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.
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 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
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
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.
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
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.
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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.
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.
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?
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.
CHASING THE ILLUSIVE MILLIVOLT & NANOSECOND – PART II
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Letting the scope automatically measure the 462 MHz frequency via. the red HELP button, indicated 474.7 MHz, which is 2.3% high.
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Great - let us all know how it goes! The Aries adapters are good quality.
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.
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?
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?
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?
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.
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.