It is currently Mon Dec 11, 2017 4:49 am

Tektronix 7603 with 7A26 and 7B53A plug ins

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Mon May 11, 2015 2:52 pm

I have just acquired one of these huge well built scopes and it almost all there with the beam finder button missing and two knobs not original.
Thanks to Spot-Wobble and Norman Raeburn for the FCS :aad
I have powered it up on full mains and it looks like dirty switches with them all being intermittent.
They are the gold pad with gold finger kind so oil free cleaner. I have Ambersil FE10 and would like to check that it will do although I am pretty sure it will work just fine.
There are at least 10 screws to undo to get to the switch on the 7B53B plug in so that the timebase can be got working again.
The attenuators also need to be done in the two 7A16 plug ins.
If that does not fix the on screen displays there will have to be even more switch cleaning.

The search for the manual will now begin :cch
Attachments
DSCF2184.JPG
DSCF2191.JPG
DSCF2193.JPG

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektrinix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Mon May 11, 2015 4:07 pm

I have just got back from manual hunting.
The 7603 manual was first followed by the 7A26.
The 7B53B has proved illusive however there is a 7B53A out there.
They took ages to download on my country internet but they are well scanned and clear.
The first thing I have spotted it that the manual says don't take the screws out of the switch PCB.
I will have to show it some cleaner first and see if it works.
Yes indeed I am a test gear fan and intend to use it regularly when I have got it all fixed up.

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Tektrinix 7603 with 7A26 and 7B53A plug ins

Post by crustytv » Mon May 11, 2015 9:31 pm

Seriously tasty scope you've got yourself there Simon. Will look forward to you bringing it back to good health

 
Posts: 763
Joined: Sun Aug 07, 2011 5:17 pm
Location: Edinburgh

Re: Tektrinix 7603 with 7A26 and 7B53A plug ins

Post by Alistair D » Mon May 11, 2015 10:43 pm

Recently I have been working on a number of TM500 series modules that use the same pad and finger switches described by Refugee. I have never had any problems removing the screws and the switches falling apart but I live and learn.

The usual method for cleaning the contacts is to slip a piece of paper soaked in IPA, no not the beer :aak, under the open contact then rotate the switch until the switch closes and carefully slide the paper in and out to rub the contact surfaces clean. On a few occasions that has not worked. My solution is then to drip Electrolube contact oil onto the pad and leave it a day or two. After that use a fine paintbrush dipped in IPA to clean the oil out. So far it has worked 100% and seems to be a lasting fix.

Al

 
Posts: 2665
Joined: Sun Sep 01, 2013 6:19 pm
Location: Behind the sofa

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Cathovisor » Mon May 11, 2015 11:08 pm

Once upon a time Electrolube made some stiff paper/card strips soaked in 2AX or similar designed for cleaning non-wiping contacts (e.g. older wavechange switches like those on a Murphy A24). I kept a set in my toolkit for years but I'll bet they've long dried out :(

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektrinix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Tue May 12, 2015 1:29 am

CrustyTV wrote:Seriously tasty scope you've got yourself there Simon. Will look forward to you bringing it back to good health


Yes it is a big boys scope and I was expecting you to say that it is far too complicated for your workshop :bba

I have begun diagnosis today.
I have powered it up and the tube is bright and as reported by the vendor there is something wrong with the timebase.
I have downloaded the 7B53A manual as a close guide for the 7B53B and it does not have an awful lot of differences.
Faults found so far are the time base only has three speeds with a little bit of variation on the settings in between the steps that work. There is a -50V supply that does not do much apart from feed a reference to the time base switching. I will have to get the covers off the frame and check it before I go in any further.
There is a bit of noise on the Y amps so capacitors in the power supply need to be checked too.
The scale lamps are not working so if these are NLA the old ones will have to be stuffed with LEDs.
The on screen display will also need to be looked at. There are little bits missing from the trace when the switch is on so some of the logic is working but not the character generator.

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Tue May 12, 2015 1:43 am

The paper or card method will be worth a try but to avoid stripping down I will first check with a meter to see if it really is the switches.
I have had an open circuit via hole on a Tektronix scope in the year that I worked for a test equipment repair and cal shop. I was not the first engineer to look at that one. I had to measure the two ends of the wire and then follow it in the manual circuits checking at each board entry/exit terminal only to find that it was on the main board that the plug ins go into. The tube was about the only thing I didn't have to take out to get far enough in to fix it.
There are signs that this one has not been best stored so I shall not rule out a bad via hole at this stage.

 
Posts: 2665
Joined: Sun Sep 01, 2013 6:19 pm
Location: Behind the sofa

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Cathovisor » Tue May 12, 2015 12:18 pm

Refugee wrote:I have had an open circuit via hole on a Tektronix scope in the year that I worked for a test equipment repair and cal shop. I was not the first engineer to look at that one.

I've also encountered that one in of all things, a very expensive Sony CD radio-cassette. It was intermittent though, and caused crackling. Bridging it diminished the crackling, only then by cutting the tracks did the crackle finally stop. Likewise, it had been through a few people.

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Tue May 12, 2015 1:38 pm

That via hole must have been arcing to an adjacent track or hole.
I have started to study the manual in order to establish what is not there between the frame and the plug in and then I will go in and measure it. I will keep the on screen display switched off to avoid confusion while I get the timebase going again.

 
Posts: 27
Joined: Sat May 12, 2012 9:21 pm

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Wave Solder » Tue May 12, 2015 11:03 pm

One cautionary note about the plastics used in the plugins on the 7000 series, only use the isopropanol to clean the switches as recommended by TEK, don't be tempted to use Servisol switch cleaner as it attacks the plastic. Guess how I found out. :ccb

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Wed May 13, 2015 9:13 am

It is a sort of nylon like plastic in those switches.
The stuff I used does not melt plastic or contain anything oily and it has worked.
I have been testing the switches and so far all have been OK so I am still on it.

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Tue May 26, 2015 12:27 am

I have been off this restore doing the garden and getting all the indoor plants outside for there summer vacation.
I have made a mistake with the part number of the timebase plugin. I will PM Chris if he does not spot this post. It is indeed a 7B53A. My fault for not cleaning the finger prints off my glasses :ccg

In the switching it is the resistor bank that looks like it has something wrong in it and I am going to have to check every contact in the switch bank. I am pretty sure at this stage that the special chip is all right.

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Mon Jun 01, 2015 3:11 pm

Sunday was officially bad FET day.
The FET is Q596 and I got a reading a little over 700 ohms between source and gate.
It was shunting the resistor section of the timebase switch so that the only change was seen when a capacitor was switched.
7B53Asnap.jpeg

DSCF2233DF.jpg

Lifting the FET out of the socket cleared the short from pin 8 of U580 and disabled the delayed timebase.
All the main timebase steps came back.
Next session is to try a 2SK43 in it to get the delayed timebase back again.

On screen displays next.
Attachments
DSCF2227.JPG

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Tue Jun 02, 2015 1:43 am

I have put a 2SK43 in place of the faulty FET and now both timebases are working correctly.
I will now start looking at the on screen display parts in the frame so it is now fast TTL time for me.
Also that spike on my pulse generator is going to have to be looked at now I have a fast enough scope to tackle it.
Attachments
DSCF2235.JPG
DSCF2238.JPG
DSCF2242.JPG

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Thu Jun 04, 2015 1:47 am

I have been doing some testing and a lot of reading and began to tackle U2126 first. On pin 12 the waveform is shown as roughly -6 volts and this is wrong on mine.
It varies with the display brightness control and will not budge above -0.5 volts. Pin 11 where the signal from the brightness pot connects also will not budge above -0.5 volts unless I power up with U2126 removed. This allows it to go from +4.5 volts for minimum brightness to -13.5 volts at maximum brightness on pin 11.
With U2126 in place disconnecting the Z amp cable does not restore it.
CR2124 and CR2125 have been tested as have R2122 and R2123.
Pin 12 has narrow positive going pulses and these are present also on pin 11 but these are narrow enough that a DVM ignores them and also they only come up to 0 volts.
The pulses vary with the settings on the plugins so that part is working.
Has anyone got a U2126 I could borrow?
The part No is 155-0021-01
Readings from pins 11 and 12 for maximum and minimum brightness would be useful if anyone has got the cover off there 7000 series.
Attachments
7603OSD.jpeg

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by crustytv » Thu Jun 04, 2015 8:29 am

Hi Simon,

Following this thread with interest, great work so far dmm . Scope repairs are complex so its good to get some tips from those with test equipment repair experience. I've only repaired one scope, that was substituting a Gould CRT into a TEK 2205 which was great fun and learning curve working out the rewiring and subsequent re-set up.

Do you suspect the U2126? If so and it does turn out to be faulty, what on earth are you going to, aren't theses TEK custom chips?

 
Posts: 83
Joined: Sun Aug 07, 2011 10:56 pm
Location: Fife, Scotland

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Norman Raeburn » Thu Jun 04, 2015 8:42 am

Hi, I did a quick google search on Tektronix U2126 and there was a scope site which states an LM3086 is a generic replacement which is easier to get. Best regards, Norman

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Thu Jun 04, 2015 9:46 am

That sounds interesting.
Have you got a link to the site?
It looks like the Tektronics sites are out of stock.
A data sheet check has just revealed that the LM3086 is a 14 pin and the part I need is 16 pin so it looks like a false lead but a look at the site will still be fun.

 
Posts: 83
Joined: Sun Aug 07, 2011 10:56 pm
Location: Fife, Scotland

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Norman Raeburn » Thu Jun 04, 2015 10:40 am

Hi, I am not sure how to put links in so here goes, http://www.logwell.com/tech/oscilloscop ... notes.html

 
Posts: 3712
Joined: Sun Feb 12, 2012 7:43 pm
Location: North Hykeham, Lincolnshire and Ilford, Essex (but not for much longer ...!)

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Terrykc » Thu Jun 04, 2015 2:31 pm

Norman Raeburn wrote:Hi, I am not sure how to put links in ...

You do now ...! :aad

 
Posts: 83
Joined: Sun Aug 07, 2011 10:56 pm
Location: Fife, Scotland

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Norman Raeburn » Thu Jun 04, 2015 4:23 pm

Hi Terry, I think that's about the first time I have successfully managed it. I am glad the link is working. Norman

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Thu Jun 04, 2015 5:36 pm

The chip the link leads to has a different Tektrinix part number so I will just have to keep looking.

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Fri Jun 05, 2015 6:26 pm

I have now completed the diagnosis of the on screen display. During my final test to check for an open circuit pull up resistor on the Z axis amplifier board at the other end of the coax that connects to pin 10 of U2126 I found a twiddler fault and promptly fixed it.
DSCF2260.JPG

DSCF2264.JPG

Now the other twiddler problem is two panels are missing. These are the bottom blue one and the white finger guard that covers the power transistors at the back.
So do I go for silver for the side panels and wait for a frame with a smashed tube for replacement panels and the screws that hold them on?
Attachments
DSCF2267.JPG

 
Posts: 83
Joined: Sun Aug 07, 2011 10:56 pm
Location: Fife, Scotland

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Norman Raeburn » Fri Jun 05, 2015 7:13 pm

I am glad to see you are making good progress with the 'scope. I am not guilty of the twiddling, I didn't have the covers off. I was given the 'scope but I didn't want or need it. I am glad it has found a good home. Norman

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Tektronix 7603 with 7A26 and 7B53A plug ins

Post by Refugee » Fri Jun 05, 2015 11:35 pm

It looks like it has been assembled from plugins and a frame from a pile of stuff cleared prior to refurbishing the technicians store at a college.

Next

Return to Test Equipment



Who is online

Users browsing this forum: No registered users and 1 guest