Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Oct Sat 20, 2018 7:56 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 10 posts ] 
Author Message
 Post subject: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Tue 02, 2018 7:32 am 
Member
User avatar

Joined: Oct Tue 29, 2013 9:42 pm
Posts: 402
Location: Fountain Valley, CA 92708
(seems like this guy is rebelling against me or is deteriorating.)

The panel light for the controls in the front middle of the mainframe are dead. That is the button lights for the Vertical and Horizontal Mode buttons have gone out. (Scope still works.) Additionally, the A and B trigger Source lights no longer work as well. Before some worked and some did not. Now the whole thing is dark.

In looking at the service manual, I stumbled onto page 6-3 and note that there are four boards ("board 11", "board 12", "board 13", "board 14" which are Vertical Mode, Horizontal Mode, A Trigger Source, and B Trigger Source respectively.) and each of these is supplied with a "+5V Lights" source from the Calibrator Board 10 but the schematic shows no originating source and I have not been inside the uni yet to see what's what.

Anyone troubleshoot this problem and can offer advice and information?

Thanks in advance.

_________________
Bill, k6whp
"Cheer up, things could get worse.
So I cheered up and things got worse."


Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Tue 02, 2018 7:48 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 33354
Location: Maryland 20709, USA
Hi Bill,

I have a large collection of Tek 7xxx 'scopes in the shop. I love 'em.

They're very good, reliable instruments. But they're getting old.

The first suspect with any power supply problem is always the electrolytic capacitors.

Most likely the +5V regulator has protection, so it's hopefully not blown.

- Leigh

_________________
73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Tue 02, 2018 7:59 am 
Member

Joined: Feb Sun 17, 2008 11:36 pm
Posts: 1942
Location: Dayton, Ohio
If I remember correctly, the 7904A has a slide switch (inside) for switching the lights from "bright" to "dim" or "off". The 7704A may also have a switch. If it does, try "exercising" the switch or cleaning it.

Charlie


Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Tue 02, 2018 6:48 pm 
Member
User avatar

Joined: Oct Tue 29, 2013 9:42 pm
Posts: 402
Location: Fountain Valley, CA 92708
tinwhisker wrote:
If I remember correctly, the 7904A has a slide switch (inside) for switching the lights from "bright" to "dim" or "off". The 7704A may also have a switch. If it does, try "exercising" the switch or cleaning it.


Charlie,

BINGO!

Would have blown right by that in my rush to get to the A32 board to check the +5V supply! So, articulating it a few times brought the lights back.

Well, that gets me back to square one but with a little more knowledge than before. As mentioned, the individual B SOURCE TRIGGER lights don't work but I have reason to suspect that it is the +5 lights connection to board 14. One rainy weekend, I will tear down the front and poke around with a probe but, for now, that's good enough!

Sincere thanks to you both! As good as the service manuals are, they do not seem to address these trivial problems in a readily researchable manner.


Attachments:
Glows in the Dark.jpg
Glows in the Dark.jpg [ 66.34 KiB | Viewed 574 times ]
Glows in the Light - Copy.jpg
Glows in the Light - Copy.jpg [ 70.66 KiB | Viewed 574 times ]
Right Hand Side 1 - Copy.jpg
Right Hand Side 1 - Copy.jpg [ 71.65 KiB | Viewed 574 times ]

_________________
Bill, k6whp
"Cheer up, things could get worse.
So I cheered up and things got worse."


Last edited by k6whp on Jan Tue 02, 2018 6:51 pm, edited 1 time in total.
Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Tue 02, 2018 6:49 pm 
Member
User avatar

Joined: Oct Tue 29, 2013 9:42 pm
Posts: 402
Location: Fountain Valley, CA 92708
..oops! Forgot the money shot!


Attachments:
Back Panel Illumination Switch - Copy.jpg
Back Panel Illumination Switch - Copy.jpg [ 71.82 KiB | Viewed 573 times ]

_________________
Bill, k6whp
"Cheer up, things could get worse.
So I cheered up and things got worse."
Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Wed 03, 2018 3:23 am 
Member

Joined: Feb Sun 17, 2008 11:36 pm
Posts: 1942
Location: Dayton, Ohio
Happy for your success. I would keep the switch in the "MEDIUM" position, to prolong lamp life. Another idea is to add one more diode in series with the ones used, in series, to drop the lamp voltage an additional 0.7 volts. Some of those lamps aren't fun to replace.

Charlie


Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Wed 03, 2018 3:36 am 
Member
User avatar

Joined: Oct Tue 29, 2013 9:42 pm
Posts: 402
Location: Fountain Valley, CA 92708
Charlie,

Will certainly keep that in mind! Do you know offhand if the small lights on the A & B TRIGGER boards are replaceable?

Thanks!

_________________
Bill, k6whp
"Cheer up, things could get worse.
So I cheered up and things got worse."


Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Wed 03, 2018 4:31 am 
Member

Joined: Feb Sun 17, 2008 11:36 pm
Posts: 1942
Location: Dayton, Ohio
All of the lamps are replaceable. (all of this is from memory), The "MODE", "COUPLING" and "SOURCE" switches on a typical TIME BASE plug-in, each have one soldered in bulb. The "button" that is pushed in gets the light from the single bulb, the other buttons are "out" and the light path does not illuminate these other buttons.

The inner most switch lamp is the most involved to get at. The manual for the particular VERTICAL or TIME BASE plug in gives the procedure. It usually takes several hours to do. You'll wish they were LEDs.

The bulbs on the MAIN FRAME are easier to get at, but as I recall, ALL bulbs are the soldered in, wire lead type.

Good Luck,

Charlie


Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Wed 03, 2018 8:53 pm 
Member
User avatar

Joined: Oct Thu 18, 2007 11:34 am
Posts: 3790
Location: Port Orchard, Wa 98366
Remove the modules and look at the rear connectors to make sure they're clean and no corrosion including the mating rails. sometimes just reseating them will work. of course, a little cramoline never hurt after cleaning them.

_________________
Visit our Webpage:
http://antique-radio-lab.forumotion.com/


Top
 Profile  
 
 Post subject: Re: Tek 7704A Mainframe Panel Lights Died; Scope Works
PostPosted: Jan Wed 03, 2018 10:24 pm 
Member
User avatar

Joined: Oct Tue 29, 2013 9:42 pm
Posts: 402
Location: Fountain Valley, CA 92708
tinwhisker wrote:
All of the lamps are replaceable. (all of this is from memory), The "MODE", "COUPLING" and "SOURCE" switches on a typical TIME BASE plug-in, each have one soldered in bulb. The "button" that is pushed in gets the light from the single bulb, the other buttons are "out" and the light path does not illuminate these other buttons.

The inner most switch lamp is the most involved to get at. The manual for the particular VERTICAL or TIME BASE plug in gives the procedure. It usually takes several hours to do. You'll wish they were LEDs.

The bulbs on the MAIN FRAME are easier to get at, but as I recall, ALL bulbs are the soldered in, wire lead type.

Gentlemen, thanks for all this help! It's good to know and, when a rainy day comes, I will snoop around the B TRIGGER board and see about replacing the light. As for reseating the plugins, that's my first course of action. Additionally, I went after the socketed ICs in the two freq counter plugins. Those were pulled, pins straightened, DeOxit used on them, and they were carefully reseated. Additionally, the backplane connectors were cleaned with a pencil eraser and DeOxit. (By the way, does anyone happen to know the numbering of these connectors?)

This regime woke up the 7D14 and -- to some degree -- the 7D15. The latter seems to have resumed its nap. But I persist.

Again, I am hugely grateful for the prompt responses and great advice here. You folks are the best!

_________________
Bill, k6whp
"Cheer up, things could get worse.
So I cheered up and things got worse."


Top
 Profile  
 
Post New Topic Post Reply  [ 10 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB