Topics

2215 CRT problem, PSU filtering?


Maxsimmonds1337@...
 

Hi Everyone,

I have just bought a scope (tek 2215) which initially would not power on. I was able to fix this (it was a simple faulty power switch). Everything seems to be working except that there's a distinct rippled on both channels - even when they're set to ground!

Does anyone know what's the first thing I should look into? My guess is some sort of power supply filtering caps need replacing - but a visual inspection doesn't show any blow electrolytics. Here's an image of the ripple I'm talking about:

https://imgur.com/a/Yc4GrBi

You can see it's about 20mV ripple, at around 125KHz.


On another note, should the probe adjust output be negative? I'm sure it's showing a -500mV square wave?!

Thanks in advance!


 

First, do you have any LED lamps in the near area? Some of them radiate a lot of trash.

Make sure the CRT shield has a good ground connection.

It probable is a good idea to check/replace the PS filter caps while you are in there. See manual for what to order.

The probe waveform is a negative 0.5 volts. See waveform #34 in the service manual.

Regards,

Tom

On 6/26/2020 1:28 PM, Maxsimmonds1337@... wrote:
Hi Everyone,

I have just bought a scope (tek 2215) which initially would not power on. I was able to fix this (it was a simple faulty power switch). Everything seems to be working except that there's a distinct rippled on both channels - even when they're set to ground!

Does anyone know what's the first thing I should look into? My guess is some sort of power supply filtering caps need replacing - but a visual inspection doesn't show any blow electrolytics. Here's an image of the ripple I'm talking about:

https://imgur.com/a/Yc4GrBi

You can see it's about 20mV ripple, at around 125KHz.


On another note, should the probe adjust output be negative? I'm sure it's showing a -500mV square wave?!

Thanks in advance!

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Maxsimmonds1337@...
 

Hey Tom,

Thanks for replying. I don't have any LED lights but I do have a florescence one (but that's spitting out crap at 50Hz so I assume it's fine). Either way, I took the scope to another room in the house and it's still the same. In fact, I'm facing a very similar problem to what's outlined here - https://groups.io/g/TekScopes/topic/7638108

I checked the grounding on the CRT tube, the resistance from the earth pin to the top of the tube, and it was in the order of ohms, so I cleaned up the ground clip contact, it reduced the resistance to sub-ohm, but this did not help.

So, I guess I had better start replacing some caps, the rifa ones looked cracked, so I'll start with these. The PSU filtering caps, are they all on A18?

Thanks again!

Max


 

Hi Max,

I guess you mean A10, the main board. At least on my schematic.

Anyway, do you have access to an ESR meter? That would be a little easier than a shotgun approach.

But here are the caps to look at:

C937 1800 uF/ 75 V

C961 33 uF/ 160 V

C965 270 uF/ 40 V

C971, 972, 975, 976, 985    840 uF/ 12 V

Be sure to use caps from a reliable source. Avoid the china caps or ebay.


Have you checked the tightness for all the PC board mounting hardware?


Any way, good luck. Being in 50Hz land the RIFA caps should be the first step. Be sure to use safety caps.

Regards,

Tom

On 6/28/2020 6:22 PM, Maxsimmonds1337@... wrote:
Hey Tom,

Thanks for replying. I don't have any LED lights but I do have a florescence one (but that's spitting out crap at 50Hz so I assume it's fine). Either way, I took the scope to another room in the house and it's still the same. In fact, I'm facing a very similar problem to what's outlined here - https://groups.io/g/TekScopes/topic/7638108

I checked the grounding on the CRT tube, the resistance from the earth pin to the top of the tube, and it was in the order of ohms, so I cleaned up the ground clip contact, it reduced the resistance to sub-ohm, but this did not help.

So, I guess I had better start replacing some caps, the rifa ones looked cracked, so I'll start with these. The PSU filtering caps, are they all on A18?

Thanks again!

Max

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Maxsimmonds1337@...
 

Hi Tom,

Sorry, yes you're correct, that'll teach me for posting late at night! Unfortunately, I don't have access to an ESR meter, however the need for one arises often these days so perhaps it's time I look into purchasing one. The best I have is a capacitance meter, that will do little for ESR, but it may help spot any outliers.

I did go through and check all the mounting points previously, to make sure there's good contact to the chassis - but I'll take another look. I does feel like a grounding issue. One thing that does concern me is that lifting the upright (CRT facing the ceiling) I can hear what sounds like glass clinking as it falls to the back of the scope (inside the tube?). Is this Phosphor that's come off, or something worse?

Thanks very much for listing the caps - that's super helpful. I'll take a look at these, and most likely replace them all (I couldn't agree more about the cheap caps from China/Ebay!)

That's interesting about the RIFA caps, are they worse at 50Hz? I've never had any run ins with them before - I just know they tend to crack and I can see they have on this!

Thanks very much again, I'll be sure to post any updates here :)

Max


Maxsimmonds1337@...
 

Good news! I replaced the PSU filter caps, and I noticed the 33uF/160V on the 100V PSU output, and it's all good!

Looking at the base of this capacitor, it was quite obvious that it was the failed one, the black epoxy has come off near one of the legs and when I attempt to measure it's capacitance on my (cheap) multi-meter it reads almost 0nF. In fact, I think the black epoxy had come off under such pressure that it pushed the cap up, and crack the solder joint!

Look at the difference nice new caps have ! https://imgur.com/a/J9nxtNl

Thanks very much for your help, Tom, very much appreciated!

Max


Maxsimmonds1337@...
 

Sorry that should say "and I noticed the 33uF/160V on the 100V PSU output WAS DAMAGED, I REPLACED IT,...."


tekscopegroup@...
 

While in there you might want to replace all the caps that where listed above, so as to future proof the PS section some more. Use nearest value and voltage equal or higher. Modern caps will be smaller in size, so a somewhat higher value will still be an easy fit. Order good quality caps (and any other parts in general) from Mouser.com or similar reputable outfits, avoid ebay china crap.

C937 1800 uF/ 75 V --> Use 2200uF 100V
C961 33 uF/ 160 V --> Use 33uF 160V
C965 270 uF/ 40 V --> Use 330uF 50V
C971, 972, 975, 976, 985 840 uF/ 12 V --> Use 1000uF 16V


Michael W. Lynch
 

On Wed, Jul 1, 2020 at 09:10 AM, <tekscopegroup@...> wrote:


While in there you might want to replace all the caps that where listed above,
so as to future proof the PS section some more.
This is Very Good advice. I would not go into a scope and just replace one of the caps. They all can easily be in a similar condition in the near future.
--
Michael Lynch
Dardanelle, Arkansas


Maxsimmonds1337@...
 

Yep - I replaced them all just for good measure!


 

That's great Max. Good job. They are nice little scopes.

Regards,

Tom

On 7/1/2020 2:16 AM, Maxsimmonds1337@... wrote:
Good news! I replaced the PSU filter caps, and I noticed the 33uF/160V on the 100V PSU output, and it's all good!

Looking at the base of this capacitor, it was quite obvious that it was the failed one, the black epoxy has come off near one of the legs and when I attempt to measure it's capacitance on my (cheap) multi-meter it reads almost 0nF. In fact, I think the black epoxy had come off under such pressure that it pushed the cap up, and crack the solder joint!

Look at the difference nice new caps have ! https://imgur.com/a/J9nxtNl

Thanks very much for your help, Tom, very much appreciated!

Max

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On Sun, Jun 28, 2020 at 11:22 PM, <Maxsimmonds1337@...> wrote:
So, I guess I had better start replacing some caps, the rifa ones looked
cracked, so I'll start with these. The PSU filtering caps, are they all on
A18?
Did you find the 0.01uF X2 mains filter cap hidden underneath the mains input socket (on the main PCB)? You have to remove the socket to see it clearly and to replace the cap.

Regards,
John