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
- TekScopes
- Messages
Search
|
Re: 2400 series of scopes -- automatic voltage measurement
Steve
Hi Victor,
toggle quoted message
Show quoted text
Yes, I was referring specifically to a 2456B. TEK specifications indicate that the automatic voltage reading is good up to 1MHz. Interesting that you are seeing it function up to 200MHz. Thanks. Steve On 2/18/2013 10:33 PM, victor_j_silva wrote:
I assume you mean a 2445A/65A/67 and 2445B/65B/67B. |
|
|
Re: Tektronix 2465 capacitors etc.
I had sent a response earlier but it didn't appear to have made it.
toggle quoted message
Show quoted text
I checked some of the voltages on the board, but can't say I entirely know what to make of all of them (newb alert again hah) Ok, I've got 94v on the unregulated rail On the op-amp, pin 1 vref is 10.00v Pin 2 from the voltage divider is reading as ~1v or just under. Pin 1 is reading 15.19v. Q1222: Emitter 8v, base is grounded of course, and 11.6v on the collector. Q1220: (sorry, not sure which is emitter/base/collector, I'd have to look up a datasheet - more newb showing through). So looking down on the power supply as it's mounted in the chassis: 11.3v on the left pin, 94.7v on the middle pin (must be the collector) and 11.8v on the right pin. Q1221: 94v on the collector, 11.1v on the base and 10.6v on the emitter. I didn't measure Q1223 - hard to reach that one. R1212: 94v on the unregulated rail side, 10.5v on the other side of it. R1220: 94v on the unregulated rail side, 9v on the other side. Curious how I got 15.19v on pin 1 of U1281A with a 10v ref and a 1v comparison from the voltage divider off the regulated line - looking at the datasheet it looks like it should be operating as two separate op-amps with one half regulating the 87v line and the other the 42v line, so I fired it up again and checked the voltage on all of it's pins: pin 1: 15.57v pin 2: 1.05v pin 3: 10.00v pin 4: -6.86v pin 5: 10.00v pin 6: 1.58v pin 7: 15.58v pin 8: 16.42 So thinking about it for a bit, the schematic shows a voltage of -1.53v for pin 1 (a far cry from the 15v I'm getting)which I assume is the voltage I should see when the line is regulated to 82v. And I assume then that the 16.42v is the positive power for U1281, and the -6.86v is the supply that lets it pull Q1222 low when the voltage from the voltage divider feeding pin 2 = the 10v ref from pin 3. So I guess I learned something, but as far as using the voltages to give me an indication as to what's gone wrong I'm not sure. That will take a better man (or woman) that's more educated than I! I would have to resort to the shotgun repair method at this point - replace all the components :) (certainly not to the point of wanting to shoot the scope yet lol) As a note, when reading these voltages they can vary a bit while checking them. Sometimes it's not uncommon to see some of the voltages vary ~0.5v it seems, so that accounts for some of the variance in the first vs 2nd measurements in areas. Earlier I was reading ~9.5v on the 87v regulated line, but tonight it was just under 9v. Thanks! Chris --- In TekScopes@..., "John Snyder" <Kochcal@...> wrote:
|
|
|
Re: Tektronix 2465 capacitors etc.
Chris
toggle quoted message
Show quoted text
The CR1244 is across the B-E junction of the transistor, so in circuit it would not measure Open like a diode out of the circuit would. I have my board out waiting for the inverter board to dry from it's cleaning, and I measure .706V forward (of the diode) and .581V reverse (instead of open, which is forward for the transistor junction.) You could measure all the voltages Q1220, Q1221, Q1222, and Q1224 E,B and C along with U1281A pin 1, 2 and 3 CR1220 anode to see what is out of wack John -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Chris Sent: Monday, February 18, 2013 8:37 PM To: TekScopes@... Subject: [TekScopes] Re: Tektronix 2465 capacitors etc. John, A HUGE thank you on checking that and giving me your value! I was hoping the short wasn't in the main board somewhere as that doesn't look like fun to pull in the least. I just checked the resistance from the pin 7 (blue 87v wire) on the connector (power supply still out and on the bench) and I got a value of 25.55Kohm, so it would appear I should be OK to go at that (assuming that powering something else up on the main board doesn't cause it to short/overload the supply). I was testing the diodes on the power supply and diode CR1244 is giving me 0.538V forward and 0.630v reverse. I think I might pull it and check it out of the board later tonight after I eat etc. Thanks for the help! Chris --- In TekScopes@..., "John Snyder" <Kochcal@...> wrote: the J121 connector unitBehalf Of Chrisget into all this, so maybe my understanding is skewed. :)three groups, and the wrong voltages on the right side, so it would seem that'slook at the three 10 uF caps and all the diodes in that area. Be sure to onlyuse fast diodes for any replacements.capacitors can come from the factory new. Did you measure all these voltages in the ------------------------------------ Yahoo! Groups Links |
|
|
Re: DC504 counter display
If it displays a "8" as a "0" and a "0" as
a "U" it is almost certainly a driver issue.
toggle quoted message
Show quoted text
If it were a bad display segment the "0" would display as a "0" if the "8" displayed as a "0". Do all positions display the same incorrect digits? 73 Glenn WB4UIV At 11:52 PM 2/18/2013, you wrote: Anyone familiar with the TM500 counter, model DC504 ? |
|
|
Tek 485
I have two Tektronix scopes: a 485 and a 2465. Both of them need a little TLC, but I'm going to focus on the 485 at the moment as it is non-functional. I'm not an experienced electronics tech, but I'm not a complete novice either.
I really like the blue phosphor of the 485. For the moment the traces will show up, but the traces don't respond to input on either channel. I think the problem lies with the attenuator cards, but I'm not 100% sure thats the only problem. This I know for sure: if I take my signal gen and hook up its output to the place on the vertical amplifier where the attenuator plugs in, the signal is displayed on the scope. Another strange symptom is that on Channel 1, if the impedance is on the 50 Ohm setting, the trace is there, but on the 1 MegaOhm setting it disappears. Any thoughts guys? Have any experience with this sort of thing? I've taken out the channel 1 attenuator and have it in my hands right now. Where should I start troubleshooting? Thanks! John |
|
|
Re: DC504 counter display
¿ªÔÆÌåÓýTektronix had propensity to use chip IC sockets. Try to remove display package and reseat it. That might re-establish pin connection. Sometimes it takes several re-seatings to clear the socket.Miroslav Pokorni On 2/18/2013 9:18 PM, David wrote: ? |
|
|
Re: DC504 counter display
--- In TekScopes@..., HankC <hankc918@...> wrote:
Common problem - FND357 displays go bad - fixed mine with two new LED displays. 6 bucks each, do a google search to see who might have them cheap. Cheers, Taylor |
|
|
Re: What use for a 640 Ohm 1x Probe?
I agree with what Don posted. The 640 ohms is just the resistance of
the inner conductor of the coaxial cable for a x1 oscilloscope probe. I measured about 250 ohms on a x1 probe I happen to have in reach. On Tue, 19 Feb 2013 04:55:41 -0000, "Philip" <ndpmcintosh@...> wrote: Yeah. It doesn't have any markings on it other than the name "Fairchild" on the cable, and I am glad I checked it before I actually tried to test it. |
|
|
Re: DC504 counter display
Going by the schematic, the display digits are multiplexed which is
the common configuration so if the middle horizontal segment is working on at least some digits, then the 7 segment display driver is fine. If some segments of every 7 segment display work, then the column display driver is fine as well. That pretty much narrows any problem to bad display segments or possibly an open connection to the missing display segments. I would normally consider the later less likely than the former except that two of the same segment are missing. On Mon, 18 Feb 2013 20:52:57 -0800 (PST), HankC <hankc918@...> wrote: Anyone familiar with the TM500 counter, model DC504 ? |
|
|
Re: What use for a 640 Ohm 1x Probe?
Yeah. It doesn't have any markings on it other than the name "Fairchild" on the cable, and I am glad I checked it before I actually tried to test it.
toggle quoted message
Show quoted text
In looking at an old but classic oscilloscope book it mentions a "direct" probe that has essentially 0 resistance used for checking low impedance, low frequency circuits. And, it also describes the "isolation" probe which has an R of 4.7 to 10kOhms. It might be something intended to serve as one of these. It looks like it is from the early 60's and perhaps was used on the Fairchild 766H. I doubt there would be much current use for this probe.
|
|
|
Re: DC504 counter display
More than likely the LED read outs.
toggle quoted message
Show quoted text
Chris VK4CVL At 03:52 PM 19/02/2013, you wrote: ? |
|
|
DC504 counter display
Anyone familiar with the TM500 counter, model DC504 ? I just picked one up & I noticed a couple of the digits are missing the middle horizontal segment. So, it displays an "8" as a "0", or a "0" as a "U". In your experience, is this a display problem or one of the chips driving the display ? HankC |
|
|
Re: What use for a 640 Ohm 1x Probe?
Don Black
¿ªÔÆÌåÓýI think you are measuring the inner conductor resistance. This is made of resistance wire (often wound in a spiral) to damp reflections back the cable. The cable isn't terminated (the input impedance of the scope is 1 Meg) and like any transmission line energy is reflected where it isn't absorbed by matching termination. This is a compromise to damp such reflections, useful at low frequencies.Tektronix explains their techniques in their concept book series, the one you want is called 'Oscilloscope Probe Circuits". It's available to download on the Internet and is an excellent guide to probe design. Silicon Chip also has a good article on probes a while back that I think explained it. Don Black. ? |
|
|
Re: Tektronix 2465 capacitors etc.
John,
toggle quoted message
Show quoted text
A HUGE thank you on checking that and giving me your value! I was hoping the short wasn't in the main board somewhere as that doesn't look like fun to pull in the least. I just checked the resistance from the pin 7 (blue 87v wire) on the connector (power supply still out and on the bench) and I got a value of 25.55Kohm, so it would appear I should be OK to go at that (assuming that powering something else up on the main board doesn't cause it to short/overload the supply). I was testing the diodes on the power supply and diode CR1244 is giving me 0.538V forward and 0.630v reverse. I think I might pull it and check it out of the board later tonight after I eat etc. Thanks for the help! Chris --- In TekScopes@..., "John Snyder" <Kochcal@...> wrote:
|
|
|
Re: What use for a 640 Ohm 1x Probe?
|
David Hess
to navigate to use esc to dismiss