Trouble shoot and extremely stubborn 465B


Zentronics42@...
 

I have a 465B on the bench that I have been working on a restoration on. I have most of the gremlins worked out but there is one annoying one that is stumping me. Work done so far.

Cleaned and rebuilt the entire attenuator section of the scope. Needed to completely replace on of them due to a destroyed AC-DC-Gnd switch. Cleaned the control and added publication to the proper places in the scope. Checked power supply are rails are present and ripple looks good. There is one odd ball situation in the trigger section that is weird. Channel 1 works as expected triggers in norm and channel 1. Channel 2 will not trigger in normal mode however it will trigger in Chanel 1 and Chanel 2 mode. any one run in to this before. the trigger circuit seems to be ok it will lock the waveform just with the switch in the wrong position. All the IC's check out good and the verticual is nice and stable. Also the tunnel diodes checked out ok on the curve tracer so they are good. Wondering if anyone has any thoughts. I am trying to wrap my head around the trigger logic sections of this scope.

Zen


Bert Haskins
 

On 7/5/2021 1:13 PM, Zentronics42@gmail.com wrote:
I have a 465B on the bench that I have been working on a restoration on. I have most of the gremlins worked out but there is one annoying one that is stumping me. Work done so far.

Cleaned and rebuilt the entire attenuator section of the scope. Needed to completely replace on of them due to a destroyed AC-DC-Gnd switch. Cleaned the control and added publication to the proper places in the scope. Checked power supply are rails are present and ripple looks good. There is one odd ball situation in the trigger section that is weird. Channel 1 works as expected triggers in norm and channel 1. Channel 2 will not trigger in normal mode however it will trigger in Chanel 1 and Chanel 2 mode. any one run in to this before. the trigger circuit seems to be ok it will lock the waveform just with the switch in the wrong position. All the IC's check out good and the verticual is nice and stable. Also the tunnel diodes checked out ok on the curve tracer so they are good. Wondering if anyone has any thoughts. I am trying to wrap my head around the trigger logic sections of this scope.

Zen
Swap the A and B tunnel diodes and see if it makes any difference.

I have a 465B that I've had for a long time and over the years I've built up a pile of TDs that look fine on the curve tracer but just don't work well in my 465B.

They also don't work well in HF oscillator test circuits.

I really don't have a clue as to what the problem is.


 -Bert





Zentronics42@...
 

Swapping the tunnel diodes did not change the behavior of the scope at all.


 

Ch1 and Ch2 trigger circuits are almost identical.
Making sure A is triggered, see if you have the same behavior when triggering B. Consider swapping identical components like U7131 and U7331.

Raymond


 

On Mon, Jul 5, 2021 at 08:43 PM, Raymond Domp Frank wrote:


Ch1 and Ch2 trigger circuits are almost identical.
Add to that: "Timebase A and Timebase B trigger circuits are almost identical".

If it's a matter of triggering as such being OK, "just with the switch in the wrong position", as you write, it shouldn't be too difficult to find the fault in the circuits and switches between A1 and E2 on dwg6 of the SM (mine is 070-2757-00).
Don't forget to check switches and correct fixing of levers (hex screw fastened) on moving switch parts.

Raymond


Zentronics42@...
 

At the moment I am not having trouble with A and B trigger it is channel 2 is not triggering the scope on A trigger Normal mode. Will trigger the scope when a trigger is set to Chanel 1 or 2. Channel 1 works as expected. At the moment I have confidence in the Tunnel diodes and the following trouble shooting has been done:

Q1719
Q1426
Q1215
Q1188
Test ok on atlas DCA Pro

U7131
U7331
U7375
U1605
U1705
U1805
U1905
Swapped with known good unit no effect on fault

One thing to know the scope will trigger in channel 1 even when channel 1 is not selected. Was proved by feeding a signal in to channel 1 and 2 and ground out channel 1 with the AC-GND-DC switch. With only channel 2 selected.

I have cleaned the switches already but I am hitting them again cause this one is weird.


Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Raymond Domp Frank
Sent: Monday, July 5, 2021 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trouble shoot and extremely stubborn 465B

Ch1 and Ch2 trigger circuits are almost identical.
Making sure A is triggered, see if you have the same behavior when triggering B. Consider swapping identical components like U7131 and U7331.

Raymond


Zentronics42@...
 

I also checked the B trigger and it is behaving exactly the same as the A trigger. So the issue in the scope has to be before the trigger boards.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Zentronics42 via groups.io
Sent: Monday, July 5, 2021 2:57 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trouble shoot and extremely stubborn 465B

At the moment I am not having trouble with A and B trigger it is channel 2 is not triggering the scope on A trigger Normal mode. Will trigger the scope when a trigger is set to Chanel 1 or 2. Channel 1 works as expected. At the moment I have confidence in the Tunnel diodes and the following trouble shooting has been done:

Q1719
Q1426
Q1215
Q1188
Test ok on atlas DCA Pro

U7131
U7331
U7375
U1605
U1705
U1805
U1905
Swapped with known good unit no effect on fault

One thing to know the scope will trigger in channel 1 even when channel 1 is not selected. Was proved by feeding a signal in to channel 1 and 2 and ground out channel 1 with the AC-GND-DC switch. With only channel 2 selected.

I have cleaned the switches already but I am hitting them again cause this one is weird.


Zen
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Raymond Domp Frank
Sent: Monday, July 5, 2021 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trouble shoot and extremely stubborn 465B

Ch1 and Ch2 trigger circuits are almost identical.
Making sure A is triggered, see if you have the same behavior when triggering B. Consider swapping identical components like U7131 and U7331.

Raymond


 

On Mon, Jul 5, 2021 at 08:56 PM, <Zentronics42@gmail.com> wrote:


At the moment I am not having trouble with A and B trigger it is channel 2 is
not triggering the scope on A trigger Normal mode.
I understood that and you've already checked components. I meant to make sure nothing's wrong already where the trigger signals enter the trigger generator(s). Don't ignore the possibility of someone having made an assembly error.

Did you check the switches (levers/arms and their positions), as I suggested in my previous message? The levers could incorrectly position the switches of S7312A.

There really aren't many other places where the Ch1 signal could inadvertently get through and the Ch2 not.

Did you check at measuring points 43 (or 44), dwg 6?

Raymond


 

On Mon, Jul 5, 2021 at 09:14 PM, <Zentronics42@gmail.com> wrote:


I also checked the B trigger and it is behaving exactly the same as the A
trigger. So the issue in the scope has to be before the trigger boards.
That was and is my idea with my earlier two messages: See if B does the same as A. If so, checking and swapping of all the IC's and transistors to the right of S7112A and S7312A isn't necessary. That's in the past now.

I'd check the trigger inputs to the trigger logic board (dwg6 area A1 -A2). You may check and disconnect Ch1 and Ch2 trigger input cables there. Even swap if no result.

Raymond


Mark Vincent
 

Zen,

Check: Q1636, VR1824, VR4421, VR4495, VR4394 and VR4496. One of the VR is in the power supply. If Q1636 is bad, use KSP10BU. For the VRs, BZX85B9V1. The Q1636 is a 151-0367-00. These can to will be leaky between C and E. It will check as a diode. Ones with the round leads will be leaky. Ones with the square leads likely will be leaky. The VRs are 9V types that I will replace as the ones I have seen in scopes will be open.

Mark


Zentronics42@...
 

After a night of trouble shooting I think I have traced it to at least the offending section if not the dead part. Putting a square wave on the channel 2 input I have what I think is the expected wave forms. At the base of Q1215I also have what seems to be a very low signal 10's of mv at the collector of Q1215 but I have almost 0 signal at the base of Q1118. I am starting to this R1202 or R 1205 might be toasted. There is however the 4.2 V dc Bias at the base of Q1118 One thing Is for sure nothing is making it through Q1118 in the J1101 to head to the trigger circuit.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Mark Vincent
Sent: Monday, July 5, 2021 5:08 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trouble shoot and extremely stubborn 465B

Zen,

Check: Q1636, VR1824, VR4421, VR4495, VR4394 and VR4496. One of the VR is in the power supply. If Q1636 is bad, use KSP10BU. For the VRs, BZX85B9V1. The Q1636 is a 151-0367-00. These can to will be leaky between C and E. It will check as a diode. Ones with the round leads will be leaky. Ones with the square leads likely will be leaky. The VRs are 9V types that I will replace as the ones I have seen in scopes will be open.

Mark


Zentronics42@...
 

*SOLVED* seems the tech before me that was in this unit flipped 2 of the micro coax lines. J1101 and J1002 were flipped on the vertical board side. Seems everything was testing good because it was. I was chasing an elephant with a microscope.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Zentronics42 via groups.io
Sent: Monday, July 5, 2021 11:36 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trouble shoot and extremely stubborn 465B

After a night of trouble shooting I think I have traced it to at least the offending section if not the dead part. Putting a square wave on the channel 2 input I have what I think is the expected wave forms. At the base of Q1215I also have what seems to be a very low signal 10's of mv at the collector of Q1215 but I have almost 0 signal at the base of Q1118. I am starting to this R1202 or R 1205 might be toasted. There is however the 4.2 V dc Bias at the base of Q1118 One thing Is for sure nothing is making it through Q1118 in the J1101 to head to the trigger circuit.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Mark Vincent
Sent: Monday, July 5, 2021 5:08 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trouble shoot and extremely stubborn 465B

Zen,

Check: Q1636, VR1824, VR4421, VR4495, VR4394 and VR4496. One of the VR is in the power supply. If Q1636 is bad, use KSP10BU. For the VRs, BZX85B9V1. The Q1636 is a 151-0367-00. These can to will be leaky between C and E. It will check as a diode. Ones with the round leads will be leaky. Ones with the square leads likely will be leaky. The VRs are 9V types that I will replace as the ones I have seen in scopes will be open.

Mark


 

On Tue, Jul 6, 2021 at 06:07 AM, <Zentronics42@gmail.com> wrote:


*SOLVED* seems the tech before me that was in this unit flipped 2 of the micro
coax lines. J1101 and J1002 were flipped on the vertical board side. Seems
everything was testing good because it was. I was chasing an elephant with a
microscope.
Congratulations!

I hope my two suggestions
"Don't ignore the possibility of someone having made an assembly error"
and
"I'd check the trigger inputs to the trigger logic board (dwg6 area A1 -A2). You may check and disconnect Ch1 and Ch2 trigger input cables there. Even swap if no result"
saved you some time.
Been there, done that...

Raymond