Test Equipment Anonymous (TEA) group therapy thread

[m k]

Eager repairman troubleshooting Fluke 8505A power.

Testpoints checked, 5V missing.
But where is the regulator, under the transformer cover ?!?!
Dang, imperial hex.

[Vince]

Metrix type 920 RF generator

OK could not resist ! I emptied my box of BANANIA where I have been keeping all my salvaged power resistors for the past 30 years now, in search of a suitable dropper resistor for the power supply. Manual says it's 10K 10% and 2 Watts. The one in place is 8.2K and more like 10 Watts, way too big.

Spent an hour sorting through all these resistors, eventually got lucky and found not one but two 10K ones, with a more reasonable wattage to boot. 7 Watts, half the size of the existing one, and still 3+ times more than what Metrix meant to use... so should do it.

One is a ceramic bodied / sand packed one, with radial leads, and reads 9,75K which is 2,5%, so plenty accurate enough, meets the required 10% easily.

However I chose to use the other one, as was much better : much older package, looks more period / fitting, has axial leads which is what we need, and Fluke DMM measured it between 9,99 and 10.00K ! good enough for me ! 

So I soldered that in place, and measured voltages. Previously we got 157 Volts instead of 135 indicated on the schematic. Now I get 145 V ! Half way there, still 10 more Volts to go... hmmm... what gives.

Anyway, it was enough of  a change that IF that was causing my problems, it would now show SOME change, at least some... change. But it did not.. at all.
Modulation signal still runs at 360HZ bang on, no change at all. Did not make any effort to even slightly towards the  expected 400Hz.
As for modulation factor, same thing. Still stuck at 50% instead of the required 30%.

So.... it was good fixing the power supply, needed doing, but it's not what's causing me problems.
So not sure there is much point trying to increase the value of the dropper resistor above the specified 10K. Voltage levels on schematics, I find, are really only a mere guide line... plus they are measured usually with a low-ish impedance analog meter not with a VTVM, so me using a DMM is bound to read a bit higher than what they measured with an analog meter...though it should not be enough to justify a 10 volts difference... that's a bit much.

Anyway, it does not worry me more than that, I would happily leave it at that...

So back to the other most likely cause : a resistor somewhere that drifted, or some bad cap...

But that's not the end of the world eh...I am just nit picking here. Most important was fixing the power supply.

[BU508A]

Merry Christmas to all of you! Enjoy your time with family and friends and have a lot of fun!

Regarding fun: Some nice science toys:

[factory]

Does anyone know under which COMMERCIAL other designation the Wayne Kerr 2400L signal generator does appear and from which company? That it is also an SG-1207A/U I do know. But I am also sure that I did see in in another guise. Maybe that one was indeed the OEM.

Some Wayne Kerr stuff was also sold under the Farnell brand (not the component supplier with the same name), that sig gen looks similar to the Farnell PSG2400A, but I can't comment on whether it is the same spec inside.

David

[mnementh]

Metrix type 920 RF generator


Just worked a bit more on it, now reporting. Had a Eureka moment that might well explain why the output amplitude was dropping progressively, and so much, as frequency increases.... I mean other than a weak RF tube.

I realized that it was most likely operator error (again... again.)

LOL... my take after decades of tinkery in many different lines of work... is that these moments (and trust me, there have been plenty) are really a blessing in disguise.

Once you get over the initial      moment (and the rush of embarrassment; good on ya for sharing nonetheless ), comes the sense of relief that your tool is fully functional   , and you have a new toy to play with on your bench. Or that a favorite "old faithful" really still is.

One thing I have finally learned (okay, tried to learn) in recent years and Ifni knows how many wasted hours... is to RTFM at the first signs of something wrong with my instrument.

*looks at thein the mirror*   Yeah, I'm talkin' to YOU.


Congrats on saving a nice bit of vintage kit from the abyss... keep up the good work!

But uhhh... dust your damn scope every once in a while, 'kay...? *cringe*

I keep a fine-bristle paintbrush in a drawer that I only use for this, to keep it from getting fouled with contaminants that leave streaks on the screen.

mnem

[factory]

Metrix type 920 RF generator

OK could not resist ! I emptied my box of BANANIA where I have been keeping all my salvaged power resistors for the past 30 years now, in search of a suitable dropper resistor for the power supply. Manual says it's 10K 10% and 2 Watts. The one in place is 8.2K and more like 10 Watts, way too big.

Spent an hour sorting through all these resistors, eventually got lucky and found not one but two 10K ones, with a more reasonable wattage to boot. 7 Watts, half the size of the existing one, and still 3+ times more than what Metrix meant to use... so should do it.

One is a ceramic bodied / sand packed one, with radial leads, and reads 9,75K which is 2,5%, so plenty accurate enough, meets the required 10% easily.

However I chose to use the other one, as was much better : much older package, looks more period / fitting, has axial leads which is what we need, and Fluke DMM measured it between 9,99 and 10.00K ! good enough for me ! 

So I soldered that in place, and measured voltages. Previously we got 157 Volts instead of 135 indicated on the schematic. Now I get 145 V ! Half way there, still 10 more Volts to go... hmmm... what gives.

....snip....

Umm, looking at the circuit diagram you posted, the power supply will vary from what is given on the diagram because it is unregulated, changes in line/mains voltage will cause it to go up or down.

And the solid state rectifier will have a lower voltage drop than the hollow state one, you would normally add a resistor in series to compensate for this.

David

[BU508A]

Just a little reminder:

Launch of the James Webb Space Telescope tomorrow.

Countdown here: https://jwst.nasa.gov/content/webbLaunch/countdown.html

Live stream here: https://www.nasa.gov/nasalive

Keep my fingers crossed!

[Brumby]

Keep my fingers crossed!

.... and thumbs pressed?

[BU508A]

Keep my fingers crossed!

.... and thumbs pressed?

Of course!

Not sure about doing it at the same time ...   

[Vince]

Metrix type 920 RF generator


Just worked a bit more on it, now reporting. Had a Eureka moment that might well explain why the output amplitude was dropping progressively, and so much, as frequency increases.... I mean other than a weak RF tube.

I realized that it was most likely operator error (again... again.)

LOL... my take after decades of tinkery in many different lines of work... is that these moments (and trust me, there have been plenty) are really a blessing in disguise.

Once you get over the initial      moment (and the rush of embarrassment; good on ya for sharing nonetheless ), comes the sense of relief that your tool is fully functional   , and you have a new toy to play with on your bench. Or that a favorite "old faithful" really still is.

But uhhh... dust your damn scope every once in a while, 'kay...? *cringe*


mnem

It was clean 3 days ago ! but two days ago I sanded 100% of the concrete floor in the bedroom, to get rid of all the filler and paint blobs, and make the entire floor smooth enough to then lay and glue the cork layer, so I can then lay the floating parquet which I am soon to go shopping for.
While doing so I closed the bedroom door and opened the window of course, but still was lot of  cement dust. I am sure I lost 2 years worth of life expectancy in the process. I thought it would be enough. It was not. I should also have gone the extra mail and put a wet mop to seal the bottom of the door to keep dust from escaping from the gap. Too late. Now dust everywhere in the living room aka the lab.

[Cerebus]

Ah, I am sure it is a very beautiful area.  I checked, and I have not had the pleasure to visit there.  The name sounded familiar, but I was in fact remembering Varena, Trentino.

I've been to Trentino-Alto and can attest that it's beautiful, at least in Winter - never been there in Summer. The area is also known as Sudtirol because over the years it has flipped backward and forward between what passed for Italy at the time and what passed for Austria at the time. The area has a bad dose of food schizophrenia, you never know whether you're going to get served a mountain of pasta, a heap of dumpings or an avalanche of Kartoffelsalat.

[Vince]

Umm, looking at the circuit diagram you posted, the power supply will vary from what is given on the diagram because it is unregulated, changes in line/mains voltage will cause it to go up or down.

And the solid state rectifier will have a lower voltage drop than the hollow state one, you would normally add a resistor in series to compensate for this.

David

Yes I agree !    What I omitted to say is that the voltage at the other end of the dropper resistor, 240V, is spot on in agreement with the schematic. So that's why I thought if correct voltage on one side / input but not correct at the other side / output of the dropper...

[Vince]

Just a little reminder:

Launch of the James Webb Space Telescope tomorrow.

Countdown here: https://jwst.nasa.gov/content/webbLaunch/countdown.html

Live stream here: https://www.nasa.gov/nasalive

Wow, spot on for X-mas day ?! That's pretty neat...

[Cerebus]

I case I don't get a chance later let me wish you all a Very Merry, Very Messy* Christmas.

Right, back into the fray. Currently up to the elbows in butter, flour and mushrooms.

* I agree with Baldrick, a good Christmas is populated with sticky, messy, delicious things.

[mnementh]

The view from my front window this morning.

Well, the window for getting leaves raked has passed... gonna have to deal with the mess and tripled work sometime later.

The last package was delivered this morning; 250 liters of bean bag beans for my daughter's Christmas present. My poor postal carrier. 

mnem

[Cerebus]

Oh, just found this:

[Martin.M]

have a nice christmas.

[FransW]

Just a little reminder:

Launch of the James Webb Space Telescope tomorrow.

Countdown here: https://jwst.nasa.gov/content/webbLaunch/countdown.html


Live stream here: https://www.nasa.gov/nasalive

Keep my fingers crossed!

Boarding time?

[AVGresponding]

It was the morning before Christmas, and all about the house, not a creature was stirring, except the postie who rudely awakened me at 10:30 or so to deliver a package from Gettysburg, address: mine.

No pics, just spent all day tinkering with the HP 5245L thanks to the arrival of three display boards, a power lead, and a secret bonus of four spare nixie tubes (untested), from nixiefreqq.

I now have 8 fully functional display boards, one has a Russian tube and has to sit in A10 as it's too big to fit between the decimal point neons!   
The spare tubes made it possible to resurrect two of my faulty boards; two of the spare tubes work, though dimly, one does not work, one works on all numbers except "3".
The third faulty board has another fault on it anyway and so is being used as a donor; more on that later.

With all displays working I am now able to get a clearer idea of the other issues, or at least some of them.
1) Incorrect readings on some time base settings.
2) Incorrectly flipping "0" to "1" during gating, resets to "0" at end of gate period. Two digits are affected.

The perfect stability of the incorrect readings pointed to a divider problem, and swapping the divider boards around confirmed this at least was part of the problem. Found a borked transistor on one of the boards, naturally it's a germanium selected HP special part. Fortunately the faulty display board has them, so sucked one out and replaced the dead one.

Worked for a while, but now I'm getting stable incorrect readings in the opposite direction!   
(Was reading 0.6 for a value of 1, now it's 1.67) I suspect the A35 Time Base Control board, but I've had enough for today.



In any case, felicitations of the season, and goodwill to all, and especially Mr Nixiefreqq!

[mnementh]

...But uhhh... dust your damn scope every once in a while, 'kay...? *cringe*

It was clean 3 days ago ! but two days ago I sanded 100% of the concrete floor in the bedroom, to get rid of all the filler and paint blobs, and make the entire floor smooth enough to then lay and glue the cork layer, so I can then lay the floating parquet which I am soon to go shopping for.
While doing so I closed the bedroom door and opened the window of course, but still was lot of  cement dust. I am sure I lost 2 years worth of life expectancy in the process. I thought it would be enough. It was not. I should also have gone the extra mail and put a wet mop to seal the bottom of the door to keep dust from escaping from the gap. Too late. Now dust everywhere in the living room aka the lab.

I have no idea what you're talkin' about! 

Now it's fixed, I can use it to make a proper rip fence for my huge-arse table-saw; got me some old bed frames to cut up for angle iron. 

How huge arsed ?Pics ?

   
Craftsman Model 113; 10"/3HP. Cast iron deck, with both cast iron extensions. Weighs almost as much as a mnem. 

Here's a pic of its huge arse (and mine) from when I was cutting hardwood for my "recycled from and with recycled" patio chair project.  I think I posted about this project before.

mnem
"That's not sawdust. It's man glitter." ~me

[Saskia]

been driving all night my hand on the wheel ...

4th tour complete.

The V70 for towing does not cut it, it barely makes it across Hunsrück and Eifel. Gas mileage is appaling.

Unloaded my stuff. Sinking in moving boxes.
Still no end, but I brought most of my test equipment. will need approximately 3 - 4 additional tours to get everything up here.
mah back hurtz ...

Merry Christmas to you Christians out there.
Can someone loan me the Coke truck ? Moving might go easier with that one ...

[Saskia]

in Other News:
my Reichelt Care package arrived. 20 IRL 540N ... that should suffice for a few hours ...

[Cerebus]

I developed a taste for this particular combination back in my student bartending days, it was the favoured after work tipple of the Bar Manager, Assistant Bar Manager, and floor mopper (me). Haven't had one in probably thirty years and decided to treat myself this Christmas.

Cheers!

[Saskia]

Skol !

Wouldn't the Rum be better without the Coke ?

[Cerebus]

Skol !

Wouldn't the Rum be better without the Coke ?

Weirdly, no. This combination just works^TM.