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475M metal can caps


Bob Isselhard
 

I recently acquired a TEK 475M and purchased a hard-copy manual for it. I put the probe on channel A input and attached it to the calibrator. Then I moved the probe plug to channel B input. The amount of signal is correct (square wave, 300 MV) on either channel. I can not stabilize the trace however. It continues to slide to the left no matter where I move the TRIGGER SOURCE controls. I have only one probe so I can't exactly try the "connect both probes to the CALIBRATOR routine.

I checked the power supply voltages as per the manual and found the following:

+50 volts = +49.7 volts
+110 volts = +110.4 volts
+15 volts = +14.96 volts
+5.0 volts = +4.94 volts
-15 volts = -21.93 volts
-8 volts = -5.3 volts
UNREGULATED +50.volts = +64.3 volts

I looked at the large can caps and removed C1472, the filter cap across the diode bridge for the -15.0 volt supply. It actually looks good (3700 MFD, .47 ohms ESR).

Now the problem comes in. I have never worked with these before and did not realize there was an additional lug on the cap that was soldered to the lead that comes out on the other side of the board and is connected to the -15 volt test point.

I would like to obtain an exact replacement physical configuration-wise and re-solder the can lug to the test point and have it held down to the circuit board that way. However, if I can't find one, I can obtain a radial-lead, wired-in electrolytic and bridge the necessary connections. I wonder what to use to secure it to the metal piece adjacent to it? Hot glue? Super glue? Seal all? (one tube epoxy). I wonder what others have done here when replacing these large can caps? Granted, this one appears good, but why re-insert an old cap when I can replace it with a new one?

Any ideas gratefully accepted.

73, Bob K5INW


Michael W. Lynch
 

I have restored several of this family of scopes. Finding OEM style caps that are good is not a really viable option.

I use Modern radial lead caps and these adapters:

www.ebay.com/itm/Capacitor-Adapter-15-5mm-triangle-recapping-vintage-equipment-Tek-465-kit-x5/273254508468

I would say that you have issues with you -15 and -8V Supply. Caps may help rectify some of those issues. A Good place to start in any case. Get you supplies back in spec and you will go a long way to fixing the scope.

Good Luck!
--
Michael Lynch
Dardanelle, AR


Paul Amaranth
 

I will second Michael's recommendation. The little adapter boards make
for a very neat and professional looking repair. In a pinch I've used
PNP blue to etch my own, but it's easier to buy them ready made.

Use 105C caps if you can.

On these scopes if the power supplies are not right, nothing works right.
Always ensure the power supplies are correct before looking at anything
else.

Paul

On Fri, Nov 06, 2020 at 10:15:53AM -0800, Michael W. Lynch via groups.io wrote:
I have restored several of this family of scopes. Finding OEM style caps that are good is not a really viable option.

I use Modern radial lead caps and these adapters:

www.ebay.com/itm/Capacitor-Adapter-15-5mm-triangle-recapping-vintage-equipment-Tek-465-kit-x5/273254508468

I would say that you have issues with you -15 and -8V Supply. Caps may help rectify some of those issues. A Good place to start in any case. Get you supplies back in spec and you will go a long way to fixing the scope.

Good Luck!
--
Michael Lynch
Dardanelle, AR
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


Michael W. Lynch
 

Trying to "fix" a TEK scope that has faulty power supplies is almost like trying to push a rope.

--
Michael Lynch
Dardanelle, AR


Leon Robinson
 

Or herd cats.  Electronic equipment is like a house, the power supply is the foundation, 
If it,s not right nothing else is.


Leon Robinson  K5JLR

-------- Original message --------
From: "Michael W. Lynch via groups.io" <mlynch003=yahoo.com@groups.io>
Date: 11/06/2020 4:41 PM (GMT-06:00)
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475M metal can caps

Trying to "fix" a TEK scope that has faulty power supplies is almost like trying to push a rope.

--
Michael Lynch
Dardanelle, AR


Bob Isselhard
 

Thanks Paul, Michael and Leon.   I told Michael in a PM I ordered five of the spacers off Ebay immediately after following his link.  Yeah, I know, power supply problems can doom the best of efforts.  That’s why I ordered the hard copy manual as soon as I saw the problem with the trigger. I wanted to see exactly where all the test points were and exactly what they should read.  I don’t have a second scope to check ripple  but getting the voltages correct on the -15 and -8 volt rails may solve this.  If not, I’ll no longer be a TEKSCOPE beginner, but a “veteran” with solder splashes and flux odor to boot.  When I pulled the -15 volt electrolytic, I checked it and it shows 3700 uf and .47 ESR.  But I’m not about to put a 10 + year old cap back in.

Thanks to all for the assistance so far.

Bob

Sent from Mail ( https://go.microsoft.com/fwlink/?LinkId=550986 ) for Windows 10


Liam Perkins
 

Here's some work I did 20 years ago on a Tek 570 S/N 215:

https://www.pearl-hifi.com/07_Facility_Tour/Tek_570_215/Internal.jpg

I made the parts from FR-4 and used stake-in solder terminals from Keystone.

Bill

I will second Michael's recommendation. The little adapter boards make
for a very neat and professional looking repair. In a pinch I've used
PNP blue to etch my own, but it's easier to buy them ready made.
Use 105C caps if you can.
On these scopes if the power supplies are not right, nothing works right.
Always ensure the power supplies are correct before looking at anything
else.
Paul
On Fri, Nov 06, 2020 at 10:15:53AM -0800, Michael W. Lynch via groups.io wrote:
I have restored several of this family of scopes. Finding OEM style caps that are good is not a really viable option.

I use Modern radial lead caps and these adapters:

www.ebay.com/itm/Capacitor-Adapter-15-5mm-triangle-recapping-vintage-equipment-Tek-465-kit-x5/273254508468

I would say that you have issues with you -15 and -8V Supply. Caps may help rectify some of those issues. A Good place to start in any case. Get you supplies back in spec and you will go a long way to fixing the scope.

Good Luck!
--
Michael Lynch
Dardanelle, AR


greenboxmaven
 

One thing Tektronix did a great deal was to only have one voltage supply with a zener reference, it's output was the reference for other voltage supplies. Sometimes there would be a cascade of supplies giving reference to others. Needless to say, if any one of them is not accurate and clean, the following ones won't be either. The absolute worst examples I ever dealt with were some Yamaha stereo receivers where one zener ultimately controlled cascaded power supplies producing nine different voltages.

Bruce Gentry, KA2IVY

On 11/6/20 5:27 PM, Paul Amaranth wrote:
I will second Michael's recommendation. The little adapter boards make
for a very neat and professional looking repair. In a pinch I've used
PNP blue to etch my own, but it's easier to buy them ready made.

Use 105C caps if you can.

On these scopes if the power supplies are not right, nothing works right.
Always ensure the power supplies are correct before looking at anything
else.

Paul

On Fri, Nov 06, 2020 at 10:15:53AM -0800, Michael W. Lynch via groups.io wrote:
I have restored several of this family of scopes. Finding OEM style caps that are good is not a really viable option.

I use Modern radial lead caps and these adapters:

www.ebay.com/itm/Capacitor-Adapter-15-5mm-triangle-recapping-vintage-equipment-Tek-465-kit-x5/273254508468

I would say that you have issues with you -15 and -8V Supply. Caps may help rectify some of those issues. A Good place to start in any case. Get you supplies back in spec and you will go a long way to fixing the scope.

Good Luck!
--
Michael Lynch
Dardanelle, AR