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Re: Tek 2445 High Voltage Board replacement

 

Hi,
Did you solve your no display problem?
I have the exact same problem with my 2465, in that removing the red wire pin 7 to U1830 Q1981 no longer gets extremely hot and the -15v returns.
Did replacing U1830 the HV multiplier fix your problem?
gazza
2465. CR1110

 

Trying to find a current replacement for this, has any got a suggestion? Found reference to MBR40H45CT-E3/45 but this is no longer available.
Re: FG502 with no working FREQUENCY control

 

Mark,

Thanks for the support, I will probably need it.

I have taken some measurements of the front panel controls (AMPLITUDE and OFFSET pots) and the AMPLITUDE pot is all over the place, not linear at all, so that explains one of the problems. I will need to rehab or replace the front panel controls. I still need to look at the trim pots and caps, but I'm betting I will find that they are also dirty/faulty.

Again, the moral of the story is: don't overlook the obvious stuff.

I already checked a bunch of the carbon comp resistors, and every one that I looked at was in spec (surprising!), but now I'm going to sample some of the tantalum caps, because I've already had the experience of apparently pristine tantalum caps being secretly bad (had one on the vertical board in a 485 that looked perfect, but was shorted, and took down the +15 V rail).

The trim pots are the open "pancake" variety (Bourns 3352 series?). I will try hitting them with some DeOxIT FaderLube, but exercising them will mean that I need to do a full recalibration on the unit. Fun. I will use my brush+IPA plan for the trim caps. If I can't rehab the existing trim pots, however, I am planning to replace them with modern blue Bourns multi-turn trimmers (Bourns 3299 series?), because it looks like I can get them with a similar footprint (gotta be able to fit them into the same pads on the PCB).

For the trim caps it looks like I can get an exact replacement. I'm not sure that's the best option, but at least I know they will match the pads on the PCB. The only thing I don't understand about the trim caps is why they seem to have three terminals, but if I've got exact replacements I guess I don't need to understand that.

-- Jeff Dutky
Re: Type 106 Saga (Again)

 

I don¡¯t think so, it¡¯s the original one. But I did, at some point, change it for the 3 other modern ones I have, and they were performing perfectly¡­. When the unit ¡°was¡± working¡­
Re: Type 106 Saga (Again)

 

On Tue, Mar 15, 2022 at 04:26 AM, P F wrote:


Stephen,

It's not just that control setting but its effect upon the three main power
supplies that is what is so remarkable and is why I had emphasized following
the set up in the manual for measurements.
Unless I was distracted, I¡¯ve always followed the setups in the manual as far as measurements.

It was also why I did effect the
change for Q247 with the TO-3 NTE175, which is rated for around 500 volts (but
as I am a valve man, I can't tell you which electrode on the transistor!
Sorry.)
A TO-3 will barely even fit in there¡­. Is that what you used? Maybe a TO-220, I don¡¯t know.
So far the 2N3585 I have in there seems ok. All the voltages at it¡¯s pin are within specs. I believe it¡¯s a direct replacement for the 2N4240; same specs.

Anyhow, if you haven't, you might want to change to an NTE175 or 2N4240 for
Q247, along with the 27 ohm dropping resistor for the collector, etc., etc.
Also, the 1 mF capacitor is actually soldered to that blasted Amplitude pot.!
Upper leg for the positive and the bottom, which should be connected to
chassis, at least eventually, for the other.
I will check R242 (27R). Maybe it has drifted.

As for my difficulty, I found that loading Q257 with the aforementioned meter
probe killed the oscillation. I have another 2N3441 from a different vendor
and will see if it behaves better. When it doesn't, I'll probably bang in a
low value ceramic across the output of the bridge rectifier.
I have a few of them that were working beautifully until, well¡­ now.

I will post some photos I took of the waveform, although it's just a very,
very high frequency sine wave, per my dear old 547 at its highest sweep speed
(I am away from my notes and don't remember the actual frequency, alas.).
Sure!

Yes, it is a very frustrating instrument and has made me want to chuck all of
the Tek gear at times, but I am hanging in there - and learning from the
damned thing!
Me too.
Re: Type 106 Saga (Again)

 

could Q257 have either too high a beta or too high a frequency response?

Harvey

On 3/14/2022 11:26 PM, P F wrote:
Stephen,

It's not just that control setting but its effect upon the three main power supplies that is what is so remarkable and is why I had emphasized following the set up in the manual for measurements. It was also why I did effect the change for Q247 with the TO-3 NTE175, which is rated for around 500 volts (but as I am a valve man, I can't tell you which electrode on the transistor! Sorry.)

The other power transistor, Q257, seems to be in a better designed circuit that is not whipped around to the limits of it. I lost mine due to a slip of a probe and an ensuing short circuit. First time I saw smoke in my electronics hobby career!

Anyhow, if you haven't, you might want to change to an NTE175 or 2N4240 for Q247, along with the 27 ohm dropping resistor for the collector, etc., etc. Also, the 1 mF capacitor is actually soldered to that blasted Amplitude pot.! Upper leg for the positive and the bottom, which should be connected to chassis, at least eventually, for the other.

As for my difficulty, I found that loading Q257 with the aforementioned meter probe killed the oscillation. I have another 2N3441 from a different vendor and will see if it behaves better. When it doesn't, I'll probably bang in a low value ceramic across the output of the bridge rectifier.

I will post some photos I took of the waveform, although it's just a very, very high frequency sine wave, per my dear old 547 at its highest sweep speed (I am away from my notes and don't remember the actual frequency, alas.).

Yes, it is a very frustrating instrument and has made me want to chuck all of the Tek gear at times, but I am hanging in there - and learning from the damned thing!

PMF
465/475 to 485 front cover swap

 

Hello,

I do have an original front cover for scope models 465/475 in perfect condition, and would like to swap it by one for model 485.

I can send pictures upon request.

Note: I am not interested in 3D-printed, wood-made or any other replacements.

Thanks !

Rubens
Re: Type 106 Saga (Again)

 

Stephen,

It's not just that control setting but its effect upon the three main power supplies that is what is so remarkable and is why I had emphasized following the set up in the manual for measurements. It was also why I did effect the change for Q247 with the TO-3 NTE175, which is rated for around 500 volts (but as I am a valve man, I can't tell you which electrode on the transistor! Sorry.)

The other power transistor, Q257, seems to be in a better designed circuit that is not whipped around to the limits of it. I lost mine due to a slip of a probe and an ensuing short circuit. First time I saw smoke in my electronics hobby career!

Anyhow, if you haven't, you might want to change to an NTE175 or 2N4240 for Q247, along with the 27 ohm dropping resistor for the collector, etc., etc. Also, the 1 mF capacitor is actually soldered to that blasted Amplitude pot.! Upper leg for the positive and the bottom, which should be connected to chassis, at least eventually, for the other.

As for my difficulty, I found that loading Q257 with the aforementioned meter probe killed the oscillation. I have another 2N3441 from a different vendor and will see if it behaves better. When it doesn't, I'll probably bang in a low value ceramic across the output of the bridge rectifier.

I will post some photos I took of the waveform, although it's just a very, very high frequency sine wave, per my dear old 547 at its highest sweep speed (I am away from my notes and don't remember the actual frequency, alas.).

Yes, it is a very frustrating instrument and has made me want to chuck all of the Tek gear at times, but I am hanging in there - and learning from the damned thing!

PMF
Re: Type 106 Saga (Again)

 

Did I mention that the maximum amplitude on the full blast Hi-Amplitude setting, is only around 50mv?

I¡¯m wondering what gave this time¡­
This is definitely THE most frustrating piece of equipment I¡¯ve ever owned¡­
Re: Type 106 Saga (Again)

 

David,

The TO-220 you mentioned are indeed more robust. But due to a significant difference in the form factor, I can only assume that mounting them correctly may not be that easy or pretty, but it¡¯s definitely doable.
Re: Type 106 Saga (Again)

 

Well¡­. It seems I spoke too soon.
While checking the calibration, the unit started to fail again. But this time R233 and D233 are fine.
At first, the negative part of the square wave started behaving when the unit warmed up after a few minutes.
Now it¡¯s from the start.

Images:
Here on a DSA602A.
/g/TekScopes/photo/273030/3397297?p=Created%2C%2C%2C50%2C2%2C0%2C0

Here on a 466.
/g/TekScopes/photo/273030/3397298?p=Created%2C%2C%2C50%2C2%2C0%2C0
Re: Tek 2465 stuck in horizontal sweep

 

On Mon, Mar 14, 2022 at 03:09 PM, clunche wrote:


Hi Ozan,

I was able to remove the time base knob and there were two screws hidden by
the moving plastic part mounted on springs: you need to gently push and then
you can access the two screws. It took me time to figure out where the A-B
I think service manual hints to pushing the knob to see the set screws too.

...

Regarding the knobs I crushed, I asked for a 3D printing of this one
() and the guy charges 15 € for
three parts in either color : )
I bought some 3D printed ones and their finish was too rough. I ended up not using them. I don't know if it is the same vendor though. You can watch knobs on the auction site or try one of specialized Tek parts vendors.
Ozan
Re: Tek 2465 stuck in horizontal sweep

 

Hi Ozan,

I was able to remove the time base knob and there were two screws hidden by the moving plastic part mounted on springs: you need to gently push and then you can access the two screws. It took me time to figure out where the A-B lever was but it right under the panel and I think it was the guilty part so I cleaned carefully and it seems operational now. I have partly brought everything back now and will continue tomorrow but I spotted another bad contact, apparently on one of the three pot meters accessible by the shafts: the one associated with CHAN 1 seems glitchy so I will clean the three of them tomorrow.

Regarding the knobs I crushed, I asked for a 3D printing of this one () and the guy charges 15 € for three parts in either color : )

Cheers,

Christophe
Re: Tek 2465 stuck in horizontal sweep

 

Hi Christophe,
My comments are below.

On Mon, Mar 14, 2022 at 12:58 PM, clunche wrote:


Hello gents,

Almost there! I received the Allen key 1/16" today and could remove the upper
knob of the time base switch and I did inject cleaning spray along the shaft
and it seems to help. Actually, I located the issue in the delayed B time base
actuation via the pulling of the knob: it sometimes does not go back correctly
and I can see the DLY sign still on time to time. However, and this is good
now because when properly pushed back, then powering on and off the scope
brings the correct screen and the trace is nice! So the issue is truly located
there.
Great news, looks like you are close to fixing the scope for good.



Now, if I have successfully removed the first time base knob, I am stuck at
removing the plastic part associated with the 3 springs. I have seen what I
thought to be a miniature screw but it is not - a kind of key - which keeps
the spring always in tension. I need to carefully remove this small black part
but it seems well locked inside. I've tried with a small thin plier but I'm
afraid to break it. What do you recommend?
Unfortunately 2465 knob is different than 2467B knob so I don't have any direct knowledge. However, page 6-27 of service manual describes removal of the A/B timebase knob. It only mentions set screws.


Could you also please confirm from the schematic diagram that the B switch is
J601 marked as PUSH ALT PUSH B and it could the one I really need to clean?
But if it is part of the switch also I'm afraid I am kinda stuck to reach it.
Any advice there will be appreciated.
Yes, it is the switch. Hopefully by following page 6-27 you will be able to access to it.

Ozan
Re: Tek 2465 stuck in horizontal sweep

 

On Mon, Mar 14, 2022 at 3:58 PM clunche via groups.io <clunche=
[email protected]> wrote:

Now, when I mount the upper know it back, I can rotate fully CCW and CW
and meet the XY slot without issue. Could it be a bad service at some point
that hampered this section which now seems ok?
I've never been into a 2465 SEC/DIV switch, but there will be some kind of
interlock between the A/B switches, and presumably the knobs need to be
timed right for this to work right.
Re: FG502 with no working FREQUENCY control

 

Jeff,

Yes, the four C numbers are the ones I meant. Being across such a low resistance, I would reject anything over 3,3 ohms which is 10% the resistance. Having high ESR could make the output distorted. For standard decoupling like elsewhere in the circuit, a higher ESR will work. The film will measure "0" ohms (almost but never zero) and give better decoupling. The 1mfd tantalums can range from a couple of ohms to 20, 35, etc.. The axial types in older pieces usually are higher in ESR due to being older. There will be some of the 1mfd tantalums that have a few or less ohms ESR. Because one tests one way in a piece, does not mean the others do. Test each one if in question. Usually I put in film to make sure all are low ESR and new. Tantalums that are small will get a higher ESR over time in things that operate at higher temperatures and/or close enough to a heat generating device. If you are suspect, replace them with film. Values less than 1mfd, I will automatically replace tantalums/electrolytics with film. If you have enough items with 1mfd tantalums/electrolytics, you can get a bulk amount (say 100) and get a larger price break. In this piece, the emitter resistance and bypass is close to the cathode circuit of a video amplifier output stage, usually B/W. The condenser bypasses higher frequencies to keep the gain constant at higher frequencies, to a point. The bypass here is to help lower the lower output Z at higher frequencies.. I hope this helps you understand better. Do not feel bad about not knowing something. We are happy to help each other.

The brush and IPA sounds like a good idea. I have done this on variable C in scopes before to make sure the contacts are not open any more, a 453/4 type comes to mind.. Sometimes contact cleaners will work. Some variable R will have to be replaced. Clean first to see. Usually cleaning is enough. Ones that had a dirty/damp life may need replacing.

If I be of any further help, ask.

Mark
Re: Tek 2465 stuck in horizontal sweep

 

Hello gents,

Almost there! I received the Allen key 1/16" today and could remove the upper knob of the time base switch and I did inject cleaning spray along the shaft and it seems to help. Actually, I located the issue in the delayed B time base actuation via the pulling of the knob: it sometimes does not go back correctly and I can see the DLY sign still on time to time. However, and this is good now because when properly pushed back, then powering on and off the scope brings the correct screen and the trace is nice! So the issue is truly located there.

Now, if I have successfully removed the first time base knob, I am stuck at removing the plastic part associated with the 3 springs. I have seen what I thought to be a miniature screw but it is not - a kind of key - which keeps the spring always in tension. I need to carefully remove this small black part but it seems well locked inside. I've tried with a small thin plier but I'm afraid to break it. What do you recommend?

Could you also please confirm from the schematic diagram that the B switch is J601 marked as PUSH ALT PUSH B and it could the one I really need to clean? But if it is part of the switch also I'm afraid I am kinda stuck to reach it. Any advice there will be appreciated.

Just a remark: this scope was part of a past MOT lab and it has been serviced already, I can see it. One thing that I noticed is that before removing the time base knob, I could not rotate CCW enough to reach the XY position, it was blocked before. I had to pull the B switch and then use the transparent plastic part to move the time base to XY. Now, when I mount the upper know it back, I can rotate fully CCW and CW and meet the XY slot without issue. Could it be a bad service at some point that hampered this section which now seems ok?

Thanks!

Christophe
Re: FG502 with no working FREQUENCY control

 

Jeff,

FYI it's not epoxy, it's a lacquer sealant similar to fingernail
polish. Manufacturers used to apply it to pots to prevent them from moving
and also sometimes so that they could see if they had been tampered with.

FWIW during WW-II the US Navy used to apply it to torpedo guidance
mechanisms to prevent the crews on US submarines from tampering with them.
And the American torpedoes were highly inaccurate (they ran too deep)
during the first part of the war. It was only after the crews started
breaking the sealant and adjusting the depth setting mechanism in the
torpedoes that they were finally effective.

On Mon, Mar 14, 2022 at 12:57 PM Jeff Dutky <jeff.dutky@...> wrote:

Update on the high amplitude and clipping of the sine wave: I traced the
"problem" to the sine wave buffer between the sine shaper network and the
output amplifier. After thoroughly (or obsessively) checking all resistors
and transistors in the circuit, and finding nothing out of spec, I decided
to give the low and high frequency trimmers a tweak, just to see how much
they could do for the amplitude problem (which appeared to be the source of
the clipping issue). I was not going to touch the low frequency amplitude
pot, because it had some epoxy (or something) on it to keep it from
turning, but when I applied very gentle torque with a adjustment tool the
epoxy (or whatever) broke right off. A very slight tweak of the low
frequency amplitude trimmer cleared up the entire sine wave amplitude
"problem"!

The moral of the story is: try the adjustments before you search for
failed components?

There is still an "issue" with the instrument. The low and high frequency
trimmers are very touchy, and even the slightest adjustment can send the
sine amplitude to nothing (or close to it). The front panel amplitude
control is similarly touchy, and the amplitude swings pretty wildly while
you turn the knob: not at all the nice, linear behavior you might expect
from a properly working instrument.

I haven't done a proper investigation of the control pot or the trimmers
yet, but I'm wondering if the behavior is expected? Maybe the sine buffer
and output amplifiers are just touchy?

I'd like to post a video showing the behavior. Where should I post videos,
or should I put them on an external service and just link to them here?

-- Jeff Dutky
Re: FG502 with no working FREQUENCY control

 

Mark,

I assume that you are talking about C530, C532, C540, and C542 in the output amplifier (1 uF caps in parallel with 33 ¦¸ resistors). Pardon my ignorance, but what would be considered "high ESR" for these caps? Also (to put the depth of my ignorance on full display) would these caps having high ESR explain some of the touchiness of the front panel amplitude control? Are we saying that these caps stabilize the output amplifier? There don't appear to be similar bypass caps in the sine buffer

I had considered that the trimmers may have degraded. Is it worth trying to clean them (e.g. the trim cap for the 1 MHz sine amplitude), or should I just replace them (I've got some replacement parts lined up)? If I were going to clean the variable caps, how would that be done (my first instinct is to use a fine paintbrush and IPA)?

-- Jeff Dutky
Re: FG502 with no working FREQUENCY control

 

Jeff,

The 1mfd bypass across the 33 ohm emitter resistors are 35V. They may have high ESR. I have seen enough high ESR 1mfd tantalums and replaced them with film types in my items. It may be better to use 1mfd 63V films like Arcotronics R82 series, unless someone else here advises otherwise. The 10mfd decoupling for the outputs is 25V. Notice the B+ is 30V. Something like Nichicon ULD series 50V would be better, at least for the increase in voltage rating. Any of these that are bad may cause your problems. That is my guess by your description and schematic. If I am wrong, I apologize.

Maybe the other trimmers have dirty contact(s). Sometimes one control affects another so it is back and forth until the item works stable. I am looking at the schematic. I do not own this piece. Great you have it working enough then will get it more stable.

Mark
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