TekScopes Yahoo Group - diyAudio
Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th March 2009, 02:03 PM   #1
PB2 is offline PB2  United States
diyAudio Member
 
PB2's Avatar
 
Join Date: Sep 2004
Location: North East
Blog Entries: 1
Default TekScopes Yahoo Group

Anyone familiar with this group? I tried to join a few weeks ago and it is still pending. Emailed the moderator directly with no response.

I have a Tek 7704A in need of repair.

Planning to recap the power supply, as a start.

Thanks,
Pete B.
  Reply With Quote
Old 18th March 2009, 11:54 PM   #2
bwaslo is online now bwaslo  United States
diyAudio Member
 
bwaslo's Avatar
 
Join Date: May 2006
Location: Cinciinati, OH
Yeah, I'm in that one. If I remember correctly, it took over a week to get 'approved'. So hang in there, the mod evidently has a lot of other stuff going on.

Sorry, I know zip about your scope model. Do you have a service manual? If no, there are some manuals for it at the "boat anchor manual archive" www.bama.sbc.edu/ , doesn't say whether they are owners' or 'service' though.
  Reply With Quote
Old 19th March 2009, 12:34 AM   #3
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
The mod might be out of town or something. Just give it time.

"planning to recap the power supply" IMHO, general replacement of parts not proven to be defective is usually a bad idea in quality test equipment. Get a bridge and check the caps. If the values and dissipation factors are reasonable, leave 'em alone. The odds of creating problems where none exist is far greater than of improving anything. I refer to the problem as "technician blight", having purchased many things that would have been better off left alone. OTOH, if I find a particular brand and style of part where more than a couple are going bad, I do replace all of that particular type that may be present.
__________________
I may be barking up the wrong tree, but at least I'm barking!
  Reply With Quote
Old 19th March 2009, 01:00 AM   #4
PB2 is offline PB2  United States
diyAudio Member
 
PB2's Avatar
 
Join Date: Sep 2004
Location: North East
Blog Entries: 1
I understand what you're saying, but this piece is from the early 80s and it needs it. Several caps have leaked, one already replaced. I'm only doing the aluminum electros not the tantalums which there are a lot of. There are not that many electros and most are in the power supply.

I agree, I seriously dislike working on equipment that has been previously screwed up.

Pete B.
  Reply With Quote
Old 19th March 2009, 02:21 AM   #5
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
Tantalums don't generally have age problems so maybe I'm just unlucky, but check those as well. I've seen them go bad (ok, in HP stuff, not Tek) and it seems that either type of cap is much more prone to failure if the value is high and the voltage is low, say 500uF/6V. I have a Tek 7834 and a full compliment of plug-ins that works well, though I usually only pull it out when I need speed or storage. Believe it or not, a 545B fulfills all my space heating and daily troubleshooting needs
__________________
I may be barking up the wrong tree, but at least I'm barking!
  Reply With Quote
Old 20th March 2009, 02:40 AM   #6
PB2 is offline PB2  United States
diyAudio Member
 
PB2's Avatar
 
Join Date: Sep 2004
Location: North East
Blog Entries: 1
Tantalums are fussy, low ESR but do not handle high current spikes. Reverse voltage kills them fast.

Pete B.
  Reply With Quote
Old 21st March 2009, 08:58 PM   #7
PB2 is offline PB2  United States
diyAudio Member
 
PB2's Avatar
 
Join Date: Sep 2004
Location: North East
Blog Entries: 1
Quote:
Originally posted by bwaslo
Yeah, I'm in that one. If I remember correctly, it took over a week to get 'approved'. So hang in there, the mod evidently has a lot of other stuff going on.

Sorry, I know zip about your scope model. Do you have a service manual? If no, there are some manuals for it at the "boat anchor manual archive" www.bama.sbc.edu/ , doesn't say whether they are owners' or 'service' though.
Yes, got these manuals:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=220332800087
  Reply With Quote
Old 30th March 2009, 12:16 PM   #8
PB2 is offline PB2  United States
diyAudio Member
 
PB2's Avatar
 
Join Date: Sep 2004
Location: North East
Blog Entries: 1
Fixed a few mechanical issues in the power supply, then powered it up carefully. Pre-regulator outputs were fine, but the +15V and +5 V reg were 0 Volts. Measured voltage on the current sense resistor for the +15V and it was limiting at 3.33A. +15V measured .3 ohms to ground - essentially shorted. Narrowed this down to a shorted big blue tantalum 100 uF 25V on the main interface board. People on the TekScopes group confirm that this is a fairly common failure. The 5V reg uses the +15V in the driver stage and that is why this output was 0V.

Most tantalum caps are not designed for power supply decoupling. Many have peak ripple current specs of about .5A, and we see above that the 7704A will supply 3.33A max during each power up cycle. Tantalums unfortunately fail shorted which can cause burnt traces and smoke in systems that do not have current limited power supplies. There are newer tantalums designed for power supply decoupling, some have max ripple currents of over an Amp, others have internal fuses so that if the cap section shorts the fuse blows rather than traces on the board.

This blue tantalum has no markings indicating the brand and I wonder if it is a low quality part.

The scope is working fairly well at this point.

Pete B.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Behringer DCX2496 User's Group at yahoo groups sendler Digital Line Level 2 28th December 2012 09:19 PM
hifi_dsp Yahoo group dfklink Multi-Way 2 1st November 2007 12:29 AM
Sam - LWE - Erath - Acoustron users group on Yahoo sam562 Subwoofers 1 28th February 2007 09:51 PM
http://groups.yahoo.com/group/DCX2496/ sendler Digital Line Level 0 10th August 2004 10:30 PM
Behringer DCX2496 user's group at yahoo sendler Digital Line Level 0 10th August 2004 10:26 PM


New To Site? Need Help?

All times are GMT. The time now is 12:09 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2