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The photovoltaic MOSFET approach would work of course. Current is more than enough but regulation is compulsary at >13 V open circuit. The sampler diodes in reverse bias hardly allow any current

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

Another possibility on the photovoltaic approach is Vishay's LH1262 photovoltaic MOSFET drivers. It has two photovoltaic generators in a DIP or SOIC package. You can get a minimum of 2.6uA each

Kevin, Don't try a 470 uF 35V cap. unless you're looking forward to an early firecracker party a few seconds or minutes after switching on... Raymond

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

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

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

The difference of 0.1 volts is insignificant as far as risk to the sampling gate diodes but as Raymond points out, zinc-air batteries are a poor choice because of their short life once activated. I

I wouldn't consider zinc-air batteries a good choice for this purpose. Zinc-air batteries have a relatively long shelf life unopened but once opened (activated), they discharge rather quickly, even

Hi Kevin, 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

I wish I could direct this question to the engineer who designed the sampling bridge in the 7S14 plug-in. The original design made use of Mercury batteries in the sampling gate back-bias (BT1 and

Connect a BNC Tee to the lowest, most central connector. 2 fingers around that and your thumb against the bottom of the mainframe while operating the release with your other hand should be enough

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

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

What'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

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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

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

Hi everyone. My AM503B shows error 355 for some days now - NVRAM error. Checked the battery and it is dead (shouldn't it show "LO" before that?). Does this mean the calibration is

And I'm not too far away from Tom, in Waldorf MD. Dittos on if you are ever in the area. Mark