Tek 475A CH1 bandwidth
Hello all,
I have a Tek 475A whose CH1 bandwidth falls off as the input frequency increases. At 200MHz, the vertical amplitude is about half of what it should be. CH2 is working fine. The fault seems to exist no matter what the vertical sensitivity is so I don't think that it's the extenuator, and the 100 and 20MHz bandwidth limiter also appear to be working. Does this fault suggest anything in particular to the experts out there? Thanks! |
Tek 475A CH1 bandwidth
On Wed, 20 Feb 2008 05:46:44 -0500 JW wrote in Message id:
: extenuator Ahem. Attenuator Spell checkers... |
Tek 475A CH1 bandwidth
JW wrote in
: Hello all, I have a Tek 475A whose CH1 bandwidth falls off as the input frequency increases. At 200MHz, the vertical amplitude is about half of what it should be. CH2 is working fine. The fault seems to exist no matter what the vertical sensitivity is so I don't think that it's the extenuator, and the 100 and 20MHz bandwidth limiter also appear to be working. Does this fault suggest anything in particular to the experts out there? Thanks! If the problem is just on Ch1,then you have a problem in Channel 1. Ch 1 and 2 don't combine until the delay line driver/channel switch,IIRC. the tiny HF trimmer caps in the 400 series had a habit of developing a black oxide underneath them that effectively insulates the rotor from the solder pin,making the cap -open-.(and no effect when adjusted) They also would freeze so they could not be turned without breaking the screwhead loose from the rotor disc . essentially,you have to replace the bad trimcaps. Then recal per the cal procedure. -- Jim Yanik jyanik at kua.net |
Tek 475A CH1 bandwidth
On Feb 20, 10:01*am, Jim Yanik wrote:
JW wrote : Hello all, I have a Tek 475A whose CH1 bandwidth falls off as the input frequency increases. At 200MHz, the vertical amplitude is about half of what it should be. CH2 is working fine. The fault seems to exist no matter what the vertical sensitivity is so I don't think that it's the extenuator, and the 100 and 20MHz bandwidth limiter also appear to be working. Does this fault suggest anything in particular to the experts out there? Thanks! If the problem is just on Ch1,then you have a problem in Channel 1. Ch 1 and 2 don't combine until the delay line driver/channel switch,IIRC. the tiny HF trimmer caps in the 400 series had a habit of developing a black oxide underneath them that effectively insulates the rotor from the solder pin,making the cap -open-.(and no effect when adjusted) They also would freeze so they could not be turned without breaking the screwhead loose from the rotor disc . essentially,you have to replace the bad trimcaps. Then recal per the cal procedure. -- Jim Yanik jyanik at kua.net Have you swapped probes?? |
Tek 475A CH1 bandwidth
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Tek 475A CH1 bandwidth
On 20 Feb 2008 16:01:59 GMT Jim Yanik wrote in Message
id: : JW wrote in : Hello all, I have a Tek 475A whose CH1 bandwidth falls off as the input frequency increases. At 200MHz, the vertical amplitude is about half of what it should be. CH2 is working fine. The fault seems to exist no matter what the vertical sensitivity is so I don't think that it's the extenuator, and the 100 and 20MHz bandwidth limiter also appear to be working. Does this fault suggest anything in particular to the experts out there? Thanks! If the problem is just on Ch1,then you have a problem in Channel 1. Ch 1 and 2 don't combine until the delay line driver/channel switch,IIRC. the tiny HF trimmer caps in the 400 series had a habit of developing a black oxide underneath them that effectively insulates the rotor from the solder pin,making the cap -open-.(and no effect when adjusted) They also would freeze so they could not be turned without breaking the screwhead loose from the rotor disc . essentially,you have to replace the bad trimcaps. Then recal per the cal procedure. Thanks, Jim. Given the age of this scope and lack of a schematic/service manual, I think I'll just scrap it. |
Tek 475A CH1 bandwidth
On 21 Feb 2008 02:47:02 GMT Jim Yanik wrote in Message
id: : "hr(bob) " wrote in : [...] Have you swapped probes?? you shouldn't be testing/calibrating BW using probes. you use a levelled signal generator,50ohm coax,a 50 Ohm feedthru termination,and appropriate 50ohm attenuators. Yup. |
Tek 475A CH1 bandwidth
JW wrote in
: On 20 Feb 2008 16:01:59 GMT Jim Yanik wrote in Message id: : JW wrote in m: Hello all, I have a Tek 475A whose CH1 bandwidth falls off as the input frequency increases. At 200MHz, the vertical amplitude is about half of what it should be. CH2 is working fine. The fault seems to exist no matter what the vertical sensitivity is so I don't think that it's the extenuator, and the 100 and 20MHz bandwidth limiter also appear to be working. Does this fault suggest anything in particular to the experts out there? Thanks! If the problem is just on Ch1,then you have a problem in Channel 1. Ch 1 and 2 don't combine until the delay line driver/channel switch,IIRC. the tiny HF trimmer caps in the 400 series had a habit of developing a black oxide underneath them that effectively insulates the rotor from the solder pin,making the cap -open-.(and no effect when adjusted) They also would freeze so they could not be turned without breaking the screwhead loose from the rotor disc . essentially,you have to replace the bad trimcaps. Then recal per the cal procedure. Thanks, Jim. Given the age of this scope and lack of a schematic/service manual, I think I'll just scrap it. doesn't the BAMA site have any 475 manuals? 475's were good scopes;I doubt you'll find any new scopes as good. -- Jim Yanik jyanik at kua.net |
Tek 475A CH1 bandwidth
JW wrote:
snip Thanks, Jim. Given the age of this scope and lack of a schematic/service manual, I think I'll just scrap it. Where are you located? I'd love to take a shot at it as my only modern portable as an ailing B&K 20 MHz scope. Regards, Michael |
Tek 475A CH1 bandwidth
On 21 Feb 2008 14:11:35 GMT Jim Yanik wrote in Message
id: : JW wrote in : On 20 Feb 2008 16:01:59 GMT Jim Yanik wrote in Message id: : JW wrote in : Hello all, I have a Tek 475A whose CH1 bandwidth falls off as the input frequency increases. At 200MHz, the vertical amplitude is about half of what it should be. CH2 is working fine. The fault seems to exist no matter what the vertical sensitivity is so I don't think that it's the extenuator, and the 100 and 20MHz bandwidth limiter also appear to be working. Does this fault suggest anything in particular to the experts out there? Thanks! If the problem is just on Ch1,then you have a problem in Channel 1. Ch 1 and 2 don't combine until the delay line driver/channel switch,IIRC. the tiny HF trimmer caps in the 400 series had a habit of developing a black oxide underneath them that effectively insulates the rotor from the solder pin,making the cap -open-.(and no effect when adjusted) They also would freeze so they could not be turned without breaking the screwhead loose from the rotor disc . essentially,you have to replace the bad trimcaps. Then recal per the cal procedure. Thanks, Jim. Given the age of this scope and lack of a schematic/service manual, I think I'll just scrap it. doesn't the BAMA site have any 475 manuals? Yeah, but only operators... 475's were good scopes;I doubt you'll find any new scopes as good. I'm sure that I can use parts from this one to fix the next one to come across my bench. I work as a tech for a test equipment salvage company, and I'd have to be able to justify my time and cost of calibration for this to be worthwhile. Not having the service manual (or having to pay for one) on a scope of this vintage just isn't worth it. |
Tek 475A CH1 bandwidth
On Thu, 21 Feb 2008 11:08:00 -0600 msg wrote in
Message id: : JW wrote: snip Thanks, Jim. Given the age of this scope and lack of a schematic/service manual, I think I'll just scrap it. Where are you located? I'd love to take a shot at it as my only modern portable as an ailing B&K 20 MHz scope. Well, as I said in my other post, this will be used as a parts unit. (It's not my scope.) |
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