Electronics > Repair

EG&G princeton 5210 lock in amplifier repair (almost repaired, frq offset)

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coppercone2:
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 pins

I 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 binned

Does 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 pcb


should 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.

coppercone2:
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 amnesia

doing 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.

Kleinstein:
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.

coppercone2:
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-wing

When 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 to

1) Press green key - green light turns on
2) Press key that does whatever I want, including the frequency setting keys that are normally velocity controlled - nothing happens
3) press green key, whatever I did in step 2 occurs now


So 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 only  :scared:

Makes 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

Kleinstein:
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.

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