Oscilloscope repair - Page 2 - Electronic Circuits Projects Diagrams Free

Dean Huster · 9th March 2006, 05:14 AM

The 475A is old enough that Tek may have considered it obsolete. Repair by them won't happen and new parts will be dicey. The scope DOES NOT work fine when not in the XY mode. The waveform that you displayed in your original post is the result of the problem that's messing up the beam in the X-Y mode. Since the vertical amplifier feeds the horizontal amp in the X-Y mode, you can rule that out as the culprit. The problem has to be in the horizontal amp.

I've never seen a similar Hewlett-Packard-oriented site like the Yahoo! Tek site. The Yahoo! site is an independent third-party site that is not connected to Tek in any way. Since Hewlett-Packard, now Agilent, manufactured such a broad line of electronic, computer and medical equipment, a site revolving around it would have to have lots and lots of different categories just to make it somewhat navigatable. As far as scopes go, I've really never known an hp scope that was worth repairing other than the 130C and maybe the 140-series mainframes and their plug-ins. The 180-series and most of the portable scopes had knobs that were such nuckle-busters that I hated using them.

Dean

zachtheterrible · 10th March 2006, 10:35 PM

Quote:

The scope DOES NOT work fine when not in the XY mode. The waveform that you displayed in your original post is the result of the problem that's messing up the beam in the X-Y mode. Since the vertical amplifier feeds the horizontal amp in the X-Y mode, you can rule that out as the culprit. The problem has to be in the horizontal amp.

I'm quite aware that it doesn't work fine when in XY mode. If the problem is not the supply filtering caps, I'm just 'gonna resell it on ebay, not worth the time and frustration, and lack of parts :lol:

zevon8 · 11th March 2006, 10:07 PM

I would agree ( as stated above ) that it is likely the supply and/or bypass caps. The scope is old enough that they are due for replacement anyways. Whenever this scope is listed at one of the refurb/recal places, they always state that these caps have been replaced. It is a nice enough scope to warrant a few hours and a few dollars worth of caps.

Replacing supply caps and fixing cold solder joints has kept food on the table for service techs for years.

Dean Huster · 12th March 2006, 02:10 PM

The 475A was Tek's top-of-the-line portable analog scope, second only to the 485 (which had never been exceeded in performance) and is worthy of repair, especially for this problem. Don't expect to troubleshoot any Tek product without a service manual or you might as well just take a hammer to the thing, for it will do just as well. I'm assuming that you don't have a manual since you didn't know how to remove the case.

I'm certain that this is probably a simple fix and you're going to have to run the signal path of the horizontal amp to find it. This was originally a $3500 scope and since the jug is good, it's worth the repair. It appears to be in good mechanical condition.

Dean

zevon8 · 13th March 2006, 12:16 AM

Mr. Huster is right, you will need the manual to do a proper job. It is available on the internet, complete service, operators, manitenance and calibration, including schematics, part diagrams and waveforms.

The military's version is here in the boat anchor archives:

http://bama.edebris.com/manuals/tek/475/

hope you get it fixed!

zachtheterrible · 13th March 2006, 12:36 AM

I just ordered the caps today, so I'll let y'all know how everything goes. and I did figure out how to get the case off right after I made the first post :lol:

Ol Tec · 12th December 2007, 05:29 AM

Hi everyone, first for me so Ill get right down to it.... Got a cro (Hung Chang 6502) lost the trace beam. Supply seems to deliver the right volts around the place, but without ye ol circuit too hard to trace fault with failing eye's. Anyone have a circuit by chance, the same fault diagnosis would even do for another brand, probably the same outcome anyways. Thought of the blanking and trigger networks, but just not enough info on the pcb overlay. There was a chap looking for the same fault with the same brand cro a few months ago, though I can't seem to trace his success in the other forums.... any ideas would be appreciated.....

Leftyretro · 12th December 2007, 09:11 AM

Hustler got it right. That is one jem of a scope and well worth the effort to repair, certainly because so much is working, high voltage, CRT tube, etc. I'm sure it's most likely a cap or a rectifier diode.

Here is a link to a few 475 manuals for free downloading. Not the A model but probably useful for basic power supply troubleshooting.

http://bama.edebris.com/manuals/tek/475/

whiz115 · 13th December 2007, 04:51 AM

Quote:

Originally Posted by Nigel Goodwin

An ESR meter measures the impedance (NOT the resistance) of the capacitor at 100KHz.

@Nigel impedance is the resistance in AC.

@zachtheterrible good luck with your oscilloscope

Hero999 · 15th December 2007, 02:32 PM

Impedance isn different to resistance, energy can't be dissipated in a purely capacitive or inductive load it can only be disipated in a resistive load.

Leftyretro · 15th December 2007, 03:35 PM

Reactance (L or C or both), impedance and resistance are the terms we should be defining and using.

Lefty

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9th March 2006, 05:14 AM	(permalink)
Dean Huster	The 475A is old enough that Tek may have considered it obsolete. Repair by them won't happen and new parts will be dicey. The scope DOES NOT work fine when not in the XY mode. The waveform that you displayed in your original post is the result of the problem that's messing up the beam in the X-Y mode. Since the vertical amplifier feeds the horizontal amp in the X-Y mode, you can rule that out as the culprit. The problem has to be in the horizontal amp. I've never seen a similar Hewlett-Packard-oriented site like the Yahoo! Tek site. The Yahoo! site is an independent third-party site that is not connected to Tek in any way. Since Hewlett-Packard, now Agilent, manufactured such a broad line of electronic, computer and medical equipment, a site revolving around it would have to have lots and lots of different categories just to make it somewhat navigatable. As far as scopes go, I've really never known an hp scope that was worth repairing other than the 130C and maybe the 140-series mainframes and their plug-ins. The 180-series and most of the portable scopes had knobs that were such nuckle-busters that I hated using them. Dean __________________ Dean Huster, Electronics Curmudgeon Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines). R.I.P.

11th March 2006, 10:07 PM	(permalink)
zevon8	I would agree ( as stated above ) that it is likely the supply and/or bypass caps. The scope is old enough that they are due for replacement anyways. Whenever this scope is listed at one of the refurb/recal places, they always state that these caps have been replaced. It is a nice enough scope to warrant a few hours and a few dollars worth of caps. Replacing supply caps and fixing cold solder joints has kept food on the table for service techs for years.

12th March 2006, 02:10 PM	(permalink)
Dean Huster	The 475A was Tek's top-of-the-line portable analog scope, second only to the 485 (which had never been exceeded in performance) and is worthy of repair, especially for this problem. Don't expect to troubleshoot any Tek product without a service manual or you might as well just take a hammer to the thing, for it will do just as well. I'm assuming that you don't have a manual since you didn't know how to remove the case. I'm certain that this is probably a simple fix and you're going to have to run the signal path of the horizontal amp to find it. This was originally a $3500 scope and since the jug is good, it's worth the repair. It appears to be in good mechanical condition. Dean __________________ Dean Huster, Electronics Curmudgeon Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines). R.I.P.

13th March 2006, 12:16 AM	(permalink)
zevon8	Mr. Huster is right, you will need the manual to do a proper job. It is available on the internet, complete service, operators, manitenance and calibration, including schematics, part diagrams and waveforms. The military's version is here in the boat anchor archives: http://bama.edebris.com/manuals/tek/475/ hope you get it fixed!

13th March 2006, 12:36 AM	(permalink)
zachtheterrible	I just ordered the caps today, so I'll let y'all know how everything goes. and I did figure out how to get the case off right after I made the first post :lol: __________________ I'm no electronics god, i just talk too much.

12th December 2007, 05:29 AM	(permalink)
Ol Tec	Hung Chang Cathode Ray Oscilloscope Hi everyone, first for me so Ill get right down to it.... Got a cro (Hung Chang 6502) lost the trace beam. Supply seems to deliver the right volts around the place, but without ye ol circuit too hard to trace fault with failing eye's. Anyone have a circuit by chance, the same fault diagnosis would even do for another brand, probably the same outcome anyways. Thought of the blanking and trigger networks, but just not enough info on the pcb overlay. There was a chap looking for the same fault with the same brand cro a few months ago, though I can't seem to trace his success in the other forums.... any ideas would be appreciated.....

12th December 2007, 09:11 AM	(permalink)
Leftyretro	Hustler got it right. That is one jem of a scope and well worth the effort to repair, certainly because so much is working, high voltage, CRT tube, etc. I'm sure it's most likely a cap or a rectifier diode. Here is a link to a few 475 manuals for free downloading. Not the A model but probably useful for basic power supply troubleshooting. http://bama.edebris.com/manuals/tek/475/ __________________ Measurement changes behavior

15th December 2007, 02:32 PM	(permalink)
Hero999	Impedance isn different to resistance, energy can't be dissipated in a purely capacitive or inductive load it can only be disipated in a resistive load. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

15th December 2007, 03:35 PM	(permalink)
Leftyretro	Reactance (L or C or both), impedance and resistance are the terms we should be defining and using. Lefty __________________ Measurement changes behavior Last edited by Leftyretro; 15th December 2007 at 04:44 PM.