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: Model 485 traces do not synch to triggering sources
Chuck,
If your S/N is below B15590, modify the circuit in the front end that drives the Z input relay. This change is to protect the IC from spikes from the relay turning on or off. There is a 100mfd condenser in each attenuator as a decoupling. The condenser is axial tantalum and is run almost at its rated voltage. I put in a 16V type to replace the 10V type that sees 9V. A ULD or UHE type would work. Mine has the same option as Tom G.'s. That is why I like mine even more. Mark |
|
Re: Model 485 traces do not synch to triggering sources
Good advice for Tantalums and Aluminum Electrolytics as well.
toggle quoted message
Show quoted text
One of the things I like best about my 485 is the clean, bright, well focused trace it produces. My 2465BDV is the best it can be but is no match for the thin, bright beam on my 485. One other thing that I found decades ago with my 485 that had a trigger issue was Potentiometer R755 (Trigger Sensitivity) associated with Tunnel Diode CR751 was dirty. As with servicing any equipment with calibration pots, I always mark the position of all Pots on a Board I am working on. Moving the wiper through the travel cleared whatever debris was there and I never have had a problem since. By the way, triggering and displaying a trace out to 670 MHz with the 50 Ohm Input Attenuator was no issue for my 485. Very good Analog Oscilloscope. Ross -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Tom Lee Sent: Friday, December 09, 2022 10:28 AM To: [email protected] Subject: Re: [TekScopes] Model 485 traces do not synch to triggering sources Tek learned that the voltage ratings on tants need to be chosen more conservatively. Eventually they settled on using tants rated for twice the expected nominal operating voltage. That cut down the failure rate a lot. Better late than never. When replacing a failed tant, use the 2x rule of thumb to guide your choice of replacement. --Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 12/9/2022 07:55, Chuck Moore via groups.io wrote: Mark & Tom |
|
Re: 2465B Recap
On Fri, Dec 9, 2022 at 09:55 AM, Matt Balmer wrote:
One of the maintenance routines display calibration coefficients on the screen. You could take pictures of the screen to make a backup of coefficients before replacing the battery in case something goes wrong. As Zen also said FRAM is not a drop in replacement, although it works in many scopes. Dallas chip isolates the memory when voltage starts going down, FRAM chips I know of do not have that feature. There is also a slight mismatch between Voh/Vih levels if you follow datasheet numbers although in general there is more margin. Since you don't have the Dallas chip but a battery backed RAM, there is no compelling reason for an FRAM replacement. Ozan |
|
Re: 2465B Recap
Hi,
toggle quoted message
Show quoted text
If you do lose the Calibration Constants, the calibration can be difficult and as Zen says, requires specialized equipment to perform it. With experience, it takes time - 2 to 4 hours of sequenced steps using that equipment. If you haven't done it before, you may want to consider having someone else do it. The 2465 series oscilloscopes after refurbishment will last a long time. They also hold their calibration for a long time after battery replacement and calibration. I have a rebuilt 2465BDV as my main Analog Oscilloscope on my bench. Ross -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Zentronics42@... Sent: Friday, December 09, 2022 8:46 AM To: [email protected] Subject: Re: [TekScopes] 2465B Recap Matt, In terms of reading the values of the SRAM. It is critical that voltage stay always applied to the chip. Even a momentary loss of voltage for example shorting the power pins the data will be lost to the either and a recal will need to happen. This is what the battery is for to hold over the data when the scope is off. For replacing the sram for a flash chip. This will be a larger challenge as the different types of memory are accessed written too and red from differently. There might not be the correct drive voltages present for the flash chip. Lots of data sheet diving will need to happen for a suitable replacement if any. One other issue here is timings. During boot up the chip will need to respond within the current time as well as with the correct speeds. So this will need to be taken in to account as well if looking for a replacement memory chip. Given all the hurtles the "normal" path walked is refresh the power source (battery) data can be preserved with a bench supply when switching out the battery. If caution is to the wind wiping the data and running the scope through a recal would not be a bad idea given its age. I find the calibration routine will bring any areas that need attention to light. But before going in to the deep end on the calibration make sure ALL sources are available to you the 2xxx scopes are picky when it comes to alignment/calibration tolerances especially in the high frequency compensation section. The edge speed needed here can get in to an "exotic" source depending on the speed of the scope. Zen -----Original Message----- From: [email protected] <[email protected]> On Behalf Of Matt Balmer Sent: Friday, December 9, 2022 10:30 AM To: [email protected] Subject: Re: [TekScopes] 2465B Recap Those that messaged me privately, I appreciate it. I am learning a lot as I go. I can't tell you how many times I've asked a question on an electronics forum and been eaten alive by folks because I didn't "google enough" or I'm doing something that they personally view as frivolous or unnecessary. Suffice it to say that I did not expect to get read the riot act when I've decided to undertake replacing worn-out parts that are now almost 40 years old, especially with some of the stories I've read about some parts in these units failing in rather spectacular fashion due to age, stress, or both. I am a public school teacher, and I often get frustrated at how my students fear asking questions. This experience clarifies why that happens. In case my point isn't clear, when someone asks a question about something, if your response is to immediately jump down their throat and tell them that what they're doing is stupid, then that's probably not going to have the effect you wanted. What it's going to do is make the person do one of a few things: -- They are going to proceed with their plan (ill-advised or not) without hearing any advice that may have been embedded in the message -- They are going to stop everything and abandon the project -- They might take your advice, but they will stop asking further questions out of fear of being attacked again I hope this clarifies my hesitance to post a further response. Additionally, it would seem that the spreadsheet that's hosted here may either be out-of-date, incomplete, or (oddly enough) over-complete. I (now) know Menahem does recap sets for these, and have opted to use one of his kits to redo my scope. Most of the caps from DigiKey were returned (I did keep a couple of the smaller values for my parts bin). I've prepared the system for its recapping and am just waiting on Menahem's cap kit to arrive. The thing I'm now concerned about is retaining the calibration values, and potentially replacing the SRAM chip and battery combination with a FRAM chip instead. Is it possible to get the calibration values out of the SRAM chip without powering the system on? I have a DIP chip test clip that would allow me to attach header pins to the SRAM in-circuit and then run those to my EPROM programmer, but I'm not sure that would do the job if the system isn't powered. It's not a huge deal (if I have to do a re-cal on the thing after replacing the chip, oh well) but if it's possible to extract the cal values during servicing, that would be ideal. |
|
Re: 2465B Recap
So is the calibration memory more of an "if it ain't broke, don't fix it" kind of thing in my case? My A5 board doesn't have the Dallas NVRAM chip, so my guess is that the urgency to replace it is probably somewhat lower.
Considering that, I almost wonder if the better question would be to try and grab the cal values once the board is recapped and reassembled, and then attach the DIP-clip to it and try and read them with the system powered on. |
|
Re: Model 485 traces do not synch to triggering sources
Tek learned that the voltage ratings on tants need to be chosen more conservatively. Eventually they settled on using tants rated for twice the expected nominal operating voltage. That cut down the failure rate a lot. Better late than never.
toggle quoted message
Show quoted text
When replacing a failed tant, use the 2x rule of thumb to guide your choice of replacement. --Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 12/9/2022 07:55, Chuck Moore via groups.io wrote:
Mark & Tom |
|
Re: Model 485 traces do not synch to triggering sources
On Fri, 9 Dec 2022 at 15:55, Chuck Moore via groups.io <wd4hxg=
[email protected]> wrote: Mark & TomThe 485 is the scope on my bench. I've had it stably triggering on a >1GHz signal, the limit being the greatly reduced signal amplitude rather than the trigger circuit. The 485 has two rare features: - the cal out has a risetime of <1ns, i.e. suitable for testing the scope's risetime - it has a real 50ohm input attenuator, i.e. not a crappy 50ohm resistor slapped across a 20pF//1Mohm input. It also has a separate traditional 1Mohm attenuator. Plus I like the blue trace :) |
|
Re: Model 485 traces do not synch to triggering sources
On Fri, 9 Dec 2022 at 15:12, Mark Vincent <orangeglowaudio@...> wrote:
Tom, Have a look at both sides of u960 on the power distribution schematic 17. C911 is also a a 15V tant on a 13V line. I've had it destroy R965. C962 is either a 22uF 15V tant or a 0.02uF ceramic! It too is at 13V. It is on the input to the u960 which acts as a *1 opamp. C2101 is a 20V tant on a 15V line, and a "nearby" voltage is marked as 13.1V. Not sure what the actual operating voltage is, but looking at the schematic it won't be vastly different. See the calibrator schematic 16. As I indicated, the other two are only "possibly" an issue. |
|
Re: Model 485 traces do not synch to triggering sources
Chuck Moore
Mark & Tom
Thank you for the navigation on this scope. I bought a 465 about ten years ago and it has been a gem despite its age. It actually does everything I need, but a scope with 300 MHz bandwidth is just to much to not repair. I will post my findings and as closely as possible what solves the problem. My big concern was the proprietary IC's might be an issue but it sounds like the tantalum vexations struck Tek also. Never imagined such an expensive cap would be such a problem child. Again thanks Chuck |
|
Re: 7623A HV dead - how to troubleshoot it?
Hi Miguel,
I just did the test you suggested. Result here: /g/TekScopes/photo/281947/3538491 All other windings left open. From calculation I obtain L = 8.3 mH. Definitely different from yours. Max |
|
Re: 2465B Recap
Matt,
toggle quoted message
Show quoted text
In terms of reading the values of the SRAM. It is critical that voltage stay always applied to the chip. Even a momentary loss of voltage for example shorting the power pins the data will be lost to the either and a recal will need to happen. This is what the battery is for to hold over the data when the scope is off. For replacing the sram for a flash chip. This will be a larger challenge as the different types of memory are accessed written too and red from differently. There might not be the correct drive voltages present for the flash chip. Lots of data sheet diving will need to happen for a suitable replacement if any. One other issue here is timings. During boot up the chip will need to respond within the current time as well as with the correct speeds. So this will need to be taken in to account as well if looking for a replacement memory chip. Given all the hurtles the "normal" path walked is refresh the power source (battery) data can be preserved with a bench supply when switching out the battery. If caution is to the wind wiping the data and running the scope through a recal would not be a bad idea given its age. I find the calibration routine will bring any areas that need attention to light. But before going in to the deep end on the calibration make sure ALL sources are available to you the 2xxx scopes are picky when it comes to alignment/calibration tolerances especially in the high frequency compensation section. The edge speed needed here can get in to an "exotic" source depending on the speed of the scope. Zen -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Matt Balmer Sent: Friday, December 9, 2022 10:30 AM To: [email protected] Subject: Re: [TekScopes] 2465B Recap Those that messaged me privately, I appreciate it. I am learning a lot as I go. I can't tell you how many times I've asked a question on an electronics forum and been eaten alive by folks because I didn't "google enough" or I'm doing something that they personally view as frivolous or unnecessary. Suffice it to say that I did not expect to get read the riot act when I've decided to undertake replacing worn-out parts that are now almost 40 years old, especially with some of the stories I've read about some parts in these units failing in rather spectacular fashion due to age, stress, or both. I am a public school teacher, and I often get frustrated at how my students fear asking questions. This experience clarifies why that happens. In case my point isn't clear, when someone asks a question about something, if your response is to immediately jump down their throat and tell them that what they're doing is stupid, then that's probably not going to have the effect you wanted. What it's going to do is make the person do one of a few things: -- They are going to proceed with their plan (ill-advised or not) without hearing any advice that may have been embedded in the message -- They are going to stop everything and abandon the project -- They might take your advice, but they will stop asking further questions out of fear of being attacked again I hope this clarifies my hesitance to post a further response. Additionally, it would seem that the spreadsheet that's hosted here may either be out-of-date, incomplete, or (oddly enough) over-complete. I (now) know Menahem does recap sets for these, and have opted to use one of his kits to redo my scope. Most of the caps from DigiKey were returned (I did keep a couple of the smaller values for my parts bin). I've prepared the system for its recapping and am just waiting on Menahem's cap kit to arrive. The thing I'm now concerned about is retaining the calibration values, and potentially replacing the SRAM chip and battery combination with a FRAM chip instead. Is it possible to get the calibration values out of the SRAM chip without powering the system on? I have a DIP chip test clip that would allow me to attach header pins to the SRAM in-circuit and then run those to my EPROM programmer, but I'm not sure that would do the job if the system isn't powered. It's not a huge deal (if I have to do a re-cal on the thing after replacing the chip, oh well) but if it's possible to extract the cal values during servicing, that would be ideal. |
|
Re: 2465B Recap
Those that messaged me privately, I appreciate it. I am learning a lot as I go. I can't tell you how many times I've asked a question on an electronics forum and been eaten alive by folks because I didn't "google enough" or I'm doing something that they personally view as frivolous or unnecessary. Suffice it to say that I did not expect to get read the riot act when I've decided to undertake replacing worn-out parts that are now almost 40 years old, especially with some of the stories I've read about some parts in these units failing in rather spectacular fashion due to age, stress, or both.
I am a public school teacher, and I often get frustrated at how my students fear asking questions. This experience clarifies why that happens. In case my point isn't clear, when someone asks a question about something, if your response is to immediately jump down their throat and tell them that what they're doing is stupid, then that's probably not going to have the effect you wanted. What it's going to do is make the person do one of a few things: -- They are going to proceed with their plan (ill-advised or not) without hearing any advice that may have been embedded in the message -- They are going to stop everything and abandon the project -- They might take your advice, but they will stop asking further questions out of fear of being attacked again I hope this clarifies my hesitance to post a further response. Additionally, it would seem that the spreadsheet that's hosted here may either be out-of-date, incomplete, or (oddly enough) over-complete. I (now) know Menahem does recap sets for these, and have opted to use one of his kits to redo my scope. Most of the caps from DigiKey were returned (I did keep a couple of the smaller values for my parts bin). I've prepared the system for its recapping and am just waiting on Menahem's cap kit to arrive. The thing I'm now concerned about is retaining the calibration values, and potentially replacing the SRAM chip and battery combination with a FRAM chip instead. Is it possible to get the calibration values out of the SRAM chip without powering the system on? I have a DIP chip test clip that would allow me to attach header pins to the SRAM in-circuit and then run those to my EPROM programmer, but I'm not sure that would do the job if the system isn't powered. It's not a huge deal (if I have to do a re-cal on the thing after replacing the chip, oh well) but if it's possible to extract the cal values during servicing, that would be ideal. |
|
Re: Model 485 traces do not synch to triggering sources
Tom,
C861 is the one that will give trouble, 13V on a 15V tantalum. I keep 47mfd 25V ULD types in stock to replace the tantalums that are bad. Higher capacitance for others such as 100mfd can be higher in value if wanted. The decoupling off the 50V supply, I put in 15mfd in place of the ,68mfd. The original tantalum, ,68mfd, was already high in ESR. I prefer to use a 25V electrolytic to replace a 20V tantalum on a 15V supply. Mark |
|
Re: TDS3032 does not boot. LCD backl-ight and fan working.
Hello David,,,
I Tried the B-Trig reset with no effect unfortunately. While probing the main board with a scope, I determined that the power on reset circuitry is working (at least the 'MAX708R' generate the reset correctly), but there are *no* signs of life from the processor. Checking the A0 address line on various pins on the other chips, shows no activity whatsoever. I am now starting to suspect that the MPC860 processor is either dead or needs re-balling. Hmm, not the easiest of tasks to do. Paul. |
|
THS7XX LCD Screen Rapair
You can get plastic "razor blades" in either single or double sided types & several hardness grades quite cheaply on eBay if you need to scrape & are concerned about using a metal razor blade.
toggle quoted message
Show quoted text
Ibought some & they fit straight into the holders that normal razor blades fit into. The car detailers use them to remove decals from vehicles. I also bought a few different types of razor blade holders off eBay at the time. I got them to remove gummy adhesive off some engraved signs. Regards, Brian. On 09-December-2022 10:48 pm, tccotham@... wrote:
Sounds like I have the same issue, thanks for the info! |
|
Re: Model 485 traces do not synch to triggering sources
ISTR seeing a problem with a resistor somewhere in the U730/38/40 chain.
Check voltages and waveforms in the vicinity. On Fri, 9 Dec 2022 at 01:44, Mark Vincent <orangeglowaudio@...> wrote: Chuck,Consider putting a tiny drop of Deoxit (possibly D100 but not necessarily) on the end of a jeweller's screwdriver, and applying that directly to a socket. Also IPA any of the switches in the vicinity, talking the usual care with the gold fingers. There is a tantalum rated at 15V for a 13V supply on that board that will There are more than one :( My notes indicate c861 c911 c965 c2101 (possibly c844 c902). Good luck spotting them :( |
to navigate to use esc to dismiss