Topics

New Member Dead 7704


volvoboy242@...
 

Downloaded the pdf. You're right. I was twisting knobs at random.
I read through and set the scope as per TEK 7704 Instruction pdf initially but until wiggling, twisting and pushing every knob and switch, there was no activity at all on screen.
The youtube vid actually captured the first blip and was a surprise to me.
I expected to show you all a blank screen.
As for my knowledge of oscilloscopes, my erratic Velleman was used to diagnose intermittent automotive drivability issues.
Obsolete now, with data logging.


I did replace a power supply transistor in it once, which was a service bulletin from Velleman.
So I guess that would be my oscilloscope repair experience!


volvoboy242@...
 

I'll clean the contacts with CRC and a PEC pad, unless there is a better way. I'll post an update later.


Jerry Massengale <jmassen418@...>
 

92% alcohol from walmart is fine with cotton swabs

On Thu, Jan 5, 2017 at 3:49 PM, volvoboy242@... [TekScopes] <
TekScopes@...> wrote:



I'll clean the contacts with CRC and a PEC pad, unless there is a better
way. I'll post an update later.

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



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


volvoboy242@...
 

I have Everclear also. I cleaned the plugin contacts with CRC and a PEC pad.
I've gotten more muck off a dirty camera sensor. However, I did notice the readout moved to the upper right of the screen, but only visible with the beam finder.


 

That should be OK, but once again, you have much bigger issues that you need
to solve than the readout.
Also, cleaning the plugin contacts doesn't clean the contacts that the
plugin mates with in the back plane so you may not see a big change in the
readout.

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Thursday, January 05, 2017 1:50 PM
To: TekScopes@...
Subject: [TekScopes] Re: New Member Dead 7704

I'll clean the contacts with CRC and a PEC pad, unless there is a better
way. I'll post an update later.






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Posted by: volvoboy242@...
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Yahoo Groups Links


volvoboy242@...
 

With Cal out (.4v 1Khz) to sig1 (set to 1v) I get a flat line, only visible with the beam finder.


 

With your DVM you will need to measure the power supply voltages. This is a
very important step since they affect everything in the scope and this may
explain why you are not getting anything on the screen. In the back of the
manual in the "Maintenance" section it explains how to check and adjust
those voltages.

Skip the Everclear. Do what Jerry Massengale said. Use 92% or 99% alcohol on
a swab. It is safe and above all non-abrasive.

Dennis Tillman W7PF

-----Original Message-----
Sent: Thursday, January 05, 2017 2:32 PM
Subject: Re: [TekScopes] Re: New Member Dead 7704

I have Everclear also. I cleaned the plugin contacts with CRC and a PEC pad.
I've gotten more muck off a dirty camera sensor. However, I did notice the
readout moved to the upper right of the screen, but only visible with the
beam finder.
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Posted by: volvoboy242@...
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volvoboy242@...
 


volvoboy242@...
 

OK studying now. I'll need some time to familiarize myself with the procedure, component locations and order of operations.
I'll update once completed.
I have a feeling that this is where I'll find what's causing most of my symptoms.


Vince Vielhaber
 

Is there more than one thing called Everclear? I have a couple of bottles of 190 proof Everclear that I certainly wouldn't waste cleaning something with - even if it was only a few drops!

Vince.

On 01/05/2017 05:43 PM, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] wrote:


With your DVM you will need to measure the power supply voltages. This is a
very important step since they affect everything in the scope and this may
explain why you are not getting anything on the screen. In the back of the
manual in the "Maintenance" section it explains how to check and adjust
those voltages.

Skip the Everclear. Do what Jerry Massengale said. Use 92% or 99% alcohol on
a swab. It is safe and above all non-abrasive.

Dennis Tillman W7PF

-----Original Message-----
Sent: Thursday, January 05, 2017 2:32 PM
Subject: Re: [TekScopes] Re: New Member Dead 7704

I have Everclear also. I cleaned the plugin contacts with CRC and a PEC pad.
I've gotten more muck off a dirty camera sensor. However, I did notice the
readout moved to the upper right of the screen, but only visible with the
beam finder.
------------------------------------
Posted by: volvoboy242@...
------------------------------------


Richard Knoppow
 

Edge connectors will respond to being wiped with Deoxit and worked
in the sockets. You may have to do it a couple of times.
Isopropyl alcohol is effective for some types oil and grease. The
best is 99+% which is available from many stores selling computer
supplies. The problem with isopropanol is that it absorbs moisture
from the air and give is up when it evaporates. Exposed to air dry
isopropanol will become 91% at which point it stops. However, ten
percent of what you are applying will be absorbed water which will be
left behind.
Edge connectors and, in general board connectors of all sorts, are
fixed once connected, they do not have the self cleaning wiping action
of most switches, so they tend to become oxidized a little. Sometimes
just reseating a board or socketed IC is enough to wipe off the oxide
layer but a bit of oxide remover will help.

On 1/5/2017 2:37 PM, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] wrote:

That should be OK, but once again, you have much bigger issues that
you need
to solve than the readout.
Also, cleaning the plugin contacts doesn't clean the contacts that the
plugin mates with in the back plane so you may not see a big change in the
readout.

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Thursday, January 05, 2017 1:50 PM
To: TekScopes@...
Subject: [TekScopes] Re: New Member Dead 7704

I'll clean the contacts with CRC and a PEC pad, unless there is a better
way. I'll post an update later.



------------------------------------
Posted by: volvoboy242@...
------------------------------------

------------------------------------

Yahoo Groups Links

--
Richard Knoppow
dickburk@...
WB6KBL



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


volvoboy242@...
 

I started reading at about page 85 of the 7704 manual. Unfortunately, the circuit descriptions are way over my head.
I'm taking in about a quarter of what I'm reading.
Also no pics! So no component locations, test points etc.


There is a 25Khz filter and some neon tubes that I'd like to know more about.


Also, I'm wondering if there might be some oxidized pins on the back of the CRT.
Might be worth sliding the CRT and cleaning those contacts.
More tomorrow.


volvoboy242@...
 

I may have a sniff if I can't fix my scope. There is a bottle under the kitchen sink with the rest of my cleaning supplies.
Makes an excellent lens/sensor cleaner as well as a very good solvent for cleaning flux from PCBs.
Of course, not the apple flavored medley.
Also cheap.


Vince Vielhaber
 

So we are talking about the same stuff...

C'MON MAN! That's alcohol abuse!

Vince.

On 01/05/2017 07:54 PM, volvoboy242@... [TekScopes] wrote:


I may have a sniff if I can't fix my scope. There is a bottle under the
kitchen sink with the rest of my cleaning supplies.
Makes an excellent lens/sensor cleaner as well as a very good solvent
for cleaning flux from PCBs.
Of course, not the apple flavored medley.
Also cheap.



volvoboy242@...
 

LOL! I'd use Coca-Cola but it dissolves solid rock...also leaves a residue of ectoplasmic goo

Back to business, I may need a local ham club member to help me reverse engineer my scope.
My confidence is dwindling with each Google search.
If I could figure out where (and where not) to probe, and what voltage should be present when....
But I think my next course of action should be cleaning and re seating the big 14 pin CRT connector.


I need help with testing the power supply(s).
It looks like there are about 12 different outputs including the 2 deadly ones (which I have no intention of messing with..... they obviously work).
I'd be very surprised if there were not at least one dead cap.
One of my radios had, if I remember, 3 shorted electrolytics and is about 15 years newer then my 7704.


 

You're doing fine. There is a lot to learn as you are discovering. Local ham
club or community college are both good choices for help with your scope. If
you tell us where you are maybe there are some forum members near you.

There is absolutely no reason to reseat the CRT socket connector at all. It
has nothing to do with the problem you are experiencing.

It doesn't sound like you have a complete manual for the 7704 if there are
no pictures or schematics. You can get the complete manual here
http://bama.edebris.com/manuals/tek/7704/

The BAMA (Boat Anchor Manual Archive) is an excellent resource you should
bookmark. The main Tektronix page is at
http://bama.edebris.com/manuals/tek/

Another excellent site is TekWiki. Its main page is at
http://w140.com/

Dennis Tillman W7PF

-----Original Message-----
Sent: Thursday, January 05, 2017 5:57 PM
Subject: Re: [TekScopes] Re: New Member Dead 7704

Back to business, I may need a local ham club member to help me reverse
engineer my scope.
My confidence is dwindling with each Google search.
If I could figure out where (and where not) to probe, and what voltage
should be present when....
But I think my next course of action should be cleaning and re seating the
big 14 pin CRT connector.


I need help with testing the power supply(s).
It looks like there are about 12 different outputs including the 2 deadly
ones (which I have no intention of messing with..... they obviously work).
I'd be very surprised if there were not at least one dead cap.
One of my radios had, if I remember, 3 shorted electrolytics and is about
15 years newer then my 7704.
------------------------------------
Posted by: volvoboy242@...
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volvoboy242@...
 

Downloaded, bookmarked and already bookmarked. I discovered a couple major issues with the physically damaged time base.
The other one came today. Plugged it in and ran it through it's paces. Check's AOK.
I removed the left side cover and wiggled a couple things.
The wires going into the top (what I believe to be X+- plate) of the CRT are under a bit of tension.


Well now I have fog from about 7/8 of the screen down.


I think it's time to dismantle the scope and clean it thoroughly.
Chasing bad connections while trying to diag real problems makes me feel like punching a baby.


One side at a time I guess.
Right it is.


volvoboy242@...
 

Oh... also I was able to get a waveform of sorts. With the beam finder, I was able to "view" the .4V square wave 1Khz (Cal) and garbled display (which seems to appear top left or right at random).
All functions of both (good) plugins (except delay) are verified.
One slot (B Horiz) in the mainframe is bad, for whatever reason. Not worried about that just yet.


Once I clean all contacts, I'll update.


volvoboy242@...
 

So pouring through the correct manual this snowy day. Very happy to find a comprehensive test procedure for every section of the scope.
Also lollipop test pins on every board with values printed next to them.


Tested the low voltage regulator board as per the manual. Everything measured within <.2V.
That verifies operation of the main power unit, rectifier, DC converter/regulator and low voltage regulator.


I removed the rear panel upper half and found two screws missing.
Until then, I was sure I was in unexplored territory. No evidence of human intervention anywhere.


I read over how to R&I the CRT but chickened out when I couldn't see the two hex head cap screws mentioned in the manual...or how to remove the delicate looking CRT base socket other then to tug on the little plastic puller thing.
Also no preferred method of discharging the CRT, other then "Oh yeah, you just grab the anode plug and touch the chassis with it! No problem!"
Also couldn't see any blinking neon light thing in the power unit that's supposed to discharge some large caps.


I found some landmarks but couldn't identify others.
I did flip the swing down chassis and had a look. I familiarized myself with the Z axis board and connections, which I suspect are working properly anyway.


I think my CRT problem must be oxidized deflection plate pins.
Too chicken to mess with them yet.


I did give the CRT base plus a wiggle and powered up the scope.
No more fog and I'm back to this:
https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1304650996/lightbox/1002836943?orderBy=ordinal&sortOrder=asc&photoFilter=ALL#zax/1002836943 https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1304650996/lightbox/1002836943?orderBy=ordinal&sortOrder=asc&photoFilter=ALL#zax/1002836943

Only with the beam finder though.


I'm thinking the CRT may have been replaced at some point and that's where the two screws went.
Same guy who lost my screws may have gotten greazzy pizza fingers all over the connections and now my scope is acting up.


volvoboy242@...