Tek 475 SWEEP CONTROL IC

[baumfred]

Hello,
I'm repairing a Tek 475 scope with following problem: the scope is well running but I have no sweep in Auto mode without input signal and the trigger lamp is always on.
I bought three new sweep controll IC 155-0049-01 in the last weeks from different suppliers, but none is running in this 475. Otherwise they are all running in the Tek 465!

Is there a different between 155-0049-01 and 155-0049-01 In the 475 only the original IC is running. When I use the new IC's, I have no sweep and no function of horizontal board.
Could someone help me?

Thanks, baumfred

[tggzzz]

The folks on the Yahoo TekScopes group may well have an answer.

[oldway]

In my documentation, I found U600 ref. 155-0049-02 and not 155-0049-01
I confirm this, on a spare board that I have, it's indeed 155-0049-02.

[baumfred]

Hello,
it depends on the version of the scope. I tested the ..02 also with the same result.
In Tek 465 both are running - the 01 and 02.
Thanks, baumfred

[oldway]

Check voltages at pins 12 and 19 of U600

[baumfred]

Hi oldway,
I have 0V on both pins.

[PaulAm]

You might have a problem in the trigger generator.  There's one for each channel; do you get the same behavior if you set the trigger source to Channel 2?  What if you use an external trigger?

[David Hess]

Hello,
I'm repairing a Tek 475 scope with following problem: the scope is well running but I have no sweep in Auto mode without input signal and the trigger lamp is always on.

That makes some sense.  In order for the automatic sweep to activate, the RC delay at pin 6 needs to timeout but the trigger lamp indicates that this is not happening.

I bought three new sweep controll IC 155-0049-01 in the last weeks from different suppliers, but none is running in this 475. Otherwise they are all running in the Tek 465!

Is there a different between 155-0049-01 and 155-0049-01 In the 475 only the original IC is running. When I use the new IC's, I have no sweep and no function of horizontal board.

Usually there is no functional difference between minor revisions of the integrated circuits and your test indicates a problem with the 475.

I would take a close look at C609 and R609 off of pin 6 of the sweep integrated circuit.

Here is a bittorrent magnet link to the data for the 155-0049-01:

magnet:?xt=urn:btih:EE37420AE83694F7FD67E53840541FED33CFB906

[baumfred]

Hello,
to PaulAm: the problem is the same with channel 2 or extern trigger.

To David Hess:
- I tested the C and R at pin 6 - they are ok. (1,1uF and 100,5kOhm)
- Sorry - I'm not familiar with bittorrent.

The problem is that I get no sweep sawtooth in Auto mode and without an input signal.
With input signal from the calibrator the scope is running well with the original sweep control integrated circuit.

But when I put any other sweep control integrated circuit in this scope I have no horizontal function. No signals at the tunnel diodes, no sweep sawtooth, no display, no signal at TP572. Only two points with the beam finder. The IC's are ok, they run well in a 465 scope.

It looks like that only the original sweep controller is running in this scope, and this controller is not 100% ok   (Trig'd lamp always ON and no line without input signal).....

[tggzzz]

If I understand you, the ICs work in a 465, but in a 475 "norm" works but "auto" doesn't.

First question: are the auto and norm switch control inputs "reaching" U600 pins 12, 18 and 19?

Second question: in auto mode, are the "auto RC" and +TDout waveforms on pins 3 and 6 correct?

If all that is correct, then are Q574, Q572 and associated components operating correctly?

[baumfred]

If I understand you, the ICs work in a 465, but in a 475 "norm" works but "auto" doesn't.

Yes, so it is.

First question: are the auto and norm switch control inputs "reaching" U600 pins 12, 18 and 19?

- Pin 12: 0V in AUTO, 0V in NORM, 5V in Single SWP
- Pin18: 0V in all positions, 4.4V in X-Y
- Pin19: 0V in AUTO, 1.45V and 1.6V in NORM and Single SWP

Second question: in auto mode, are the "auto RC" and +TDout waveforms on pins 3 and 6 correct?

- Pin 6: without input signal: 2.8V DC. With input signal (calibrator 300mV on CH1) : sawtooth pulses with 80mV on 50mV +DC
- Pin3: without input signal: 180mV DC. With input signal 15mV pulses on 180mV +DC.
- In my manual are no informations about waveforms...

If all that is correct, then are Q574, Q572 and associated components operating correctly?

- without input signal I have on each collector -800mV. With input signal 50mV pulses on this DC levels.

[tggzzz]

The only obvious difference I see on my schematic (a high-res schematics-only document from somewhere on the web) shows U6006 as 5.2V with an 80mV sawtooth that looks like a sharks fin in the water:)

Are R609/C609 faulty?

[baumfred]

The only obvious difference I see on my schematic (a high-res schematics-only document from somewhere on the web) shows U6006 as 5.2V with an 80mV sawtooth that looks like a sharks fin in the water:)

Are R609/C609 faulty?

Hi, thanks for the answer!
- I found the hi-res schematics on the web, thanks!
- I have the sawtooth, but only with the original sweep control IC. (155-0049-01)
- I checked R609 and C609 - they are ok.

But when I use one of my new sweep control IC's, I have no function of the tunnel diodes.
At Q552/556 and Q562/566 the DC levels are ok. I can measure the trigger signal until the base of the two last transistors.
I checked the transistors, and tested also the transistors from B-trigger. There is no function from the tunnel diodes.
With the original sweep controll IC the tunnel diodes are running well.

I have three sweep control IC's which are all running in a 465 scope, but not in the 475. In the 475 is only the original IC running, but in this case the trigg'd lamp is always on and I have no line in auto mode.

[PaulAm]

If you haven't seen this, there's a data sheet on the -02 version at the Tek wiki

http://w140.com/tekwiki/wiki/155-0049-02

Unfortunately, I can't find specs on the -01 version.  Generally, later versions can replace earlier versions, but it's possible the reverse may not be true.  The 475 has twice the bandwidth of the 465, so it is possible it needed a higher performance chip.

Can you find any of the -02 versions to try?  It's possible your original was selected for the 475.

If the triggering works correctly when you put the original into a 465, then it's likely the problem lies in some other component.

Hmm, my manual shows -00 suffix for u600, so that shouldn't be a problem.

How did you test the capacitor?

[tggzzz]

Have you checked the power rails near the IC, to ensure there are no spikes that might upset a faster IC's operation?

Consider soldering (or even just touching) a short-lead decoupling capacitor across the power rails nearby.

[baumfred]

Hi,
sorry for the delay!

Have you checked the power rails near the IC, to ensure there are no spikes that might upset a faster IC's operation?

Consider soldering (or even just touching) a short-lead decoupling capacitor across the power rails nearby.

Yes, I have done. There are ok, no spikes, best soldering. All supply voltages ok, measured with scope and DMM.

If you haven't seen this, there's a data sheet on the -02 version at the Tek wiki

http://w140.com/tekwiki/wiki/155-0049-02

Unfortunately, I can't find specs on the -01 version.  Generally, later versions can replace earlier versions, but it's possible the reverse may not be true.  The 475 has twice the bandwidth of the 465, so it is possible it needed a higher performance chip.

Can you find any of the -02 versions to try?  It's possible your original was selected for the 475.

If the triggering works correctly when you put the original into a 465, then it's likely the problem lies in some other component.

Hmm, my manual shows -00 suffix for u600, so that shouldn't be a problem.

How did you test the capacitor?

Yes, I checked the capacitors, all ok.
I have also the 02 version of the U600, but in this 475 they all do not start. No pulses at TP572, 0V at the tunnel diodes.
I have the spec from the 02 version, from version 01 and 00 there is no spec in the net.
The new U600 are all running in the 465, version 01 and version 02.
The original U600 from the 475 shows the same problems in the 465. (no beam in AUTO mode, and trigger lamp always on)

Now I bought a complete horzontal board in US and will test it in my 475, but this takes some weeks until it is delivered.
I will be back when I have new informations.

Thanks, Fred

[tombi]

Hello,

Could it be the circuit that detects the end of the sweep (that triggers the hold-off state) isn't working correctly? Maybe auto-mode isn't happening because it thinks it hasn't gone into hold-off yet. Could try looking at the signals going to Q594/Q596 and if they aren't right look at Q944/946. Does twiddling the hold-off knob change anything?

If you have problems with the trigger circuits you can swap parts between the A and B trigger and see if it changes things (tunnel diodes, paraphase amps etc).

Good Luck!

Tom

[whitevamp]

sorry to hijack this thread but i wanted to say thanks for some of those tek links.
they helped me find figure out what some of the tek parts are that i have, that i couldn't find info on.   

[Ray.B]

I found a Tek Troubleshooting manual on this sight EEVBlog (2230 problem)

    http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

This has troubleshooting charts for 465 and 475 scopes and for troubleshooting sweep circuits, auto circuits, end of sweep, etc...

    later Ray B.