465 dot only, no sweep


james_55@...
 

Hi all,
I have a early 465 which only displays a dot and only with the intensity high.
Reading the power supply voltages reveals that the -8v rail has -4.89v.

Does anyone recognise this situation?


 

Do you have the service manual? If not, Artekmanuals.com has the low serial manual.

My first guess would be check C1562, a 3000uF can capacitor on the main board.

Regards,

Tom, WA3PZI

On 4/4/2020 10:49 AM, james_55@mail.com wrote:
Hi all,
I have a early 465 which only displays a dot and only with the intensity high.
Reading the power supply voltages reveals that the -8v rail has -4.89v.
Does anyone recognise this situation?

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Mlynch001
 

You must have the correct Service Manual. Study the Circuit description section, starting with the power supplies. After that, all the LV supply voltages need to be correct voltages. Then and only then can you move to diagnose the problems with the sweep. Start at the bottom and work up, do not try to start in the center and work in all directions.

--
Michael Lynch
Dardanelle, AR


Bill
 

More than likely a capacitor has shorted. Probably a Tantalum.
Bill


Bill
 


Abc Xyz
 

What would cause Both Traces to be Shifted Right on a 465B?

On Sat, Apr 4, 2020, 12:44 PM Bill via groups.io <ko4nrbs=
yahoo.com@groups.io> wrote:

More than likely a capacitor has shorted. Probably a Tantalum.
Bill




james_55@...
 

On Sat, Apr 4, 2020 at 04:12 PM, Tom Miller wrote:



My first guess would be check C1562, a 3000uF can capacitor on the main
board.
That was what I was testing in another thread, and it seemed ok.


james_55@...
 

On Sat, Apr 4, 2020 at 08:44 PM, Bill wrote:


More than likely a capacitor has shorted. Probably a Tantalum.
Bill
Don't think so, as if it was shorted the voltage would be close to zero.

But thanks


james_55@...
 

After drawing up a list of every component in the -8v rail, I set about testing them all.

As R1565 (8K) was being removed it revealed itself to be broken in two. So that is some kind of progress, and I have temporarily installed a 10k which took the -8v rail down to -6.09v

By switching over op-amps U1554 and U1524 there were clear differences on the -8v, +5v and +15v rails, so therein lies another part to be ordered.

If I select the X10 Mag, a small (1") sweep does now appear, but without any vertical deflection.






I was trying to attach the power section of the schematic here


Bert Haskins
 

On 4/5/2020 10:17 AM, james_55@mail.com wrote:
After drawing up a list of every component in the -8v rail, I set about testing them all.

As R1565 (8K) was being removed it revealed itself to be broken in two. So that is some kind of progress, and I have temporarily installed a 10k which took the -8v rail down to -6.09v

By switching over op-amps U1554 and U1524 there were clear differences on the -8v, +5v and +15v rails, so therein lies another part to be ordered.

If I select the X10 Mag, a small (1") sweep does now appear, but without any vertical deflection.






I was trying to attach the power section of the schematic here
Go back to the op amps and clean the pins and sockets.

Reinsert the chips and wiggle them around.

Then remeasure and see if you have a different result from your step two .

You may just have a poor contact problem.

Been there, done that.




david
 

My 465 had the same problem, no sweep, found that tantalum capacitor C1220 on horizontal amplifier was shorted out. Cap C1220 is connected to the -8V supply through resistor R1220. I replaced it with an aluminum electrolytic and scope is working fine now.This doesn't explain the low value for the -8V supply but it is a worth checking. If you need a good schematic I have cleaned up a lot of the 465 schematic's. They are PDF files if you need them. I read an old service bulletin that said to replace Capacitor C1220 in units below serial number 294620, but I didn't replace it and it went bad a couple months ago.
David


james_55@...
 

On Sat, Apr 4, 2020 at 05:13 PM, Mlynch001 wrote:


You must have the correct Service Manual. Study the Circuit description
section, starting with the power supplies. After that, all the LV supply
voltages need to be correct voltages. Then and only then can you move to
diagnose the problems with the sweep. Start at the bottom and work up, do not
try to start in the center and work in all directions.

Not sure I have the correct service manual and have been trying to find out which component is pulling the voltage towards ground.

Made a list of all components in the -8v rail and tested each one, however the other day, after the scope had been on for five minutes, it started buzzing and glowing up the two neons under the HV cover.
I assumed it was the -8v rail 3000µF filter cap that had failed, so pulled that, however the buzzing persisted.

It was around then that I found a vid of a 475A with a failing -8v rail, where the fella explained that it had to do with his +5v rail having a defective bridge rectifier...

...which I hadn't realised was related...

So I pulled the +5v 500µF filter cap,

...and the buzzing stopped!

Thing is, the cap seems fine... Measures 8000+µF and doesn't appear to draw any current when connected up to my bench power supply.
I have a Peak Atlas ESR70, a MK-328 and a DMM with capacitor test to do my testing.

So, pulled the +5v rail bridge rectifier but that tested fine too.

My question, is, "why would the +5v filter cap have been making the neons buzz if it is ok?"


james_55@...
 

Hi all.

So....

Replaced one of the op-amps, replaced the broken resistor, replaced the bridge rectifier and filter caps...

+55v TP = 55.05v
+110v TP = 107.7v
+15v TP = 15.00v
+5v TP = 5.01v
-8v TP = -8.05v

BUT... there is no trace nor spot, even with beam finder, and after a few minutes the buzzing neons return with a flickering trace on the CRT


Does anyone know, where do I look now?


james_55@...
 

One other thing to mention, is that as the screen and neons buzz and flash, the 'Trig' light flickers in unison


james_55@...
 

Should I just leave it turned on til whatever is making the neons buzz explodes?


Bill
 

I would take the cover off the HV section, turn off the lights so it's dark then turn on the 465.  You may be able to see what is arcing.
Be safe!!
Bill

On Friday, April 24, 2020, 5:21:27 PM CDT, <james_55@mail.com> wrote:

Should I just leave it turned on til whatever is making the neons buzz explodes?


james_55@...
 

On Fri, Apr 24, 2020 at 11:35 PM, Bill wrote:


I would take the cover off the HV section, turn off the lights so it's dark
then turn on the 465.  You may be able to see what is arcing.
Be safe!!
Bill
Thanks.

Still alive.

Removed the HV cover and sure enough the two tubes arc whenever the scope is turned on.

I am finding this all definitely very interesting.

With the power supplies all correct, it seems to me that the fault must be on the trigger and sweep board, although scope design and theory is not my forté.

Gonna keep looking...


james_55@...
 

Progress...

reseating the transistors on the A8 sweep/trigger board made the buzzing stop.... almost.

When the scope is on it's side it runs without problem (other than the minor detail of no trace).

When it is turned upside down however, it runs, although still produces this intermittent buzzing from the HV section, and I mean REALLY intermittent, a blip every 30 seconds or so...

Could that be the residue of the isopropyl acohol that was used to clean the soldering?


Bill
 

If the area is dirty clean it before continuing.  Use compressed air in a can for use on computers and at least 91% isopropyl alcohol.Bill

On Friday, April 24, 2020, 5:53:48 PM CDT, <james_55@mail.com> wrote:

On Fri, Apr 24, 2020 at 11:35 PM, Bill wrote:


  I would take the cover off the HV section, turn off the lights so it's dark
then turn on the 465.  You may be able to see what is arcing.
Be safe!!
Bill
Thanks.

Still alive.

Removed the HV cover and sure enough the two tubes arc whenever the scope is turned on.

I am finding this all definitely very interesting.

With the power supplies all correct, it seems to me that the fault must be on the trigger and sweep board, although scope design and theory is not my forté.

Gonna keep looking...


Mlynch001
 

When you replaced all the filter caps, how did you deal with the grounds that are completed by the base ground lugs of the various caps. Each caps’ ground lugs connect the various grounds on the board. These connections need to be maintained when replacing “non stock” type caps.
How about that auxiliary ground connector between the main board and the sweep board? This is a short piece of bare braided wire that connects the two boards and provides a common ground.
Trying to think of some off the wall stuff that I have encountered.

--
Michael Lynch
Dardanelle, AR