Try to find 070-6863-01 which is newer, preferably the searchable version.
Ok dried the board for a while and popped in temporary elco subs for the removed leaky caps so I could take some measurements around the DAC. Please see attached image with schematic of the DAC input resistor network. All voltages in red taken with a HP974A DMM. I have not checked yet any of the resistor values, which I assume cannot be checked in-circuit anyhow.
Not sure if anyone has records of what the correct voltages should be around these nodes so as to compare and try to figure out which ones are probably bad without having to pull one by one to test them. For me once a SMD part out it will probably stay out and a new replacement will go in instead. So i rather will try to keep as many as possible of the undisturbed originals and try to deduce which might be bad with these voltage measurements.
The +1.36V out at the + side of C2420 only measures a mere +0.25V or so (all measurements where a bit jumpy and dance around 0.1-0.2V). Likewise the -1.25V output has only 0.23V (at pin 13 of IC2420).
Anyone out there that has done these same measurements on a good scope?
So I build a simulation of the resistor divider of the DAC input with 5% resistors on a protoboard so I could make some voltage reading comparisons. I am assuming that the two DAC reference inputs are high impedance and do not account for much if any change on the actual resulting voltages (please correct me if I am wrong on this). I also adjusted the 10V input voltage to match the 9.988V actually seen on the scope, and adjusted the wiper of the 20K trimmer to match 5.51V as seen on the scope as well. The results are on the attached picture.
The total series resistance of this network measured roughly about 38~39K (I left out the 15uF C2010 capacitor on purpose to be able to measure this resistance). I measured about 268uA current flowing through the divider, which I calculated taking the voltage across the 1K R2016 resistor, the upper leg of the divider, which is 9.988v - 9.72v = 268mV / 1K = 268uA. Again, these are 5% resistors, so readings will be slightly off here and there, but should definitively be good enough for a general comparison.
Now going back to my original readings on the scope (I re-posted the picture showing those readings as well), the voltage difference on the 1K R2016 resistor is only 9.988-9.926 = 62mV, which if I assume the 1K resistor is still within its value, there are only 62uA of current flowing into the resistor network. Way too low. This I would think would mean that one or more resistors have gone high (or open). My first suspect would be R2012 10K, as the voltage on pin 15 of the DAC (-Ref) is more than twice as high as expected, and this resistor is the lower leg of the voltage divider. Then again, maybe R2013 has gone high (or open), as the +Ref voltage is about 2.25v low compared to my simulation.
I could try to further tweak my breadboard simulation to see if I can find a combination that would arrive at the actual voltages read on the scope. That would of course only be practical if one assumes that only one or maybe two resistors have sustained damage, but given that more than two might be bad, it might be a futile exercise.
Time now for a break, get some Zzzzs.... its almost 4am.
@AMR Labs
Wouldn't you just measure a few of your 5% resistors on hand to find some that fall within a 1% tolerance and use those ?
My 2465B bought in 2011 had 292 on hours & and on/off counter at 349, I guess that depends on previous owner usage, but yours look pretty low count, assuming its not tampered.
My 2465B bought in 2011 had 292 on hours & and on/off counter at 349, I guess that depends on previous owner usage, but yours look pretty low count, assuming its not tampered.
I guess that must be the scope that started this thread? I saw you also got lucky that the front cover and a storage pouch where included, mine came with those as well, but no probes. Very hard to get those accessories included nowadays on a low or even mid priced 2465x on ebay, specially the front cover. I have seen these sold separately for $100, just for the cover. And you also have a TEK made U800. In what serial number group is yours? Mine is 55xxx and most chips inside have a 1990 date code, including the NVRAM. From the inscriptions and labels on the front cover and on one side, this might have been a field unit that was not really taken out that much, and who knows maybe even less once the problems created by the leaky caps started to show up. The inside is almost pristine, very little dust only in a few places, if any at all. No signs of anyone tampering inside either.
Actually that kind of socket fits the DS1225 poorly, at least the ones I have, but the pins on the converter (standard pin headers) fits very well. They may damage the socket because of sharp edges but I don't plan on removing it again so no problem. The same is true for machined sockets I believe.
Yes the 2467B is nice, but since they are in great demand prices are through the roof, compared to the 2465B. Lots of people looking to get one, but waiting for the right/fair price.
I agree the front cover is very important to have, more so to get it with the scope in the first place, and yes definitively makes it easier to rest the scope on its face upside down to safely remove the back panel. I was even feeling a bit apprehensive of buying a scope like this without the front cover, as it is a very effective layer of protection against bent/broken controls due to shoddy packaging or in-transit mishandling. More than a few horror stories out there of mangled front panels.
Was going back to page one and looking at your pictures of the scope, very nice indeed. Which reminds me, at some point I will probably have to check on the power supply caps, and wrestle with those two boards to get them out.
BTW looking at you options sticker in the back, mine is a bit different, and the only option marked on this one is numbered 46, which I still have not been able to figure out what it is. Do you (or anyone ) know what option 46 is for? Asked before but no answers, so give it another try.
So from the origin of your scope I assume you are located on the other side of the "pond". Bet you never thought about this thread lasting so many years.
I normally wouldn't clutter a technical thread with such stuff, but since this is the definitive 2465 thread, I'll mention I've posted a probe pouch and a front cover over in the buy/sell forum:
https://www.eevblog.com/forum/buysellwanted/fs-(canada)-tek-2465-2467-front-cover-and-probe-pouch/
Good deal on getting your DAC issues straightened out. And yes, recapping the Regulator and Inverter boards should be next on the agenda. You can follow my post back in July on getting those boards out with minimal hassle.
Edit, starts at reply 1091.
Already have 2 probe pouches and while I'd really like to have a front cover for my 2465 I think $76 USD plus shipping is a little (no, a lot) too much. (And yes, I understand they are rare and sell at a premium which is why mine will remain naked)
Good deal on getting your DAC issues straightened out. And yes, recapping the Regulator and Inverter boards should be next on the agenda. You can follow my post back in July on getting those boards out with minimal hassle.
Edit, starts at reply 1091.
Thanks for the heads up Med, will certainly take a look at it! The traces seem a bit fuzzy under certain conditions, specially while using the 10x horizontal magnification, and most probably recapping the PS might help cleaning up the traces. On the other hand, it really helps using the 20MHz BW limit, it makes the traces much sharper. That tells me there must be HF noise probably creeping in through the power supply.
Here is a pic of the scope still triggering on a 800.000MHz signal, even tough at this point the trace looks quite fuzzy due to the vertical input amp gain running way out of bandwidth (the input signal was 400mV). The automatic counter would only read up to 650MHz. But in general the counter doesn't seem to be very accurate, always seems to be off by 10% or so. Even with an accurate 10MHz signal the 2465B was showing a counter best reading at something like 10.173 MHz. I guess that is what that 2465B C/T option is all about to tighten up the counter accuracy. My 2247A was effortless counting the same signal as 10.000071MHz (yes the scope counter calibration is actually off by about 71Hz), and counter is good and stable to about 300-350MHz.
BTW the traces look much brighter on this picture than they actually where, was trying to avoid using a flash, so the camera opened way up. Nowhere near what looks like CRT melting levels.
Already have 2 probe pouches and while I'd really like to have a front cover for my 2465 I think $76 USD plus shipping is a little (no, a lot) too much. (And yes, I understand they are rare and sell at a premium which is why mine will remain naked)
Not too long ago a 2465B cover (new style with the indentation) sold on ebay for a cool 100 bucks plus shipping from the Philippines. But it took quite some time to sell. Supply and demand market, unfortunately. I was looking for these for some time anticipating my future scope would not have it, and not even one other ever came up. I'm glad I actually got lucky, makes me think the scope alone actually sold for a mere $110, plus the cover (and a pouch).
Was going back to page one and looking at your pictures of the scope, very nice indeed. Which reminds me, at some point I will probably have to check on the power supply caps, and wrestle with those two boards to get them out.
BTW looking at you options sticker in the back, mine is a bit different, and the only option marked on this one is numbered 46, which I still have not been able to figure out what it is. Do you (or anyone ) know what option 46 is for? Asked before but no answers, so give it another try.
So from the origin of your scope I assume you are located on the other side of the "pond". Bet you never thought about this thread lasting so many years.
Does your 2465B have the Counter/Trigger option? If yes and you don't have the equipment as per the manual to calibrate it I have an alternate procedure that came from an old gray bread on the Yahoo Tek group that is simple and will get it dead nuts.
Does your 2465B have the Counter/Trigger option? If yes and you don't have the equipment as per the manual to calibrate it I have an alternate procedure that came from an old gray bread on the Yahoo Tek group that is simple and will get it dead nuts.
I would be interested to see it if you don't mind sharing.