Is this scope defective? See pics - Page 3

K-amps · 12th March 2005, 03:08 AM

Better pic:

K-amps · 12th March 2005, 03:17 AM

Quote:

Originally posted by Mark A. Gulbrandsen
Yea, put the 7A26 in the left compartment nd the sweep in the right compartment. Leave out that odball module till we figure out what it is...... I saw that scope on E-Bay...... Do you have a link to that auction?

Mark

Ok here 7a26 on left, and sweep on right, oddball comparator left out.

same %@%

Mark A. Gulbrandsen · 12th March 2005, 03:19 AM

Nope, couldn't get mine to do that sort of trace at all. Possibly may be a bad sweep amplifier but with the on-screen display working fine that would be hard to fathom.... perhaps one of the power supply caps or regulators are shot. There are quite a few regulated supplies in that scope. The power supply is in the back. I would suggest going over to TEKSCOPES forum at Yahoo. There are quite a few ex-Tektronix service engineers that moderate that board and they will be able to help you for sure..... With a little luck someone there may be able to e-mail you the manual in PDF form if you don't already have it....... If you do start checking power supply test points.... none of them should be more than a tenth or two off, some are more tightly regulated than others. You could also use your 7904 to check for excessive ripple but be careful where you go stickin that probe...watch the max DC input rating and use a X10 probe!

http://groups.yahoo.com/group/TekScopes/

Photo shows the verticle amp on the side and the horiz on top. Yours is a later scope and may have a blown power amp I.C.. Mine has a discrete amplifiers whilst the later scopes have power op-amps. Many parts can be had from this link...... Walter is a real nice guy and if he doesn't have what you're looking for he will more than likely refer you to someone else......

http://www.sphere.bc.ca/test/index.html

Mark

K-amps · 12th March 2005, 03:24 AM

Ok ,

Thanks guys!

Mark A. Gulbrandsen · 12th March 2005, 03:33 AM

Actally its doing more than it was. Obviously its sweeping the beam across but there is some sort of noise or fast imbalance in the vert. amp and that may be where the problem lies. Let me know what you find out...... If you can't repair it I may be able to.

I blew up your photo.... Is the top left button pushed in...... that selects that left hand vert. module...?
Mark

tekman · 14th June 2005, 11:51 AM

Looks like the fault is in the LV power supply. The 76xx series tend to have problems with the electrolytics caps , so 50/60 Hz (cps) hum goes into the circuits. So I'd recommend you check for caps.

hth,
Andreas

K-amps · 14th June 2005, 12:21 PM

All caps or the ones in the PSU?

thanks.

tekman · 14th June 2005, 12:35 PM

Looks like the fault is in the LV power supply.

K-amps · 14th June 2005, 12:43 PM

Danka Tekman!

Mark A. Gulbrandsen · 14th June 2005, 01:21 PM

Thats exaactly what I was thinking. If the supply is similar to the 7704A supply then the two 550uf @ 200 volt caps would be the first to check. They were bad in my 7704A as it had quite a bit of ripple in the trace when I got it. I've been told by retired tektronix techs that they were a bit of a problem in those scopes.

Next check the rest of the smaller amumnuim electrolytics and all the regulator transistors.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Great deal on Digital scope. Is this enough scope?	hifimaker	Pass Labs	1	1st May 2007 09:59 PM
Wanted: Your Defective USB 1 Cable	valveitude	Swap Meet	6	21st December 2006 05:27 PM
defective playstation - need help	maps	Digital Source	0	26th February 2006 09:44 AM
Do I have a defective RIAA? Opinions, please! :D	miksin	Analogue Source	2	20th December 2005 09:45 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

12th March 2005, 03:24 AM	#24
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Ok , Thanks guys!

12th March 2005, 03:33 AM	#25
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Actally its doing more than it was. Obviously its sweeping the beam across but there is some sort of noise or fast imbalance in the vert. amp and that may be where the problem lies. Let me know what you find out...... If you can't repair it I may be able to. I blew up your photo.... Is the top left button pushed in...... that selects that left hand vert. module...? Mark

14th June 2005, 11:51 AM	#26
tekman diyAudio Member Join Date: Oct 2004	Looks like the fault is in the LV power supply. The 76xx series tend to have problems with the electrolytics caps , so 50/60 Hz (cps) hum goes into the circuits. So I'd recommend you check for caps. hth, Andreas

14th June 2005, 12:21 PM	#27
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	All caps or the ones in the PSU? thanks.

14th June 2005, 12:35 PM	#28
tekman diyAudio Member Join Date: Oct 2004	Looks like the fault is in the LV power supply.

14th June 2005, 12:43 PM	#29
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Danka Tekman!

14th June 2005, 01:21 PM	#30
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Thats exaactly what I was thinking. If the supply is similar to the 7704A supply then the two 550uf @ 200 volt caps would be the first to check. They were bad in my 7704A as it had quite a bit of ripple in the trace when I got it. I've been told by retired tektronix techs that they were a bit of a problem in those scopes. Next check the rest of the smaller amumnuim electrolytics and all the regulator transistors.