Ringing on 2235 100 volt supply


John G
 

Hi Tek group members!
I'm an new member and just acquired a 2235 scope. It works great except it has an intermittent horz sweep problem. Checking the power supplies, all were in spec except the 100v supply ripple at 90 p-p, spec is 40 p-p.
Mainly out of spec due to ringing on every other cycle. Anyone seen this before? So far I have only replaced the cap and diodes in this supply. I'll cover the sweep problem in different thread.
Photo at: https://groups.io/g/TekScopes/album?id=242594
Thanks,
John


John G
 

Upon further searching it looks like this is a common problem and no resolution found. It apparently doesn't cause any problems. So back to the horz problem.
John


 

On Sun, Mar 8, 2020 at 04:56 AM, John G wrote:


Checking the power supplies, all were in spec except the 100v supply ripple at
90 p-p, spec is 40 p-p.
This certainly is *not* common or even normal for the 100 VDC supply and certainly *not* without negative effects.
Are you really talking about the voltage across e.g. C954?

Raymond


 

On Sun, Mar 8, 2020 at 03:32 PM, John G wrote:


Upon further searching it looks like this is a common problem and no
resolution found. It apparently doesn't cause any problems.
Where did you find this is a common problem (and no resolution found)? I can't make sense of your "90" and "40". What unit? Spec is +/- 3 VDC off.
Unfortunately, settings for your image are unknown.
OTOH, the kind of problem with the 100 V would suggest more problems than an intermittent horizontal problem. Speaking of that, what does that intermittent problem consist of? One in n sweeps missing? The sweep not working on odd dates?

Raymond


John G
 

Hi Raymond,
Let me clarify a bit. Table 6.4 in the service manual shows 40.0 P-P Ripple (mv) as the limit on the +100 V supply. I see about 90 mv P-P as pic 1 shows. Scope set at 20mv per div.
If it wasn't for the ringing it would be in spec. I see the same result measuring itself or on another scope. Measured at Test Point W954 which is adjacent to C954.
The thread that I believe is the same issue, but I couldn't find the photos referred to is:
https://groups.io/g/TekScopes/topic/7646253#62131

I added more picts showing the horz sweep problem:
https://groups.io/g/TekScopes/album?id=242594
2 is normal, 3 is after it fails and settles down, 4 is the transition between the 2 states, very erratic sweep. Moving any control, switch or tapping on components doesn't cause it to fail or fix it. Random when it happens, usually about 30 minutes after you turn it on. It will fail for 5 sec to 2 minutes, work properly 10 sec or 30 minutes. Totally random. All other functions seem normal. S/N B024573
Thank You for any light you can shed on these issues.
John


 

On Mon, Mar 9, 2020 at 04:12 AM, John G wrote:


Table 6.4 in the service manual shows 40.0 P-P Ripple (mv) as the limit on the
+100 V supply. I see about 90 mv P-P as pic 1 shows. Scope set at 20mv per
div.
Hi John,
So it's 40 - 90mV. That sort of ripple won't cause your (or any) real problem.
More often than not, it's just a loose or oxidized wire connecting the horizontal amp to the CRT. You'll find the connections underneath the CRT. Be careful not to short any to gnd (that includes the CRT's screen); it'll kill the amp.

Raymond


John G
 

Hi Raymond,
It turned out to be a dirty R740 "A Sweep Gain" adjustment. I had a scope probe on both sides of it when it failed so I'm 99.99% sure that was it.
I did also have a flaky connection to the horz plates as you mentioned.
Thanks for your help!
John


 

Hi John,
Happy that your 2235 is fine again. PSU problems can be nasty with these series but mostly it's flaky contacts, including adjustment pots, as in your case. Good that you found the flaky plate connection, since damage will be done if amp outputs touch e.g. a grounded point.
Thanks for letting us know what was wrong and how things went.

Raymond


alfa beta
 

my 2235 has an intermittent contact when I select the XY mode (for my home-made curve tracer)

Was wondering how difficult is to get access to selector for giving it a shot of deoxit

adri





----- Messaggio originale -----
Da: Raymond Domp Frank <hewpatek@gmail.com>
Rispondi a: <TekScopes@groups.io>
A: <TekScopes@groups.io>
Inviato: 10/03/2020 11:46:25
Oggetto: Re: [TekScopes] Ringing on 2235 100 volt supply
________________________________________________________________________________

Hi John,
Happy that your 2235 is fine again. PSU problems can be nasty with these series but mostly it's flaky contacts, including adjustment pots, as in your case. Good that you found the flaky plate connection, since damage will be done if amp outputs touch e.g. a grounded point.
Thanks for letting us know what was wrong and how things went.

Raymond


John G
 

I finally got around to replacing the "Sweep Gain" adjustment pots (Digi-Key # 3329H-102LF-ND) and recapping it. My problem is the screws that secure the front of the attenuator board from the bottom. I can't seem to find the right one's. Either too short to hold or too long and they bind up the input coupling switch. Any one know what length they should be? The service manual doesn't have a description.
Picture of location:

https://groups.io/g/TekScopes/photo/242594/0?p=Created,,,20,2,0,0

Thanks
John


barry.ballenger@...
 

John, I can get you the info tomorrow, I have several 2235s in the process
of being redone. I may even have a couple of the screws extra.

On Fri, Apr 3, 2020 at 9:07 PM John G <mnjgfl@centurylink.net> wrote:

I finally got around to replacing the "Sweep Gain" adjustment pots
(Digi-Key # 3329H-102LF-ND) and recapping it. My problem is the screws
that secure the front of the attenuator board from the bottom. I can't seem
to find the right one's. Either too short to hold or too long and they bind
up the input coupling switch. Any one know what length they should be? The
service manual doesn't have a description.
Picture of location:

https://groups.io/g/TekScopes/photo/242594/0?p=Created,,,20,2,0,0

Thanks
John




John G
 

Thanks Barry, I have the screws somewhere in the scope, obviously not in the right place. The length would be helpful.
Thanks
John


barry.ballenger@...
 

john where is a pix of the screw from my scope, it is 6 mm long

On Sat, Apr 4, 2020 at 8:48 AM John G <mnjgfl@centurylink.net> wrote:

Thanks Barry, I have the screws somewhere in the scope, obviously not in
the right place. The length would be helpful.
Thanks
John




John G
 

The 6 mm is just a bit short. I cut a 4-4 screw about 7 mm long and it worked perfect. Maybe the holes are slightly stripped.
Thanks for affirming it should be 6 mm.
John

On Sat, Apr 4, 2020 at 11:49 AM, <barry.ballenger@gmail.com> wrote:


john where is a pix of the screw from my scope, it is 6 mm long

On Sat, Apr 4, 2020 at 8:48 AM John G <mnjgfl@centurylink.net> wrote:

Thanks Barry, I have the screws somewhere in the scope, obviously not in
the right place. The length would be helpful.
Thanks
John




barry.ballenger@...
 

John did you have the attenuators board.out to repair. My B channel quit
working and believe it may be the B attenuator board.

On Sat, Apr 4, 2020 at 1:37 PM John G <mnjgfl@centurylink.net> wrote:

The 6 mm is just a bit short. I cut a 4-4 screw about 7 mm long and it
worked perfect. Maybe the holes are slightly stripped.
Thanks for affirming it should be 6 mm.
John

On Sat, Apr 4, 2020 at 11:49 AM, <barry.ballenger@gmail.com> wrote:


john where is a pix of the screw from my scope, it is 6 mm long

On Sat, Apr 4, 2020 at 8:48 AM John G <mnjgfl@centurylink.net> wrote:

Thanks Barry, I have the screws somewhere in the scope, obviously not
in
the right place. The length would be helpful.
Thanks
John






John G
 

I removed it when I re-capped everything.

On Sat, Apr 4, 2020 at 01:55 PM, <barry.ballenger@gmail.com> wrote:


John did you have the attenuators board.out to repair. My B channel quit
working and believe it may be the B attenuator board.


barry.ballenger@...
 

Same here worked fine then quit when I put it back in to test. Have you
worked on any attenuator boards. Looking for what might be wrong on mine.

On Sat, Apr 4, 2020 at 2:47 PM John G <mnjgfl@centurylink.net> wrote:

I removed it when I re-capped everything.

On Sat, Apr 4, 2020 at 01:55 PM, <barry.ballenger@gmail.com> wrote:


John did you have the attenuators board.out to repair. My B channel quit
working and believe it may be the B attenuator board.



John G
 

Barry,
BTDT. I missed plugging in one of the ribbon cables.
John

On Sat, Apr 4, 2020 at 03:00 PM, <barry.ballenger@gmail.com> wrote:


Same here worked fine then quit when I put it back in to test. Have you
worked on any attenuator boards. Looking for what might be wrong on mine.


barry.ballenger@...
 

On Sat, Apr 4, 2020 at 3:47 PM John G <mnjgfl@centurylink.net> wrote:

Barry,
BTDT. I missed plugging in one of the ribbon cables.
John

On Sat, Apr 4, 2020 at 03:00 PM, <barry.ballenger@gmail.com> wrote:


Same here worked fine then quit when I put it back in to test. Have you
worked on any attenuator boards. Looking for what might be wrong on mine.
this is my first will let you know what I learn.