Tektronix 475 & 547, servicing notes - UK Vintage Radio Repair and Restoration Discussion Forum

The Philpott · 13th Feb 2018, 6:57 pm

My father has been recommissioning some old Tek 'scopes and has submitted some notes as follows, which we hope will be of use fault-finding in future:

Tektronix 475 series- Loss of EHT
Reference the Service Instruction Manual, page 4-16,
'Troubleshooting the High Voltage Circuit'
Insert step 6a as follows:-
'Check CR1320,CR1321,C1320,C1322,C1323,C1328'

(Access to these is easy and you could avoid a lot of tricky, time-consuming dismantling and reassembly.)

In a recent case C1328 (Sprague 0.01uF @5kV) was found to have a leakage resistance (not s/c) which so loaded the HV oscillator that it stopped working.

Note: In the parts list C1328 is 0.0068uF @ 5kV.

Tektronix 475 series- Noisy Vert. Posn. controls
Allen-Bradley ceased production 20yrs ago. Traced replacements in USA, quote USD 80 each, min. order 10! Found NOS single section ones,with push-pull switch, in Lancashire. Easily dismantled, being 'Modpots', fitted 2 sections onto original end-fittings/shafts. Snag- not PCB pins. Cropped tags, soldered on wires, mounted by rotating 90 degrees anti-clockwise, held in place on PCB by fillets of Evostik. A cringeworthy mod, but easily reversible. (A pity Tek. didn't specify the 'Cermet' version.)

Tektronix 547- s/n 100962
-First used on Development Work for the MOD, in the middle of the Cold War. Many years later Timebase B succumbed to a blown tunnel diode - the long unobtainable GE type TD253. Very sad, but a common problem.

Another 20yrs on the 547 is fully operational following the fitting of a now easily available diode, type 31306L. Ironically ex-Russian military stock!
Admittedly not an exact match, but very close and, at 8 US Dollars for 5 (incl.shipping) very welcome!

MrBungle · 13th Feb 2018, 8:45 pm

Useful info. Thank you for this. I've got really noisy vertical position pots on my 465.

If you have the black AB ones, they aren't riveted so you can actually dismantle and clean them if you are extremely careful. This is a last resort really though. I haven't plucked up the courage to do this (yet).

Main problems I have on those scopes is the tantalum caps. Constantly shorting out!

Brian of Romsey · 23rd Apr 2018, 3:24 pm

Quote:

Originally Posted by The Philpott

Another 20yrs on the 547 is fully operational following the fitting of a now easily available diode, type 31306L. Ironically ex-Russian military stock!
Admittedly not an exact match, but very close and, at 8 US Dollars for 5 (incl.shipping) very welcome!

Could you give us a pointer to where the diodes came from, or was it just a lucky eBay.ru find?

Thanks, Brian.

cmjones01 · 23rd Apr 2018, 3:50 pm

Quote:

Originally Posted by MrBungle

If you have the black AB ones, they aren't riveted so you can actually dismantle and clean them if you are extremely careful. This is a last resort really though. I haven't plucked up the courage to do this (yet).

Don't be scared! I've done this lots of times on 7000-series plugins. Loosen or remove the screws, wiggle the case apart a bit, squirt in a bit of DeoxIT D5, do screws up. Good for another 20 years.

Quote:

Main problems I have on those scopes is the tantalum caps. Constantly shorting out!

True, though I find they usually go short-circuit on things which haven't been used for a number of years. Once a piece of equipment of this vintage is in regular use, the tantalums seem reliable. I use 1970s and 80s Tek stuff every day, and have only had to replace tantalum capacitors when I get plugins which have obviously been in storage for a while. I've never had further failures after the replacing the inital duds, even though some tants are clearly still in there. Touch wood!

Chris

MrBungle · 24th Apr 2018, 10:27 pm

Excellent - will do that then

Purely by chance when I cracked my 465 open to measure some voltages for someone today, I discovered the main 1000uF 10V electrolytic in mine had some not insignificant burns on it. Was still quite happily churning away still. Have ordered a replacement!

Rileyman · 24th Sep 2018, 8:42 pm

Quote:

Originally Posted by Brian of Romsey

Could you give us a pointer to where the diodes came from, or was it just a lucky eBay.ru find?

Sorry if this is too late, I only became a member today ! Try searching (worldwide) on eBay for the seller's I.D. elena8913. Name is Maxim, located in Tomsk.

https://www.ebay.co.uk/str/elena8913...p2047675.l2563

Good Luck!

Rileyman · 29th Sep 2018, 12:23 am

Forgot to mention:- When troubleshooting the long-dead B Timebase on my Tek.547 I came across some useful info. on http://w140.com/tekwiki/wiki/tunnel_diodes .Scrolling-down I found a useful article on page 14 of "Service Scope 49, April 1968". Not having a Tek.454 or 571 I was lucky that the A Timebase was fully operational (and calibrated) so I was able to employ the method described to select a "best" diode from those Russian tunnel diodes I bought on-line, and used the 100v. (not 10v. !) A Sweep Output via suitable resisters to give the current/div.scales I needed. Finally,after replacing two leaky diodes in the Alt. Sweep switching cct. I was really chuffed to be able to display 8 traces - using a 1A4 Plug-In and the Alt. Sweep modes.
Next task:- Still trying to find a Sweep Control I.C.(Tek.155-0056-00) for another dead B Timebase (no pun!) in my Tek. 5103N. So far it seems my best chance would be to find an otherwise scrap,or mutilated, 5B12N or 5B10N Plug-In. Fingers crossed !

13th Feb 2018, 6:57 pm	#1
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,107	Tektronix 475 & 547, servicing notes My father has been recommissioning some old Tek 'scopes and has submitted some notes as follows, which we hope will be of use fault-finding in future: Tektronix 475 series- Loss of EHT Reference the Service Instruction Manual, page 4-16, 'Troubleshooting the High Voltage Circuit' Insert step 6a as follows:- 'Check CR1320,CR1321,C1320,C1322,C1323,C1328' (Access to these is easy and you could avoid a lot of tricky, time-consuming dismantling and reassembly.) In a recent case C1328 (Sprague 0.01uF @5kV) was found to have a leakage resistance (not s/c) which so loaded the HV oscillator that it stopped working. Note: In the parts list C1328 is 0.0068uF @ 5kV. Tektronix 475 series- Noisy Vert. Posn. controls Allen-Bradley ceased production 20yrs ago. Traced replacements in USA, quote USD 80 each, min. order 10! Found NOS single section ones,with push-pull switch, in Lancashire. Easily dismantled, being 'Modpots', fitted 2 sections onto original end-fittings/shafts. Snag- not PCB pins. Cropped tags, soldered on wires, mounted by rotating 90 degrees anti-clockwise, held in place on PCB by fillets of Evostik. A cringeworthy mod, but easily reversible. (A pity Tek. didn't specify the 'Cermet' version.) Tektronix 547- s/n 100962 -First used on Development Work for the MOD, in the middle of the Cold War. Many years later Timebase B succumbed to a blown tunnel diode - the long unobtainable GE type TD253. Very sad, but a common problem. Another 20yrs on the 547 is fully operational following the fitting of a now easily available diode, type 31306L. Ironically ex-Russian military stock! Admittedly not an exact match, but very close and, at 8 US Dollars for 5 (incl.shipping) very welcome!

13th Feb 2018, 8:45 pm	#2
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Tektronix 475 & 547, servicing notes Useful info. Thank you for this. I've got really noisy vertical position pots on my 465. If you have the black AB ones, they aren't riveted so you can actually dismantle and clean them if you are extremely careful. This is a last resort really though. I haven't plucked up the courage to do this (yet). Main problems I have on those scopes is the tantalum caps. Constantly shorting out!

24th Apr 2018, 10:27 pm	#5
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Tektronix 475 & 547, servicing notes Excellent - will do that then Purely by chance when I cracked my 465 open to measure some voltages for someone today, I discovered the main 1000uF 10V electrolytic in mine had some not insignificant burns on it. Was still quite happily churning away still. Have ordered a replacement!

29th Sep 2018, 12:23 am	#7
Rileyman Pentode Join Date: Sep 2018 Location: Maldon, Essex, UK. Posts: 227	Re: Tektronix 475 & 547, servicing notes Forgot to mention:- When troubleshooting the long-dead B Timebase on my Tek.547 I came across some useful info. on http://w140.com/tekwiki/wiki/tunnel_diodes .Scrolling-down I found a useful article on page 14 of "Service Scope 49, April 1968". Not having a Tek.454 or 571 I was lucky that the A Timebase was fully operational (and calibrated) so I was able to employ the method described to select a "best" diode from those Russian tunnel diodes I bought on-line, and used the 100v. (not 10v. !) A Sweep Output via suitable resisters to give the current/div.scales I needed. Finally,after replacing two leaky diodes in the Alt. Sweep switching cct. I was really chuffed to be able to display 8 traces - using a 1A4 Plug-In and the Alt. Sweep modes. Next task:- Still trying to find a Sweep Control I.C.(Tek.155-0056-00) for another dead B Timebase (no pun!) in my Tek. 5103N. So far it seems my best chance would be to find an otherwise scrap,or mutilated, 5B12N or 5B10N Plug-In. Fingers crossed !