Date   

Re: DC503 Not Working

Stephen
 

BTW, it may be worth mentioning that R331, which is connected to pin 6 of U330(B), reads 1K in circuit.


Re: DC503 Not Working

Stephen
 

On Tue, Jul 28, 2020 at 12:39 AM, <scm@...> wrote:


I finally printed the manual out and figured out what scan clock disable (pin
6) is. It is an input from the backplane connector (pin 27A). This should not
be low resistance to ground, either on the DC503 or on the backplane. It
probably won't be, however. I suspect that since there seems to be some
intermittancy involved, that something is marginally disrupting the
multivibrator. Check the driven circuits as Roger suggested. Otherwise
suspicion returns to the multivibrator, itself. Resolder all the connections,
clean the socket and IC pins carefully and, possibly for good measure, replace
the capacitors (I know they look OK DC wise).
I will do and check all what you guys very kindly suggested, and report back as soon as it’s done.
I will replace those two 0.1uF capacitors for good measure. All I have readily available at the moment are rated at 600V instead of the 100V the schematic calls for. Overkill and way much bigger as you can imagine, but that’s all I have. Will try to make them fit as the top board needs to sit on top without shorting them.


Re: DC503 Not Working

SCMenasian
 

I finally printed the manual out and figured out what scan clock disable (pin 6) is. It is an input from the backplane connector (pin 27A). This should not be low resistance to ground, either on the DC503 or on the backplane. It probably won't be, however. I suspect that since there seems to be some intermittancy involved, that something is marginally disrupting the multivibrator. Check the driven circuits as Roger suggested. Otherwise suspicion returns to the multivibrator, itself. Resolder all the connections, clean the socket and IC pins carefully and, possibly for good measure, replace the capacitors (I know they look OK DC wise).


Re: DC503 Not Working

Stephen
 

On Mon, Jul 27, 2020 at 10:52 PM, Roger Evans wrote:

Interleaved answer.


Stephen,

You have (at least) two distinct issues with comments coming in which are
relevant to one or the other and are randomly interleaved.

1. The LCD display does not scan so typically only one LED is lit.
You mean that when the unit is on, only 1 “zero” should show?
I’ve never had one of these. I thought 4 should be show (from picts I’ve seen).

This you have traced to U330. One thing that hasn't been mentioned here is that the
output from U330 pin 10 also goes to U332 pin 6 so a fault in U332 (which I
don't think you have changed)
I have changed ALL the IC’s on that board but the 2 that I mentioned in an earlier post.

would stop the multivibrator from working. If
U332 is socketed, just remove it and see if you can get the square wave on
U330 pin 10.
Will do.

2. The -22V supply is somewhere around 0V. This completely changes the bias
of the analogue input stages and makes it less likely that any inputs will
actually trigger the digital circuitry.
When I measured 0V across that capacitor, the top “Trigger Board” was removed. Hence the cap was not
connected to the coil.

Here, I at least, am confused as to
whether there is too much current draw or a fault in the voltage regulator.
Both Voltage regulators were also changed. I really changed EVERY IC’s on that board but 2.

If you can measure the voltage across R546 it should help to narrow down the
problem.
Will do and report back.

If the voltage across R546 is more than about 0.6 - 0.7V it will
turn on Q540 and shut down the regulator as intended - then you have to track
down what is drawing too much current. If the voltage is much less than this
then there is likely to be a fault in the -22V regulator and you could measure
the voltages on the base, emitter and collector of Q548. It is also worth
checking that R546 is close to its nominal value, if it has drifted high it
will shut down the regulator prematurely.

Roger
Thank you Roger.


Re: DC503 Not Working

Roger Evans
 

Stephen,

You have (at least) two distinct issues with comments coming in which are relevant to one or the other and are randomly interleaved.

1. The LCD display does not scan so typically only one LED is lit. This you have traced to U330. One thing that hasn't been mentioned here is that the output from U330 pin 10 also goes to U332 pin 6 so a fault in U332 (which I don't think you have changed) would stop the multivibrator from working. If U332 is socketed, just remove it and see if you can get the square wave on U330 pin 10.

2. The -22V supply is somewhere around 0V. This completely changes the bias of the analogue input stages and makes it less likely that any inputs will actually trigger the digital circuitry. Here, I at least, am confused as to whether there is too much current draw or a fault in the voltage regulator. If you can measure the voltage across R546 it should help to narrow down the problem. If the voltage across R546 is more than about 0.6 - 0.7V it will turn on Q540 and shut down the regulator as intended - then you have to track down what is drawing too much current. If the voltage is much less than this then there is likely to be a fault in the -22V regulator and you could measure the voltages on the base, emitter and collector of Q548. It is also worth checking that R546 is close to its nominal value, if it has drifted high it will shut down the regulator prematurely.

Roger


Re: 11801/A/B/C differences

Egge Siert
 

Hi Reginald,

I think the quickest indication of differences is page 14 of the following document:

http://www.hakanh.com/dl/docs/kitinstructions/1180fc.pdf

With CSA803C and 11801C's these are all yours. In addition: the CSA803C has only two (instead of four) Active Sampling Head Compartments and is missing the 10x Attenuator on its Direct Trigger Input.

Greetings,

Egge Siert


2440 Scope failure 9300

joe@...
 

I have been able to get my 2440 scope to pass all tests except 9300 which is identified as REPET* Does the asterisk have meaning? Any suggestions on how to trouble shoot this? I have done all of the procedures in the service manual Section 5.


Re: DC503 Not Working

Stephen
 

Thank you all.


Re: DC503 Not Working

Stephen
 

On Mon, Jul 27, 2020 at 10:57 AM, <scm@...> wrote:


It looks like you found the place where a needed signal is missing. The next
step is to trace backwards to see why. Next to check is pin 6. If it is LOW,
the multiplex clock will be disabled. If it isn't LOW, something is wrong with
the circuitry around U330 (short, open connection, bad component). If it is
LOW, we have to trace backwards to look for a problem where the signal for pin 6 comes from
Ok. I will check that tomorrow and report back. It’s past 12:00 AM over here. We are worlds apart.


Re: 11801 diagnostic help

Perdad
 

Egge, thank you for the info about 'Edge', had missed that one. Just one more button to press before doing Autoset.
Now I get the first 'clean' edge at once :o)

Reg, you live in a dream world 'over there'. Shipping alone to Europe for a CSA 803, 11801 is more than $200...
As I understand it you have a 11801 with a Calibrator output with a 20 ps pulse generator output and that is
to be able to do TDR without a SD-24 head.

What I am curious about is the importance of a fast edge for the calibration of the heads. Is there a benefit ?

Thank you for filling in !

)) Regards, Per


Re: DC503 Not Working

Stephen
 

On Mon, Jul 27, 2020 at 10:34 AM, satbeginner wrote:


Hmm, should be ok-ish.
I measured it in circuit.

Is that cool accessible?
So you can measure the voltage across it when powered on?
It’s pretty accessible, yes. It’s on the top « Trigger » board.

Is it possible to trace the voltage from where it is coming from to the C-L-C
combination?
Hmmm... maybe. I’ll have to look into that tomorrow. It’s 12:00AM over here....

I mean, maybe there is a broken wire or dodgy connection before it gets to the
C-L-C filter.
Could be.. but if you don’t mind me asking, how is it relevant to the display issue?


Re: DC503 Not Working

SCMenasian
 

It looks like you found the place where a needed signal is missing. The next step is to trace backwards to see why. Next to check is pin 6. If it is LOW, the multiplex clock will be disabled. If it isn't LOW, something is wrong with the circuitry around U330 (short, open connection, bad component). If it is LOW, we have to trace backwards to look for a problem where the signal for pin 6 comes from


Re: DC503 Not Working

satbeginner
 

Hmm, should be ok-ish.

Is that cool accessible?
So you can measure the voltage across it when powered on?

That way you would know if there is a real current flowing, or the voltage is already low when it arrives.

Is it possible to trace the voltage from where it is coming from to the C-L-C combination?

I mean, maybe there is a broken wire or dodgy connection before it gets to the C-L-C filter?

Leo


Re: 11801 diagnostic help

Reginald Beardsley
 

The key is patience and a copy of the diagnostics manual so you can find out what the error is. I've been kicking myself for missing an 11801C w/ a bad NVRAM fault which went for $80. But there will be another one.

FWIW I'm not entirely sure the SD-32 in SD-30 dress is worth the $850 I paid Tek.

I got a full refund on the dead SD-24 and have opened it up to examine under the microscope. Wow!!!!!

I knew this stuff existed and had seen photos, but those don't give you a true sense of scale. I wish there was a video of the production line for these.

The 11801C specifies jitter as:

Delay Jitter -

1.1 ps + 4 ppm of a position typical

2.0 ps + 5 ppm of position maximum (RMS)

So it increases rather a lot as you get away from the initial step. So the jitter on the 2nd step is 21-27 ps which is quite large if the rise time is 20 ps.

The rather poor spec on the 11801C calibrator makes me think Leo should offer a replacement based on his design. In 2.92 mm it would sure beat the factory calibrator and almost be as good as the 11810 calibrator. It would certainly meet the <35 ps in the 11801 manual.

Have Fun!
Reg


Re: DC503 Not Working

Stephen
 

On Mon, Jul 27, 2020 at 10:12 AM, satbeginner wrote:

And, the coil, was it really low resistance, or just 'conducting'?
The coil measures 2.2 ohms


Re: DC503 Not Working

Stephen
 

On Mon, Jul 27, 2020 at 10:12 AM, satbeginner wrote:

Interleaved

My 2 cents:

Just temporarily remove the two chips you couldn't replace, to see what the
voltage does at power on.
In order to do that, I’m gonna have to take in apart because those chips are on the main board underneath a pretty substantial “triggering” top board.
And, the coil, was it really low resistance, or just 'conducting'?
I didn’t check its resistance, just the conductivity. But I will right away.

Leo


Re: DC503 Not Working

satbeginner
 

My 2 cents:

Just temporarily remove the two chips you couldn't replace, to see what the voltage does at power on.

And, the coil, was it really low resistance, or just 'conducting'?

Leo


Re: DC503 Not Working

Stephen
 

Pin 10 of U330 checked. All I have is about 180mV DC riding on top on 25 to 30mV of AC gibberish.


A pending addition to the TekWiki

Bill Perkins
 

I lately bought a good but expensive hardcopy of Tek's 'Oscilloscope Camera Concepts' off eBay from a seller in Japan.

Due however to complications arising from the COVIDiotic Pandemographic Panic-demic he can ship only by surface mail.

S-o-o-o once it finally wends its way here I'll do a top-grade scan and up it to the TekWiki where's there's presently an empty space.

Here's a pic of the front cover:

https://www.pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/35_Tektronix/Tek_Scope_Camera_Concepts.jpg

Best,
Bill


Re: DC503 Not Working

Stephen
 

On Mon, Jul 27, 2020 at 09:23 AM, Harvey White wrote:

Interleaved

If the two capacitors are ok (when one leg lifted), yet are not shorted,
and there's still a short measured across them, then what else can be
shorted?
I didn’t measure a short across them; neither in circuit nor with one leg lifted.
They read the correct value (within specs), and there is no resistance reading with one leg lifted.

TTL Chips will measure a low resistance from vcc to gnd  when
properly biased, so many times, you may be tempted to blame the
capacitor.  Assuming, then, there's a short somewhere.
I have replaced ALL the chips on that main lower board, except for U270 & U272 which I couldn’t find.
This is frustrating as hell.
I have yet to check for a signal on pin 10 of U330.

Harvey