The cable Tektronix used was cut to a specific length and had a repeatable loss which was suppose to be compensated for by the response of the SG503 to meet its specifications. The loss at higher frequencies that you observed on your oscilloscope was not the cable; it was the response of the oscilloscope which is exactly the type of measurement the SG503 was intended for. The response of the SG503, and its cable, can be verified with a sampling oscilloscope, sampling RF voltmeter, or maybe a thermally based RF power meter. I rebuilt my SG503 many years ago and had to replace one of the 4-bit latches for the display. With a 2 nanosecond RG400 cable, its amplitude flatness was about half of the specification.
on mine ive found that the vains on the HF section of the variable capacitor were touching . Easy fix . Thanks for the extra info and your video. Hmm I wondered why mine keeps stopping .Hay please chance on getting a copy of the cct diagram .
I tried that as mentioned, but the pins were so corroded that the plating was missing in a lot of places, which meant the pins were starting to rust and some pins were actually breaking off. Often a gentle polish will make things nice again (good for switch contacts too), but in this case it was too far gone to save.
@@NearFarMedia Must have been stored / used in a less than ideal location 🤔 BTW, I have a way of saving 'legless' chips that I could show you (if you're interested). It's allowed me to save many an unobtanium (but otherwise functional) IC from meeting the trash can.
I just got this model that came in a tm504 and it isnt booting up either. I get no display and no signal into my tek 465. Ill have to check the oscillator to see if thats my problem. I know the tm504 is fully functional as I swapped plugins and all slots are functional.
I tested the oscillator and I get no waveform on my scope so I'm pretty sure it's dead. Is there an oscillator that I can easily swap in that you recommend?
The crystal in these units is only used for running the display. The actual output frequency doesn't use a discreet oscillator. The service manual for these is pretty good, with schematics, circuit description and waveforms. w140.com/tekwiki/wiki/SG503 First thing to check after checking voltages is that there are no shorted tantalum capacitors (A very common problem with equipment of this age) and no worn out electrolytic capacitors too. Also, try reseating any socketed chips. If there are any Texas Instruments (TI) sockets, they need to be replaced as they are notorious for being absolute and complete rubbish.
The cable Tektronix used was cut to a specific length and had a repeatable loss which was suppose to be compensated for by the response of the SG503 to meet its specifications. The loss at higher frequencies that you observed on your oscilloscope was not the cable; it was the response of the oscilloscope which is exactly the type of measurement the SG503 was intended for. The response of the SG503, and its cable, can be verified with a sampling oscilloscope, sampling RF voltmeter, or maybe a thermally based RF power meter.
I rebuilt my SG503 many years ago and had to replace one of the 4-bit latches for the display. With a 2 nanosecond RG400 cable, its amplitude flatness was about half of the specification.
Excellent work, we all missed you in the past few weeks!
Great video and nice overkill with oscillator!! 👍 Excellent mounting idea for daughter board!
Brilliant work.
Funny, a insrument with a unrivalend stable display control frequenz.
on mine ive found that the vains on the HF section of the variable capacitor were touching . Easy fix . Thanks for the extra info and your video. Hmm I wondered why mine keeps stopping .Hay please chance on getting a copy of the cct diagram .
OXCO! Of course you did that 😂 nice to see another fun video
I got a few more OCXO projects still to come too! 😁
Nice project. Thank you.
The black stuff on the pins isn't terrible, it's only silver oxide. Just burnish them with an ink eraser to 'pretty them up'. 😉
I tried that as mentioned, but the pins were so corroded that the plating was missing in a lot of places, which meant the pins were starting to rust and some pins were actually breaking off.
Often a gentle polish will make things nice again (good for switch contacts too), but in this case it was too far gone to save.
@@NearFarMedia Must have been stored / used in a less than ideal location 🤔
BTW, I have a way of saving 'legless' chips that I could show you (if you're interested).
It's allowed me to save many an unobtanium (but otherwise functional) IC from meeting the trash can.
good video!!
I just got this model that came in a tm504 and it isnt booting up either. I get no display and no signal into my tek 465. Ill have to check the oscillator to see if thats my problem. I know the tm504 is fully functional as I swapped plugins and all slots are functional.
I tested the oscillator and I get no waveform on my scope so I'm pretty sure it's dead. Is there an oscillator that I can easily swap in that you recommend?
The crystal in these units is only used for running the display. The actual output frequency doesn't use a discreet oscillator.
The service manual for these is pretty good, with schematics, circuit description and waveforms.
w140.com/tekwiki/wiki/SG503
First thing to check after checking voltages is that there are no shorted tantalum capacitors (A very common problem with equipment of this age) and no worn out electrolytic capacitors too.
Also, try reseating any socketed chips. If there are any Texas Instruments (TI) sockets, they need to be replaced as they are notorious for being absolute and complete rubbish.
Also, this link may provide some help too:
w140.com/tekwiki/wiki/SG503/Repairs
What is the part number of that divider IC?
It's a 74HC390, but almost any 74**390 would work. (The center letters define what 7400 series variant the chip is).
@@NearFarMedia thanks