Re: 7B50 - No Trace
n4buq
Ozan,
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I'm not sure, but I may have made some mistakes in those voltage measurements (conflated one resistor with another) because I checked the voltage across L267 and it is nearly zero. I just did a bit of looking further down the signal path and found that the base of Q305 is about -0.5V instead of +0.27V as shown on the schematic. I suspected Q293 might be responsible (in part) for that and I pulled it. It checks "ok" on my component tester; however, with it out of the circuit, the base of Q305 is now a bit closer to the positive value on the schematic. I think it's around 0.5V but I didn't write that down so I'd have to check for a more precise value. At any rate, with Q293 out, I now get what appears to be a single-shot trace. At a slow sweep speed (e.g. 1s/div) I can switch the display mode to AMPLIFIER and then back to TIME-BASE and can see two dots moving across the screen (using the calibrator as input so two dots makes sense). This isn't the case with Q293 in place. Am I chasing a ghost or is it possible there's a problem with Q293 that my component checker doesn't reveal? Note that CR299 is also at play at the base of Q305 and I'm now wondering if that might be part of the problem. BTW, I put a 220-ohm across R394 which brought it down to 50-ohms but that didn't seem to change anything. I'm wondering what the true values of the decoupled voltages should be. The schematic simply shows them as their standard values (e.g. +15, -15, etc.) and I'm not sure what should be the correct values. I haven't found anything in the manual that defines that either. Thanks, Barry - N4BUQ
----- Original Message -----
From: "Ozan" <ozan_g@...> On Mon, Nov 15, 2021 at 01:55 PM, n4buq wrote:I think I discovered where R394 and C395 are. They're in plain sight just onGood detective work.
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Re: 7B50 - No Trace
Ozan
On Mon, Nov 15, 2021 at 01:55 PM, n4buq wrote:
I think I discovered where R394 and C395 are. They're in plain sight just onGood detective work. In any case, R394 measures 65 ohms so I'll be looking to replace that. IAlthough I agree R394 looks a little too high and changing it should help, it is unlikely the root cause of the fault you are seeing. Your measurement of voltage difference between bottom of R264 and base of Q266 needs another look. We don't expect so much DC drop across L267. Another data point is voltage across CR262 was 0.249V and voltage across R267 is 0.47V that again says there is some DC drop across L267. Ozan
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Re: Tek 575 Mod Lit Redone
Thank you so much for doing that! I just brought home a 575 yesterday. It runs perfect at the moment. My 576 acts up sometimes, so it will be a nice back up.
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Re: Removing the Adhesive From Hell
bill koski
CRC Brakleen in the red can works well on many adhesives. Also a very good degreaser. It doesn't hurt most rubber parts and fine on any raw metal parts. Some paints it's OK with others it will attack. OK with most plastics. So test before use.
I usually spray it on a rag and use that to rub off the crud especially if it's a possibly sensitive area. It evaporates quickly.
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Re: 7704A - Grid Bias
Albert Otten
I agree with Barry's comments, the time base setting of the test scope is not specified at all. Why not leave that setting at fast speed all the time, like done for the ground reference? [BTW: Where is that large hold-off (?) time coming from?] Later on In the video, while judging "just visible", the 7704A is apparently set at much faster speed than the prescribed 0.2 s/div. When I understand the Rigol readout correctly, it's more like 10 ms per sweep or 1 ms/div.
Barry, even with Intensity fully CCW the TP voltage still switches between two levels, unblanked and blanked. A DMM can be used when its settling time is well within a trace time, here 2 s.Then the unblanked TP voltage can be read and increased by 4 V. BTW: the procedure simply talks about "the" TP DC level which in my opinion has to be read as the unblanked level.. Albert
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Re: 7704A - Grid Bias
n4buq
Oops! I didn't realize the video was yours(?). I still don't see where setting the test scope's timebase to 0.2s/div accomplishes anything for measuring the voltage on it. In fact, I don't understand why the test scope is needed and a digital volt meter would work. I know I must be missing something...
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Thanks, Barry - N4BUQ
----- Original Message -----
From: Zentronics42@... Barry,
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Re: TEK 5111A
Roy Morgan <k1lky68@...>
Just add the "R" to the name. All done.
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Roy Morgan K1LKY Western Mass
On Nov 15, 2021, at 8:01 PM, byterock@... wrote:
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Re: TEK 5111A
byterock@...
ok 'R' for rack I would take it.
This is what I though Cheers John
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Re: 7704A - Grid Bias
Zentronics42@...
Barry,
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I have tried for a while to get the setting copied here but PDF's just wont cooperate with me at the moment. The YouTube video is the correct procedure based on the service manual. You could easily do this same procedure based on X-Y mode as well however you will be stuck when you get to step 6 transient response. This will need a moving sweep of about 10 Mhz. What they mean in the manual by free running sweep is the time base in auto untriggered. This means that you do NOT need the calibrator a 7aX set to GND on the input would be fine. But this does lead me to another question. If step 6 is transient response, do you have brightness issues with A sweep at faster time base settings? Relevant pages in the service manual are 4-7 and 4-8 Then manual just does the grid bias with a moving untriggered sweep and them moves right in to transient response. This set up allows you to go both adjustments with out having to reconfigure the test set up. The digital scope used in the video was to get the +4v set point as well as the transient response. Sorry about the confusion. This is what I get for trying to do things from memory at this point. Zen
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of n4buq Sent: Monday, November 15, 2021 9:46 AM To: tekscopes <TekScopes@groups.io> Subject: Re: [TekScopes] 7704A - Grid Bias Zen, Regarding that calibration video, I notice the fellow is setting the timebase in the "test" oscilloscope to 0.2s/div. That doesn't make sense to me and I presume it's incorrect. He switches to a digital scope to measure the +4V delta but the image on the 7704A is a line, not a dot. I don't suppose it really matters exactly what's displayed but I presume the timebase in the 7704A is not set per the instructions(?). Thanks, Barry - N4BUQ ----- Original Message ----- From: Zentronics42@... Barry a question about the setup. Do you have any plugins in the frame
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Re: Type 531 parting out
wallace.dg@...
I reside in Georgia.
Davis
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Re: Older current probes with newer amplifiers?
Xu Wang
Another problem is to figure out how the checksum is calculated. That would pave the way for us to generate meaningful data set. Without it, even simple changes to the serial number will make the data unusable.
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Re: Removing the Adhesive From Hell
Geoffrey Thomas
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On 15/11/2021 22:17, Geoffrey Thomas via groups.io wrote:
Iso-propyl alcohol (IPA) may be less reactive, but again try on a small area first.
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Re: Removing the Adhesive From Hell
Geoffrey Thomas
Iso-propyl alcohol (IPA) may be less reactive, but again try on a small area first.
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Geoff.
On 15/11/2021 19:50, Greg Muir via groups.io wrote:
I’ve had varying success with all of the “popular” methods of removing dried masking tape adhesive. Most leave you still with a cleanup job at best.
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Re: TEK 5111A
Yes, this is just a rearrangement of the scope for rack mounting. Technically you might call this an R5111A, but it was easy to convert a desktop 5111A to a rack mount unit (and vice versa), with just a few extra parts (e.g. the metal side panels on the desktop unit are replaced with different top and bottom panels in the rack mount configuration), so it's perfectly likely that someone did this to a 5111A and did not alter the badging.
-- Jeff Dutky
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Re: 7B50 - No Trace
n4buq
Make that "I think I discovered where R394 and C394 are."
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Thanks, Barry - N4BUQ
----- Original Message -----
From: "n4buq" <n4buq@...> I think I discovered where R394 and C395 are. They're in plain sight just on
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Re: 7B50 - No Trace
n4buq
I think I discovered where R394 and C395 are. They're in plain sight just on the other side of a metal shield - just across from R264. The parts layout image labels those as R265 and C264; however there are no such parts (at least not that I can find) in the parts list and I could not find those numbers on the schematic either. You can see those about mid-way vertically and to the left side in the image for the Trigger Generator (next to Q315 on Figure 4-4). Apparently the schematic folks and the manual folks got something out of sync(?).
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In any case, R394 measures 65 ohms so I'll be looking to replace that. I probably should replace the electrolytics in the decoupling section just for good measure. If those are leaking, then it would further explain excessive voltage losses due to the drops across R393, R394, and R395. Thanks, Barry - N4BUQ
----- Original Message -----
From: "Barry" <n4buq@...> Hi Ozan,
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TEK 5111A
byterock@...
Ok the scope says 5111A but all the pics of such of scope have the CRT sitting on top of 3 plugins. My newly acquired one has the RT on the left and 3 plug ins to the left.
Is this only a chassis difference? What am I dealing with here.
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Re: Removing the Adhesive From Hell
Greg Muir
I’ve had varying success with all of the “popular” methods of removing dried masking tape adhesive. Most leave you still with a cleanup job at best.
The best approach I have found is using ethyl alcohol (ethanol). Even applying over the masking tape if it still remains soaks through the paper backing and loosens the adhesive but the best method is to remove the tape first if you can. Be patient and keep the adhesive wet to allow the alcohol to do its job. Then periodically wipe away the part that has softened repeating a few times until the adhesive is gone. I often get inpatient and use my thumbnail to scrape the softened adhesive to speed the process along. Using the edge of an old credit card will also do the trick. A word of caution – ethyl alcohol will soften some paints and attack some plastics. It’s best to try it on a small spot to see if the surface is safe to apply the alcohol. I have found the paint used on the cast frame that surrounds the front panels of earlier HP equipment has a tendency to be softened by the alcohol. A sidebar - when working for one large organization that had its own internal construction department I asked the head painter about what he used to remove unwanted latex paint. He told me that ethyl alcohol was his standard product. I tried it and found ti to be 100% effective at the job. Greg
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Re: Removing the Adhesive From Hell
Jim Strohm
Try xylene on an inconspicuous area of the part.
I've had excellent results with this stuff on occasion... including on those indestructible anti-slip stickers that get put in bathtubs. I'm out of it now, and I don't have any cal tag or inventory tag residue to try it on. 73 Jim N6OTQ
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Re: Type 531 parting out
Dave Voorhis
If you're within a fifty mile radius of Derby, UK, I'll come get the lot if you're willing to part with it whole. Thanks!
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I'm guessing you're not, though. I mean, I'm guessing you're not within a fifty mile radius of Derby.
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of wallace.dg@... Sent: 15 November 2021 15:11 To: TekScopes@groups.io Subject: [TekScopes] Type 531 parting out I recently helped clean out a shop for a retired EE, and was given a Type 531 oscilloscope. It powers on, and the CRT shows a trace. However, I don't have any probes to determine functionality. At 60 some-odd pounds, this thing is a beast. Although the case is pretty rough, I will part it out, if anyone wants knobs, tubes, CRT, sub boards, etc. Regards, Davis
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