2465 Blank screen when warm


david
 

Hi Guy's, I need your help again, My 2465 was working fine till I left it on for several days. Then the screen went blank. No display, no Trace, and no Readout visible. When I hold in the beam finder button , the Trace, Readout, and Cursors are visible in center of screen in miniature. Works OK when just turned on cold, but goes blank after a minute or two. When I remove the case and start to troubleshoot , whatever is failing cools down and display starts working again. Real pain in the behind, Any help will be greatly appreciated.
David


Mark Vincent
 

David,

Have you recapped it? If so, then check in the high voltage section. There are some resistors that are known to go hi or open. They are: R1871, R1872, R1853, R1854 and R1991. The first two should be 1W, the second two 1/2W or 1W and the last can be 1/2-2W. The first two can be the H4P series, the second two CCF60 series and the last 588-SM104031006FE. Mouser has these parts in stock. There are some others that should be raised in wattage.

If you have not recapped it, Condor Audio has a kit. Let him know you have the plain version as there are different kits for variants and S/N ranges. He is in Israel so shipping time may be still long from overseas (ask him for confirmation of delivery time), if you are in the US/CAN. He is great to deal with. If you prefer a list instead of the kit, ask. I will give you the list. Replace those RIFAs!

If your fan seems to be slow, it may have a 36,000 ohm resistor on the board. Putting a 10,000 ohm in parallel with it will speed it up. You can replace the pair with a 7800 or 7870 ohm resistor as this is close to the parallel combination of the two.

Do any voltages change when the display blanks off when warm? See if the B+ voltages from the power supply are accurate. See if the high voltage is still there when warm. See if the 300VP-P is at TP71. That is a good test point. A high voltage probe close to pin 8 on the multiplier will show an arc meaning there is high voltage going in. The ac voltage at the collector of the oscillator will tell if it is oscillating. If the transistor is hot, add a heatkink and add good compound. See about voltages on the outputs.

I have mentioned likely things with what you said. More information will help in determining your problem. We will happy to help you.

Mark


Jean-Paul
 

David: I doubt that the lytoics and divider resistors would produce that symptom.

The HV transformer is most vulnerable, as it dissipates heat and has insulation that degrades over time (crazing, oxidation, corona) and has properties that are affected by temperature.

I would suspect the HV transformer

Suggest: After you check caps and HV divider resistors

Use freon or other "freeze mist", wait till it fails and then spray onto the HV transformer.

Many threads are available to discuss the HV transformer and its replacement.

DANGER: BEWARE of the HV!

Bon Chance,

Jon


HV transformer is


david
 

I went through the steps on page 281 of service manual. Vertical troubleshooting, Horizontal troubleshooting, and Verified the Control Data and Control Clock Lines. All voltages are close to specs when working correctly, and values are the same when not working. Step 3 in Vertical troubleshooting CH 1 & CH 2 voltage's are 100mV low, checks +600mV and -580mV. Step 4 in Vertical troubleshooting values are high, +13.4V and -13.4V. Low voltage supply values are correct during both conditions, display and no display. Occasionally pressing the beam finder switch will cause display to start working. When the screen goes out, if I turn the intensity control to full clockwise, There is a glow on the entire screen, turning the vertical position control moves it up and down but still covers entire screen with a dim green. I don't have a high voltage probe and don't want to get near the 1900V. Step 5 in Vertical Troubleshooting Hints, Pg. 281 says to check the crt termination resistors, but lists Part no's CR1513 and CR1514, this must be a miss-print . Think it should be LR1513 & LR1514 ?
David


Mark Vincent
 

David,

Since the trace will come back right at times when you press the beam finder, the switch could be dirty. Clean the switch. That might be the problem. What Jean-Paul says about the freeze mist is also an excellent idea.

Mark


Michael W. Lynch
 

On Tue, May 25, 2021 at 04:41 PM, Mark Vincent wrote:


David,

Since the trace will come back right at times when you press the beam finder,
the switch could be dirty. Clean the switch. That might be the problem. What
Jean-Paul says about the freeze mist is also an excellent idea.

Mark
Mark has a good point. Simple stuff first. A bit of oxidation inside a switch can be a show stopper. Limited experience with 24xx series, but this has been a major failure point in the 50 or so TEK scopes that I have repaired.

--
Michael Lynch
Dardanelle, AR


david
 

Checked High Voltage, Pin No.4 on U1830 High Voltage Module is Low, measures -600V, Should be -900. How can I tell which component is bad ? The Tranny or the U1830 ? The -300V Supply is good.
David


david
 

I already cleaned the beam finder switch with DeOxit, that was my first guess. Tried cooling Tranny, no effect.
David


david
 

Letting it cool till it starts working, then I'll check the -900V again when its working.
David


 

On Wed, May 26, 2021 at 01:18 AM, david wrote:


Checked High Voltage, Pin No.4 on U1830 High Voltage Module is Low, measures
-600V, Should be -900.
Just dropping in:

1. So yours is a 2465B, not a 2465.

2. Measuring at U1830 pin 4, your meter is driven by a high-ohm resistor (10MOhm) and your meter is in parallel with a 9MOhm resistor to GND. Depending on the internal resistance of your voltage meter, you may well be measuring a much lower voltage than that which is actually there without the meter. I bet that's what gives the -600V.

3. Using freeze spray in HV circuits must be done with expertise and "at the right time", if at all, because of conductivity of the condensate that is likely to form.


Occasionally pressing the beam finder switch will cause display to start working.
4. What does that mean? Brightness appearing, traces flashing, correct image appearing?

Raymond


david
 

No , this is not a 2465B, it is a 2465, When it was intermittent and the case was off, whatever was going bad would cool down, I would push beam finder and release it, Then correct display would appear. Put back in case and leave running, after some time display would disappear again. Last time I tried it I pushed the beam finder switch and when I released it correct display would appear only for a couple of seconds. Now its no longer intermittent it's Kaput. Still dim green glow on screen visible if intensity pot turn full clockwise. Vertical position control moves the haze up and down. You could be right about the meter, the only one I have that goes to 1500 volts is a VTVM. Whatever was failing just went completely, The Transformer and the U1830 are not getting hot, are cool to touch.
David


durechenew@...
 

Check the deflection plates (both vertical and horizontal) voltages when working and when not working
TT


david
 

When you hold the beam finder switch in there is a miniature display on screen with the trace , the cursors, and the readouts, About 1 inch square in center of screen. Have to start over now that it finally quit. I have repaired and re capped my 465 many times with the help of all the smart folks on this site. Thank you, I appreciate it. I'm like Joe Walsh song " Analog Man" , Mainly work on tube equipment and old test equipment. I have no experience with Digital equipment or Hybrid like this scope. Gonna need help.
David


 

On Wed, May 26, 2021 at 02:48 AM, david wrote:


No , this is not a 2465B, it is a 2465,
Sorry, David, my bad.

Because of the green glow, I'd suspect off-screen image, either vertical or horizontal or both.

Did you already pull all hybrids and carefully reseat them? They and their sockets often suffer from bad contacts. Don't use any cleaner on either, except perhaps some IPA if you really want to. Just be very careful when refastening them: Gently push the hybrid down until flush with the PCB surface, then fasten nuts hand-tight plus 1/8th turn at most. Don't touch the black horizontal soldered-in U800 (yet). Especially don't touch its nuts, unless you know the story behind them.
If reseating the hybrids doesn't help, move your attention to U800. It's a known point of failure, resulting in the crt image moving off-screen. This group is full of threads about it. Its failure usually causes the image to move off-screen horizontally when it warms up.
You might also do as durechenew suggests. Just be careful, since shorting a plate against GND (or many other points) will very likely destroy the module driving it.

Raymond


david
 

I just tried it again. turned on, no display at all just the glow, pushed beam finder, released it, Correct display ,all the trace, the cursors and all readouts, then it moved off the left side and disappeared. Display was only visible for one or two seconds. But it definitely went off the left side of screen.
David


Jim Ford
 

I don't know that Joe Walsh song (Will check on YouTube), but Rush did have "The Analog Kid" and "Digital Man" on theSubdivisions album in 1982.      Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: "david via groups.io" <davide_us=yahoo.com@groups.io> Date: 5/25/21 6:01 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2465 Blank screen when warm When you hold the beam finder switch in there is a miniature display on screen with the trace , the cursors, and the readouts, About 1 inch square in center of screen. Have to start over now that it finally quit. I have repaired and re capped my 465 many times with the help of all the smart folks on this site. Thank you, I appreciate it. I'm like Joe Walsh song " Analog Man" , Mainly work on tube equipment and old test equipment. I have no experience  with Digital equipment or Hybrid like this scope. Gonna need help.David


 

On Wed, May 26, 2021 at 03:45 AM, david wrote:


I just tried it again. turned on, no display at all just the glow, pushed beam
finder, released it, Correct display ,all the trace, the cursors and all
readouts, then it moved off the left side and disappeared. Display was only
visible for one or two seconds. But it definitely went off the left side of
screen.
That’s one typical way of U800, the vertical driver, to show it failed. Unfortunately, since it’s difficult to get and therefore expensive.

Raymond


david
 

Yeah, read some other posts on this forum about U800 failure. This scope has all the symptoms, before it stopped working the readouts and the cursors were all shifted to the left one whole division. Sometimes the readouts would start to jitter bad you couldn't read them, pushing the beam finder switch would stop the jitter. Just turned it on this morning and still has the same problem, pressing beam finder causes display to appear for about 2 seconds , it is shifted left a division, then disappears off left side and will not come on again. The beam finder display is shifted to the left of center also about 1 division. Think that U800 is bad, expensive, not going to pay that much for a used chip. Going to put it on the shelf for now , this is a winter time job. Has anyone had good results having the U800 "re-baked" ? Don't think I can find a NOS chip.
David


satbeginner
 

If it is the u800, you could try this:

https://youtu.be/nfc_z2FNeb8

So far I was lucky with my 2465x/2467B...

Leo


Dave Daniel
 

There is, somewhere, some posts about a newly-designed replacement for U800 that consists of a small PCB assy.

DaveD

On May 26, 2021, at 07:57, david via groups.io <davide_us=yahoo.com@groups.io> wrote:

Yeah, read some other posts on this forum about U800 failure. This scope has all the symptoms, before it stopped working the readouts and the cursors were all shifted to the left one whole division. Sometimes the readouts would start to jitter bad you couldn't read them, pushing the beam finder switch would stop the jitter. Just turned it on this morning and still has the same problem, pressing beam finder causes display to appear for about 2 seconds , it is shifted left a division, then disappears off left side and will not come on again. The beam finder display is shifted to the left of center also about 1 division. Think that U800 is bad, expensive, not going to pay that much for a used chip. Going to put it on the shelf for now , this is a winter time job. Has anyone had good results having the U800 "re-baked" ? Don't think I can find a NOS chip.
David