EG&G princeton 5210 lock in amplifier repair (almost repaired, frq offset) - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2021, 09:10:28 pm
content: Ok So I had a working 5210 lock in amplifier that came in off ebay, but when I opened it up I saw a gigantic capacitor leak. Like 4 square inches of PCB were covered with some kind of shit that flowed out of it, and it would not come off with a q-tip and alcohol, so I had to wash the whole thing in simple green after total disassembly. There were several chips that seem corroded but I did not replace anything but the capacitor because it was working before cleaning. The stuff leaked out on the chassis too. I am not sure I guess its also possible something spilled on the capacitor since there is a vent hole above it, but anyway it looks corrosive on the IC pinsI undid every single header, ribbon cable, pin, socketed chip and cleaned it carefully with alcohol after 24 hours of drying, and I replaced the capacitor (470uF) with a identical value. The header connectors near the capacitor were the most corroded.When I try to power it back on, the digital meters read full scale and the front panel is unresponsive. If I connect a power circuit to where the backup battery used to be (it was dead, but I cut it off prior to cleaning), its just as unresponsive but a bunch of front panel lights light up, its built like a sony stereo which I fucking hate working on, so I suspect it might get binnedDoes anyone have a manual for this thing? I have no idea what I did, maybe I should not have touched the socketed chips.I found a random 5V rail on the logic and it seems OK.How do I troubleshoot this? I have a logic analyzer and DIP clips, I thought a start might be to look at the processor to find a clock signal or something like that? Anyone have experience fixing princeton lock in amps? The displays sometimes miss a segment and sometimes the analog display is pinned to a random low value (1 out of scale of 10, but usually at 0). Does anyone have any ideas on which chips to start on? Particularly verifying if the EEPROM is intact because I know if that goes off I am fucked. I thought maybe a bond wire fractured when I was removing them, but I used a real IC extractor on it.I am mega pissed off because if I just ignored the giant white pool and did not spend 3 days cleaning it, I would have had a working unit. fuck my ocd, but I can't help it since it looked like a horse splooged on the pcbshould I replace the corroded chips? try to figure out what the processor is doing? I figure it must have only been surface damage and I damaged something with ESD or mechanically (i did wear a wrist strap and used a real electronics dip puller tho and set the chips on a esd mat and used a wooden chair).the leader chip looks like a mc68008 and the usual associates. when I unplug the big gang switch and the floating shield can from the PCB, it has no change, so I assume its something with the big square board on the bottom.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2021, 02:42:54 am
content: might be related to moisture, after 20 min in the oven I got 2 keys to work. maybe i underestimated the PCB, the guidelines are long, it able to tell and remember the GPIB and Serial port settings, maybe its not suffering from amnesiadoing an aggressive 2 hour bake cycle at 170F because thats the lowest the oven will go. the first time I opened it after 30 min it certainly seemed to let out some humidity. Maybe there is water trapped some where.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 17, 2021, 06:49:57 am
content: A larger amount of water can be a problem, but especially the digital part should not be effected if the board is otherwise clean. Humidity can be a problem if there is still quite some residue from a leaking capacitor or batterie that should be cleaned. For cleaning the residue of leaking part alcohol is not very effective - plenty of water is usually the better way. Alcohol is only the last step, helping to remove the water residues.Humidity, but also alcohol absorbed in the PCB can cause indirect effects from swelling and baord stress, effecting contacts and maybe poor solder joints.Given the age of the instrument I would look for drop shaped tantalum caps - they are prone to failure, sometimes catastrophic if at a powerful supply.I have no manual, but some 25 years ago I had a look at it, and it even included schematics, at least for some parts, so one could fix a flaw with the DAC ouputs, but this is nothing to worry right now.First the CPU part should be working before worrying about the analog readings.EPROMs are usual not sensitive to mechanical stress, if they come in the classic ceramic case. So no worries on the bond wires. It is more that if used at high temperature they may start loosing there contend.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2021, 07:28:07 am
content: Ok I got it working kinda, the dial indicator melted but this is whats going on (fucking stupid oven, oh well). I had it setup in a weird angle in the oven but when I left it like decided to slide over and touch the side wall of the oven. Maybe I will find a big mirrored analog gauge on a flip down bracket from some simpson or something there one day if Iget it working. like the targeting system in the x-wingWhen I turn it on, I need to press the Green function key then the other key then the green function key again to change anything. When it was working normally I could use the button to select voltage range, filter setting, so forth. Now I need to1) Press green key - green light turns on2) Press key that does whatever I want, including the frequency setting keys that are normally velocity controlled - nothing happens3) press green key, whatever I did in step 2 occurs nowSo its basically unusable. I checked all the keys for continuity (I thought one of them was shorting, but the buttons all make a multimeter peep). The local/remote switch disables the front panel but it does not make the LED next to it go off. Interestingly the 'red' shift key (like the green shift key) works, so it can do an 'auto' measurement. Setting the oscillator, offset, amplitude, etc.. is a fucking game now. Guess at how long to hold the button, feel like im playing some stupid boxing game on a NES. It seems that every key works, you just need to play games with the green key (labeled control)I took all the keys off and tried to squirt deoxit on the little plastic they put on to act as a key, so my bad, at least they gave you push buttons, but anyway I don't think its a mechanical issue, I tested continuity on every key to make sure its not shorted out, don't think I really got water in that place. I wish you can desolder the buttons but it looks like careful reflow on plastic onlyMakes me think of some kind of interrupt or something. That the green key is making something check some kind of register whereas it should normally check that automatically. But I can't just push the green key after pushing the button, I need to 'prime' it by pushing the green key and then push the button then push the green key to send it through. wtf is this behavior. like the green key is substituting some refreshing clock? something with shift registers? I also did try shorting it manually with some probes to see if maybe the button is misbehaving with like bounce but the ones that work, work, and the ones that don't, have no difference.You think its still something with caps causing this weird ass issue? any idea what the green shift key is associated with? its something with some kinda scan I think, there has got to be a missing periodic waveform I think.. it seems like an odd way to build a keypad, you would think everything there would cause a interrupt, why is it enabled and 'read' with the green key now? I feel like if I put a high frequency square wave as the input to the green key and disconnected the LED light it would essentially be fixed lol, but I hope there is a better way to fix it then to rig a 555 timer in there

author: Kleinstein
author_rank: Super Contributor
timestamp: May 17, 2021, 11:08:31 am
content: The describtion on the green botton is weired. I remember that there was a green key, but not what it was good for. It is quite a complicated Instuments with quite some functions, so working keys would be nice.There are quite a lot of things that can go wrong with the computer part and it is hard to tell from the symptoms what is wrong.I would not expect the keys to cause an interrupt. A keymatrix is usually scanned to a regular time and this signal should be measurable at the keys. There may be something like a missing pull up, that could cause floating pins and this way effects, like the need to "Prime" with the green key.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2021, 12:49:14 pm
content: so like some how when you push the green key you are getting current into something by accident to charge gates?the green key is like a shift button on a computer, some stuff is dual use so you press the green key and then press it and its supposed to do the alternative function. I.e. there is a setting button for display #2 that its green key function is the instrument lights.So if you do the greenkey + pushbutton + greenkey methodyou get1) setting 12) setting 23) setting 34) setting+ no lights (turns off lights, not sure if its 3 or 4)5) setting 4 + turns lights back on6) setting 57) setting 1so when you get to selection #4 it fights between turning the lights off and getting to setting #4normally when you push the button its supposed to change settings, and when you greenkey the button its supposed to trigger the light on/off. but they are merged now. so you think the master key is not causing the CPU to do anything with the program, its just keeping the circuits running by some kind of unwanted effect on current paths? I am not quite able to imagine the circuit you are talking about where the greenkey some how helps pull up other things in a matrix, but I don't work with this kind of stuff usually.Do you think there will be a scan signal (pulse signal) going to the keypad on the ribbon cable that I should look for?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 17, 2021, 04:43:35 pm
content: With some 20 bottons going to the computer, I would expect them to use a kind of key matrix, though one knever knows and there are alternative ways.The number of lines on the ribon cable could give a hint.The PCB for the front should also give a hint on how the keys are connected.Nomally there should be a scan signal, though there is also a way to first check for any key and only than check which key by a scan. So I would expect a periodic scan signal, but not sure.Fighting with 2 functions may be something like a short between lines.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2021, 07:09:48 pm
content: Ok I tried to probe aroundIt seems every signal in the 40 pin connector is either logic high or logic low outside of what looks to be some spikes that are hard to trigger on (logic high line spiking low every 600uS), maybe this is it? I can't freeze on it so I am not sure if its variable duty cycle or what, I can just measure it with the redicule while its flashing in an out of existence.When I hold down the green button I see like a really high duty cycle square wave show up on some pins, around 99% duty cycle, probing the top if the IEC connector, wheras normally these pins are logic lowdon't really know how to proceed, areas near the clock are buzzing with activity

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2021, 12:20:43 am
content: Bought new socketed stuffP8254-2 (hope its drop in for P8254.. not sure what the -2 and -5 do). does this have to be programmed?MC68008P8TC5565P-15MC68681Pand I will replace (think I have these in parts boxes, will find out today), they have signs of corrosioncd74hct00sn74hc03nlm339nThe system is complicated so I will spend a couple of dollars to see if there are drop in replacements that work to possibly fix the problem, because when I see corroded parts in a broken system and have to trouble shoot it, its driving me fucking crazy, hopefully those intel parts will be fun to play with at least, because for a while I was thinking about doing a discrete system with a zilog or other discrete CPU, so I can tolerate the likely spare partswhen I do that and it still does not work I think I have a doomsday stockpile of tantalums that can pretty much do the whole unit, and i reckon that this is itthen when its still not working I can take out the logic analyzer and operate it with some semblence of sanity, since I have a floppy drive for my VNA and alot of DIP clips I can upload big logic communications plots with 128 inputs (pay off the old logic analyzer), if anything having no corrosion will facilitate the use of dip clips for trouble free telemetry

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2021, 03:40:33 am
content: Hmm I did the 74 series logic gate and there is a significant amount of corrosion underneath the chip despite the extended bath. I wonder if a clock signal was being pulled to ground some where, but unfortunatly I installed it backwards and will rework it tomorrow, the unit failed to power on but no smoke etc, hopefully its not damaged because it was my last oneI think I should replace everything that was bathed in the white gooI feel like I can probobly replace a good deal of these chips for small sums of money

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2021, 04:33:41 am
content: reworked the chip because it was bothering me, looks like its not broken and the device is in the same state it was, but there is another nasty chip under neath and a few near by, I will order them on digikeyIf I spliced in a logic analyzer to all 40 pins and posted a logic diagram, would that help someone trouble shoot my issue?

author: ebastler
author_rank: Super Contributor
timestamp: May 18, 2021, 05:38:38 am
content: This thread in another forum supposedly has a user manual (and some other "high level information" in the following post). I am not a registered user there, hence could not download the attached files, but it might be worth registering?https://www.electronicspoint.com/forums/threads/eg-g-5210-lock-in-amplifier.291898/#post-1790845

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2021, 05:47:00 am
content: I have both of those documents but they don't get into the discrete TTL based logic in these thingssearch for manual (its on a japanese site) and for technical notes (its on their website or one of their parent companies)they just give you a overhead of the circuit but this is pretty specific user interface bug that probobly comes down to a single bad gate inside of somethingbefore I started I did the 'verify your equipment is good using the internal generator routing into the input" thing and it worked fine.this is more a thread on how to trouble shoot discrete gate/processor control boards then the lock in circuits, which I think should be fine. It's something really stupid because I can use the instrument if I wrangle with the green shift key. I have a feeling its either gonna be blind luck, a circuit trace or a logic analyzer investigationI just got a male-female 40 pin cable so I can splice in the logic analyzer to the ribbon cable because right now its ridiculous to trouble shoot the way its built. The most similar thing I have seen is like non archaic but old wavetek units. its probobly built like that

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2021, 06:08:19 am
content: https://www.ameteksi.com/-/media/ameteksi/download_links/documentations/supportcenter/signalrecovery/instruction_manuals/18978-a-mnl-a.pdf?la=enThis is a manual for like a earlier version but it looks like the same stuff is going on the front for switchesmaybe someone can notice something, they were kind enough to give a schematicpage 119 shows what they use for their switch matrix, maybe that will be the most helpful, but there is no shift keyI am trying to think of what the shift key must do, it looks strait forward in that schematic.119 goes to BD2 on page 117, which goes into a 74LS245, which goes into a MC68488. I think I want to put a tap on that equivalent circuit if I can find it on the other pcb.Am I correct in thinking that the 68488 is locked up and not accepting the inputs from bd2345 unless the shift key is pushed first for some reason and that I should try to trace out that signal chain? So see what those traces are doing once I find them when the button is not pushed, after its pushed, and after the buttons are pressed after its been pushed and what happens when its been pushed again, but the 5410 should have the MC68681P in place of the 68488, which is a interface adapter, reciever transmitter sounds like the same thing as a interface adapter with different lingofrom the looks of the schematics, the types of parts they use, and so on, i am guessing the company migrates about as fast a lichen between designs, they usually try to drop in stuff that does the same thing in their mind, thats what I always see, the same paths just with different materialsBTW does anyone know anything about the P8254-2 part? The PCB just says P8254, the seller I buy from says 2/5, but the marking is 2. What the heck is this ?

author: capt bullshot
author_rank: Super Contributor
timestamp: May 18, 2021, 07:28:17 am
content: These are speed grades:nothing: 8MHz-5: 5MHz-2: 10MHzhttps://www.scs.stanford.edu/10wi-cs140/pintos/specs/8254.pdf

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2021, 07:35:31 am
content: ok, I read the datasheet. I see what is going on now.Too many little details. I got the correct part. I wanna keep things moving along without getting stuck with another disassembled instrumentThis is a non eeprom chip right? i assume its programmed on power up every time, I don't see any mention of memory in the datasheetThis chip or one of the other peripherals might be a good way to see what the system is doing since I can see how its getting programmed on LA.I also thought to setup a EEPROM dump. I have a data generator and a logic analyzer so I think I can write the program to a floppy. Or maybe I think the pickit does it so I can read it with that and save it.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 18, 2021, 08:11:58 am
content: The 8254 has no internal EPROM or similar. So it is just programmed by the main CPU for use and a simple replacement with a new chip is possible.The 68488 IO chip should control the GPIB interface and the MC68681 should be be for RS232. Both may also be used for some additional smaller tasks - maybe the keys.I would no worry so much about the corrosion products shortening a clock - these are usually relatively low impedance. The more tricky part may be 74LS... chips, that us an open input to be logic H. This was sometimes used in the old days to safe a resistor.

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2021, 01:13:34 am
content: One more observation,1) the velocity control still works, once I prime it, I can hold the button down for a while, then trigger it, and it will offset whatever thing I want on channel 1 proportional to the key hold duration. Longer = faster, so acceleration works.Channel 1 shows the correct thing, I can adjust reference level, oscillator, phase, so forth. I can display the input but since I melted the panel meter I don't know if they track2) Channel 2 display shows off scale +1.99, the only way I can get it to display anything else is to use shift + gpib or shift + rs232 to get like the port information printed.I also verified that undoing every single connection, apart from the keypad ribbon cable, has no effect on the unit. I can disconnect all the shielded floating cans, etc, without a noticeable control system change.3) Channel 2 has the up/down buttons to adjust offset. So in channel 1, if I select a function, then use the velocity keys, I can adjust frequency. I think on channel 2 if I have 'offset' high lighted, I should be able to change the offset in the same way. But, it is pinned on +1.99, no matter which setting I have it in, other then the 'print GPIB or rs232 channel' setting. So this means that the fault is related to here, since there is partial lack of function.The manual also calls the shift key a 'dual key' functionAnd possibly evidence of damage, the light bulb that got hit by a stray which the circuit detective missed:the local remote switch does not cause a light change when it is activated. It has a LED on it that is totally dead, but the key works. This might relate to the god damn thought you had about some kind of bias impedance being incorrect. I have a feeling this might be a very good place to start a diagnostic. The LED is going to be the highest power consuming device there, and it shows sign of a bad driver, unless the LED is broken. I will measure this guy. Maybe there is a low voltage/current limit that is preventing the LED from turning on

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2021, 02:21:38 am
content: I traced the IC to a HC377 flip flop on the front panel, and a resistor network. The resistor network seems intact. The flip flop is going right to the ribbon connectors.I need to figure out this flip flop, is it possible for a working flip flop to light neither of the LEDs up? I assume yes, since there is an option to disable all lights on the front panel, with the shift key, and it works. This function works. Since those 2 lights refuse to light up, it can either be a signal not reaching the flip flop, or a broken flip flop that is ignoring the signal, or not carrying it out.But I am not getting this: how do you disable the lights with a flip flop? It should be stuck on either of them, right? So if its an octal flip flop, this must mean that its just being used as a buffer, not as a hard switch, right, so 1 flip flop circuit per LED rather then 1 flip flop sub circuit per 2 leds, which would leave one LED on unconditionally, but it would not be able to disable front panel lights. ?I am being confused because the previous model uses a latch, but this uses a flip flop. why, they are similar. Maybe its less overhead since it uses a pulse. That would explain why the shift key does something, it must be causing the flip flops (there are multiple) to flip.So being that they are flip flops, and the shift key is causing them to flip for some reason, a defective flip flop on the output should not effect the rest of the flip flops, unless its a issue related to input impedance and fanout? Most likely a circuit controlling the whole shebang is the issue, not the end flip flop, so the particular flip flop I found is just closer signal wise to a damaged PCB region (imagining a area that has a damage gradient across it with multiple signal paths), and maybe its being triggered my coincidental inrush spikes, from the shift key for whatever reason that happens to cause electromagnetic radiation, maybe the fact that there are green and red LEDs that are triggered that have a different voltage threshold then the yellow leds or possibly a higher current (they do seem alot brighter then the yellows) are emping it and making it shift? (controller is dead, carnosaur is in the control room smashing its tail across a panel every time someone is trying to key the radio? (carnosaur 2 analogy))I will put soic clips on the flip flop to see what its doing

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2021, 05:27:54 am
content: Any idea what the operating temp on those IC's is? Some of the bigger chips run hot, the eeprom is cool, the hottest chips are the two interface adapters, one of them is 126F, the other 115F. Well within normal semiconductor operating parameters but it stands out super hard on the PCBThe hottest chip is the TSM9901. It says its an interface adapter that provides interrupts to the CPU. I think that is the main contender for whats controlling the input to those flip flops. I wonder if it has a reason for being so hot?

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2021, 05:36:17 am
content: looks like its fixed, god damn chip logic interface bent its leg over and it looked like it was fully inserted after I resocketed and cleaned the goo. fully responsive. oh well useless chips inbound from ebay, the unusually hot running temp made me investigate it. now its responsive but I need to put this back togetherUsually the legs slide off to the side, but this one curled up under neath the chip and made it look from a sideways inspection that it went into the socket unless you get really close, I only noticed after I turned it upside down, its the one right near the back of the chassis with a wire over it.at least I have replacements I guess, and its a step above to make a system without just reaching for a PIC one of these years$46 down the drain but oh well. Might be worth while to replace that chip anyway because its been running a leg short for quite a few troubleshooting minutes, perhaps it will benefit from replacements... at least I got rid of most of the corrosion too, could have been a time bomb

author: Kleinstein
author_rank: Super Contributor
timestamp: May 19, 2021, 06:38:41 am
content: Some of the old inteface chips run quite hot (old N-MOS versions - not all are avialable as a lower power CMOS version). 74F... need quite some power too and thus run quite hot.

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2021, 07:44:57 am
content: Yeah I usually see high temp near high speed clocks, I know when I saw the high speed 74 series logic run at really high speed, it was running pretty hot, but I also noticed sometimes when I replace old 74 series chips, they run cooler, I think it has something to do with aging or maybe manufacturer (I keep track of HC, LS, etc, don't mix)Do you have modern version of the same HC/LS/etc chip that uses different transistors with the same parameters? So you can have say a NMOS HC and a CMOS HC? I saw a big ~30F drop in temperature once in a spectrum analyzer repair when if I recall I replaced a working chip with the same exact chip name type (I thought it was broke, and it cooled down, but all signals were the same). I think it was a multiplier? maybe. I thought it was just thermal aging but maybe they improved the process some how. I also see it alot when I replace old discrete transistors (sometimes just replace 5-6 transistors near a broken one just to be safe), they often run significantly cooler.

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2021, 08:04:30 am
content: So the only thing I need is unfortunately a replacement for a 2900 0105 panel meter, which unfortunately warped from the heat due to the oven mishap.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 19, 2021, 01:21:29 pm
content: One can not directly mix 74LS or similar (BJT based) with normal CMOS based (e.g. 74HC). The output H level of 74 LS and simlilar is only marginal for the CMOS inputs. So one would need 74HCT or similar to work with the smaller input signal (or a signal coming from a 3.3 V domain).The current demand of the logic series is quite different. 74LS , 74S, 74F and similar are BJT based and also use quite some power if the frequency is low, with the faster ones using more power. The modern CMOS versions like 74 HC, AC, AHC or similar use very little power at low frequency, but can be similar or in some cases even higher power at there maximum speed.NMOS was used for some of the IO chips, AFAIK there is no standard NMOS logic series, only BJT based or CMOS. It is the P8254 or MC68681 where there may be a lower power alternative. I have not checked if the origianals are NMOS or already CMOS. The other point may be changing 74F... to ACT or similar. With different levels at the ouputs they can still behave different and the timing is also slightly different. I would not really bother.

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2021, 09:11:25 pm
content: Damnit, I found another problem. Maybe its because I pulled the battery. When I set the frequency the actual frequency is off. The internal measurement is fine, but the set point is off by the axis.I set for 10KHz, the output is like 8.3KHz, measured on both the oscilloscope and the internal measurement to match. at 125khz its output is 121 khzAny ideas?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 20, 2021, 06:33:34 am
content: AFAIR the internal generator is still a more classic analog fequency generator and not stabilized by a PLL or a DDS generator as one might expect for a computer controlled instrument. So some tolerance for the frequency is normal, though some 15% is a bit on the high side.I also remember some differences and what caused more problems for me some drift in the frequency - but this is a different story.I would not expect an accuracy of better than some 1% for the set frequency - if critical the read back should be used.It may be some capacitors / resistors drifted out of tolerance. PS type caps may have suffered at high temperature.Chances are there are multiple ranges with different caps to set the frequency. So it would need a measurment at more frequencies and than maybe changing / adding capacitors for the worst effected ranges.There may have been a correction table for the frequencies, that was lost with the battery. With the internal frequency measurement (relativ to the crystal) the instrument in principle would be able to rebuild such a table.It may be worth to also check the amplitude - a detuned wien bridge can also show a wrong amplitude and increased distortion, as the range for loop gain adjustment is limited. I don't remember what type of generator is used. It could be a XR2206 as well.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 12:17:02 pm
content: Well I don't think it got over hot, I just forgot acrylic has a low temp (thought it was good to like 100c), the oven is pretty new, but I suppose its possible, I don't think its because it slid, I think its because the acrylic is the lowest temperature stable material in there. The setpoint amplitude is a little off but I need to sit down and get data across the range to see what it looks like because I am just guessing values. That bridge is probably sensitive too so the capacitor ratings might be considerably lower, + age.I did not really play with it too much prior to cleaning and drying because I thought maybe the capacitor leaked more during shipping and I was scared of damaging the circuit more with like electrolysis. the big problem is the damn construction of this thing, I am not sure where to look for that circuit so I might have to remove big PCB's and build some kind of scafolding to run the circuit when its open + have cable extensions. I do not have a good method to clean or dry or do anything with gigantic PCBs like this, usually they have reasonably small cards. I read its considerably worse to work on then other lock in amps.Thankfully the unit does auto-tune and adjusts everything, so it does not really matter, you just need to set it with an oscilloscope if you want a precise frequency, it seems the filters adjust correctly and so forth, but maybe their off also. But I would consider it in bad shape with all the cleaning I had to do, and the price was low.BTW what the fuck is the stuff in the capacitor, or maybe from the vent, that starts bubbling when you put simple green on it? It was literary slowly fizzing. I never seen that before. It really got under my skin. I never saw simple green fizz before. I know lock in amps are used for weird stuff, and those guys seem to sell alot of chemistry equipment, I wonder if someone spilled some weird shit on it. Usually I have the weird stuff happens with chemistry related electronics, they are alwayssuper fubar. Like any equipment thats not only for hard core analytic expenisve chemistry is usually super chowdered. From what I have seen chemistry lab technicians/researchers are not my people, everything is crusty. The BNC connectors on this were in worse shape then stuff from the 60's.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 20, 2021, 01:36:28 pm
content: AFAIR in the auto tune mode he fitlers are tuned to the measured frequency. This is usually OK, but can lead to the filters changing when the frequency drifts and thus can give a small jump in the gain and phase. This was may bad experience with the fitler auto tune part.Polystyrene caps are also quite temperature sensitive and also alcohol from cleaning can damage them. 100 C may already cause some change to the capacitors.There are really 2 possible reasons for the frequency beeing off: it could be the capacitor drift or missing correction constants. In theory the computer could measure the needed constant for an correction and thus with relatively low effort get a reasonable accurate (e.g. 0.5%) direct frequency setting. Maybe measure the actual frequencies, and write them to a list at the instrument - so one knows to set 12k if one wants 10 kHz.It may be interesting to look at the specs to see how accurate the frequency is supposed to be. This could give a hint if they rely on accurate caps or on digital corrections. With better than 1% accuracy I would strongly suspect a digital correction.It is not that common to by hand set the frequency and than use it in a critical way. With control from the PC one can use a frequency measurement and itarative adjustment to get closer, or include correction factors in the PC program.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 01:47:14 pm
content: the value is 2% for frq accuracyI know it did not get to 100C because I touched the chassis real quick near the closet part of the oven walls and it was hot but not 100c hot, I don't think it got too much over 75. I will set the oven right now and measure what temp it gets to after 30 minutes with a graphing temperature logger that uses a thermocouple (fluke 289). I should have done this before but the goo and washing made me generally insane, i started to wonder what the hell they were doing with it. I think it might be external because I was trying to detail the meter and there seems to be alot of crud on both sides of the chassis, not just the bottom, some kinda white shit. Alot came off with alcohol but it needs to be buffed with compound (I will try mequires #8 and a polish) to look decent. Prior to alcohol on the external chassis I did a soak for 20 minutes with goo-gone spray, a heavy scrub with a scotch brite pad with simple green and hot water, then heavy scrubbing with kim wipes dipped in pure IPA. I got it to a point right now that I feel like it won't fuck up my foam buffing pad with heavy loading when I really mechanically clean and deoxidize the plastic coat on the chassis (if you know how to get a show car finish, thats how you can do painted/plastic/epoxy covered metal panels looking non disgusting).PCB cleaning/baking order:The white stuff btw, after simple green, turns alcohol soluble. My initial attempt was to use just alcohol on q tips, and it failed, so I dumped concentrate simple green on it, let it bubble, poured hot water on it to warm it up, then more simple green, then some mild scrubbing with a nylon ESD brush in my stainless steel sink with water spray, then alot of hot water, then alcohol from a spray bottle after it drip dried for a while, then the power on fail after a 24 hour air dry in an open chassis then the short bake then the longer bake after resocketing incorrectly (the longer bake deformed the acrylic meter), then the resocket/bent lead fix, corroded chip rework and deoxit 100% liquid concentrate. It may have been functional after the short bake, but I guess thats when I resocketed the chip with the bent lead. Each time I went to clean it I found more goo.The oven was set to 170F at all times. First bake was 20 min the 2nd bake was 2 hours. But AFTER all that, when I was replacing chips, I desoldered some chips and the 'weakened' goo under the corroded chips was cleanable with a q-tip and alcohol, where it was not really cleanable before the wash/bake process.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 20, 2021, 02:07:29 pm
content: 2% frequency accuracy could be be just accurate caps - I would expect digital correction to work better than 1%.Lock in amplifiers are used quite a bit with optics in combination with a photodiode and a machnical chopper for the light.The 5210 was already quite a good one for it's time and it may be used for advanced parts too, especially with scanning different frequencies and looking at the response.I don't see much use in a chemistry lab, but it is very flexible so there may be some uses too.The simple green cleaner may be accid. Leaking batteries ( alkaline and NiCd) give some NaOH or KOH that over time can capture CO2 from the air and form some kind of soda. This would than react with acid to form bubbles. Here lots of water would probably do more than alcohol. For leaking alkaline batteries it does not need a chemistry lab.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 02:22:07 pm
content: ph is 8.5 to 9.5 for the cleaner I useI am doing the bake cycle now with a fluke 52 because I ended up ordering a new probe for the 289, the old one is MIA, so I can just give min max and averageI put the probe in the middle of the oven wrapped around the grate a little. It should facilitate baking also. I did replace this oven last year and it does not have much hours put on it because I bought a sous vide at the same time, which greatly reduced oven use.. only major use was thanks giving and some pizzas, its a good induction LG stove..When I was playing with the amplifier I noticed one segment on display #1 was malfunctioning by a single segment, so I think replacing those chips in order when they come in. I think its also possible a damaged chip is giving bogus values to the DAC.Does it do digital correction? I only see a feedback used to adjust the filter, I don't think the feedback is used to adjust the oscillator also?

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 02:42:38 pm
content: damn, it looks like the oven is around 188 degrees after 20 min and the peak was 193 when set to 170F.that is near glass transistor temperature for polystyrene. maybe it was there for too long. that is 85 degrees C.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 03:15:49 pm
content: Frequency vs measured,0.5 0.5 01 1.04 42 1.78 -115 4.69 -6.210 9.55 -4.520 16.86 -15.740 35.2 -1280 72 -10100 90.4 -9.6160 145 -9.375270 235 -12.962962963510 458 -10.1960784314900 821 -8.77777777781200 1100 -8.33333333331700 1566 -7.88235294122300 1942 -15.56521739133500 3030 -13.42857142865700 5030 -11.75438596498600 7670 -10.813953488411000 9840 -10.545454545515000 13470 -10.220000 17650 -11.7530000 27200 -9.333333333340000 36700 -8.2555000 51000 -7.272727272770000 65200 -6.857142857185000 79300 -6.7058823529100000 93300 -6.7110000 102600 -6.7272727273120000 111900 -6.75Set/measured/errorWhen I took reading on an oscilloscope it was all +-10mV of 1V on all settings, depending on the time/div (rigol 1052e)after 1 hour oven is 195F, but I did run it on a cooler day at night, maybe it was better. It was actually 1.5 hour bake, turn off for 15 min, then partially open door for 15 min, then fully open door for 15 min then 1 hour with the shelf extended for like an hour, I wanted to not shock it thermally.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 03:50:24 pm
content: So I have a feeling if I find every foil capacitor in there and replace it, it has a good chance of going back to normal?the panel meter might still work if I put new cover and needle.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 04:09:22 pm
content: if I use heat sink clips and fast extraction with a pace solder extractor, it should be possible to desolder it with little harmful effect I think? then measure

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 04:19:57 pm
content: there was also a peice of paper taped in there, with a bunch ofParameter #1 =-37, and so forth, to parameter 65=5. Don't know what it is. It was taped to a shield can.at 1 hr 30 min the over peaked to 210F, the average over the test duration was 173F (1hr 30 min), but when I was doing it I opened the door to the oven more then a few times to check on it, and to get rid of humidity (the first time I opened it I thought I felt the air being humid so I kept doing it every 15 min or so), and I noticed when you do that it drops a bit, so I don't think it ever got much past 195F. This oven has a small fan btw, to circulate the air, its always turned on, the speed varies with mode (high RPM for 'quick bake' mode).I did notice however, in the SRS530, which may be similar, they only used 3 polystyrene capacitors in the whole thing. most of is stacked metal film (I assume polypropylene), polyester and mica. The 'stacked metal films' are all rated to 85C. I assume they are ok.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 20, 2021, 06:12:40 pm
content: I would not heat torture the instrument any more. This is doing more harm than good. It may cause the EPROMs to loose the contents faster than normal.Most of the film caps should be OP with a short time at close to 90 C. It is mainly PS and maybe PP caps that can suffer from relatively low temperatures.PS caps may also be damaged / effected from alcohol - though this may be in parts reversible with the heating.After the heat treatment it may take some weeks for some parts to get back to equilibrium humidity. So some drift for the next few weeks would no be such a surprose.Besides the oscillator the filter section is also frequency dependent and may have similar errors, that may be corrected digitally. AFAIR the filters where on an extra board, so should be relatively easy to identify. One can measuren the filter response by setting the filter to a manual fixed frequency and than sweep the frequency via PC control. It may be woth checking if the filter frequency is OK. This may be more important than the oscillator, as the auto tune function likely depends on the filter frequency to be reasonable close to nominal. With so many caps in the filter I would definitely expect some digital correction to set the correct filter.There is an older thread on this lockin:https://www.eevblog.com/forum/metrology/lock-in-amplifier-built-in-oscillator-adjustment-model-5210-egg-princeton-etc/msg1358016/#msg1358016

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 06:39:36 pm
content: do you think the filter would be in the shielded board or the non shielded board? It has a shielded board with the input ( I assume LNA), then a shielded board with banana connectors going under it, then a non shielded board. I figure its the big shielded board, it looked kind of like how a wavetek adjustable filter looks like inside. Or the filter might be along side of the LNA in the sideways shielded board (bastard to get into).The signal out comes from either the floating shielded board or the board underneath. Anyway before prying into it I will try to install a GPIB or rs232 card into the lab computer and see if I can connect to it.What do you mean by sweeping the frequency from a computer after I manually set the frequency of the filter?I thought maybe I can test the filter by setting the oscillator to loop into the lock in circuit then doing an auto tune and shifting the frequency of the filter and keeping track of the response to see if there is an area where the autotune is inaccurate and that manually adjusting the frequency helps in an obvious way with the correct readout from the PSD. I can move the filter up and down by some percent then do an autophase and see if the response improves to the response that is wanted to see if the filter has some kind of similar error.sounds like I should re-run the numbers after a week to see what it does and if its stabilizing.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 20, 2021, 07:29:11 pm
content: AFAIR the instrument has a monitor output - a very nice feature. So one can look at quite some internal signals. So one could just set the fitler fixed and just send an external signal to the input and look at the moinitor signal - so just check the amplifier and filter part.Looping back the oscillator to the input was what I had in mind. So the lockin would measure it own oscillator and filter. For the test I would keep the filter fixed and change the frequency, not keep the frequency fixed and chang the filter. Different filter settings may show different errors. There is no need to redo the autophase - just the the response with phase.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 08:42:00 pm
content: the notch filter is there. adjusting for maximum cancellation should tell the most right? it also bypasses any phase shift, since the signal is simply not there to begin with, so you don't worry about phase through the filter. then i can directly adjust the filter to test its sweepif i recall the notch topology is somewhat temperamental ($$ distortion meter) so it should be a good health indicator. i don't mean the line, i mean the adjustable notch.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 20, 2021, 10:17:53 pm
content: The notch filters for mains are fixed and much less prone to drift. One should test them, but this is a different point. Here looking for the point of best cancelation makes sense.I don't remember an adjustable notch - at least there is not really that much use for it. I agree that a notch can be quite sensitive to detuning.The point would be the adjustable bandpass filter used for the signal to remove the response to higher harmonics. These are adjusted via the computer and if this is no working right (like with the oscillator), it could be a problem. If there are digital corrections involved there is a chance for such a malfunction.For the tests it may make sense to get the PC interface working, so the PC could record the test curves. There are quite a few possible fitler settings and thus many frequenices to test. A test for a single filter setting may need some 20 oscillator frequencies to test.

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2021, 10:52:53 pm
content: no, this has a adjustable notch filter for offending frequencies but you can put it on the signal output frequency if you want for 0 output, it must be in the same place as the band pass notchthen another notch filter thats fixed at mains and mainsx2you select tunable bp, lp, notch or nothing (flat). when you switch between them the frequency you adjusted stays constant (same DAC). When I am cycling through it with the filter set at the frequency I am operating on, output goes very low. You can set the notch at the same frequency you can set the BP filter.then you select if you want a mains notch and/or a rectified mains notchif you put the adjustable notch at 60 and then the mains notch on, you have a super notch i guess if you are dealing with some crazy fieldsso if you automeasure, it sets up the filter, then you change the filter type to notch, the output goes to 0. i assume the 60Hz filter will also block the input signal if you set the output of the generator to 60Hz but I have not tried that one yet, it seemed to have no effect on measurement, maybe because I am using a good HP cable and the output voltage is high.flat changes the demodulator type though, so I don't think you can expect the same result from the flat and bandpass even if the bandpass is tuned correctly ( the error should be proportional to distortion of the oscillator)

author: coppercone2
author_rank: Super Contributor
timestamp: May 21, 2021, 06:01:30 am
content: I left it in the instrument storage area, I want to leave it for 2-3 weeks before I look at it again so it has a chance to possibly stabilize. I might get GPIB and RS232 with working stuff working on the computer by that point, and find the cables. The bake must have done something to it since its at least 30 years old.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 21, 2021, 07:17:46 am
content: I did not remember that the adjustable filter was slectable between LP, HP , BP and notch. I only used the BP and already with a working instrument the setting of the BP center frequencies was not super accurate. Unless one has a really bad signal with lots of hum there is not that much need for the notches. The instrument can live with quite some hum, unless one usus the reduced dynamic reserve mode for highest stability. However if one neede this more, one would also not want the drift from the filters. So low dynamic reserve and notch (or a close tuned fitler) does not make much sense.It definitely makes sense to get the PC interface working, even of only the RS232, which should be reasonable easy for the hardware side (USB to RS232 adaters are plenty and cheap). Frequency scans many make sense with a PC, and also recording the data is often nice. For most uses the RS232 should be fast enough.

author: coppercone2
author_rank: Super Contributor
timestamp: May 21, 2021, 08:20:12 am
content: before I put it away I did this1) try to compare the optimum frequency for LP, HP, Notch 0 to off2) When the input is connected to reference, the auto-scale for HP gives an error (say 37% for a 33% signal, or 4% full scale difference for 50Khz). The "flat" setting gives like 33% exactly.3) if I switch to notch, and adjust to empirically for 0, then switch to HP, the HP is the same as flat. (33% at 48Khz, with 46Khz measured, and 50Khz set)5) noticed the 2nd display when the notch is set to 0 (aka HP is set to 48KHz, notch is just used to 'zero it') has a offset (x/y%) that is significant, so if you set the frq of the filter to get 33% reading, the display #2 has a offset, and the manual seems to say the offset should be small in this case, it goes from like 1.1 to 17 (not 1.7,17)5) noticed when you adjust the LP to get 33% (as measured by oscilloscope, which is accurate to reference amplitude), the frequency is differentSo for like a 50Khz signal, the autotune finds 46KHz, the filter output matches the flat if you set it to 48KHz, so the rule of thumb is, if you ignore the 2nd display, for the 'correct' signal amplitude, you do setpoint - (setpoint - auto measure). That gets you real close. But I don't know if its correct because of the 2nd display. When you do auto measure, despite the amplitude error, the 2nd display is very close to 0.not sure what is more accurate. I assume if its just a coaxial cable going back into the instrument it should not by 17. Not sure if it has something to do with impedance, since its a 900 ohm line to 1 meg, is this causing something with display #2?. Hmm maybe I forgot to autophase it after doing the manual frequency adjustment to 48Khz from 46Khz after the automeasure. I think I did.How do I communicate with this thing once I get the interface hardware set up? I only ever did putty with RS232 but thats not much better then using the front panel.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 21, 2021, 10:04:38 am
content: The most common case to use the filter is the bandpass. So when using autotune the bandpass should be reasonably hitting the frequency and after that the setting with bandpass and flat should be rather close for a sine input. This should be for both the 1st and 2nd display, thus amplitude and phase (or X and Y).To check position of the filter manually, I would used the amplitude and phase mode for the display. start with a frequency in the middele of a band (e.g. 5 kHz). Initially use auto tune (but only one - keep the filter frequeny fixed after that) and than manually change the frequency up and down to find the points wiht 70% of the amplitude. Ideally these shoul be about symmetric around the starting frequency.Communication with the Instrument could be with Putty or similar to just send the results to a file. For more special use one would need a compilter / interpreter to write a program. This could be something like Python (I prefer a compilter to find the simple errors up front) or C or Pascal. How the comunication with RS232 works depends on the language and maybe even the compiler / OS. This are usually relatively short programs, e.g. to do a frequency scan and send the results to a text file. Much of the program would be the same for different type of measurement.

author: coppercone2
author_rank: Super Contributor
timestamp: May 21, 2021, 02:50:24 pm
content: you think it will be a symmetric plot with a 4 th order function? I suppose they did a good job, but for some reason I think it might be lop sided by designi wonder if the filter topology they used is tunable with potentiometers

author: Kleinstein
author_rank: Super Contributor
timestamp: May 21, 2021, 04:56:24 pm
content: If I remember right they used an awful lot of CMOS switches (e.g. 4066 or the like) to combine resistors and switch capacitors for the decades.Chances are the filters are a kind of state variable filter that can be switched relatively easy between different modes.I don't think there would be trimmers for the adjustment, maybe pairs of capacitors to get reasonable good accuracy there instead of high accuracy caps. I would not expect very high resolution for the filter frequency setting and normal resistor accuracy could be sufficient. The actual filters (or at least the decades) may be measured and than the computer decides which setting would fit. This may need quite some cal constants that may have been lost with the battery. Possibly lost cal factors are a reason to do the test.I remember that the bandpass was not very narrow - the main reason is to suppress higher harminics and far off interference / noise. A narrow filter would have quite some effect on the phase and is thus not good.

author: coppercone2
author_rank: Super Contributor
timestamp: May 21, 2021, 05:19:12 pm
content: oh they went with state variable, i thought they might have used continuous time filters of some kind in this kind of application. i have no experience with those, I always went for continuous time ones. I do suppose it would be around 2-3 times taller of an instrument if they had continuous time decade filters

author: Kleinstein
author_rank: Super Contributor
timestamp: May 21, 2021, 06:24:42 pm
content: The filters are contineous time and not switched capacitors. The state vaiable filter type is just the use of multiple integrators with OPs instead of the 1 OP multiple feedback or sallen key form of active filter. The state variable type filter uses some 3 or 4 OPs and has easy switching between LP, HP and BP and sometimes also notch. Because it is so universal it is popular with switched capacitors, but it can also be used with resistors.

author: coppercone2
author_rank: Super Contributor
timestamp: May 21, 2021, 07:32:28 pm
content: oh I found it, like the TI tunable filter chip, UAF42 something

author: coppercone2
author_rank: Super Contributor
timestamp: May 28, 2021, 07:08:47 pm
content: I found a scrap of paper I scribbled on because I am looking for a collet like crazy,I thinkwritten before this whole 'cleaning' started, the frequency error was present BEFORE i started anything, i.e. out of the box day of receiving from ebay. *not 100% sure, its a haze unfortunatelyI think I assumed that there was a counter module inside and that it would be trivial to trim it and then I forgot about it, so I was almost certain the output was correct and the readout was wrong, and I think I got confused with the dim LED which setting is readout and which setting is setting.This must be why I got a spectacular deal on ebay on the instrument. (20% of usual price it seems)If its not thermal related, what do you think it can be? I thought to maybe try to characterize the DAC in the system since its socketed.I don't see any change in frequency when it rested for a while now, and I got a frequency change of 1hz by pressing hard on the PCB some where.I am kind of thinking this: maybe corrosive crystal growth shifted a trimmer.Why would minor mechanical pressure on a PCB shift a output digit? I think maybe that is a sign of a cracked potentiometer or something like this. Or it could be natural strain error, I have seen a thermometer RTD that shifted digits when you squeezed it a little.but anyway,I also replaced most of the digital socketed IC's related to the CPU, so I don't think its a problem with the high speed main logic (other then I got ripped off 10$ on a broken processor on ebay lol)I will still hook it up to the PC to characterize it after it humidors a little longer to be sure (it is in 50-60% RH enviroment right now), but I am thinking, maybe.. I just need to trim the DAC, there is a potentiometer next to it. A little worried about touching it but I feel like it might be related to all the offsets.I am thinking to measure the output with either a thermal AC voltmeter or a 34401A in AC mode, rather then to use the scope, to see how linear that is.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 28, 2021, 09:03:04 pm
content: For the set frequency, there is still a chance that some software corrections are applied that are lost. 2 % accuracy is not easy to get from capacitors and with a CPU already in the system it would be easy to correct numerically. I would not expect 1 pot to fix the scale factors for different ranges.The lockin system with digital switches can be quite linear also for small fractions of the range. I would not expect much non-linearity - the ADC may not be the very best however.Trimmers can drift for several reasons, like oxidation, chemical interactions or just natrural aging of plastics / the conductive layer. Still the frequency error is large and nothing be come from normal level drift of a pot.

author: coppercone2
author_rank: Super Contributor
timestamp: May 28, 2021, 11:40:20 pm
content: looking over the chassis that has been really deeply cleaned right now, after its been sitting for I guess 1 week, there are two circular stains near the top vent. They are too big to be D cells, I noticed it when I was checking the demodulator accuracy based on the reference (seems to have the biggest error of 6% near 10KHz with error decreasing as it goes to lower or higher frequency). Like someone put 2 coke cans on top still in a 6 pack thing, I can see the outline of the rings under the crappy basement lighting on my new repair bench.I think maybe someone put a beaker or something on it and it spilled in there. or maybe it bubbled over.going to see if i can make their serial cable