Tek 465B
in [Repair]
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From: bg on 9 Nov 2007 07:15 Jim Yanik wrote in message ... >"bg" <bg(a)nospam.com> wrote in news:fgvkea$n3d$1(a)news.xmission.com: > >> >> Jim Yanik wrote in message ... >>>"bg" <bg(a)nospam.com> wrote in news:fgt74f$idp$1(a)news.xmission.com: >>> >>>> Both channels on the verticle front end are damaged. One dual FET >>>> follower is a definite (Q1297). It is tek part number 151-1090-00. I >>>> haven't seen one yet using google. Is there a replacement or two >>>> discretes out there that will work? >>> >>>They would have to be matched,else you get an offset. >>> >>>check this out; >>>http://www.sphere.bc.ca/test/tek-parts/tekparts2.html >>>it appears they have some 151-1090's for sale. >>>they also cross ref to a "2N5911 family". > > >>> >>>the 155-0078-xx is used in a lot of different scopes,several 7000 series >>>plug-ins,too. >>> >>>-- >>>Jim Yanik >>>jyanik >>>at >>>kua.net >> Thanks Jim. I had already been to that site and didn't see it the first >> time, even with my glasses on! >> Offset is the issue I am having. >> bg >> >> > >I've seen the input BNC connector cause DC offsets! >seems it absorbs contaminants and becomes a weak "battery". > > >-- >Jim Yanik >jyanik >at >kua.net I replaced the ch1 connector, but connected a power connector backwards. It blew one of the dual FETS and the other seems to have a leakage problem. There is DC on the gate where the attenuator output connects. The one meg resistor in the attenuator output is not low enough to pull the gate to zero. Out of the circuit, I don't see anything wrong with the fet. BTW , you are a great resource for these tek products, thanks.
From: James Sweet on 8 Nov 2007 21:55 > > I've seen the input BNC connector cause DC offsets! > seems it absorbs contaminants and becomes a weak "battery". > > Now that's certainly not something I'd have expected. I'll keep it in mind should my 465 ever misbehave in that way.
From: Jim Yanik on 8 Nov 2007 23:33 "bg" <bg(a)nospam.com> wrote in news:fh08m1$2og$1(a)news.xmission.com: > > Jim Yanik wrote in message ... >>"bg" <bg(a)nospam.com> wrote in news:fgvkea$n3d$1(a)news.xmission.com: >> >>> >>> Jim Yanik wrote in message ... >>>>"bg" <bg(a)nospam.com> wrote in news:fgt74f$idp$1(a)news.xmission.com: >>>> >>>>> Both channels on the verticle front end are damaged. One dual FET >>>>> follower is a definite (Q1297). It is tek part number 151-1090-00. >>>>> I haven't seen one yet using google. Is there a replacement or two >>>>> discretes out there that will work? >>>> >>>>They would have to be matched,else you get an offset. >>>> >>>>check this out; >>>>http://www.sphere.bc.ca/test/tek-parts/tekparts2.html >>>>it appears they have some 151-1090's for sale. >>>>they also cross ref to a "2N5911 family". >> >> >>>> >>>>the 155-0078-xx is used in a lot of different scopes,several 7000 >>>>series plug-ins,too. >>>> >>>>-- >>>>Jim Yanik >>>>jyanik >>>>at >>>>kua.net >>> Thanks Jim. I had already been to that site and didn't see it the >>> first time, even with my glasses on! >>> Offset is the issue I am having. >>> bg >>> >>> >> >>I've seen the input BNC connector cause DC offsets! >>seems it absorbs contaminants and becomes a weak "battery". >> >> >>-- >>Jim Yanik >>jyanik >>at >>kua.net > > I replaced the channel 1 connector, but plugged in one of the power > connectors backwards. So I blew one of the dual fets and the other one > seems to have a leakage problem. There is DC on the gate lead right > after the attenuator. The 1 meg resistor in the attenuator output > isn't low enough to pull the gate to 0 volts. Out of the circuit I > can't measure anything abnormal with the FET but in circuit the DC is > there. BTW , you are a great weath of info for these tek products. > bg > are there input protection diodes on that FET input? did you disconnect the atten PCB and still have the DC? (and then GND the gate and the offset goes away?) -- Jim Yanik jyanik at kua.net
From: Jim Yanik on 8 Nov 2007 23:34 "James Sweet" <jamessweet(a)hotmail.com> wrote in news:A_PYi.24184$Cb.6275(a)trnddc08: > >> >> I've seen the input BNC connector cause DC offsets! >> seems it absorbs contaminants and becomes a weak "battery". >> >> > > > Now that's certainly not something I'd have expected. I'll keep it in > mind should my 465 ever misbehave in that way. > > > definitely a weird one. only had a couple of those,as I recall. -- Jim Yanik jyanik at kua.net
From: bg on 10 Nov 2007 06:32 Jim Yanik wrote in message ... >"bg" <bg(a)nospam.com> wrote in news:fh08m1$2og$1(a)news.xmission.com: > >> >> Jim Yanik wrote in message ... >>>"bg" <bg(a)nospam.com> wrote in news:fgvkea$n3d$1(a)news.xmission.com: >>> >>>> >>>> Jim Yanik wrote in message ... >>>>>"bg" <bg(a)nospam.com> wrote in news:fgt74f$idp$1(a)news.xmission.com: >>>>> >>>>>> Both channels on the verticle front end are damaged. One dual FET >>>>>> follower is a definite (Q1297). It is tek part number 151-1090-00. >>>>>> I haven't seen one yet using google. Is there a replacement or two >>>>>> discretes out there that will work? >>>>> >>>>>They would have to be matched,else you get an offset. >>>>> >>>>>check this out; >>>>>http://www.sphere.bc.ca/test/tek-parts/tekparts2.html >>>>>it appears they have some 151-1090's for sale. >>>>>they also cross ref to a "2N5911 family". >>> >>> >>>>> >>>>>the 155-0078-xx is used in a lot of different scopes,several 7000 >>>>>series plug-ins,too. >>>>> >>>>>-- >>>>>Jim Yanik >>>>>jyanik >>>>>at >>>>>kua.net >>>> Thanks Jim. I had already been to that site and didn't see it the >>>> first time, even with my glasses on! >>>> Offset is the issue I am having. >>>> bg >>>> >>>> >>> >>>I've seen the input BNC connector cause DC offsets! >>>seems it absorbs contaminants and becomes a weak "battery". >>> >>> >>>-- >>>Jim Yanik >>>jyanik >>>at >>>kua.net >> >> I replaced the channel 1 connector, but plugged in one of the power >> connectors backwards. So I blew one of the dual fets and the other one >> seems to have a leakage problem. There is DC on the gate lead right >> after the attenuator. The 1 meg resistor in the attenuator output >> isn't low enough to pull the gate to 0 volts. Out of the circuit I >> can't measure anything abnormal with the FET but in circuit the DC is >> there. BTW , you are a great weath of info for these tek products. >> bg >> > >are there input protection diodes on that FET input? did you disconnect the >atten PCB and still have the DC? >(and then GND the gate and the offset goes away?) > >-- >Jim Yanik >jyanik >at >kua.net I've disconnected the gate completely from all of the external circuitry and then connected it to ground thru a 1.5 meg resistor , which I assume is what it sees from the attenuator. Seeing as the gate draws no current , there should be no voltage right, or perhaps just microvolts. I get way too much. If I short the gate to ground or use low resistance like about 50 ohms, I can drive it with a generator and all is fine. But with High Z to ground, the offset is too high for the verticle position control to bring the trace back on screen and none of the balance or position pots have enough range. bg
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