Author Topic: Keithley TF-245 Replacement Options? (K2000 models)  (Read 3606 times)

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Offline nidlaX

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Keithley TF-245 Replacement Options? (K2000 models)
« on: October 12, 2015, 03:01:53 am »
I'm in the process of repairing a Keithley 2000, 94/95 vintage, and I suspect that the TF-245 resistor network might be out of spec. This is preemptive, but I am wondering what solutions people have come up with to replace said resistor network? I heard from this thread that newer 2000 revisions use a different circuit instead of TF-245, but page 2 of that thread is still broken.
 

Online TiN

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #1 on: October 12, 2015, 04:34:23 am »
I measured my TF245 before, here are results, also with other owner's measurement data.
You could replace broken resistors with stable standalone resistors, or perhaps order new TF245 from Keithley or resellers..
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Offline nidlaX

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #2 on: October 12, 2015, 05:08:41 am »
I measured my TF245 before, here are results, also with other owner's measurement data.
You could replace broken resistors with stable standalone resistors, or perhaps order new TF245 from Keithley or resellers..
I saw that TiN, thanks so much for all of your documentation! It's been one of my best resources for this repair, especially with the references to other people's repair logs.

Do you know what parts the newer K2000s use for the resistor network? I see some blurry pictures on 38hot, but nothing with part numbers or a circuit.
 

Online TiN

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #3 on: October 12, 2015, 10:00:40 am »
Could not be possible without people contributing, I cannot have all the meters in the world :)

Newer 2000's using BI Model 668 5K array, Tracking TCR 5ppm/K and few other foil networks:

Photo from 38hot BBS

You can try bodge fixed resistors on top of TF instead of broken ones to see if that fixes issues, and if it is, then you can think of investing more money into more stable resistors.
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Offline nidlaX

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #4 on: October 14, 2015, 11:32:42 am »
Could not be possible without people contributing, I cannot have all the meters in the world :)

Newer 2000's using BI Model 668 5K array, Tracking TCR 5ppm/K and few other foil networks:

Photo from 38hot BBS

You can try bodge fixed resistors on top of TF instead of broken ones to see if that fixes issues, and if it is, then you can think of investing more money into more stable resistors.
Thanks. I actually see a lot of random suppliers who list a 16 pin TF-245 part for sale in large quantities.
 

Online TiN

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #5 on: October 14, 2015, 11:35:12 am »
Most I think are fake nonstock , taken from google search requests :-)
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Offline nidlaX

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #6 on: October 17, 2015, 03:07:48 am »
I put 6.4K in parallel with 9-6 1K (which measures ~1.19K in circuit) and my 304.1 and 200.2 passed, so I suspect TF-245 will need replacement.

Next step is debugging amps circuit and 100.1 / 100.2. I'm not sure if those are related, but I'll start with the dead amps signal and hope for the best.
 

Offline nidlaX

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #7 on: October 19, 2015, 10:29:51 am »
Does anyone have any good leads on sourcing these TF-245s? costas' original supplier no longer has them in stock, and the prices I'm getting from other sources are a bit exorbitant. It just leaves a sour taste in my mouth knowing that I'm installing an out of production part with a high failure rate.

The other option I'm considering is making a small adapter board for extant resistor networks to solder in place of TF-245, but I'm worried that performance will suffer.

Update: Pricing from Keithley Tektronix USA is reasonable, $17 for the TF-245 with a $30 minimum order. Not sure if these are new (probably not) or old stock, but as of today they had around 20 units left.
« Last Edit: October 19, 2015, 09:01:07 pm by nidlaX »
 

Offline pigrew

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Re: Keithley TF-245 Replacement Options? (K2000 models)
« Reply #8 on: January 07, 2019, 03:46:11 pm »
Prices have gone up to $20 each, with a 13 week lead time if not in stock. I'm about to order two (to meet the minimum order).
 


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