Test Equipment Anonymous (TEA) group therapy thread

[xrunner]

The stated total gain for the unit is +8 dB (it has a pre-amp in it using an MRF 901), but it was actually -10 when I got it. I managed to tweak it up to -1 dB gain while moving the peak response over to 144.730 MHz, but that's all I can get out of it. The transistor is working because if you disconnect power you get barely anything out, but I think it's weak, so I ordered another one to see what happens. Really that's about all I can see that can go wrong, everything else is pretty much intact.

How is the current drain? They say it should be in to 10-25mA range so if you see something different then it's time to blame the transistor. I think your tuning is fine, stated as -28dB for a 600KHz offset @ 150MHz and that is what your plot shows.

It's 15.8 mA @ 13.8 V. I attached a pic of the new tuning.

For BJTs putting too much reverse bias across the base emitter junction, i.e. a voltage in excess of V_ebo with any significant current, can permanently reduce the H_FE (and h_fe) of the transistor. Know as 'zenering' the transistor as the base emitter junction acts like a zener diode in reverse bias. Far too much current and it obviously goes 'pop!'.
It typically happens (for a common emitter amplifier) when the base voltage gets dragged out of spec (often beyond the rails) because of excess system input voltage getting past what, if any, input protection there is.

Ok thanks. I do not know the history of this unit or what could have happened. It's probably 15 - 25 years old and no telling what action it's seen. There was no schematic for the amp available so I drew one up.

Here's a few more tests. I've peaked up the system to 144.730 MHz (see pic). Tracking gen. is at -20 dB and normalized. System gain is -1.8 with power.  With no power supplied the output is at -39 dB.

I pulled the transistor and put it on the infamous transistor tester. It doesn't show the typical results for a good transistor, but shows two diodes in series. I have not seen this display on the tester, it may indicate a weak transistor but I have never tested this type of transistor before on it before and I do not know what it displays for a "weak" transistor.

[bd139]

The transistor testers seem to misbehave on RF transistors. I’ve got one that won’t read an MPSH10 and that’s not that fast. Was oscillating in the fixture.

Current is about right for that circuit. Might be weak transistor. Only way to really find out is replace it. This is quite common in high Ic circuits I’ve seen.

[PA0PBZ]

Since you see a 37 dB difference with the powered/not powered amp I can only conclude that it is now used as a (diode) switch, since the maximum you can expect from such a circuit is around 17 dB. Time to swap the MRF, it has probably been used with a repeater and it is so very easy to get your transmit power into your RF amp. 

[xrunner]

The transistor testers seem to misbehave on RF transistors. I’ve got one that won’t read an MPSH10 and that’s not that fast. Was oscillating in the fixture.
Current is about right for that circuit. Might be weak transistor. Only way to really find out is replace it. This is quite common in high Ic circuits I’ve seen.

Since you see a 37 dB difference with the powered/not powered amp I can only conclude that it is now used as a (diode) switch, since the maximum you can expect from such a circuit is around 17 dB. Time to swap the MRF, it has probably been used with a repeater and it is so very easy to get your transmit power into your RF amp. 

Yes sir(s).  Thank you for you input.

I did order the transistor yesterday and it's currently leaving CINCINNATI, OH.

I keep repeating "nothing else can be wrong" ... "nothing else can be wrong" ... 

[Cerebus]

A quick look at the datasheet for the MRF901 shows a BV_ebo of only 2.0V @ 0.1mA. As the "input protection" on that circuit is an inductor and middling value resistors to the rails I can see how even a little abuse at the input could only too easily lead to a messy end for the MPF901.

[mnementh]

In Other News...

Looking like the resistance measurement issues with my 3478A are in fact F/R jack switch-related. Cleaning seemed to help; went from fluctuating between .6 ohms and .3 ohms shorted (using banana patch cords, not clips; these measure 0.9 ohm and 0.045 ohm on my Fluke 189 and DE-5000 respectively) down to fluctuating 0.22xx - 0.19xx ohms. After reviewing the schizzmatics, I discovered I could bypass 1/2 of the switch by swapping a couple leads at J107; that dropped shorted resistance to 0.116x - 0.1170 ohms.

Part of me is saying, as I know I'm likely going to really want the rear jacks about twice in my lifetime, that I should just bypass the switch completely and solder the front ports into service; it'll be more accurate and reliable anyways... meanwhile, the purist in me keeps trying to strangle that part.  We'll see who wins after dinner. 

mnem
"There's no rest for the wicked, but the virtuous have no pillows."

That switch was my first and only suspect for the cause and also the only part of the meter that is likely to be dormant for long periods. As such it would allow crud to be building up undected  until someone activated the switch and allowed crud to migrate courtesy of the contact wiper which has some under its wiper. I'd give it another of contact cleaner and give it some beans while operating the switch remove that crud, also I'd try some pure alcohol on it, nothing to lose. [emoji38]

I've tried spraying contact cleaner in it three times; gently lifting up the top cover so I can spray inside. Last time I undid the metal stakes and removed the spring & ratchet so I could lift that end to spray inside. I'm considering to remove and immerse in alcohol while working back/forth as a last ditch effort before attempting to disassemble; it's almost as much work as disassembling though.

mnem
 

I'm eagerly awaiting the arrival of my latest acquisition, another Tek TDS210, not that I need another but it comes with a differential probe, something I have been looking for at a sensible price.

Wow, isn't that probe worth more than the scope? Nice score.

Well ordinarily yes but this one was incomplete, but I sorted that and it only has a bandwidth of 25MHz. Apart from that it is almost brand new and comes with its own pouch and manual.

 



Fine then... you're only half a Jammy Git today... a Jammy Gih...?   

Tant-Slayer? Without a doubt. I hate the little bastards. 

"Necromancer of Test Equipment"?  There you go with them big words again. I had to look that up. Wizard or Warlock practicing the occult such as raising the dead. OK, I'll buy that. I've brought numerous pieces of test equipment back from the gates of hell and made them useful again. I've also killed my share. Just yesterday through my own carelessness and stupidity I had a fatality. And I'm not gonna say right now what it was and don't ask because I am super pissed at myself. It's gonna go in the DOA (Dead On Arrival) closet to perhaps work on and possibly revive at a later day. But I don't hold out much hope that my future necromancy will work. We'll see.

Agitator-at-large? Absolutely. Never pass up the opportunity to create chaos and watch the hilarity that results. 

You see, that's where the Necromancy part comes in... as with Alchemy; for everything you gain, something must be sacrificed...   

The transistor testers seem to misbehave on RF transistors. I’ve got one that won’t read an MPSH10 and that’s not that fast. Was oscillating in the fixture.

Current is about right for that circuit. Might be weak transistor. Only way to really find out is replace it. This is quite common in high Ic circuits I’ve seen.

Mmokay... So I guess my question is... did I remember this right from back in the radio cave with grand-dad, or am I completely blowing smoke out my arse? Either is quite possible today...

I'm not the greatest with RF, but with active notch filters like this one, it's my understanding that overall gain is supposed to be relatively small, somewhere between unity and a few dB. But what's important is how much the device lowers the noise floor so that you can receive weak signals being sent at the correct frequency (and only at the correct frequency) with clarity. The lower the noise floor, the less noise gets amplified in the next stage.

I'm sure bd or med can explain it better than I; I'm a bit of a hack as far as RF goes. 

mnem
*Kindof buzzing on 4 hours sleep and 3 cups of coffee*

[tautech]

7Mhz. That’s 25W of RF. Enough to burn you (minor RF burn on finger from the LPF  ). I’ve got a Hammond box on the way from CPC. Will chuck it inside that and see if it’s radiation from the PA or up the feed. I haven’t stuffed an RFC on the DC inlet yet. This is very prototype phase stuff so I don’t want to piss on their party until I’m a good citizen

Joe's been looking at Brymen RF sensitivity based on this ^ and what you'd posted earlier........... can't replicate it.......whatever the 'mental' behavior was you mentioned. 

https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1905791/#msg1905791
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1906376/#msg1906376
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1907354/#msg1907354
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1907489/#msg1907489
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1907507/#msg1907507

@bd139
If there's something Joe's missed do engage with him so he can attempt to find the RF behavior you described.

[bd139]

I will post in that thread.

Incidentally it doesn’t do it now I’ve got the amp in a box and added a large choke.

Also incidentally I just got a VK callsign down your way with that amp at 5W out 

[tautech]

I will post in that thread.

Incidentally it doesn’t do it now I’ve got the amp in a box and added a large choke.

Also incidentally I just got a VK callsign down your way with that amp at 5W out 

That's OZ, not NZ and we're a mere 1500km further away.
Maybe that HAM has an optimized antenna. 

[bd139]

Yeah know that. Closer to you than me

[Specmaster]

@mnementh, I'll take that half a "Jammy Gih" and wear it with pride, currently looking for next super bargain while munching my KFC after just playing the "Dads taxi" role fetching no. 3 son back from his girlfriends at Woodbridge, a 100 mile round journey. Now then lets see what I go for this time, another diff probe... oir another TDS221 or perhaps a TDS220 or maybe that 6.5 digit bench meter decisions, decisions.

How are you getting on with that DE-5000 by the way?

[bd139]

Damnation now I want chicken 

TDS224 this time.

Quick video I did. This is the awesome power of a 500Hz filter:

[Specmaster]

Chicken is a bit kinder to you than that double burning curry , just hope your KFC drive through is a bit quicker then ours is. When I joined the queue my chicken was just a chick fresh from the egg, hell they are so sllllllllllllllooooooooooooooooowwwwwwwwwwww at times.

EDIT;
Hang on a cotton picking minute, what's this about a TDS224??

[bd139]

Is that the one next to the Tesco Express? If it is I've been in it on the way back from Ipswich a couple of months back and it was bloody slow then as well.

I meant go for the TDS224 this time as it is a 100MHz 4 channel TDS210 aka "the motherlode" of that series. I have been trying to hunt one down to no avail.

Edit: I mention Tesco because my oldest actually got out of the car and went and got a snack in there while we were queuing 

[mnementh]

Damnation now I want chicken 

TDS224 this time.

Quick video I did. This is the awesome power of a 500Hz filter:

Neat... so what, once you toggle the filter in, you can creep the coil up/down the with the encoder?

mnem
Any day you learn something is a day not wasted.

[bd139]

The filter is 100% fixed. You can change the IF offset slightly however which has the same effect. This is done by changing the BFO frequency I think in the 818. Whack CLAR on the bottom left and turn the left encoder.

[Neomys Sapiens]

With all that talk about LeCroys (granted, it was only I talking ), I just had to pull my 9450 out of its hiding place (didn't even remember which model I have!) and see how it did. Now that I have a decent signal generator, I'm no longer limited to AF.

The advertised 350 MHz are not too well:



But up to 200 MHz it should be pretty usable:



Of course, all controls show the LeCroy disease. Touching the Y attenuator only slightly makes it jump all over the place from 20 mV/cm to 1 V/cm.

And while I took these pictures, the doorbell rang ... (to be continued)

the Innovators of instrumentation 
I have one here where the both 1M input modules are destroyed and don`t know if a day will come I can repair that.
50 ohms works allready. The Dallas batterie is empty, like yours.

Martin

I'm not sure if it applies to this model, but on one of them I found out that your carefully set triggerlevel jumps proportionally if you change another vertical attenuation. this is the sickest, most annoying function I ever saw on a scope.
Since that time, I dream of winning a Le Croy scope at some publicity action at a fair, so that I would have a chance to answer their question, what I am going to do with it, by: 'sell it of and get a decent used Tek, of course'!

[Specmaster]

Is that the one next to the Tesco Express? If it is I've been in it on the way back from Ipswich a couple of months back and it was bloody slow then as well.

I meant go for the TDS224 this time as it is a 100MHz 4 channel TDS210 aka "the motherlode" of that series. I have been trying to hunt one down to no avail.

Edit: I mention Tesco because my oldest actually got out of the car and went and got a snack in there while we were queuing 

Yep, thats the same one alright, I was in there tonight on my way back from Woodbridge, just a few miles further on then Ipswich.

That filter is awesome by the way.

[mnementh]

@mnementh, I'll take that half a "Jammy Gih" and wear it with pride, currently looking for next super bargain while munching my KFC after just playing the "Dads taxi" role fetching no. 3 son back from his girlfriends at Woodbridge, a 100 mile round journey. Now then lets see what I go for this time, another diff probe... oir another TDS221 or perhaps a TDS220 or maybe that 6.5 digit bench meter decisions, decisions.

How are you getting on with that DE-5000 by the way?

It confuses the eff outta me. Nothing I've measured with it seems to coincide, even in the same ballpark, with any other test gear I have. The difference between my Fluke and the DE-5000 on those test jumpers is the closest it's come on anything (0.9 ohm vs 0.045 ohm, both leads) I've tested. I meant to go buy some somewhat precision caps and chokes to do some comparisons against known value components, but that got waylaid by IRL, kid's birthday and other projects. 

I'm ready for sghetti. Again.

mnem
*Easily confused*

[Specmaster]

@mnementh, I'll take that half a "Jammy Gih" and wear it with pride, currently looking for next super bargain while munching my KFC after just playing the "Dads taxi" role fetching no. 3 son back from his girlfriends at Woodbridge, a 100 mile round journey. Now then lets see what I go for this time, another diff probe... oir another TDS221 or perhaps a TDS220 or maybe that 6.5 digit bench meter decisions, decisions.

How are you getting on with that DE-5000 by the way?

It confuses the eff outta me. Nothing I've measured with it seems to coincide, even in the same ballpark, with any other test gear I have. The difference between my Fluke and the DE-5000 on those test jumpers is the closest it's come on anything (0.9 ohm vs 0.045 ohm, both leads) I've tested. I meant to go buy some somewhat precision caps and chokes to do some comparisons against known value components, but that got waylaid by IRL, kid's birthday and other projects. 

I'm ready for sghetti. Again.

mnem
*Easily confused*

Oh, OK so I won't be pulling the trigger anytime soon on a DE-5000 then, currently its not looking to be shining star its meant to be. 

[mnementh]

The filter is 100% fixed. You can change the IF offset slightly however which has the same effect. This is done by changing the BFO frequency I think in the 818. Whack CLAR on the bottom left and turn the left encoder.

*Goes back and looks again*

Oh fu***... somewhere I got the notion it was a multi-stage inductor-capacitance-crystal filter tuned with a moving ferrite connected to a servo motor. I have NO idea where, as the page from wa3key's site clearly describes it as a fixed-frequency design using mechanical harmonics as the filter.   

mnem
Of all the things I've lost, it's my mind I miss the most.

[mnementh]

Oh, OK so I won't be pulling the trigger anytime soon on a DE-5000 then, currently its not looking to be shining star its meant to be. 

No, I've seen other folks using it to amazing accuracy. I honestly believe my problems are 100% fuckwit user error; it is a real-live LCR Bridge with an automated testing process I don't fully understand.

Problem is, I've always been easily confused with time constant math and substitution transforms, so even using a regular LCR bridge effs with my head.   

mnem
I am too old for this shit.

[bd139]

Random question - is it worth buying something TEA related if it's worthless, mostly useless, really quite shit and broken for £25 but just because you couldn't afford one when you were a kid and feel like there's a hole?

[Neomys Sapiens]

The only thing that's missing are schematics for the A version, 5334B's are readily available (the user's manual covers both, A and B).
As long as it works, there's no real need, however.

Oh, and it actually has its original feet!

That is indeed a decent counter. As opposed to mine, even with grips!
One guy at a company where I was once, who was yet unaware of my TEA, was praising the 5328 beyond it's merits. He was  astonished when I told him that the successor (the 5335) is a nicer instrument and that I have it. Maybe he thought that someone who states that he keeps a lab at home has to be content with Heathkit or ELV.

But if you find that manual somewhere, please let me know - same situation here! (Applies reciprocally, of course) If you would like to exchange those pesky feet and grips for a set of rack mounting brackets, I would be able to help, too.

[Specmaster]

Oh, OK so I won't be pulling the trigger anytime soon on a DE-5000 then, currently its not looking to be shining star its meant to be. 

No, I've seen other folks using it to amazing accuracy. I honestly believe my problems are 100% fuckwit user error; it is a real-live LCR Bridge with an automated testing process I don't fully understand.

Problem is, I've always been easily confused with time constant math and substitution transforms, so even using a regular LCR bridge effs with my head.   

mnem
I am too old for this shit.

Yeah, its basically as far as I understand it much the same as my Digital Bridge XJW01, the only parameter on that, which I can change is the test frequency between 100Hz, 1KHz and 7.8KHz and for my purposes 100Hz is adequate for the electrolytic caps in audio gear, maybe the 1KHz at times but not the 7.8Khz thats more for the RF guys in my view. But like I said before, the XJW01 always seems to be pretty accurate in my findings. But I still keep hearing people wax lyrical about how amazing their DE-5000 is and yet I'm still not convinced it's going to offer me any greater accuracy over the XJW01 at all.