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New file uploaded to TekScopes

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New file uploaded to TekScopes

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New file uploaded to TekScopes

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Re: 465B No Beam Problem

 

Be warned about Ft statements in datasheets unless the datasheet says Ft
(typical) of 0.2MHz, then you should read that as Ft(min) of 0.2MHz (which
could mean 100MHz). Ask me how I know :) (hint 2N3055)

Dave

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com]
Sent: 27 May 2016 08:05
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: 465B No Beam Problem

Just check the specifications for the part from that specific manufacturer.
I thought all 2N3773s were the old 0.2 MHz types until today.


Re: 465B No Beam Problem

bc
 

Thanks, I unfortunately never figured out how to mess with magnet: BT links with Linux yet. However I got a copy from Mike U. and now a lot of the ongoing experiments make more sense.


Re: 465B No Beam Problem

bc
 

The circuit looks like an intrinsic base capacitance + inductance of 6-7 winding of the transformer LC Armstrong oscillator. I couldn't find typical intrinsic capacitance of the base of these transistors so not sure what's a good value to try, but perhaps trying a couple tens of pF capacitance from B to E could slow down the oscillation as well.


Re: 465B No Beam Problem

Rob Overman
 

David and Group,
OK I will do that. My experience tells me that usually a problem can be traced to a single fault unless the fault causes a cascade of failures. The Q14009 transistor was definitely bad, so I am making the assumption that it is the root cause and no other failures exists. Of course there could be other circuit faults after I get the beam working. This scope is basically in mint condition. There was zero dust in the unit when the outer case was removed. With the exception of some scratches on the outer case there are no visible flaws elsewhere.
Regards,
Rob 

Sent from Yahoo Mail. Get the app

On Friday, May 27, 2016 12:21 AM, "David davidwhess@gmail.com [TekScopes]" <TekScopes@yahoogroups.com> wrote:


  While you are waiting for those parts to show up, I suggest checking
the rest of the transistors in the regulator circuit for at least
shorts and opens. I would also look for bad resistors.

My personal preference when running across problems like this is to
modify the circuit to work with commonly available and inexpensive
parts. I would be extra careful when risking a relatively expensive
replacement transistor. $4 is not that much but it adds up if they
keep failing.

On Fri, 27 May 2016 07:13:14 +0000 (UTC), you wrote:

David and Group,
Thanks again for your excellent help! Now I just need to wait for the part to arrive. Will update status when I retest with the new part.
Regards,
Rob 
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Re: 465B No Beam Problem

 

While you are waiting for those parts to show up, I suggest checking
the rest of the transistors in the regulator circuit for at least
shorts and opens. I would also look for bad resistors.

My personal preference when running across problems like this is to
modify the circuit to work with commonly available and inexpensive
parts. I would be extra careful when risking a relatively expensive
replacement transistor. $4 is not that much but it adds up if they
keep failing.

On Fri, 27 May 2016 07:13:14 +0000 (UTC), you wrote:

David and Group,
Thanks again for your excellent help! Now I just need to wait for the part to arrive. Will update status when I retest with the new part.
Regards,
Rob


Re: 465B No Beam Problem

Rob Overman
 

David and Group,
Thanks again for your excellent help! Now I just need to wait for the part to arrive. Will update status when I retest with the new part.
Regards,
Rob 

Sent from Yahoo Mail. Get the app

[Non-text portions of this message have been removed]


Re: 465B No Beam Problem

 

Just check the specifications for the part from that specific
manufacturer. I thought all 2N3773s were the old 0.2 MHz types until
today. The 2N3771 and 2N3772 transistors which I linked from Mouser
say they are 0.2 MHz.

The $4.62 2N3773 transistors from Newark made by Solid State do not
say so I would avoid them. The Motorola part from Newark actually
*is* 0.2 MHz although you have to understand their datasheet to figure
it out; they do not say directly. The Multicomp part is also 0.2 MHz
but again you have to study the datasheet carefully.

The $3.72 2N3773 from Digi-key looks good.

The NTE replacements are more than 10 times faster. That is NTE for
you.

On Fri, 27 May 2016 06:48:19 +0000 (UTC), you wrote:

David and Group,
I place an order thru Digi-Key for qty 2 of the 2N3773 ($3.72 ea) which the spec sheet lists an Ft of .2 Mhz. I also order qty 1 of 2N3053 ($1.91) in case Q4008 is bad.
Thanks and regards,
Rob 

On Thursday, May 26, 2016 11:03 PM, "kwm2a11@yahoo.com [TekScopes]" <TekScopes@yahoogroups.com> wrote:


   David and Group,
I see the Newark Electronics has the 2N3773 in stock for $4.62. Should I order these?
Regards,
Rob

Sent from Yahoo Mail. Get the app


Re: 465B No Beam Problem

Rob Overman
 

David and Group,
I place an order thru Digi-Key for qty 2 of the 2N3773 ($3.72 ea) which the spec sheet lists an Ft of .2 Mhz. I also order qty 1 of 2N3053 ($1.91) in case Q4008 is bad.
Thanks and regards,
Rob 

Sent from Yahoo Mail. Get the app

On Thursday, May 26, 2016 11:03 PM, "kwm2a11@yahoo.com [TekScopes]" <TekScopes@yahoogroups.com> wrote:


   David and Group,
I see the Newark Electronics has the 2N3773 in stock for $4.62. Should I order these?
Regards,
Rob

Sent from Yahoo Mail. Get the app



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[Non-text portions of this message have been removed]


Re: 465B No Beam Problem

Rob Overman
 

David and Group,
I see the Newark Electronics has the 2N3773 in stock for $4.62. Should I order these?
Regards,
Rob

Sent from Yahoo Mail. Get the app


Re: 465B No Beam Problem

 

It does seem that it is oscillating.

I wonder what simple circuit modification would fix that. I guess I
would try adding a low value resistor, like 47 ohms, in series with
the base lead of Q14009.

The original Tektronix part, 151-0140-00, is the very old 0.3 MHz
2N3055 which is why I suggested the 0.2 MHz 2N3773 which Tektronix
used in other circuits however I just checked and they are not
available either.

The 2N3771 or 2N3772 made by On Semiconductor has an Ft of 0.2 MHz.
The NTE replacement for these, the NTE181, are 2 MHz so should not be
used.

http://www.mouser.com/Semiconductors/Discrete-Semiconductors/Transistors/Bipolar-Transistors-BJT/_/N-ax1shZscv7?P=1yyx4aw

On Thu, 26 May 2016 23:42:17 -0400, you wrote:

The transistor you used to replace Q14009 may be too hot (Ft too high) and oscillating at too high a frequency. I suggest you get a real tek part.


----- Original Message -----
From: kwm2a11@yahoo.com [TekScopes]
To: TekScopes@yahoogroups.com
Sent: Thursday, May 26, 2016 10:59 PM
Subject: Re: [TekScopes] Re: 465B No Beam Problem

Hello Group,
I put everything back together and reapplied power with the CRT disconnected. Initially I used the current limited PS to power F4508. There wasn't any current problems so I reinstalled the 1 Amp fuse and reconnected the CRT. Fuse did not blow, but still no beam. Measured the anode of CR4005 and now it is correct (-4.0 V). The cathode of CR4005 measured -1 V but should be -4.5 V. CR4005 tested OK using the Fluke diode function. The voltage at the cathode of CR4004 measured -.22 V but should be -.6 V. It appears that Q4008 may be bad, but it tested OK using the Fluke when out of circuit. Measured the collector Q14009 inverter signal with a scope and did not see the 50 KHZ sine wave, only some 1 MHZ funky waveform.
It appears that Q4008 is bad even though it tests OK with the Fluke. Any other thoughts from the Group?
Regards,
Rob


Re: 465B No Beam Problem

 

On 25 May 2016 14:24:01 -0700, you wrote:

As an aside I was trying to view the schematics for the 465B but the service manual PDF I got is truncated on the right, anyone know of a good copy somewhere (of pg. 254)? Or is it just me that is not seeing the whole page? I just see the primary and feedback circuitry of the HV in the schematic, the secondary is cut off to the right...
Here is a torrent link to the 465B schematics which I assembled:

magnet:?xt=urn:btih:B2673A1D1BEF793E653F749CD78D9405965230F0


Re: 465B No Beam Problem

 

The transistor you used to replace Q14009 may be too hot (Ft too high) and oscillating at too high a frequency. I suggest you get a real tek part.

----- Original Message -----
From: kwm2a11@yahoo.com [TekScopes]
To: TekScopes@yahoogroups.com
Sent: Thursday, May 26, 2016 10:59 PM
Subject: Re: [TekScopes] Re: 465B No Beam Problem



Hello Group,
I put everything back together and reapplied power with the CRT disconnected. Initially I used the current limited PS to power F4508. There wasn't any current problems so I reinstalled the 1 Amp fuse and reconnected the CRT. Fuse did not blow, but still no beam. Measured the anode of CR4005 and now it is correct (-4.0 V). The cathode of CR4005 measured -1 V but should be -4.5 V. CR4005 tested OK using the Fluke diode function. The voltage at the cathode of CR4004 measured -.22 V but should be -.6 V. It appears that Q4008 may be bad, but it tested OK using the Fluke when out of circuit. Measured the collector Q14009 inverter signal with a scope and did not see the 50 KHZ sine wave, only some 1 MHZ funky waveform.
It appears that Q4008 is bad even though it tests OK with the Fluke. Any other thoughts from the Group?
Regards,
Rob

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Re: 465B No Beam Problem

Rob Overman
 

Hello Group,
I put everything back together and reapplied power with the CRT disconnected. Initially I used the current limited PS to power F4508. There wasn't any current problems so I reinstalled the 1 Amp fuse and reconnected the CRT. Fuse did not blow, but still no beam. Measured the anode of CR4005 and now it is correct (-4.0 V). The cathode of CR4005 measured -1 V but should be -4.5 V. CR4005 tested OK using the Fluke diode function. The voltage at the cathode of CR4004 measured -.22 V but should be -.6 V. It appears that Q4008 may be bad, but it tested OK using the Fluke when out of circuit. Measured the collector Q14009 inverter signal with a scope and did not see the 50 KHZ sine wave, only some 1 MHZ funky waveform.
It appears that Q4008 is bad even though it tests OK with the Fluke. Any other thoughts from the Group?
Regards,
Rob

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Re: Tektronix 7D20 - need some help

Dan Tru
 

Hi David

I read your post on Tekscopes in 2014 regarding your problem with a 7D20 digitizer in a 7603 mainframe. I have a similar setup and my 7D20 gives the same error codes 65432 and 654321. Only a horizontal trace is shown for each channel and the vertical position pots are non functional like yours. I’ve done some signal tracing and the preamp board A4 seems working ok.

I bought this plugin from an acquaintance who said it was working before he put it in storage. I am interested to know if you have managed to fix the faults as I ‘d like to get this plugin working again. Thank you.


Dam


Re: 465B No Beam Problem

bc
 

Just be sure you turn off the external supply before turning off the scope, don't want it to reverse power anything. I've pretty much adopted the light bulb or resistor test just because then I don't have to worry about power supply turn-on sequencing, plus instant feedback.

-Ben


Re: 465B No Beam Problem

Rob Overman
 

Ben,
Thanks for your response. I took a break from troubleshooting the past day. Will restart in the next hour. Good idea about disconnecting the CRT. Will definitely do that. I sure hope it isn't the CRT because I threw out a good CRT a few months ago because I assumed I would not need it and don't like having junk laying around. I plan on using my current limited PS to feed the + 15 Vdc source - that is a great idea that I did not think of. I do have two other functioning 465Bs.  
Regards,
Rob

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