Author Topic: Tektronix 2465B oscilloscope teardown  (Read 439513 times)

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Offline james_s

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1275 on: November 11, 2018, 06:19:57 pm »
On ebay, you can easily find Agilent 82357b USB/GPIB adapters for well under $100. Beware that most are clones/counterfeit, not Agilent-made, especially those sold as New. Fortunately, the clones are straight copies with the same 75161 and 75160 proper GPIB bus driver ICs, the same CPLD and USB interface ICs, and copied PCB layout. They use the Agilent I/O suite drivers. 


I really wish they would market them as "Agilent compatible" instead of trying to pass counterfeit products off as genuine, then it wouldn't bother me a bit to buy one. I suppose the counterfeit aspect is a way you could get one for free though. Just order it and then file a refund claim due to it being counterfeit goods. If enough people did that places might stop trying to sell counterfeit ones.
 

Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1276 on: November 11, 2018, 06:37:07 pm »
Ok, I think I found the reason for the jitter. It is +15V that bounces around for a minute or so and then stabilizes. The question now is if the LM317 - U1260 is defective or the problem comes from the input. The difficulty with this defect is that it goes away after about 1 minute and I need to wait for hours before it shows up again for a minute or less.
One thing that I've noticed is that the unregulated voltages are a bit low. For example +15V Unreg should be 19.2V according to the schematic but I measure only +18.4V, +5VD should be +5.1V but in my case it is +5.00V.
Maybe  I'm on the edge of the minimum VIO for LM317.

I am assuming that any of the unregulated voltages may vary 10% from what is stated in the manual, in accordance to the mains voltage variation at your location. Also in general, maybe not directly related to your problem but good to keep in mind is that all regulated voltages of the power supply are referenced to the +10 supply, and any deviation there will reflect on all others. This power supply should measure between +9.99 and +10.01V. Anything outside is considered out of spec. Problem is, if you attempt to readjust it, you might affect a whole bunch of other internal scope calibrations as well, so best to leave as is, unless its seriously out of spec, or you intend to perform a full scope calibration.

I would try to measure the input voltage to the LM317, if you also see variations there you know the problem is originating before the regulator. Also check the reference input of the regulator. I would think that an input of +18.4v as opposed to the expected +19.2v should make no difference whatsoever to get a stable 15V output as it is more than 3v above which I would think is still very much ok.

Maybe solder a couple of temporary flying wires at the points of interest that you can easily access to quickly make the measurement as soon as you turn on the scope without having to move things around too much.

The minimum voltage differential for a LM317 to properly regulate is +3.0V. You have a +3.4V differential which is mighty close to minimum. As mentioned verify the reference voltage. And monitoring the input and output of the LM317 is also a good idea.

LM317's are cheap and a dime a dozen. If you see a variation between input and output and it never exceeds less than +3.0V I would try another LM317.   
 
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Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1277 on: November 11, 2018, 10:10:48 pm »
The reference voltage is stable at 10.004V right after power up and goes down slowly to 10.0005V few minutes after that. Flat line on the scope and rock stable on the multimeter so it is out of the suspects list. The input voltage doesn't drop much below 8.4V so I think the min 3V I/O requirement for LM317 is met.
What's left is LM317 itself, U1371 that drives it, or a fluctuating load (a dying capacitor or hybrid IC) on the +15V line. This drives me nuts...
At one point I wanted to sell the bastard as is and be done with it but now I really want to fix it even if it is only to humiliate it...... It can't win    :rant:
That big spark at power up was by design!
 

Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1278 on: November 11, 2018, 10:33:35 pm »
The reference voltage is stable at 10.004V right after power up and goes down slowly to 10.0005V few minutes after that. Flat line on the scope and rock stable on the multimeter so it is out of the suspects list. The input voltage doesn't drop much below 8.4V so I think the min 3V I/O requirement for LM317 is met.
What's left is LM317 itself, U1371 that drives it, or a fluctuating load (a dying capacitor or hybrid IC) on the +15V line. This drives me nuts...
At one point I wanted to sell the bastard as is and be done with it but now I really want to fix it even if it is only to humiliate it...... It can't win    :rant:

Here's a thought to help narrow it down. Isolate the +15V from the LM317 and connect power supply to the load and watch the current as it powers up. If it never exceeds 1.5 amps I'd say the LM317 is weak and the source of the variation. If it does exceed 1.5 amps then your problem is on the load side.
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Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1279 on: November 12, 2018, 01:01:41 am »
The reference voltage is stable at 10.004V right after power up and goes down slowly to 10.0005V few minutes after that. Flat line on the scope and rock stable on the multimeter so it is out of the suspects list. The input voltage doesn't drop much below 8.4V so I think the min 3V I/O requirement for LM317 is met.
What's left is LM317 itself, U1371 that drives it, or a fluctuating load (a dying capacitor or hybrid IC) on the +15V line. This drives me nuts...
At one point I wanted to sell the bastard as is and be done with it but now I really want to fix it even if it is only to humiliate it...... It can't win    :rant:

Here's a thought to help narrow it down. Isolate the +15V from the LM317 and connect power supply to the load and watch the current as it powers up. If it never exceeds 1.5 amps I'd say the LM317 is weak and the source of the variation. If it does exceed 1.5 amps then your problem is on the load side.

If you look at the schematic, there's a power up sequence that goes +87V > +42V > +15V .... It would be pretty hard to do that with an external power on +15V and the result may be less than happy. I think is better to replace the LM317 and see the result. It costs only a buck or two, the hard part is to get to it.  :palm:
That big spark at power up was by design!
 

Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1280 on: November 12, 2018, 01:09:41 am »
The reference voltage is stable at 10.004V right after power up and goes down slowly to 10.0005V few minutes after that. Flat line on the scope and rock stable on the multimeter so it is out of the suspects list. The input voltage doesn't drop much below 8.4V so I think the min 3V I/O requirement for LM317 is met.
What's left is LM317 itself, U1371 that drives it, or a fluctuating load (a dying capacitor or hybrid IC) on the +15V line. This drives me nuts...
At one point I wanted to sell the bastard as is and be done with it but now I really want to fix it even if it is only to humiliate it...... It can't win    :rant:

Here's a thought to help narrow it down. Isolate the +15V from the LM317 and connect power supply to the load and watch the current as it powers up. If it never exceeds 1.5 amps I'd say the LM317 is weak and the source of the variation. If it does exceed 1.5 amps then your problem is on the load side.

If you look at the schematic, there's a power up sequence that goes +87V > +42V > +15V .... It would be pretty hard to do that with an external power on +15V and the result may be less than happy. I think is better to replace the LM317 and see the result. It costs only a buck or two, the hard part is to get to it.  :palm:

Yup, you're right. I forgot about the power up sequence. Agree, change the LM317 and see what happens. And yes, it's not the easiest to get to but you've done it before and you can use my procedure documented in this thread to help you along.

« Last Edit: November 12, 2018, 01:12:19 am by med6753 »
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Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1281 on: November 13, 2018, 02:59:24 am »
Here's a series of scope shots right after the power up. CH1 is pin 2 of LM317 and CH2 is pin 1. It looks like the inverting amplifier is not doing it's job but rather is the source of the jitter. I think the issue is with U1371B, CR1263, C1261 (unlikely) or R1261/R1262.

Edit: Bingo! U1361 doesn't like the freezing spray. Who does?  :--
Edit1: I meant U1371...
« Last Edit: November 13, 2018, 03:46:15 am by Miti »
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1282 on: November 13, 2018, 04:17:38 am »
Has anyone noticed the ripple frequency of CH1? (yellow trace). Its all over the place, first its 1.77KHz, then 1.6KHz, then 25Hz when it finally starts to be stable, then on the three last pictures its shown at around 15Hz. Maybe that power supply is oscillating somehow at startup, and the associated instability is what is causing the jitter.

Or am I looking at the wrong area of the screen shot? Never used one of those Rigol digital scopes but the CH1 label inside the rectangle on the top right side with the square wave seems to be indicating the measured frequency of the (AC) input signal.
« Last Edit: November 13, 2018, 04:20:24 am by AMR Labs »
 

Offline MarkL

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1283 on: November 13, 2018, 04:57:11 am »
...
Or am I looking at the wrong area of the screen shot? Never used one of those Rigol digital scopes but the CH1 label inside the rectangle on the top right side with the square wave seems to be indicating the measured frequency of the (AC) input signal.
It would be indicating frequency if it was a normal, repeating signal.  But the signal is essentially random noise, and in addition it's low amplitude, so who knows what points it's picking to compute the frequency.

Garbage in, garbage out.


Miti: Sounds like you found your culprit!  Did you freeze the other suspect components with little to no effect?  The problem seems to be so sensitive and subtle that the cold could have wicked along the board and traces to affect more than just U1371.

It might also be good to put a little pressure on U1371 and the other suspects to make sure it's not something mechanical like a bad solder joint or cracked trace.

In general I would agree that C1261, a ceramic, would be an unlikely candidate, but I've been surprised on a several occasions.  Suspect *everything* in these old scopes!
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1284 on: November 13, 2018, 05:23:58 am »
Hey Mark,

Last week ordered a GQ-4x4 programmer, and already have the new D1225 waiting in the drawer. Only need to get the low profile machined socket, which I thought I had ordered the correct one, but received a narrow 28 pin DIP instead, its like two 14-pin sockets end to end. Never trust pictures, they are for "reference only", although the description seemed right. Oh well. But this time I've got the right one in the cart.

Also have my eye on a FM16W08, but can't seem to get the SOIC to DIP adapter board until they are back in stock at Mouser early December. Rather buy one that has the pins installed and ready to go then those plain chinese boards on ebay.
 

Offline MarkL

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1285 on: November 13, 2018, 05:44:17 am »
Hey Mark,

Last week ordered a GQ-4x4 programmer, and already have the new D1225 waiting in the drawer. Only need to get the low profile machined socket, which I thought I had ordered the correct one, but received a narrow 28 pin DIP instead, its like two 14-pin sockets end to end. Never trust pictures, they are for "reference only", although the description seemed right. Oh well. But this time I've got the right one in the cart.

Also have my eye on a FM16W08, but can't seem to get the SOIC to DIP adapter board until they are back in stock at Mouser early December. Rather buy one that has the pins installed and ready to go then those plain chinese boards on ebay.
Great - let us all know how it goes!  The Aries adapters are good quality.

It may be a little ugly, but you could always cut the socket in half lengthwise if it's just ribs holding the two rows together.  Who's going to see it under the chip?  Or file down the cuts to make it look like two nice SIP headers.
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1286 on: November 13, 2018, 06:02:43 am »
Great - let us all know how it goes!  The Aries adapters are good quality.

It may be a little ugly, but you could always cut the socket in half lengthwise if it's just ribs holding the two rows together.  Who's going to see it under the chip?  Or file down the cuts to make it look like two nice SIP headers.

Yes I could do that if no other option, but the contacts on this socket are not machined, but rather of the one leaf swipe type, not the ideal socket for the DS1225 round pins. But it could work.

BTW, one thing I want to definitely try first is to write the template file with all the values I added from the exer 02 data. I presume it would be safe to just write the DS1225 with this data, then test the scope, and if all works out, erase the chip, and then write it again but this time with the data I hopefully was able to read to a file from the original NVRAM. Doable?

EDIT: I was thinking a good way to check the data integrity of the first programming with the exer02 values, would be to run the exer02 again with the new chip in the scope, and if all the data matches it should be good to go. Or am I missing something?

« Last Edit: November 13, 2018, 06:07:14 am by AMR Labs »
 

Offline MarkL

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1287 on: November 13, 2018, 06:37:03 am »
Yes I could do that if no other option, but the contacts on this socket are not machined, but rather of the one leaf swipe type, not the ideal socket for the DS1225 round pins. But it could work.
Ah, I was imagining it was a machined socket.

Quote
BTW, one thing I want to definitely try first is to write the template file with all the values I added from the exer 02 data. I presume it would be safe to just write the DS1225 with this data, then test the scope, and if all works out, erase the chip, and then write it again but this time with the data I hopefully was able to read to a file from the original NVRAM. Doable?
Yes, to both.  When you bring up the scope with just the template EXER 02 data, however, the settings will be random since the settings are not stored in the EXER 02 data.  When you boot with the original NVRAM data it should be indistinguishable from when you powered it off.

Quote
EDIT: I was thinking a good way to check the data integrity of the first programming with the exer02 values, would be to run the exer02 again with the new chip in the scope, and if all the data matches it should be good to go. Or am I missing something?
That would be a good check, but the scope will do it for you.  Stored in the EXER 02 data is a checksum at location 00, so if you got something wrong it's is going to complain about it at boot time with a FAIL 04.
 

Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1288 on: November 13, 2018, 01:33:47 pm »

Miti: Sounds like you found your culprit!  Did you freeze the other suspect components with little to no effect?  The problem seems to be so sensitive and subtle that the cold could have wicked along the board and traces to affect more than just U1371.

It might also be good to put a little pressure on U1371 and the other suspects to make sure it's not something mechanical like a bad solder joint or cracked trace.

In general I would agree that C1261, a ceramic, would be an unlikely candidate, but I've been surprised on a several occasions.  Suspect *everything* in these old scopes!

I froze the area first then only U1371 using a frozen Q tip. It is the culprit apparently but I will do more experiments tonight.
That big spark at power up was by design!
 
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1289 on: November 13, 2018, 01:37:44 pm »
Sounds good Mark, thanks for the confirmation. I read somewhere that all the front panel settings are stored in the NVRAM during the shutdown sequence. Then again, they don't necessarily have to be something random, but rather the scope will just boot up with the settings you had when you read your data into the template file you sent me. We'll see as I report back. Hoping programmer will be here sometime this week. Ooops still need to reorder that socket....
« Last Edit: November 13, 2018, 01:42:06 pm by AMR Labs »
 

Offline MarkL

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1290 on: November 13, 2018, 03:50:19 pm »
I froze the area first then only U1371 using a frozen Q tip. It is the culprit apparently but I will do more experiments tonight.
Great idea on the Q tip... sounds like you've really got it pin-pointed.
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1291 on: November 13, 2018, 11:00:03 pm »
CHASING THE ILLUSIVE MILLIVOLT & NANOSECOND – PART II

....
Letting the scope automatically measure the 462 MHz frequency via. the red HELP button, indicated 474.7 MHz, which is 2.3% high.
...

Hey Old-E, was rereading some older posts of this thread and came across your post. I wonder if you are still around and ever where able to draw any causes/solutions/improvements or conclusions in reference to the inaccuracy of the parametric measurements in comparison to using cursors on the waveform. I also found that in particular the frequency measurements where way off for my taste and expectation, specially for a top of the line scope as the 2465B. But to be fair and realistic, of course it deserves many merits, but frequency counting is definitively not one of the fortes of this model.

Just for kicks recently I tried to measure the frequency of a 10MHz output from my recently calibrated Rubidium oscillator, and after a few seconds after pushing the Measure and then selecting CH1 for Frequency, the scope just presented a scant measurement result of "10.16MHz" :--. If I use the cursors to measure frequency, they seem dead on. If I measure that same signal on any of my counters or with the 2247A scope, it shows of course 10-dot plus a whole lot of zero decimal places all the way into the  lower Hz region.

I also did some testing with my R2008HS service monitor that can generate up to 1GHz and has the High-Stability time base option and is calibrated within a few hertz of the expected frequency output, and got similar disappointing results while trying to measure frequency on the 2465B. The error seems to get larger as frequency goes up. At 400MHz it was showing an error of several MHz high (I seem to remember it was showing 416MHz). The frequency measurement stopped responding around 650MHz, but the scope would still trigger without any issues even at 800MHz, although the waveform was mighty fuzzy due to using the lower 10mV input range, but rock solid stable.

The semi conclusion that I have reached is that at least frequency parametric measurements on the 2465B are not very accurate, maybe unless you have the CT options things might get better (?), so don't expect much in that sense. Also, as it was explained to me recently, the way the scope actually tries to measure the frequency of a signal is not at all like a traditional frequency counter would, but it rather uses a very convoluted procedure to get to the results. Only to start with, it involves a Miller integrator, and the CPU and DAC interacting to get a result. In case anyone is interested, still do have the detailed explanation of the measuring procedure by someone that knows these scopes very well in and out, and has been working on them and calibrating/selling them for many years.

BTW: I just recently got this 2465B, and so far have not done any calibration to it. But after some testing it seems still to be quite well calibrated in both time/div and volts/div. At least with the equipment I have available which does not allow me to do a full verification/calibration.
« Last Edit: November 13, 2018, 11:05:09 pm by AMR Labs »
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1292 on: November 16, 2018, 03:09:25 pm »
Great - let us all know how it goes!  The Aries adapters are good quality.

In case anyone was also waiting for the Aries 28-pin SOIC-DIP adapter boards to arrive at Mouser, they actually came in early (ETA was early Dec-18), so I finally placed my order, plus the correct machined socket for the NVRAM and one FRAM to play with on my GQ-4X4 programmer that should arrive this weekend. BTW only 13 Aries boards came in, 12 left now. This is the board you will need to mount the FM16W08 FRAM and convert it to 28-pin DIP.

Also ordered all the recommended PS stuff needed for a full LVPS recap, which I will tackle later on (or sooner), and replace one cap at a time to avoid any mistakes due to the well documented error in the service manual pcb layout, and make sure all the new caps go into the correct location and orientation.
 

Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1293 on: November 18, 2018, 12:21:18 am »
I froze the area first then only U1371 using a frozen Q tip. It is the culprit apparently but I will do more experiments tonight.
Great idea on the Q tip... sounds like you've really got it pin-pointed.

Son of a gun, I replaced U1371, now it doesn't react to the cold anymore but it stays at 14.78V instead of 15V. Before, it would drop to about 14.8 when cold but would stabilise to 14.98V after awhile. Now it is worse. The IC is from Digikey so I don't expect it to be defective. The interesting thing is that the inverting and non inverting inputs are at different levels. The positive input (pin5) is at 10.00V sharp and the negative one (pin 6) is at 9.84V. Shouldn't they be at the same level?
« Last Edit: November 18, 2018, 12:25:50 am by Miti »
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Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1294 on: November 18, 2018, 12:37:44 am »
I froze the area first then only U1371 using a frozen Q tip. It is the culprit apparently but I will do more experiments tonight.
Great idea on the Q tip... sounds like you've really got it pin-pointed.

Son of a gun, I replaced U1371, now it doesn't react to the cold anymore but it stays at 14.78V instead of 15V. Before, it would drop to about 14.8 when cold but would stabilise to 14.98V after awhile. Now it is worse. The IC is from Digikey so I don't expect it to be defective. The interesting thing is that the inverting and non inverting inputs are at different levels. The positive input (pin5) is at 10.00V sharp and the negative one (pin 6) is at 9.84V. Shouldn't they be at the same level?

I would think they should be the same. But the big question is.....did it fix your start up jitter?
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Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1295 on: November 18, 2018, 02:54:19 am »

I would think they should be the same. But the big question is.....did it fix your start up jitter?

Yes it did, but now it stays at the jittery level without jitter. Monday I will install a socket and I'll try few more 324 that I have in my junk box. It cannot have 150mV input voltage offset, something is not right.
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1296 on: November 18, 2018, 04:55:30 am »
Son of a gun, I replaced U1371, now it doesn't react to the cold anymore but it stays at 14.78V instead of 15V. Before, it would drop to about 14.8 when cold but would stabilise to 14.98V after awhile. Now it is worse. The IC is from Digikey so I don't expect it to be defective. The interesting thing is that the inverting and non inverting inputs are at different levels. The positive input (pin5) is at 10.00V sharp and the negative one (pin 6) is at 9.84V. Shouldn't they be at the same level?

If your +15V PS buss is now at 14.78V it is a tiny bit out of spec, it should be between 14.775 and 15.225V with no more than 15mV ripple (check at J119 pin 6). Strange for a 317 not to output something closer to the expected 15V, with the associated circuitry unless something is still amiss. What is the voltage at the 317 reference input?

 

Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1297 on: November 18, 2018, 03:00:06 pm »
Son of a gun, I replaced U1371, now it doesn't react to the cold anymore but it stays at 14.78V instead of 15V. Before, it would drop to about 14.8 when cold but would stabilise to 14.98V after awhile. Now it is worse. The IC is from Digikey so I don't expect it to be defective. The interesting thing is that the inverting and non inverting inputs are at different levels. The positive input (pin5) is at 10.00V sharp and the negative one (pin 6) is at 9.84V. Shouldn't they be at the same level?

If your +15V PS buss is now at 14.78V it is a tiny bit out of spec, it should be between 14.775 and 15.225V with no more than 15mV ripple (check at J119 pin 6). Strange for a 317 not to output something closer to the expected 15V, with the associated circuitry unless something is still amiss. What is the voltage at the 317 reference input?

It is 1.23V below the output and it is where it should be. I don't suspect 317.
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Offline Miti

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1298 on: November 23, 2018, 12:14:20 am »
Done:
- Full refurbishment of A5 board. I replaced the DS1225Y NVRAM with FM18W08 FRAM. No problems whatsoever. I was able to read the contents of my original NVRAM and put them in the FRAM without any problem. The scope boots and works normally.


This is very interesting. Some time ago I bought a Ramtrom FM16W08 from Ebay and it didn't work in my 2445B. Now I bought a Cypress FM16W08 thinking that the one from Ebay was defective but this one doesn't work either. First time after it is programmed in the programmer, it starts normally but after the first power cycle, I get Test 04 Error 10.
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Re: Tektronix 2465B oscilloscope teardown
« Reply #1299 on: November 23, 2018, 03:46:36 am »
Done:
- Full refurbishment of A5 board. I replaced the DS1225Y NVRAM with FM18W08 FRAM. No problems whatsoever. I was able to read the contents of my original NVRAM and put them in the FRAM without any problem. The scope boots and works normally.


This is very interesting. Some time ago I bought a Ramtrom FM16W08 from Ebay and it didn't work in my 2445B. Now I bought a Cypress FM16W08 thinking that the one from Ebay was defective but this one doesn't work either. First time after it is programmed in the programmer, it starts normally but after the first power cycle, I get Test 04 Error 10.

I'm curious what programmer where you using? I am new to all this, never done it before, and will be receiving a FM16W08 from Mouser soon. Already have the new DS1225AD-150 chip but somehow messed up the socket PN so had to reorder it. Already received a new version GQ-4X4 programmer which is already installed with latest SW v10. So after desoldering and hopefully reading my original NVRAM without any issues, and writing the new DS1225, was also planning to try out the FRAM CHIP. Just need to wait for the Aries SOIC to DIP converter board, along with the correct 28-DIP machined socket to arrive. The FRAM and those two last missing bits where supposed to arrive by the end of this week, but thanks to Turkey day in the US the last leg of the shipment was delayed. So looks like the big date where everything will happen is now been postponed for another week.
 


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