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Problem child Tek 475A. It's had multiple issues and the last time I attempted to do compensation of the attenuators I pretty much gave up getting it calibrated properly. The attenuators are typically aligned with a 1kHz signal. Turns out the real issue is with the high frequency response. It has considerable peaking. So it's going to take a complete alignment of the Vertical Pre-amp and possibly the Final Vertical Amplifier. The manual is quite extensive and it's going to take hours. I'll post up the results.
Typical 10MHz square wave from the Heath IG-4244 Scope Calibrator. Channel 2 is worse than Channel 1.
What it should look like.
The 475A has a B/W of 250MHz vs the 2465 B/W of 300MHz so I would not expect it to fully resolve the ringing on the trailing edge of the square wave which is a normal artifact of the IG-4244 at high frequencies.
An old gray beard with an attitude. I don't bite.....sometimes
Finally got some time and inclination to start the 10 page calibration of the vertical pre-amp/amp. Everything was going good until I started channel 1 gain adjustments. It was way low and couldn't get it anywhere near spec. If I pressed with the screwdriver or my finger on R165 (10mV gain) the trace would jump significantly to almost correct level. So either the pot is open or possibly a cold solder joint. If it's the trimmer pot I probably have one in my parts stash. But either way the vertical pre-amp board has to come out. Oh joy. But at least on this 475A it's mostly modular with few connections to be unsoldered. But not today. I just lost interest.
Last edited by MED6753 on Thu Mar 21, 2024 11:33 pm, edited 1 time in total.
An old gray beard with an attitude. I don't bite.....sometimes
tggzzz wrote: ↑Thu Mar 21, 2024 9:27 pm
If you mean the Petolta cheap/small coax connectors, then they do feel fragile. But I've never broken one.
Yes. I'd forgotten the name. I've always been aware than it wouldn't take much to damage one, although I haven't had a problem yet. I recall I did bend the wire once and had to straighten it.
I have a 465 parts mule where some of them are well and truly mangled.
The other slight annoyance I've found with Tek 475s are the TO-8?? heatsinks on hybrids which can be missing and I couldn't find a source for, apart from parts mules.
These are the joys of messing with 40+ year old scopes which were leading edge in their day, and even today are pretty good, if they are working.
I've had to completely strip a couple of these - never damaged the coax connectors at all. They are surprisingly strong. The delay line is where it gets horrible.
As for the heatsinks, yes they appear to be difficult to find. I did have a few around a few years back.
Well done. I have a 465 which I am going to have to remove the vertical preamp board from and deal with, plus another from a parts mule, which may be substituted. Inspired by your fine example, I'll stop finding excuses not to tackle it.
Zenith wrote: ↑Mon Mar 25, 2024 9:58 pm
Well done. I have a 465 which I am going to have to remove the vertical preamp board from and deal with, plus another from a parts mule, which may be substituted. Inspired by your fine example, I'll stop finding excuses not to tackle it.
As I recall the 465 vertical pre-amp board is a much more difficult removal process. The 465B is more modular like the 475A.
An old gray beard with an attitude. I don't bite.....sometimes
But at least on this 475A it's mostly modular with few connections to be unsoldered. But not today. I just lost interest. 
