Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
Tek 422 HV power supply issues
|
So I'm looking at this 422 and the trace doesn't get visible until the
intensity control is around 3 o'clock. Blanking is adjusted, so that's not the problem This doesn't seem right, so I dug out the HV probe and took some measurements. The Accelerating potential is spot on at +4900. But all of the negative voltages are just a tad off. The high voltage test point at G1 on the schematic (labeled -1420 or -1400 depending on which side of the line you're looking at) never gets below -1396. (At midrange it's -1390) With the intensity at midrange, the cathode is -1360, not -1375 as spec'd on the schematic. Right now at the end of the intensity control, I get a range from -1375 to -1390, so it looks like 10 or 15V can make a difference. I hate working on HV supplies, but there's not a lot of parts in this one. Anyone have any experience with this one? I'd appreciate some pointers. Paul -- Paul Amaranth, GCIH | Rochester MI, USA Aurora Group, Inc. | Security, Systems & Software paul@... | Unix & Windows |
|
Hi Paul --
toggle quoted message
Show quoted text
Check the resistors in the series string where the focus & intensity pots live. Your voltages aren't that far off the mark. Per the schematic, 'normal' should be a bias of around -45 V. If your difference is less and the intensity is still weak, you may be looking at a crt. -ls- Paul Amaranth <paul@...> wrote: So I'm looking at this 422 and the trace doesn't get visible until the |
|
Resistors looked more or less OK, that was one of the first things
I checked. The 2 2.2M in series had drifted down to 4.2M, while the 1M focus was up to 1.2M, so more or less a wash. More measurements, here's the bias range: Intensity: Min Midrange High G1 bias -95 -42 -6 I don't have any experience with this measurment, is this reasonable? Is this pointing to low emision on the CRT? On Wed, Feb 20, 2013 at 09:54:01PM -0500, larrys@... wrote: Hi Paul ---- Paul Amaranth, GCIH | Rochester MI, USA Aurora Group, Inc. | Security, Systems & Software paul@... | Unix & Windows |
|
A little more investigation showed the blanking levels did not
match the waveform diagrams; putting a meter on the +55 showed +66, so now it's on to the LV ps. Anyone have a schematic or link to a 422 AC Only PS? I have a 016-0072-00 The online manuals I've found so far only seem to have the AC/DC supply. And I thought this was just going to be a quick clean up and toss on the shelf. Paul -- Paul Amaranth, GCIH | Rochester MI, USA Aurora Group, Inc. | Security, Systems & Software paul@... | Unix & Windows |
|
Paul,
toggle quoted message
Show quoted text
I uploaded "Tektronix 422 Oscilloscope AC Power Supply Schematic" to the ko4bb.com site. Check there under the Manuals\Tektronix directory. (It might get moved into the Manuals\Tektronix\422 directory.) --John Gord --- In TekScopes@..., Paul Amaranth <paul@...> wrote:
|
to navigate to use esc to dismiss