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Teitronix 492a : TUNING FAILURE - 1st LO


Bent Andersen
 

Hello all

I have now time to look at my old Tek492a there is showing up a error when it startup...pse look at the video link: https://photos.app.goo.gl/c3xCHVpAN6LVdvtq8 any idea where I start to look for broken parts ???

there is also another proble...is the key respons so slowly, from you hit the key and until the light is on 1-2sec ????

Best regards

Ben


Miguel Work
 

Hi,

Do you have a second SA to check the 1st output?

https://www.youtube.com/watch?v=G3A-4Jrtv3s

There´s is a document with 492P repair tips:

http://www.kolumbus.fi/oh5iy/HW/Tektronix.html

Regards!






-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Bent Andersen
Enviado el: sábado, 6 de febrero de 2021 17:32
Para: TekScopes@groups.io
Asunto: [TekScopes] Teitronix 492a : TUNING FAILURE - 1st LO

Hello all

I have now time to look at my old Tek492a there is showing up a error when it startup...pse look at the video link: https://photos.app.goo.gl/c3xCHVpAN6LVdvtq8 any idea where I start to look for broken parts ???

there is also another proble...is the key respons so slowly, from you hit the key and until the light is on 1-2sec ????

Best regards

Ben


Miguel Work
 

http://www.ke5fx.com/49x_notes.pdf





-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Bent Andersen
Enviado el: sábado, 6 de febrero de 2021 17:32
Para: TekScopes@groups.io
Asunto: [TekScopes] Teitronix 492a : TUNING FAILURE - 1st LO

Hello all

I have now time to look at my old Tek492a there is showing up a error when it startup...pse look at the video link: https://photos.app.goo.gl/c3xCHVpAN6LVdvtq8 any idea where I start to look for broken parts ???

there is also another proble...is the key respons so slowly, from you hit the key and until the light is on 1-2sec ????

Best regards

Ben


ulf_r_k
 

Following a hint from KO4BB when experiencing occasional lock errors, in the Synthesizer unit A50 there are two IC's that I had to replace.
In the larger box, the middle circuit board has two IC's U2050 = 74LS10 and U1050 = 74LS74. I had to replace both of them.
Not sure about it, I used high quality sockets but that did not affect the function of the repaired unit/analyzer.

in order for the YIG LO to lock. Also replacing electrolytic capacitors is neccessary. Be careful arond the YIG though. Tek obvisously
had a lot of problem to get the supply voltages clean, having to add several filtering components in the little harness connecting to the YIG LO.

Otherwise, the Service Note documentation on the home page of KE5FX is a good source of information.
I salvaged an old 494P that had been left in a damp shed for years. Enough to make the front panel corrode
and insects having found new homes. Eventually, I was able to revive the analyzer.


Miguel Work
 

I have found two defective DM74LS72 in other Tektronix equipment, in a 214 and 212 oscilloscopes with no clue why the chip failed

-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de ulf_r_k via groups.io
Enviado el: domingo, 7 de febrero de 2021 21:44
Para: TekScopes@groups.io
Asunto: Re: [TekScopes] Teitronix 492a : TUNING FAILURE - 1st LO

Following a hint from KO4BB when experiencing occasional lock errors, in the Synthesizer unit A50 there are two IC's that I had to replace.
In the larger box, the middle circuit board has two IC's U2050 = 74LS10 and U1050 = 74LS74. I had to replace both of them.
Not sure about it, I used high quality sockets but that did not affect the function of the repaired unit/analyzer.

in order for the YIG LO to lock. Also replacing electrolytic capacitors is neccessary. Be careful arond the YIG though. Tek obvisously had a lot of problem to get the supply voltages clean, having to add several filtering components in the little harness connecting to the YIG LO.

Otherwise, the Service Note documentation on the home page of KE5FX is a good source of information.
I salvaged an old 494P that had been left in a damp shed for years. Enough to make the front panel corrode and insects having found new homes. Eventually, I was able to revive the analyzer.







Scanned by McAfee and confirmed virus-free.
Find out more here: https://bit.ly/2zCJMrO


Bent Andersen
 

Hi Miguel

I have made a new video, and I think it is the CPU board there is defect... if you look at the video, you can see that the keypad is working slowly, and you can move the knops and 1-2sec later it move....

https://photos.app.goo.gl/HhBVr7KVjceQgpqeA

so i will try to look for bad component's maybe try the "cold-spray" !!!

Ben


Bent Andersen
 

Hi Ulf

tnx fer reply...but I think it is the cpu board there is defect.... I made a new video,,,https://photos.app.goo.gl/HhBVr7KVjceQgpqeA

Ben


John Miles
 

Until you fix the first LO unlock error, it is normal for it to be sluggish. The CPU is wasting time trying to lock a loop that won't lock.

Later versions of the 49x analyzers had a menu option to disable the tuning routine, so the CPU would run normally in the presence of an error, but I don't believe there was a way to do that in the 492.

-- john, KE5FX

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Bent Andersen
Sent: Sunday, February 07, 2021 10:30 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Teitronix 492a : TUNING FAILURE - 1st LO

Hi Ulf

tnx fer reply...but I think it is the cpu board there is defect.... I made a new
video,,,https://photos.app.goo.gl/HhBVr7KVjceQgpqeA

Ben



Bent Andersen
 

HI John

Do you have any idea what I have to do / look for ???? I have check all voltage and they are ok.

73" OZ1CT Ben


John Miles
 

One quick correction to my earlier post: if it's a 492A, as opposed to a 492, then you actually can stop the CPU from trying to lock the 1st LO. <SHIFT> FREE RUN should do it.

I don't know if there are any good copes of the 492A service manual floating around on the net, but the 494 / 494P literature is available in the Manuals section at ko4bb.com. It should be fine for troubleshooting the 492A since they were of very similar vintage. Just search volume 1 of the 494 service manual for "TUNING FAILURE" and go from there. There are built-in diagnostic aids that will get you started.

-- john, KE5FX

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Bent Andersen
Sent: Monday, February 08, 2021 11:31 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Teitronix 492a : TUNING FAILURE - 1st LO

HI John

Do you have any idea what I have to do / look for ???? I have check all
voltage and they are ok.

73" OZ1CT Ben