Author Topic: Tek 744A - Buying  (Read 2470 times)

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Offline Mukrakiish

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Tek 744A - Buying
« on: June 02, 2017, 08:57:38 pm »
So, I have the opportunity to get a Tek 744A that looks to be in very nice shape, powers up all that jazz...but unknown performance. Given that there is a big bag of probes/accessories and at least 1 HV Differential probe in the bag (worth $500+?)...the thing is, I already have a Rigol 1054z and a Tek 7300 sitting my house. The Tek 7300 needs some repair (minor) and the Rigol is new. I'm still an up and coming learning hobbyist...but I do know decently high end equipment when I see it. It's not that I NEED it...but it's a 500mhz scope for <$400 w/ high end probes...

The question is, is that worth taking a stab at? If I got it for a song (<$400) even if I don't have much use for it, I could probably resell it or even just sell the Differential probe to make up for if the scope ends up being unusable. I don't have enough experience with older 'scopes to know if this is worth the gamble. The price is right but...again, "cat in a bag".

Thoughts?  :-//
 

Online nctnico

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Re: Tek 744A - Buying
« Reply #1 on: June 02, 2017, 09:08:46 pm »
Check if the copyright says 1995 or later and whether there are no failures listed in the startup screen. Chances are it doesn't suffer from the capacitor plague if it says 1995 or later. With some effort it can be uphacked to a TDS784 which doubles the samplerate and increases the bandwidth to 1GHz. The downside is that it needs to be recalibrated for 1GHz. Unfortunately there are some non-volatile memories in these scopes which are way past their lifespan. Also the display can be a weak point. It is an old piece of equipment but I still regret selling the one I used to own.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline james_s

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Re: Tek 744A - Buying
« Reply #2 on: June 02, 2017, 09:15:49 pm »
I have a TDS784C that I absolutely love, it's a beast of a scope but if you have the space it's a great instrument. I'm a big fan of the very novel NuColor display they use.

If it's 400 bucks and comes with a bunch of accessories then that's a heck of a deal, but only if you actually have a use for it. If you already have all the scopes you need why not let someone else buy it? Don't become a test equipment hoarder.
 

Online ebclr

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Re: Tek 744A - Buying
« Reply #3 on: June 02, 2017, 10:10:29 pm »
If they come with all the probes, only the probes is worth that, But you told you already have 2 scopes in your case I would make some questions for myself

Do I really need that extra bandwidth?

What kind of  applications that I really need to have this scope that my other 2 scopes does not fit

Am I prepared to be a scope repair guy, and parts hunter?

Do I have space for this monster?

For sure this is a powerful scope on his time, But age is something that must be considered. If you have no reason or application for that power,  simply postpone the order and buy only when you really needed.

Always remember there is no free lunch, you have  access to this bandwidth for this price for a reason

 
 
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Online nctnico

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Re: Tek 744A - Buying
« Reply #4 on: June 02, 2017, 10:15:09 pm »
Compared to other options to get 500MHz (or even 1GHz) bandwidth for a rock bottom price the TDS600 & TDS700 series are very light weight and compact. Not too noisy too due to the huge fan (specially produced for Tektronix) or temperature controlled fan.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline james_s

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Re: Tek 744A - Buying
« Reply #5 on: June 02, 2017, 10:40:31 pm »
The price to performance ratio is indeed hard to beat, as I said I absolutely love mine, but if you don't need the bandwidth and already have other scopes it's harder to justify something that big and bulky. It's also not an instrument I'd recommend to someone who is afraid to tinker. On mine I had to replace all of the relays on the attenuator hybrids, not a horrible job but it was tedious and required considerable care not to damage the hybrids. The displays are also a bit of a weak point, the optical gel between the CRT and shutter panel can develop bubbles which are a real pain to correct, and the tube is run rather hard to compensate for the losses in the system. Older models are full of SMD electrolytic capacitors that leak and damage the boards, fixable but it can be a big job. Also parts are difficult to find and expensive, usually it's cheapest to buy a second scope for parts. Still, a 500MHz 4 channel scope with a color screen, even though new scopes in that class are much cheaper than these were when new, they're still far from cheap!
 

Offline eKretz

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Re: Tek 744A - Buying
« Reply #6 on: June 02, 2017, 11:25:24 pm »
I have a couple of these as well, a TDS784A and a TDS784D (both converted from 754s). I love mine, but as stated they can sometimes be a little work to get going. My 'D' needs the attenuator relays replaced - it's failing SPC when warmed up. And yes they do take up some space, good thing I have a big bench, heh.
 

Offline snoopy

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Re: Tek 744A - Buying
« Reply #7 on: June 03, 2017, 01:28:25 am »
These are excellent scopes and with Instavu switched on I managed to clock up a 390,000 waveforms per second aquisition rate just as the claimed in the spec sheet !! I have a working 784A and a 744A waiting for repair. These scopes are notorious for the relay contacts in the attenuator boards going high or open circuit. There are 4 relays in each attenuator board that need replacing. Otherwise where are you going to get a 500MHz scope with 250Gs/s repetitive sample rate for $400 ??
 

Offline Mukrakiish

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Re: Tek 744A - Buying
« Reply #8 on: June 03, 2017, 01:40:30 am »
Thanks for chiming in all of you, it's good to have a bit of "clear thinking" from folks who have been around longer than I have with this type of equipment. My bench is already pretty full between the scope, generator, parts, parts, more parts and the PSU.

Perhaps it might be best to leave it as is since I don't have any experience with circuits that would get into the 500 Mhz range (despite how cool it would be to have such). That and it's size...would mean I lose precious bench space.

But hey, if anyone in Canada is interested...it's up for grabs ;)
 

Offline snoopy

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Re: Tek 744A - Buying
« Reply #9 on: June 03, 2017, 02:02:19 am »
What probes does it come with ?
 

Offline Mukrakiish

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Re: Tek 744A - Buying
« Reply #10 on: June 03, 2017, 02:12:37 am »
Not sure, it's a Surplus sale so it's a bit of a mystery...

It has at least 4 probes + an Agilent HV Differential. N27 family is all I can get out of the photo. Basically the original "bag" of components it comes with plus a drawer full of more probes.







 

Online Jwalling

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Re: Tek 744A - Buying
« Reply #11 on: June 03, 2017, 09:47:15 am »
Unfortunately there are some non-volatile memories in these scopes which are way past their lifespan.

There are, but only one of them is unobtanium - the DS1486. I think they will last much longer than what they were rated at (10 years)
The reason? https://www.eevblog.com/forum/repair/tds-684c-nvram-backup/msg1173983/#msg1173983
Jay

System error. Strike any user to continue.
 

Offline andy2000

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Re: Tek 744A - Buying
« Reply #12 on: June 03, 2017, 08:53:30 pm »
The DS1486 does hold the options, but it's not too hard to re-enable those if you need to.  The calibration is stored in a pair of EEPROMs on the acquisition board, so that's not a concern (unlike the TDS500 series).  Having said that, I just bought a TDS544A, and it's DS1650 from 1993 still has its contents after almost 25 years. 

I would personally take the TDS744A over the Rigol 1054z, but the Tek will probably require some work sooner or later.  The CRT looks good in that picture.  The TDA744A doesn't have an problems with SMD caps, but there could be some leaking caps in the power supply, or on the monitor board.  I had to replace some in my TDS784D when I noticed a fishy smell coming from the fan exhaust. 
 


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