Date   
Re: 2N2207 replacement in 547.

Morris Odell
 

I'm sorry to say those symptoms are classic for the HV transformer thermal
runaway problem. Unfortunately the only cure is a replacement transformer -
you will have seen endless discussion on this subject if you have been
through the archives. I wouldn't advise swapping the transformer from the
other scope, it's likely to have the same problem if it's an original. You
don't want to go through the complex job of replacing the transformer with
another dud. The only source I know of for replacements is Chuck Harris of
this group and I'm sure he will reply to you. I'm traveling in the US at
the moment so have no easy access to the manual to help you with the
transistor replacement. However you are unlikely to do any harm by trying a
BC556. It's not an expensive experiment.

Good luck,

Morris

Re: 2N2207 replacement in 547.

Dave Wise
 

I agree that your transformer has lossy epoxy impregnant. Chuck sells a beautiful drop-in replacement, but it's within many people's abilities to wind your own. I did this for my 453 which had the same problem, and wrote it up under "453 HV Transformer Rewind". The 547 transformer is the same order of complexity. If you like making your own stuff, give it a look.

The 2N2207 is notorious for developing tin whisker shorts. Often it's possible to clear them with a pulse of energy. Note that the whiskers frequently short one or more elements to the case, so start there. What do you have to lose?

In the CRT beam unblanking circuits, the ability of the 2N2207 to generate a large, fast transition is exploited to the fullest, and nothing I ever found matches it. The BC556 and several others can be made to work by speeding up the base drive. I doubt that's possible in the horizontal amplifier; then again, maybe they don't need to be so fast there. You have nothing to lose. If they are being employed in a balanced circuit, replace both sides to avoid Si vs Ge Vbe mismatch. Watch the pinout, it's probably not what you expect.

HTH,
Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Morris Odell <vilgotch1@...>
Sent: Tuesday, May 28, 2019 3:56 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 2N2207 replacement in 547.

I'm sorry to say those symptoms are classic for the HV transformer thermal
runaway problem. Unfortunately the only cure is a replacement transformer -
you will have seen endless discussion on this subject if you have been
through the archives. I wouldn't advise swapping the transformer from the
other scope, it's likely to have the same problem if it's an original. You
don't want to go through the complex job of replacing the transformer with
another dud. The only source I know of for replacements is Chuck Harris of
this group and I'm sure he will reply to you. I'm traveling in the US at
the moment so have no easy access to the manual to help you with the
transistor replacement. However you are unlikely to do any harm by trying a
BC556. It's not an expensive experiment.

Good luck,

Morris

Re: 2N2207 replacement in 547.

Bob Koller
 

In the past I was able to, at least partially, alleviate the HV transformer problem by doing the following, YMMV of course.
Replace the 5642 HV rectifier tubes with fast recovery HV silicon rectifiers, and removing the filament leads, this reduces the load on the HV oscillator circuit.
Replace C808 with a high quality cap, mine was leaky, causing loss.

Also, I have a few NOS 151-0063/ 2N2207 Tek parts available, contact me off list if interested.

Re: Weird(?) behaviour in tek 492BP power distribution - Please help

John Miles
 

I agree with you, and that's why I feel helpless about this situation.
All voltages measured ok after I replaced those caps and the power supply was
disconnected from the equipment..
Unusual sort of failure, definitely. Please update the list on what the problem turns out to be when you track it down. If it's sufficiently weird I'll add it to the notes. :)

Some random thoughts:

1) If the electrolytics in the 100V/300V multiplier sections on the power supply board are bad, there might be enough ripple coming through to confuse a DMM. The load on the supply may affect this behavior. Try a different meter if possible, and see if you get the same unintuitive measurements out of it. I know you replaced the caps, but sometimes the new ones are bad too.

2) It doesn't normally make sense for the green light to be on while the rail voltages are incorrect. Taking a close look at the comparator circuit that drives the LED might provide some insight. The +300V rail isn't monitored by that circuit, but +100V is.

3) I'm not sure what documentation is available on the 492B models. It would be best to consult the 494A manuals available at ko4bb.com, IMHO. Those are the latest editions for the 49x series that were published as far as I'm aware. They have quite a few change notes in the back that may apply to your unit.

-- john, KE5FX

Re: 2215 problem

Bob Albert
 

It appears that there is more than one version of this unit. I have the one that does not have the inductor. Instead, it has the later power supply board A18. And I managed to repair the IFR820 so no need to replace it, unless it's bad.

I still don't know which way to turn. It's a complex unit and the heat sink for the IFR820 is damaged. I will try to repair it but it seems also to include a shield.

Is there anyone out there with some experience with this one?

Re: 2215 problem

satbeginner
 

Hi, I'm traveling right now, so I can not look for the details, but...

If I remember well, yes there are several (quite similar) power supplies for a 2215/2215A and others.

The power supply first stage makes a 42V , and the second part creates the other voltages from that 42V.

If you remove the IRFxxx you can feed a separate 42V into the scope and see if that works.

That way you know you have to concentrate on the first PS stage.

Look in this thread too:

https://groups.io/g/TekScopes/topic/2215a_lvps_repair/23804512?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,23804512

Success,

Leo

Re: 2215 problem

Bob Albert
 

Thanks Leo, I was beginning to despair of getting a response.  Tomorrow I plan on doing what you suggest, feeding 42V in place of the FET.  It will take some careful positioning of the various boards that now are hanging loose.  I hope I didn't confuse the + and - leads.  The manual says make notes, which I didn't, but also doesn't say how to figure out which goes where.
Bob

On Tuesday, May 28, 2019, 11:55:43 PM PDT, satbeginner <@satbeginner> wrote:

Hi, I'm traveling right now, so I can not look for the details, but...

If I remember well, yes there are several (quite similar) power supplies for a 2215/2215A and others.

The power supply first stage makes a 42V , and the second part creates the other voltages from that 42V.

If you remove the IRFxxx you can feed a separate 42V into the scope and see if that works.

That way you know you have to concentrate on the first PS stage.

Look in this thread too:

https://groups.io/g/TekScopes/topic/2215a_lvps_repair/23804512?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,23804512

Success,

Leo

This weekend is the Seaside OR HamFest

 

I will be at the Seaside OR Hamfest this weekend with a table.

You can ask anyone of the staff where my table is located.

Stop and say hello if you will be there too.

Dennis Tillman W7PF

TDS744 not 'A' has a problem , help needed

Brian
 

Hi everyone,I am in need of some help . I have a TDS744-not an 'A' that has a problem .There is a large offset on CH3 causing no trace to be displayed . It is just possible to get a trace on screen using the offset feature but doing that the gain is very low . These scopes are not easy to trouble shoot as half of what you want to get at is underneath the pcb but so far I have replaced U1201 - TL072 , U935,U1405 - TL074 and U934 - CD4051 without any joy . I have also changed the input attenuator module and swapped the contact pads underneath the input attenuators again no change . The large offset is definitely at the output of the attenuator module +/- 400mV and can be seen to change using the position control but never enough to get a trace on screen .The other 3 inputs behave normally .

Thanks in advance for any help

Re: TDS744 not 'A' has a problem , help needed

EricJ
 

Did you run an SPC? Does it change anything?Any error messages in the log?

--Eric

Re: TDS744 not 'A' has a problem , help needed

Brian
 

yes SPC  crashes out after a while saying there is an error but I dont understand the error log content . I'll have to re-assemble the scope if your going to ask for details of the contents . SPC has been run many times -- where is the most recent data , at the beginning or the end of the contents ? . I am not currently equiped to erase the log and capture fresh data , but I'm working on that .

On Wednesday, 29 May 2019, 15:58:27 BST, EricJ via Groups.Io <wyzkydd2358=yahoo.com@groups.io> wrote:

Did you run an SPC? Does it change anything?Any error messages in the log?

--Eric

Re: TDS744 not 'A' has a problem , help needed

Bob Koller
 

Tek used a DAC part called a "DACULATOR" in many instruments of this vintage. It was made by IMP, p/n I10412, 28 lead SOIC.
It contains 8 DAC's as I recall, and is used to supply control voltages.
I suspect that one of these has failed, a fairly common problem.

These are long obsolete, so you will need to find NOS or a parts unit.

Re: TDS744 not 'A' has a problem , help needed

Brian
 

Hi Bob , I was hoping it wasnt one of those as I have looked for them online , cant even find data on them , L10412 seems to have never existed - I'd rather be looking for a few EF50's lol

On Wednesday, 29 May 2019, 16:20:40 BST, Bob Koller via Groups.Io <testtech=yahoo.com@groups.io> wrote:

Tek used a DAC part called a "DACULATOR" in many instruments of this vintage. It was made by IMP, p/n I10412, 28 lead SOIC.
It contains 8 DAC's as I recall, and is used to supply control voltages.
I suspect that one of these has failed, a fairly common problem.

These are long obsolete, so you will need to find NOS or a parts unit.

Re: TDS744 not 'A' has a problem , help needed

Bob Koller
 

Yes, hard to find. I think you will have to buy a parts scope or board, it can be almost any model; ie, TDS4xx, etc, for parts.

Re: TDS744 not 'A' has a problem , help needed

Brian
 

Hi Bob thanks for that tip , I was not aware they were used on the 400 series as well . I have found a possible source , not cheap for just the IC's but fortunately possible spares for my 420A ,is there any way to check apart from replacing one ?

On Wednesday, 29 May 2019, 16:39:55 BST, Bob Koller via Groups.Io <testtech=yahoo.com@groups.io> wrote:

Yes, hard to find. I think you will have to buy a parts scope or board, it can be almost any model; ie, TDS4xx, etc, for parts.

Re: This weekend is the Seaside OR HamFest

Randy Hall
 

Dennis

I may have bought a TM500 4 slot frame filled with plug ins last year from
you. Were you in front of the stage? There was also a guy upstairs with
many Tek goodies.

Randy, K7AGE

On Wed, May 29, 2019 at 7:42 AM Dennis Tillman W7PF <@Dennis_Tillman_W7PF>
wrote:

I will be at the Seaside OR Hamfest this weekend with a table.

You can ask anyone of the staff where my table is located.

Stop and say hello if you will be there too.

Dennis Tillman W7PF




Re: TDS744 not 'A' has a problem , help needed

Bob Koller
 

There may be one on eBay, searching for the p/n returns one possible hit, but the description is poor.
You might be able to probe around the chip.
Tekwiki has the service manual for the Tek 1740A series, this part is used there as well, and the schematic <9> shows the pinout.The DACULATOR outputs go to a track and hold.

Whenever I suspect one, I just replace it, pretty much always solves the problem, but you may have something else going on of course...

Re: TDS744 not 'A' has a problem , help needed

Brian
 

Now I have to find the right Metcal tip to take one off , lol

On Wednesday, 29 May 2019, 16:39:55 BST, Bob Koller via Groups.Io <testtech=yahoo.com@groups.io> wrote:

Yes, hard to find. I think you will have to buy a parts scope or board, it can be almost any model; ie, TDS4xx, etc, for parts.

Re: TDS744 not 'A' has a problem , help needed

Brian
 

I dont know how you guys search on eBay , here in the UK it defaults to car parts when it cant find anything -- most irritating , I dont even have one now

TDS420A input assemblies have 2 chips and they are not too expensive although more than I'd like

On Wednesday, 29 May 2019, 17:13:12 BST, Bob Koller via Groups.Io <testtech=yahoo.com@groups.io> wrote:

There may be one on eBay, searching for the p/n returns one possible hit, but the description is poor.
You might be able to probe around the chip.
Tekwiki has the service manual for the Tek 1740A series, this part is used there as well, and the schematic <9> shows the pinout.The DACULATOR outputs go to a track and hold.

Whenever I suspect one, I just replace it, pretty much always solves the problem, but you may have something else going on of course...

Re: 2N2207 replacement in 547.

fiftythreebuick
 

Glad to hear that you have jumped into the vintage Tektronix oscilloscope world! Honestly, once you get spoiled by a 500 series Tek oscilloscope, you're spoiled for good... :-)

The 547 is really a nice scope and I know you will enjoy them. I hate to tell you, but the very high probability is that your HV transformer is the source of the problem. A quick test, if you'd like to run it, is to run the scope until it fails and then hit the HV transformer with a burst of freeze spray that's sufficient to cool it significantly. If the trace returns and then fairly quickly goes away again, then it's the xfmr. The 547 is one of the known bearers of this problem.

There are a couple of folks who rewind the xfmrs, but I don't know who exactly is currently doing it. My buddy who reworked them years ago is out of it now.

I have a theory but have not tried it yet. I suspect that if the transformer is put in a vacuum chamber and held at a deep vacuum for a length of time that is sufficient to pull any moisture out of it and then sealed with something like beeswax, the transformer might be recovered. Planning to give that a try when I have time.

The worst problem with HV xfmr failure that I am aware of was with the 549 mainframe. I've worked on probably 20 or more of them and have never seen one with an original transformer that didn't have the defect. In the case of the 549s that I have, once the coil was removed and replaced with a rewound one, the problem disappeared and the scope worked as new.

Interestingly enough, the problem was extremely rare in the earlier, open frame xfmrs such as those in the Type 555 and 545A, etc.

If it turns out that you do need a xfmr, I bet someone here can point you in the right direction.

Tom