开云体育

On Wed, Dec 1, 2021 at 9:57 PM James55 <james_55@...> wrote:

Did try with a PSU on that rail but couldn't feel any heat, although the
voltage did immediately drop to zero.

If you have a high-resolution DMM, you can play a game of warmer/colder by
measuring the voltage across components or traces. If you pump 1A in,
you'll have a voltage delta of 1V per Ohm. The traces carrying the current
to the shorted component will make like resistors, and the voltage will be
lowest next to the short. With a 6 1/2 digit DMM, especially if you zero on
the input voltage you can get really, really close to the short pretty
quickly.

On 2021-12-01 9:53 p.m., toby@... wrote:

Hi,
In the project of repairing something else (634 monitor) I rolled the ebay die on a local* 1900 test signal generator but definitely did not win, found it basically non-working (LEDs light arbitrarily, front panel non responsive).

The LV rails are within reasonable limits excepting about 1V ac ripple on +15v and about 0.3V ac ripple on the +5. Will look at replacing some of the huge pre-regulator filter caps before giving up...


--T

Service manuals are expensive on ebay for this unit and I'm not highly motivated to fix it. Anyone need a parts mule? And secondly, anyone interested in parting with a _working_ NTSC test signal generator?
--Toby
* Toronto Canada

I have to ask how you handle the transition from coax to the Xmas lights? And how you interpret the results.

A picture of two may be worth a 1000 words.
D.

Hmmmm.... I? wonder if the wife will let me buy an 11800 series scope and an SD-24 for finding bum bulbs?? I suppose it would only work for strings and not net lights.? ? Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone

Tom,
you definitely made my day with this very convincing excuse for having one of those instruments!! =D
Chris

Good question. I don’t think it matters. An interruption in the transmission line does not care if it’s a LED or a bulb. I’m so trying this on some recalcitrant light strings.

Glydeck KD6NEW

Hi Siggi and thanks for the reply.

Did try with a PSU on that rail but couldn't feel any heat, although the voltage did immediately drop to zero.

I must have motivated myself after making the post for I was able to find another shorted capacitor and also to identify the shorted rail as the 5 volt one. Following that I disconnected one of the ac wires supplying the 5v bridge rectifier and switched it on... only for the Op-Amp U1762 to promptly explode - Doh!

I'll replace that and the shorted caps tomorrow, make a dimbulb test rig before focusing on the 5v rail, and for sure I'll try the IPA trick too.

My suspicion is that the failed component lies further along inside the scope and the manual isn't the clearest as to where I might be needing to look.

It is in the 'Files' section if anyone is interested;

/g/TekScopes/filessearch?p=name%2C%2C%2C50%2C1%2C0%2C0&q=tek+466

Hi,

In the project of repairing something else (634 monitor) I rolled the ebay die on a local* 1900 test signal generator but definitely did not win, found it basically non-working (LEDs light arbitrarily, front panel non responsive).

Service manuals are expensive on ebay for this unit and I'm not highly motivated to fix it. Anyone need a parts mule? And secondly, anyone interested in parting with a _working_ NTSC test signal generator?

--Toby

* Toronto Canada

Was that incandescant or LED lights?

I have an entire bin full of LED strings that are dead and that might
be worth a try.

Paul

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows

Hey James,

I feel for you, I've suffered the slip of death too.
For finding shorted components, you might consider powering the afflicted
rail from a current limited PSU. Be sure and set the voltage below the
nominal rail voltage, and start with a low current limit.
You can then try two methods for locating the short:

1. Temperature.
Digital probing (with a finger) may work sometimes, or you can douse any
suspect components in freeze spray or in e.g. IPA to see what warms up
and/or where evaporation occurs.
2. Voltage.
With a 5+ digit multimeter, measure your way through the components on
the board until you find the one with the lowest voltage across it. That'll
be proximate to your short.

Also, before you apply mains power again, make yourself a dim bulb tester (
), and put it in series with the scope.
Save on fuses and save on stress for the power supply components.

Siggi

Just to add that so far have found three shorted caps.

Hi all.

Looking for some help to repair an old Tek 466 which I accidentally damaged.

The story is, that I bought it non-working and upon inspection found that the scope had been stored on it's face which had pushed the red 'VAR' button back into the horizontal channel, thereby breaking the potentiometer at the end of the rod.
Unable to find a replacement (as I am in Brazil), I was fortunate enough to be able to disassemble the board and do a workable repair. Further testing on the horizontal section revealed a shorted tantalum which when replaced led to the scope firing up fine and working fine.

Before putting it back in the case, I left it running to confirm that all was ok, and all was fine except I felt that rectifiers on the -8v and +5v rails were a little hot, so feeling confident set about upgrading them.
That all seemed to go fine, except for when I switched the scope back on, there was no longer had a trace.

What followed was that at some point (and for a reason I no longer remember) I decided to test the voltages on the J5 and J6 sets of pins which connect the main A6 board to the A2 vertical pre-amp board.

Whilst doing this, I slipped and momentarily shorted two pins.

This immediately blew the 1.5A fuse on the A6 board, sending the fan off at a higher speed and most of my LV power rail voltages out.

I don't remember the sequence of events following that, as I have since pulled and tested so many components that I can no longer see the wood for the trees.

The situation now, is that when it is plugged in to the mains it immediately blows the mains fuse, so if anyone has experience in locating shorted components then it would be greatly appreciated.

On 01/12/21 21:51, fiftythreebuick wrote:

Tom, the 1502 is one of the most useful instruments around!

I just finished finding the fault in a long string of Christmas lights with mine! :-) Definitely something essential to have around...

Now that hadn't occurred to me!

That's a really excellent example of using whatever is available to solve the problem at hand :)

Thanks!

Tom, the 1502 is one of the most useful instruments around!

I just finished finding the fault in a long string of Christmas lights with mine! :-) Definitely something essential to have around...

Tom

Hi Tim , I had that with a Chinese component analyzer with some 2N1516 and it was Tin wiskers . Once removed with a 15v psu it tested ok .
Brian (UK)

My Peak DCA55 often misidentifies some Germanium transistors as BiColor
LEDs.
In particular those such as 2N2209 with TO7 bases. (e-b-Case-c; the Case
lead has been clipped). Is this possibly Tin-Whisker or something about the
DCA55? My Chinese component analyser just says 'unknown component' (I'm
going through my collection of 1S1s and 3T77s)
Tim
--
"Success is a collection of well-curated failures"

On 30/11/21 07:10, John Parkins G8KVP wrote:

Hello Reg,

The 1502 is the first time 2 of my hobbies have come together, electronics and woodwork.

I can get rolls of paper that fit our credit card machine and with a fine blade they can be cut down to the right size on the bandsaw. Not that I use a lot of paper.

You mention the the illumination....... Something I've looked at and it all seemed a bit tight, so it never got done. Keep us informed on how you go about it, then I might have a go. I have to say it's the only downside to my machine.

ISTR that the paper has holes down one side, and that a photodetector detects the holes.
ISTR that someone has synthesised the signal from the photodetector so that the chart recorder works without the holes.

I don't know since I've never bothered with a recorder; I simply bought a cheap XY output plugin.

On 29/11/21 23:43, Reginald Beardsley via groups.io wrote:

All I have is the roll of paper that came with it. Since my post I've read the service manual and now understand the BNC output waveform. The narrow pulse is the sampling arm signal.

I just made a test with the chart recorder removed and I get a proper sweep. So it appears that the fault is in the Y-T chart recorder. The X-Y module attached to an Ardinuo/MSP430/STM32 to dump digits to a USB flash drive or SD card should be far more useful. I suspect a bspoke module for that would not be difficult to make.

The XY module is trivial to make; the mechanics are more difficult than the electrics. The schematics are in the manual.

Do have a look at the PSU caps. On mine C6246 and C6341 had spewed acid across the track. Fortunately the simple PCB was easily repaired.

I'm getting TDR responses with the 1502 from RF adapters and connectors which look to my eye to be quite comparable to the 11801/SD-24.

The 1502 is a fun instrument to use; I've a bit of a fetish for them.

Fortunately mine is calibrated in metres, so I don't have to mentally work out what 0.1ft is :)

A working 11801 & SD-24 are difficult to find, 10x+ as much money and have *no* component schematics available.

I suspect that schematics would have to include a symbol for "black arts employed here". Even the 485 schematics include capacitors that aren't on the board, because they are in the board or are other parasitics :)

The 1502 has schematics and appears to be easily hacked to be a very useful RF connector TDR system.

And take it to hamfests to measure cable impedance and? length :) People like looking at the hypnotic twinkling trace.

Very impressive work, Holger - well done!

And I am now aware that the abbreviation DPO once stood for "Digital Processing Oscilloscope" in Tektronix speech - but my TDS5054 D igital P hosphor O scilloscope strongly disagrees with this :-) I was just loooking at it over my shoulder. Youngsters these days...

Cheers,

Magnus

I doubt it, the HP self tests are pretty accurate in my experience. It
sounds like you got someone's parts mule. Their in an HP group on groups.io,
you might check with them.