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Tek 465B woes
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Kevin Crossett
Ok. Mission accomplished. Here are my measurements and an image to make
sure I probed the right test points. Test Point Measurement (VDC) -8 -7.97 +15 +14.98 +55 54.86 +5 4.97 +110 110.5 It seems the power supply is OK on DC voltage. Just for kicks, I also measured all the test points on AC. All but the +110 line went progressively down. I stopped the measurements at .4 volts. The +110 line baselined at about 14 volts AC. ? [Non-text portions of this message have been removed] |
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Hi Kevin,
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I am about 100 mi. north of you in Forest Hill, MD so if you ever are in the area, let me know. Regards, Tom ----- Original Message -----
From: Kevin Crossett kcrossett@... [TekScopes] To: TekScopes@... Sent: Wednesday, December 03, 2014 2:00 PM Subject: Re: [TekScopes] Re: Tek 465B woes Hi Tom. I live in Hampton Roads, Virginia. Not sure if there are any Tek gurus in this region of the country, but would appreciate a mentor. This high voltage stuff is scary business for someone with no formal training. Where are you located? Maybe someone on the list lives near you and can help you learn this stuff. Regards ----- Original Message ----- From: Kevin Crossett kcrossett@... [TekScopes] To: TekScopes@... Sent: Wednesday, December 03, 2014 9:17 AM Subject: [TekScopes] Re: Tek 465B woes Thanks to everyone who has emailed the list with suggestions for me to try to cure my ailing scope. I have a copy of the service manual and have taken a look at the various schematics. To say I'm intimated is an understatement. Just looking at the voltages coming out of this unit scares me. I am just starting out on this electronics hobby path, and spend my time playing with low voltage DC circuits. To be honest, I'm not even sure how to go about checking the voltage within the unit, and forget about techniques to determine ripple on the supply. I have trouble really understanding what is going on in a typical RC circuit, and that's just running off a nine-volt battery. I'm afraid this one is over my head. It's a shame as I really like the scope, and I'm finally in a position with my family life that I can start fiddling with it. The scope had been in storage for about a year as I focused on my family and work. Again, thanks to everyone who gave some practical suggestions. I will file them away. And if I can't find someone who has experience with these scopes and who can take a look at it, then, one day, when I feel more confident playing with high-voltage equipment, I might drag it out and see about repairing it. OK, back to my lurking status. Kevin On Wed, Dec 3, 2014 at 12:34 PM, 'Tom Miller' tmiller11147@... [TekScopes] <TekScopes@...> wrote: > > > Where are you located? Maybe someone on the list lives near you and can > help you learn this stuff. > > Regards > > ----- Original Message ----- > From: Kevin Crossett kcrossett@... [TekScopes] > To: TekScopes@... > Sent: Wednesday, December 03, 2014 9:17 AM > Subject: [TekScopes] Re: Tek 465B woes > > Thanks to everyone who has emailed the list with suggestions for me to try > to cure my ailing scope. I have a copy of the service manual and have taken > a look at the various schematics. To say I'm intimated is an > understatement. Just looking at the voltages coming out of this unit scares > me. I am just starting out on this electronics hobby path, and spend my > time playing with low voltage DC circuits. To be honest, I'm not even sure > how to go about checking the voltage within the unit, and forget about > techniques to determine ripple on the supply. I have trouble really > understanding what is going on in a typical RC circuit, and that's just > running off a nine-volt battery. I'm afraid this one is over my head. It's > a shame as I really like the scope, and I'm finally in a position with my > family life that I can start fiddling with it. The scope had been in > storage for about a year as I focused on my family and work. > > Again, thanks to everyone who gave some practical suggestions. I will file > them away. And if I can't find someone who has experience with these scopes > and who can take a look at it, then, one day, when I feel more confident > playing with high-voltage equipment, I might drag it out and see about > repairing it. > > OK, back to my lurking status. > > Kevin > > > > > > > |
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All those voltages look good. Since the +55 volts serves as the reference for the other rails, and it is slightly low, so are the others.
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There is an adjustment, R1538, that sets the +55 level. If you are satisfied that your DMM is within calibration, you might make that adjustment. When you measure the AC on top of a DC level, you need to wait until the input capacitor for the meter is fully charged. When the AC voltage stops dropping, you have a good reading of ripple. 15 volts AC on the +110 line is not good. I would suspect C-1512, a 550 uF, 100 volt electrolytic cap. You could try tacking a radial leaded cap, say a 470 uF/ 100 volt or higher across C1512 and see if the ripple decreases. Hit me with a direct email and I'll let you know a phone number you can reach me at if you need some verbal handholding. Regards, Tom ----- Original Message -----
From: Kevin Crossett kcrossett@... [TekScopes] To: TekScopes@... Sent: Wednesday, December 03, 2014 9:37 PM Subject: Re: [TekScopes] Re: Tek 465B woes Ok. Mission accomplished. Here are my measurements and an image to make sure I probed the right test points. Test Point Measurement (VDC) -8 -7.97 +15 +14.98 +55 54.86 +5 4.97 +110 110.5 It seems the power supply is OK on DC voltage. Just for kicks, I also measured all the test points on AC. All but the +110 line went progressively down. I stopped the measurements at .4 volts. The +110 line baselined at about 14 volts AC. ? [Non-text portions of this message have been removed] |
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Mark Wendt
And I'm not too far away from Tom, in Waldorf MD. Dittos on if you are ever in the area.
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Mark On 12/03/2014 10:20 PM, 'Tom Miller' tmiller11147@... [TekScopes] wrote:
Hi Kevin, |
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I would leave the +55 V alone for the moment. A small deviation is unimportant and any adjustment might necessitate a recalibration of the 'scope.
Your problems are not caused by the possible deviation of the DC voltages that you measured. After correction of the real problem, if your 'scope needs a recalibration, you may decide to adjust the + 55V, as is part of a full recalibration as per the manual. As Tom M. writes, 15 V AC on the +110 V line is too much and I'd do as he recommends. Raymond |
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Kevin Crossett
Thanks Tom and Raymond for the advice. Two questions from a novice
troubleshooter. 1. I don't have access to a 550 uF, 100 volt electrolytic cap. Tom, when you say "tacking a radial leaded cap across C1512" to you mean soldering it on the pads and then checking the AC measurement again. Also, I can't find C-1512 on the board or in the service manual. The manual is for 465B scopes with B06000 and up. According to the service manual, all caps on the horizontal amp are in the 4XXX range. 2. Since I don't have a cap anywhere near the 100 volts, is there another way to check the cap to see if it is faulty? |
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Mark Wendt
On 12/04/2014 10:40 AM, Kevin Crossett kcrossett@... [TekScopes] wrote:
Thanks Tom and Raymond for the advice. Two questions from a noviceWhat's the serial # of your scope? Easiest way is to remove one leg from the circuit and make a direct measurement of it, both capacitance if your DMM does it, and also ohm it out. An ESR meter would be handy to have also. Mark |
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Kevin Crossett
I don't have the scope in front of me at the moment. This image has a
partial serial number included. Its ?067605 so it should be in the range of the service manual that came with the scope. On Thu, Dec 4, 2014 at 10:51 AM, Mark Wendt mark.wendt.ctr@... [TekScopes] <TekScopes@...> wrote: On 12/04/2014 10:40 AM, Kevin Crossett kcrossett@... [TekScopes] |
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Hi Kevin,
1. I think that Tom made a mistake here. C1512 is the correct ref. for a 465. In a 465B, it's C4439. In my 465B manual, it's at the top of the Power Supply schematics (page 12), right where the fold is in the middle of the schematics on the paper page. Physical location is shown in Figure 8-7 "A4 interface Circuit Board, behind Tab 7. Location F8/9. 2. Any cap with at least 100 V working voltage and a few 100's uF would do and make a big difference if C4439 is low-cap. Just solder it on as a temporary measure. Easy to do from the bottom of the 'scope and see what happens. Raymond |
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Hi Kevin,
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Raymond is absolutely correct, I did use the wrong schematic. The cap I suspect is bad is C-4439. And I agree with his comment about what to try. If you really can't find a cap easily, let me know and I can send you one. Tom ----- Original Message -----
From: raymonddf@... [TekScopes] To: TekScopes@... Sent: Thursday, December 04, 2014 11:00 AM Subject: [TekScopes] Re: Tek 465B woes Hi Kevin, 1. I think that Tom made a mistake here. C1512 is the correct ref. for a 465. In a 465B, it's C4439. In my 465B manual, it's at the top of the Power Supply schematics (page 12), right where the fold is in the middle of the schematics on the paper page. Physical location is shown in Figure 8-7 "A4 interface Circuit Board, behind Tab 7. Location F8/9. 2. Any cap with at least 100 V working voltage and a few 100's uF would do and make a big difference if C4439 is low-cap. Just solder it on as a temporary measure. Easy to do from the bottom of the 'scope and see what happens. Raymond |
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Kevin Crossett
Eureka. I found it. Thanks Raymond. It must get confusing helping so many
people out with different scope problems. I did in fact find C4439 in the service manual. Now I have to find a 100 v cap. I guess its a trip to mouser.com. Radio shack has only 470 ohm rated at 35 v. I don't suppose that rating is adequate for the test... On Thu, Dec 4, 2014 at 11:00 AM, raymonddf@... [TekScopes] < TekScopes@...> wrote:
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Kevin Crossett
Thanks for the offer Tom. I can, of course, go to mouser, but I'm not too
keen on paying shipping for such a small part, especially if I will have to go back to that well for additional parts. I will go in my attic and look at some old computer boards. Maybe I can find something on one of the boards that will work. On Thu, Dec 4, 2014 at 12:01 PM, 'Tom Miller' tmiller11147@... [TekScopes] <TekScopes@...> wrote:
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Kevin,
All PC Power supplies contain at least one large electrolytic cap. with several 100 Volts of working voltage and at least several 100's uF capacitance. That will do the job. It doesn't matter if you have to put wires of a few cm's length on the cap or on the board to be able to solder the short connections. Just make sure you connect the polarities correctly. Since your "new" temporary cap hasn't been used for a while and it may not be of high quality, it may not like the voltage applied suddenly. Common countermeasures, like a series resistor in a temporary fuse-like role, wouldn't be completely straightforward because of the unknown power supply / load situation. OTOH, I don't think the 100 V suffers from large load or even overload so I'd put in a low-wattage resistor of say 100 Ohm, 0.25 Watt in series with the new, temporary C. The resistor will burn up if the new C has a real problem. Even with 100 Ohm in series, I think your 100 V AC will become significantly lower if C4439 is the problem. After a while, it may be safer to remove (short) the temporary resistor. Raymond |
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Kevin Crossett
That's what I figured. I will look in my junk box for an old power supply
or some other electronics gizmo for the 100 v cap. Assuming I find one in the next day or so, I am now trying to determine the positive side of the cap... I found this image on the internet of someone with a similar problem as me. He laid out what he thought were the solder points for the 4439 cap. Is he right, and if so, how can I determne which one is positive? On Thu, Dec 4, 2014 at 1:29 PM, raymonddf@... [TekScopes] < TekScopes@...> wrote:
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Kevin Crossett
Sorry, here is the image
[image: voltages] On Thu, Dec 4, 2014 at 1:42 PM, Kevin Crossett <kcrossett@...> wrote: That's what I figured. I will look in my junk box for an old power supply [Non-text portions of this message have been removed] |
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You may find the positive side for your temp. C. by switching the 'scope on and measuring DC voltage across C4439. The plus side of the cap. goes where the more positive voltage on C4439 is seen (100V)
Raymond I found this image on the internet of someone with a similar problem as me. He laid out what he thought were the solder points for the 4439 cap. Is he right, and if so, how can I determne which one is positive? |
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