in this supply are the dual NPN ones.



David

[TERRA Operative]

Germanium semiconductors and carbon composite resistors?

I'd be surprised if anything was still reading within tolerance....

[factory]

Germanium semiconductors and carbon composite resistors?

I'd be surprised if anything was still reading within tolerance....

The 6209B also uses lots of carbon, it works fine, why would I want to change the Ge transistors to Si? this defeats the point of owning the 'A', might as well have got another 'B' instead.

The out of tolerance Zener circuit uses 1% metal film already, the designers weren't stupid, there are bunch of them to the right of the SCR100 tester. 
Looking at the plots of the other two black 'AP' 1N821 Zeners, they tested around the same as the one I fitted, i.e. too high for the Harrison spec, the -6.2V rail is within spec at -6.25V (6.2V ±0.3V), the Zener is the original, around 58 years old. 1N821 are normally 5.9V to 6.5V at 7.5mA, maybe I should fit the BZX79 (non TC) as they tested closest to 6.2V. 

P.S. You forgot to criticise the Sprague caps. More pictures here;
https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg5693345/#msg5693345

P.S.S. Actually I missed the other 3 NPN Si trannystors, so 5x Ge PNP, 1x Ge PNP power, 3x Si NPN, 2x Si NPN dual matched and 1x SCR. All the diodes are listed as Si. There may be errors as I'm using the nearest manual I could find, the 6207A one from Artek (I have gone through & corrected the diagram for my 6209A).

David

[DC1MC]

Just in case someone in Germany wants this thing;



https://www.kleinanzeigen.de/s-anzeige/rlc-messbruecke/2919938194-168-2155

Cheers,
DC1MC

[Robert763]

A question for those with the Peak DCA75 component tester, does anyone else have trouble with it testing 1N82x series reference Zeners? Mine fails to detect some of them, but these do test OK with the curve tracing software, note both the firmware & software are up to date.

David

The DCA will show a 1N82x as open circuit / unknown due to the normal PN junction in reverse series with the zener element. This is for temperature compensation but causes the diode to have no forward conductivity.
 

[Robert763]

I'd say that real bargain is possible only when you find an item others have not found.
All other cases you value the item more, so it's a conditional bargain.

Best possible situation is when seller doesn't know what they are selling and use misleading name.
Then your job is just spot the revealing picture.

Yep,
Examples 2x R&S CRTU / CMU200s radio test sets and a CMW-CU controller for £82 or a HP 8920A with SA/TG for £75. Me gloat?

[factory]

A question for those with the Peak DCA75 component tester, does anyone else have trouble with it testing 1N82x series reference Zeners? Mine fails to detect some of them, but these do test OK with the curve tracing software, note both the firmware & software are up to date.

David

The DCA will show a 1N82x as open circuit / unknown due to the normal PN junction in reverse series with the zener element. This is for temperature compensation but causes the diode to have no forward conductivity.
 

The strange thing, is the DCA75 does detect some of the 1N82x, the batch of blue 1N827 for example, the Au lead ones were all detected as an approx 6.2V diode junction, but the tinned lead ones were not detected. This was the question I was asking about, maybe it's the lower nominal voltage ones that get detected. edit: can't be that as the Au ones had a higher voltage.

I'm aware of the series reverse diode, one of which is shorted out of that batch, the Zener part is still intact, shown in the curve plots attached to post #136933. 

David

[wkb]

I'd say that real bargain is possible only when you find an item others have not found.
All other cases you value the item more, so it's a conditional bargain.

Best possible situation is when seller doesn't know what they are selling and use misleading name.
Then your job is just spot the revealing picture.

Yep,
Examples 2x R&S CRTU / CMU200s radio test sets and a CMW-CU controller for £82 or a HP 8920A with SA/TG for £75. Me gloat?

* wkb hates 😆

Although... one HP and one Agilent E4418B RF power meter, together for €60 incl shipping was not bad. Needed fixing but heh.. both work now.

[44kgk1lkf6u]

How to find deals like that?

[TERRA Operative]

Anyone with a TDS500, 600 or 700 series scope with the HD option, you're welcome.

https://www.eevblog.com/forum/testgear/software-for-the-tds500-600-700-series-scopes-here-it-is!!!

[wkb]

How to find deals like that?

Sheer and utter luck/coincidence in my case.

[Robert763]

Carefully crafted searches on ebay and keeping an eye on new listings.
I have one other trick I'm not sharing 
Oh OK. If a seller has a item poorly described, even if you don't want that item, look at their other listings.

[wkb]

And don't just look at evilBay, look at countryspecific marketplaces too.

[m k]

Maybe country specific for Dutch.
Here it's the opposite, even junk is strawberries.

uPay had once misnamed PCBs.
I didn't get them, wrong method.

BTW,
I bought a set of new NAT7210BPD chips from an uPay far easterner.
Some sort of 7210 they are, no idea how 9914 goes.

[wkb]

Well, I over time bought via Dutch sites (goes to reason) but also from Germany and Tradera.se

Just be creative in where you hunt. Mailing lists sometimes also work, people offering their kit there.

[factory]

Harrison 6209A, oscillating output with control set to '0V' repair update, it's finally working. 

A few red herrings were followed in the SCR pre-regulator circuit, as I proved the other day there were no problems with it, the 6207A manual would have you think otherwise but doesn't take into account the incorrect parts fitted by others. 

From the manual I found out removing either Q3 or Q10 and fitting a short between C-E, the output should drop to zero, of course it didn't.
Checking the voltages of the series regulator driver transistor Q5 (an NPN Si device marked GE-18  ) revealed nothing strange, but measuring the voltages of the regulator power transistor Q6 revealed strange readings. The voltage between C-E was lower than expected at 7V, this should be 12 to 16V for the 6207A.

First thing I noticed after this, was the protection Zener VR4 had been replaced with a diode, a 1N1564 to be exact, it should be a 39V Zener according to both the 6209B & 6207A manuals. This is not good, this Zener is for protecting the power transistor Q6 during output shorts. You can guess what was wrong now, the pass transistor had sacrificed itself to protect the diode. 



The diode quickly got evicted, it has quite a high reverse breakdown, more than can be measured with the Megger & DVM on the 1kV range. Thankfully I found a BZY95C39 in the spares, it tested at 38V on the Megger & was fitted, original part would have been a 1N3803 or 1.5M39Z, both are 1.5W 39V Zeners.

Next for removal was the regulator transistor Q6, the Peak confirmed the C-E failure, now a nice Zener junction. The Bendix 1850-0168 is a 70V 6A device according the the NSN lists, it's not listed in the HP fiche, very few of the Ge power devices are, I'm guessing that's because they weren't being used in the 80s. From my spares I found some of the 1850-0098, checking C-E breakdown with the Megger I found one that was around 80V, in it went.





On powering up the output oscillation was gone and the voltage was finally at zero.
The shorting link was removed from the Q3 socket and the transistor refitted, voltage was now fully adjustable from 0V to 330V.





This just leaves tweaking the reference voltages, I will be selecting a better 1N82x device for this.

Edit: The above Zener selecting isn't actually needed, 6.4V is within the tolerance listed in the manual, +/-0.3V is the same as the spec for a 1N821, working while tired convinced me it was out of spec.

All the failed parts, one 20uF capacitor, a 3.3M resistor (33% high), the shorted Bendix transistor and the 2 working but incorrect diodes.



David

[doktor pyta]

Another antique device in the lab restored to its former glory. ELPO V-527 made in Poland in 1972. Loads of high quality imported components and neat assembly showing high technical culture.

Culprits? Several dry electrolytics, two germanium diodes that decided to change their characteristics (but not fail open or short) and a reed relay with slightly degraded coil-to-contact insulation (2Gohm).

As a gift for future generations, I have prepared three manuals for similar voltmeters manufactured by ELPO:
https://bama.edebris.com/manuals/elpo/


ELPO factory was established in 1958 in communist controlled Poland. After some structural changes in 1973 the name has been changed to MERATRONIK which some of you may know.
A significant part of the production was intended for export, hence the inscriptions on the devices were in English, less often in German.

[factory]

Another antique device in the lab restored to its former glory. ELPO V-527 made in Poland in 1972. Loads of high quality imported components and neat assembly showing high technical culture.

Culprits? Several dry electrolytics, two germanium diodes that decided to change their characteristics (but not fail open or short) and a reed relay with slightly degraded coil-to-contact insulation (2Gohm).

As a gift for future generations, I have prepared three manuals for similar voltmeters manufactured by ELPO:
https://bama.edebris.com/manuals/elpo/


ELPO factory was established in 1958 in communist controlled Poland. After some structural changes in 1973 the name has been changed to MERATRONIK which some of you may know.
A significant part of the production was intended for export, hence the inscriptions on the devices were in English, less often in German.

Very nice, good to see someone else repairing vintage DVMs.    Must be the first I've seen on here, the later Meratronik DVM, I've seen a few of, but none found over here yet.
This one also has ohms function, but the other in the manual links (thanks for adding them) has AC instead, I wonder if they also did a model with both?

It's also one of the few DVMs with a higher voltage range than the normal 1kV range, is the input connector something obtainable? it kind of looks similar the the Solartron ones (without seeing it disconnected), they also made translated front panel markings. And it uses the same Muirhead reference cell as quite a few UK made meters.

P.S. Seems to be the only result for Elpo on the forum, OK there is an LCR bridge on the previous page too.

David