Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

Yes! 
Finally I got one for a reasonable price!  A Rohde & Schwarz AM300 Dual Arbitrary Function Generator.   

...More pictures and a teardown will follow. 

Daaaaang! Noice unit... Eagerly waiting to see the followup, as a quick Gurrrgle shows used units being offered from ~$1300 to $4000...

mnem
 

[vk6zgo]

No don't stay tuned.... at least not tonight. I am tired, time to go to bed.... will resume work on it tomorrow.

Did you see how lovely the wiring is ? 99.99% of the wires are white ? That makes it so easy to trace wires eh ?!   

I guess someone at Matra ordered by mistake a palette of white wires instead of just one spool, and the supplier refused to take the excess back. So Matra said oh boy what are we gonna do to use up all that white wire ! Hmmm.... what about making some of these 400Hz 3Ph PSU for that missile contract we just got the other day !!! 

Nothing wrong with that, no stupid manager or scrambled eggs general involved. These wire looms are made according to a carefully planned layout, as you can see, the person who had to solder the wires to the pins can identify the wires by their position. Just like a PC Board, all the traces got the same colour on a PCB, too, don't they?

Marconi used to use a set of white, black & pink wires, with coded rubber sleeves on the ends.-----All good, till the connections to the bases of valves or to power resistors got hot, the sleeves shrivelled up, & the "white & pink wires" became black wires, disappearing into an impenetrable cable form!

[Specmaster]

www.ebay.co.uk/itm/255529155186   

If you're going to make a suicide cord you might as well go top tier. 

That should NOT be allowed to sold on eBay.

[0culus]

www.ebay.co.uk/itm/255529155186   

If you're going to make a suicide cord you might as well go top tier. 

That should NOT be allowed to sold on eBay.

Yeah, WTF. 

[TERRA Operative]

MATRA 400Hz 3 Phase PSU repair update

On the bad board, I found a group of 3 close together resistors that all read 30% lower than they should. Suspicious... Pulled one leg on each to quickly make sure that they were.... good, as I suspected. They were indeed good. So it must be some other component, related to these 3 resistors, that makes them read low.  So I then looked at all the electrolytic caps. 6 of them. Pulled a leg on each, used the cheap chinese meter... they were all good but one that detected as a 60 ohm resistor rather than a capacitor... 22uF 40V. I replaced it. Does not look pretty because the pad holes were too small to host the replacement cap leads. So had to solder two bits of wires into the holes first, then solder the cap to those wires. OTHO I would have needed to do that anyway because replacing an old axial cap with a radial cap that's salvaged hence with tiny / short leads... doesn't work.

This is how I put a radial cap in place of an axial.
Extend one leg with tinned copper wire, bend neatly and cover in clear heatshrink.




Also, my late model SG503 arived today. Needs a tweak of the trimpots etc, but after a bit of a clean with isopropyl alcohol on the front panel and some Deoxit on the range switch, it seems to be working well.

[mnementh]

   This is how I put a radial cap in place of an axial. Extend one leg with tinned copper wire, bend neatly and cover in clear heatshrink.

Nice & tidy; I like that you use heavier gauge wire on the extension... but I generally try to make it such that the (+) lead is as short as possible on any "brute force" filtering or stiffening cap, while the (-) lead gets most, if not all of the extension. I at least attempt to orient the cap and leads to make the (+) lead no longer than the original, if possible, to reduce the likelihood of it becoming a antenna.

Yeah, yeah, I know... we also need to think about common-mode noise on the (-) lead... I still consider it the lesser of two evils. 

mnem
 

[Cerebus]

If you think for a few seconds, any radiation is going to be proportional to the current in the lead, and the current in the positive and negative leads better well be equal in a passive component. Better to think "What gives me the smallest loop area?" and in this case I don't think there's actually going to be any difference which ever you chose to extend.

[mnementh]

Hmmmm... smallest loop area? Would be "the ugly way"... keep the cap vertical and the extensions just long enough to reach.

If you use sufficiently heavier gauge wire on the extensions it is immaterial in a "brute force" filtering or stiffening scenario. The smaller leads on the cap itself are the bottleneck and any "current limiting factor" will be there, not the extensions. In any kind of signal cap scenario, I'll agree attempting to keep the leads equal length is probably better.

EDIT:   Doing repairs on some high-current car audio amplifiers back in the day, I resolved false-shutdown issues in the DC-DC converter section on many different models by following this practice of heavy-gauge wire on the extensions and keeping the (+) leg short, or by "converting" the design with new holes in the rails spaced for radial caps. I was damned if I was going to pay the price for "Audio-grade" axial caps in a fucking SMPS. 

Obviously, if it were really critical, we'd shell out for same/similar type/package as the OEM.

mnem
As always... take anything I say with a grain of salt big enuf to pickle a dwagon.

[Ice-Tea]

Bricked my laptop downgrading the bios.

I'm not happy.

No you wouldn't be. Is this something you can revive by directly flashing the BIOS into an SPI EPROM with a cheapo clip on programmer?

Possibly. I actually have an elnec programmer. Question is if I think it's worth it. It's a good laptop still, but technically it's written off already. Do I want to spend way too much time on it with an uncertain outcome or do I want to treat myself to a laptop refresh.

[ch_scr]

Bricked my laptop downgrading the bios.

I'm not happy.

No you wouldn't be. Is this something you can revive by directly flashing the BIOS into an SPI EPROM with a cheapo clip on programmer?

Possibly. I actually have an elnec programmer. Question is if I think it's worth it. It's a good laptop still, but technically it's written off already. Do I want to spend way too much time on it with an uncertain outcome or do I want to treat myself to a laptop refresh.

Why not both?   

[mnementh]

If your laptop was made in the last 6 years, I'd suggest putting it on fleaBay as "upgraded FW, now won't boot", then sit back and and watch the feeding frenzy. They goin' cray-cray.

mnem
 

[nfmax]

A problem all us TEA folk have experience, but maybe not to the same extent:
https://twitter.com/mattcartoonist/status/1524062600853704705?s=21

[Ice-Tea]

If your laptop was made in the last 6 years, I'd suggest putting it on fleaBay as "upgraded FW, now won't boot", then sit back and and watch the feeding frenzy. They goin' cray-cray.

mnem
 

Exactly what I decided.. After I pull the SSD.

[mnementh]

Of course that goes widdout sayin'; yo momma dinn't raise no foos... 

mnem

[med6753]

More re-cap work on the Type 547. This round C730 in the +350V supply and C642A/B in the -150V supply.





This resistor load bank has to moved in order to gain access. That large can is C642A/B. It has to be removed. C730 behind it (not shown) can remain in place.



C642A/B removed.



New C642A/B. C642A was 250uf/350V. Replaced with 270uf/400V. C642B was 40uf/250V. Replaced with 47uf/250V.

 

New C730 installed under chassis. Old can remain in place. Was 125uf/250V. Now 130uf/250V.



Two of the capacitors (C642A and C730) are totally isolated from the chassis. C642B is installed reverse polarity. Get it wrong and you'll be testing your smoke alarm. But all is well. The -150V reference upon power up. And sharp trace on CRT. There are 6 more capacitors to do.

[mnementh]

Smurfy. 

mnem
No, not Murphy. Go away, you! 

[Vince]

MATRA 400Hz 3 Phase PSU repair update


Amp board repair

OK so I worked some more on that board. First, a thought crossed my mind.... this group of 3 resistors that all read 30% low (circled in yellow on the pic below)... that led me to check the caps and replace a bad one....I wasn't quite sure that after replacing that cap, I checked back on those resistors.... so I did that, and sure enough, it did NOT fix the problem ! Great, I mean, genuinely great, in the sense that it's was clear that I had some other components failed somewhere, i.e. some hope that replacing whatever that component might be... might fix the board. 

So I started by checking all the transistors, 6 of them... and quickly found a bad one (circled in red), yeah !! Its base-emitter junction was open-circuit.

I removed it from the board, and hey presto now the 3 resistors read perfectly in spec ! 

Shoved the transistor into the chinese meter : " No, unknown or damaged part "   

It's a 2N1711. Pulled the datasheet. NPN 50V 500mA, nothing special.

Have two boxes of new transistors and whatnot, brand new parts, that my old man donated to me 20+ years ago when he retired and "rescued" them from his work place..
Problem is, I have not yet sorted these... I just don't know what's in there. So every time I need something I have to pull them one by one and search for datasheet to try to see what I have.
Madness. It's about time I gather all the datasheet to identify them, once and for all, and put them in a little drawers with appropriate labels.  So I shall be doing that soon I think....

Anyway, I got extremely lucky in this particular case. I still can't quite believe it, but in these boxes I did have the EXACT same transistor, 2N1711 ! I just couldn't believe my eyes, what were the odds ?! 
 

So I soldered that to the board, fired up the PSU. Checked the 20V pins under the back plane.... ah, we DO get 20V now, at last !!! That's promising ! Now let's check output voltages at the rear of the PSU.... Ph3 reads 113+ Volts ! Better than the 90/100V we used to get. Now we are pretty much at the 115V you people were telling me I should get !
Now let's check Ph2... 106.5V ! A bit less well but... still not far off, I will take it.
So now what about Ph1.... suspense...... suspense...... 113+ Volts yeah !  FIXED !!!!!! 




Meter movement repair

So since the repair of the PSU was much quicker than I thought, I still plenty of time and motivation so I decided to have a go at investigating another, minor issue with this PSU. The meter movement on the front panel, that's stuck at 20V or so. Just won't budge. I feared mechanical damaged, especially since the window has a big crack in it, so I was not too hopeful but hey,let's at least check it out.

I barely wiggled the plastic window, and it came off. In the process the crack evolved into creating a now two part puzzle window... 

I noticed that the needle now reset itself, back to zero.... hmmm.... maybe the needle was simply stuck in the crack in the window, severe as it was. So tried moving the needle with my finger.... appeared to move freely and move back to the left with no problem, spring still good.

So gave it a try, fired up the PSU. Hey what do you know, meter works fine now ! 
What a relief, no mechanical damage, it's still well and alive ! 

However I noticed that it read about 10% too low, that sucks....

So I then went on to investigate that. There is a little circuit board mounted at the rear of the meter, see pics of both sides of it below. It holds the rectifier diodes and half a dozen high value resistors. I assumed some of these resistors must be doing the scaling. So I unscrewed and pulled the board free from the meter. Diodes checked OK. resistors too. No bad solder joints. Hmmm...
I drew the schematic of that little board, saw how they did the scaling, well I think...  No precision resistors, all the resistors on the board are 5%.
No trimmer either, as you can see. Instead it looked to me like teh scaling they did with a little montage of 3 resistors. They put a 120K in  // with a 220K, so about 70K for this ensemble, then put that in series with a 1Meg resistor. So the 1M clearly dominates the bunch. So I just slapped a 10M resistor across the 1M, hence aobut 10% increase in current, to balance the 10% low reading of the meter, and hey presto the meter now reads SPOT ON !      I mean, really freaking spot on, I could not believe my eyes ! Job done !!! 

So that's a working meter we have now ! 



Conclusion

So, just need to clean the plastic window (bits), try to polish it a bit as it's kinda dull / scratched up. Then glue back together the two broken pieces, slap that back onto the meter and call it a day  ! 

Then give it a clean inside as it('s freaking dirty/ dusty, even spider webs. A quick clean of the front panel as well, and then it will be ready for sale, yeah !!!  Not going to advertise it on my local leboncoin.fr web site, would be hopeless. For this specialty piece of TE, I think I need to put it on ebay if I want a chance to get an audience of connoisseurs...

will need to search a bit for similar PSU to figure out how much I can get for it.... Robert ?  50 ? 100 ? 150 ?  It's WORKING, and soon, will be clean  as well   

First and last time, I think, that I sold something on ebay was 20 years ago when I sold my car... 20 years later I guess rules have changed. Need to go learn how Ebay works today for sellers... how much it costs, how much they charge for XYZ... can't price the thing until I know how much I will get charged to advertise it 

Anyone want it ? 

[Vince]

EDIT : trying to search ebay for this type of PSU to see how much they sell for... big fail  !

I first searched for " 3 Phase 400Hz power supply " ... and got flooded with regular power bricks because most are switch mode and most SMPS are rated to accept from 50Hz up to 400Hz !

so I dropped the " 400Hz" in my search terms.... still fail : now I get flooded 3Phase power supplies but PSU's that take 3 phase as their INPUT, then output a regular DC low voltage ! 

OK so I can't even find similar supplies... which means that even if I pu tit up for sale, nobdy would be able to find anyway.

So I am screwed.... nobody wants it ? 50 Euros + shipping... .have a good heart, save its life before I take it apart !

[capt bullshot]

MATRA 400Hz 3 Phase PSU repair update

...
Successful

Congrats!
 

[mansaxel]

5245L update:

It appears that the mains inlet (a normal IEC C14) is broken. It "works" as in it gives power but is definitely dangerous and unsuitable.

The frame where the rivets sit is separated from the receptacle part so that the latter floats; held on only by the wiring. Scary. And to think that I ran it a couple hours in that condition..

Am considering taking it up with the seller, because it could be shipping damage; they sent the counter with an angled mains cable plugged in, which definitely could cause exactly this.

Now, I'm considering repair, and that is pretty straightforward, except for the rivets. What do people use to get them out? A center punch from the outside and then drilling? Need to rummage around in my boxes and see if I've got a spare too.

[factory]

The rivets often end up spinning if you try drilling them out, the plastic inlet remains will probably help this happen, I usually resort to the Dremel & grind the tops off the rivets, then push them out.

David

[dl6lr]

Started working on the free Tek 1240 LA.
First I confirmed the error description of the previous owner: No horizontal sync.

Found it was dropped or at least handled hard, as one edge on the backside was bent.
And it was disassembled before: The backside frame was mounted 180 degree rotated, so the slot for the COMMPACK was obstructed 
So first I dismantled and cleaned the outside, then  inside the card cage, fan and PSU.

Found the keys sticky, so removed the keyboard and gave it a wash.

After some more cleaning of all boards I powered up again and trimmed horizontal sync until I got a picture. Very touchy, minimal capture range and unstable image. Will not boot to the menu as the Li-Iodine battery in the RAMPACK is drained. Same battery on processor board. Can be replaced with a CR2032 holder as the pin distance is the same  Battery holders ordered
HSYNC signal from the display board seems OK and without jitter, so I suspect the MC1391's surrounding components on the CRT driver board, especially the caps for filtering the loop. Measured the +55V from the HT transformer and found it OK.

First removed the PSU to remove the RIFA madness, they are not at the mains, but from negative rail to ground. Furthermore the neon indicating voltage on the caps was not working. Found it black and the resistor way off. Replaced the neon and the resistor. Now waiting for RifasY-caps to arrive before reassembling.

[Specmaster]

Bah bloody humbug, I flipped a pair of speaker stands on the bay of evil back in April, sold though the Global Shipping Program to a buyer in Taiwan of all places. Now I've sold loads of things on the GSP system with no trouble, and they keep you updated with the parcels progress through their system. Yesterday I suddenly thought to myself that I hadn't heard from eBay about this parcel, so I did a trace on the parcel only discover that it was collected from the drop-off shop by the courier in the middle of the month and their system showed that they have it and its on-route.

I paid for the delivery to the GSP dept in Lichfield on the eBay PackLink system and as usual I paid the little extra to insure it for the full value, just in case. Today the courier has confirmed that as far as they are concerned, it is now lost in transit and apologised for any inconvenience, all the usual old crap.

So now I'm having to deal with PackLink to see what happens now about getting a refund.  The courier by the way was Evri, the new name for everyones favourite Hermes 

Here is my dilemma, I sold the stands for £50 plus delivery to any UK destination, the buyer paid almost £140 to eBay for the item and the shipping to him in Taiwan, assuming I get a refund for the value only of £50, is that going to mine to keep  or will that have to be passed onto eBay, who should be refunding the buyer's money in full, Will they claim any refund I get, or will they take it on the chin and pay the buyer back in full 

Thoughts?

[dl6lr]

Some pictures of the cards:

[Specmaster]

The rivets often end up spinning if you try drilling them out, the plastic inlet remains will probably help this happen, I usually resort to the Dremel & grind the tops off the rivets, then push them out.

David

I can confirm that the rivets are very likely to just spin as part of the steel mandrel is retained in the process of riveting. I had this issue when I replaced my car speaker recently and the only solution was to grind the head off and push them through.