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Tek492 blank CRT. Please help


pjwalczak@...
 

I have an old Tek492. Bought it second hand, but was working fine
for a couple of years. Today when I have switched it on, after a long
break (almost a year) - it powered OK, all controls seems to be ok,
but there is nothing shown on the CRT.

Can anybody share some tips what can be done to find the cause
and fix it ?


lawrenceahlstrom
 

Look for shorted tantal capacitors (general, typical) and check psu voltages.
/Lars


-------- Originalmeddelande --------
Från: "pjwalczak@... [TekScopes]" <TekScopes@...>
Datum:2017-02-15 09:16 (GMT+01:00)
Till: TekScopes@...
Kopia:
Rubrik: [TekScopes] Tek492 blank CRT. Please help

I have an old Tek492. Bought it second hand, but was working fine for a couple of years. Today when I have switched it on, after a long break (almost a year) - it powered OK, all controls seems to be ok, but there is nothing shown on the CRT. Can anybody share some tips what can be done to find the cause and fix it ? [Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]


ArtekManuals
 

First look at page 3-7 of the operators manual "turn on procedure" to be
sure that after a year some switch or control is properly set, They can
get moved bumped, etc when you put it away last year.

The next thing to do is verify that all the LV power supply buses are on
spec per the service manual, Volume 1, page 3-43.


Dave



On 2/15/2017 3:16 AM, pjwalczak@... [TekScopes] wrote:

I have an old Tek492. Bought it second hand, but was working fine
for a couple of years. Today when I have switched it on, after a long
break (almost a year) - it powered OK, all controls seems to be ok,
but there is nothing shown on the CRT.

Can anybody share some tips what can be done to find the cause
and fix it ?






------------------------------------------------------------------------
Posted by: pjwalczak@...
------------------------------------------------------------------------









Dave
Manuals@...
www.ArtekManuals.com


Chuck Harris
 

The 492 has a very compact power supply, where the 105C
ratings of all of its capacitors are being challenged
every time you run it.

I would suggest that before you do anything with a new
492, or 494 SA, you carefully remove the power supply,
and replace all of its filter caps with the very best
low impedance, high ripple current, long life 105C
capacitors you can buy.

Stay away from EBAY! This is too much work to risk on
Chinese counterfeits. Use Mouser or Digikey.

You want real UnitedChemiCom, or Nichicon, or Panasonic.
You want a minimum of a 10,000 hour life rating.

What I think you will find is a group of capacitors where
they have gotten so hot that the heat shrink tubing that
has the labeling, and makes them all insulated and pretty
will have shrunk so much that it won't cover the ends of
the capacitor anymore.

-Chuck Harris

Lars Ahlström lea56@... [TekScopes] wrote:

Look for shorted tantal capacitors (general, typical) and check psu voltages.
/Lars


-------- Originalmeddelande -------- Från: "pjwalczak@... [TekScopes]"
<TekScopes@...> Datum:2017-02-15 09:16 (GMT+01:00) Till:
TekScopes@... Kopia: Rubrik: [TekScopes] Tek492 blank CRT. Please help


I have an old Tek492. Bought it second hand, but was working fine for a couple of
years. Today when I have switched it on, after a long break (almost a year) - it
powered OK, all controls seems to be ok, but there is nothing shown on the CRT.
Can anybody share some tips what can be done to find the cause and fix it ?



pjwalczak@...
 

Thank you Dave.

I walked through turn on procedure but could not get CRT show anything.
So, most likely I will need to check PSU. Do you know by any chance
where are test points for all output voltages from the PSU ?


ArtekManuals
 

The test points are all covered in Vol-1 of the service manual on page
3-43 and 3-44 / figure 3-22

With the covers off check to see if you have a dull glow towards the
back of the CRT. If no glow could be the HV section or the CRT itself.
DO NOT TRY AND MEASURE the filament voltage ...very high voltages are
present here on the order of -3800 VDC. If it is HV problem then most
likely culprit will be the HV Multiplier module A74A1

Dave
manuals@...




On 2/16/2017 10:24 AM, pjwalczak@... [TekScopes] wrote:

Thank you Dave.

I walked through turn on procedure but could not get CRT show anything.
So, most likely I will need to check PSU. Do you know by any chance
where are test points for all output voltages from the PSU ?



--
Dave
Manuals@...
www.ArtekManuals.com