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| Keithley 2000+2015 THD |
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| muvideo:
I didnt find info, it seem a resistor network, could it be purpose built (or simply marked) just for keithley? Do they sell spares, or you are forced to go to a repair centre? Maybe the cost from keithley is not too high. Fabio. P.S. I didnt forgot about the roms :) |
| costas:
--- Quote from: muvideo on October 06, 2012, 05:52:07 pm ---I didnt find info, it seem a resistor network, could it be purpose built (or simply marked) just for keithley? Do they sell spares, or you are forced to go to a repair centre? Maybe the cost from keithley is not too high. Fabio. P.S. I didnt forgot about the roms :) --- End quote --- Hello Fabio , Unfortunately I have none of recommended possibilities Last Monday I sent out PCB's , probably next couple weeks will get it WBR Costas |
| costas:
Today I started very determined to try again solving TF245 problem, I desolder again good IC and did all the measurements possible with ohmmeter. its internal schema I do hope is correct and complete although I did not see any logic in the resistance arrangement, maybe someone has seen such a network of resistance and find an equivalent. Compared with a good IC , I found resistances 9K and 1k interrupted from terminal 9 and resistance of 27.5 k of pins 10-12. ExperimentaI l soldered the respective IC pins external resistance 0.4w 5% 1k, 9.1k, 27k, then I ran the checking test and surprise all errors are gone (Before running up test should expect to better cool the area where I did tinning) Course is only a makeshift solution using ordinary low precision resistance. .. the idea would be to find an equivalent for TF245 , but …after my schematics I do not think is possible WBR Costas |
| muvideo:
Pins 6,7,8,9 seem a voltage divider with 1:10:100 ratio. As for 1->4 13->16 are that measured values or how you imagine the resistors connected inside? I think that there are many possible arrangements for inner resistors for that part of the network. Also, are you sure you are measuring resistances only and not some semi junctions around? You can test some of the values at different voltages to see if the current is proportional to voltage to be sure. Fabio. |
| costas:
TF245A's scheme represents measurements performed by me between IC pins and no resistance positions, I made another set of measurements (scheme "C") between pin 16 – common - and pin 1, 2, 3, 4, 15, 14.13. Comparing measurements the scheme "A" and the scheme of "C" resulting scheme "B" that corresponds to the positions and value of the resistance . If somebody have a different opinion please tell us . WBR Costas |
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