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Hello All

I have a 7704A with 2 x timebase: 7B53 and 7B50

The 7B50 has developed a fault suddenly and the screen is now all lighting as green and cannot see the trace anymore when using this timebase

The led for on the 7B50 still appears to sync with the input signal but the screen of the scope is all lighting green when using that timebase

Swapping the timebases also keeps the fault with the 7B50 which shows this is not a problem with the 7704A chassis itself

I am wondering how to start troubleshooting the 7B50 and whether that fault is a known issue?

Many thanks

Thierry

Yes, both those controls work. The real-time mode still looks weird although now there is only one dot showing during the fall... still should not be any. I'm not going to go chasing that any further since I won't be using a sampler in real-time mode anyway - my other scopes can handle that, and without the risk of blowing the head :)

I played with it a bit more today. First I I threw together a quick TD pulser clocked by a 1 MHz crystal oscillator, and calibrated the sweep on the 0.1 us range using the square wave, then examined the edges after the TD. The waveform is ugly after the ~1 ns edge, but I know lead length and placement are at issue). With pulse inputs I can't go faster on the 3T77A than 20 ns/div equivalent (and using the X10 expander mode i.e. 2 ns/div) because it takes too long for the scope to trigger and display. There's no delay line in the 3S2 and I didn't want to rig one up for now.

Also hooked up my GR 220-920 MHz oscillator to both heads (the S-2 and S-4). It displays sine waves nicely up to about 500 MHz. At 620 MHz the trigger is starting to lose function so the traces get noisy, a bit better with the Smooth switch on, but at 800 MHz it's useless.

Photos in the Sampling with 3S2 album.

Candles of the Regency era were of variable composition, depending on what you were willing to spend. Faraday used whatever was handy to get the job done. He didn’t need to immerse his coils completely in sealants. His goals were modest: Just keep the thing together long enough to finish his experiments. His “Experimental Researches in Electricity” is a fun read, with lots of bits that we might find quaint and charming, but given that there was no electrical parts industry, he naturally improvised with what was at hand. That included gutta-percha, which he discovered was a fantastic insulator — and a thermoplastic one at that — allowing the first undersea telegraph cables to be made (including the first to bridge the Atlantic). It also revolutionized dentistry (where it is still used) and gave us the first non-feather core golf balls.
He was inspired to use silk-covered wire when he learned from his wife that bonnets were stiffened by iron wires around which silk thread was wound (to reduce staining from the iron).
—罢辞尘

You can use 'A' versions of transistors just about all the time. 'A'
versions of semiconductor devices
are almost always selected devices with tighter specifications than the
'non-A' version. 'A's are not a 'newer' versions with different nominal
specifications. If in doubt, consult the datasheet. "A" versions of op
amps, for example, often have much better offset and drift max limits than
their 'non-A' brothers and sisters. Transistor gain, breakdown voltage,
leakage, noise limits are often tighter.

A few oddball cases may exist. For example, the manufacturer needed a
device with specs at the extreme high or low end for a particular parameter
and selected outliers. In this case, the parts list should say "selected".
I haven't encountered a case like this in the flesh; however,such a case
might exist. For example, an abnormally low breakdown voltage might be
desired in an avalanche pulser application.