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Old 14th Aug 2020, 5:40 am   #21
Diabolical Artificer
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Default Re: Dynamco D7100 restoration

That's good, a gentle clonk or wiggling often does the trick. The Dynamco I had, used tranny bases all over the shop so loose transistors are possible causing intermittant connections so poking the scope with a stick is a valid fault finding tool.

Andy.
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Old 15th Aug 2020, 2:40 pm   #22
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Default Re: Dynamco D7100 restoration

I've now hooked the X & Y modules up and aside from misreading the calibration instructions several times the scope is now working!

I managed to follow the initial calibration procedure and everything seems to be working well, touch wood.

The only things I noticed was that lines on the display weren't wholly parallel but the manual says which trim to adjust for that, also the set cal for the X-axis won't turn enough to get one cycle per division as the manual indicates, I assume this component's value may have drifted and could be replaced.

Thank you again all for your help, I greatly appreciate it!
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Old 25th Aug 2020, 9:14 pm   #23
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Default Re: Dynamco D7100 restoration

I'm back again with another issue, or it could be user error

I'm having trouble getting the scope to lock onto a trace without it jittering about.

As you can see in this video I can't seem to get a sine wave to stay in one place on the display, it's triggering at the right level but the waveform won't stop still. The HF STAB control is set to auto but moving it manually either does nothing or removes the trace from the screen.

Am I operating the scope wrong or is there something up with the timebase?
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Old 25th Aug 2020, 9:51 pm   #24
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Default Re: Dynamco D7100 restoration

Is the input sine wave noise-free?
Try the scope cal output first then pick a 50Hz from a transformer or something non-digital.
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Old 25th Aug 2020, 11:08 pm   #25
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Default Re: Dynamco D7100 restoration

The input sine wave should be pretty noise free as it's from my audio interface however it is digital.

The calibration square wave outputs on the scope work flawlessly, I'll hook the scope up a transformer tomorrow and see if that fairs better.
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Old 26th Aug 2020, 8:01 am   #26
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Default Re: Dynamco D7100 restoration

I plugged my scope into a transformer this morning and it did work, however, at the time/div settings of 2ms or less multiple traces appeared.

I've attached an image with the timebase set to 2ms/div, what was odd is that after switching to some other timebases and back again it started to only show the one trace but at 1ms or less multiple traces showed up again.
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Old 26th Aug 2020, 8:41 am   #27
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Default Re: Dynamco D7100 restoration

That's a lovely phosphor on your scope, a really deep green. The doubling up your seeing can be normal trigger behaviour whilst the trigger tries to latch or isn't quite set right. Also on a lot of scopes triggering at low sweep speeds is problematic. Every scope has its quirks and anomalies, some trigger really well, others don't, not sure how good a Dynamco is supposed to be..


Audacity and a bit of free software called Soundcard Scope both have decent sig gens in them, Try a 1khz sine on the 1ms/div setting, if it doesn't trigger on that it'd be worth investigating into.

Andy.
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Old 26th Aug 2020, 9:23 am   #28
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Default Re: Dynamco D7100 restoration

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Originally Posted by Diabolical Artificer View Post
That's a lovely phosphor on your scope, a really deep green. The doubling up your seeing can be normal trigger behaviour whilst the trigger tries to latch or isn't quite set right. Also on a lot of scopes triggering at low sweep speeds is problematic. Every scope has its quirks and anomalies, some trigger really well, others don't, not sure how good a Dynamco is supposed to be..


Audacity and a bit of free software called Soundcard Scope both have decent sig gens in them, Try a 1khz sine on the 1ms/div setting, if it doesn't trigger on that it'd be worth investigating into.

Andy.
Yes, the phosphor really is a lovely colour. I've just tried the 1kHz sine wave and it triggers at 1ms/div, it's only when I get to 0.1ms/div that it stops triggering well.

In my limited experience with the scope the triggering seems to be a little hit-and-miss but that might just be my own inexperience with oscilloscopes in general. I seem to be able to get it to trigger well most of the time but then when I try and "zoom in" using the time/div it stops working so well and shows multiple overlapping traces.
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Old 26th Aug 2020, 4:38 pm   #29
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Default Re: Dynamco D7100 restoration

If it still behaves like your video on that 50Hz waveform then either the stability control is set too high or the trigger circuit is over sensitive.
I don't have any manual for that scope but on a Solartron 1400 (1443 timebase) the setup was something like:
With no signal set stabilty control to just not run.
With 1kHz signal adjusted to 5 cm height the trig level pot should allow setting at any height along the sine (both positive and negative depending on polarity switch). Any instability can be corrected by adjustment of the internal trigger sensitivity preset.
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Old 27th Aug 2020, 8:10 am   #30
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Default Re: Dynamco D7100 restoration

"Yes, the phosphor really is a lovely colour. I've just tried the 1kHz sine wave and it triggers at 1ms/div, it's only when I get to 0.1ms/div that it stops triggering well" Right, so that means the triggering circuit is working ok, no need to dig into the innards. In my experience what you describe IE the scope not triggering on a faster or slower timebase setting can be normal, every scope is different and it takes a while to learn how to drive it.

That said the only way to discover if your scope can do better and is as per spec is to run through the calibration/check tests. Some scopes have decent step by step procedures, the Dynamco 7200 I had did not if i remember right. Unfortunately the plethora of calibrated test gear needed to properly tweak a scope is daunting, so, with a lot of my analogue scopes it's a case of learning little wrinkles to get round the bits that aren't 100%, much like a lot of vintage motorbikes I've had.

The best thing to do is to use your scope a lot and have a play with the controls, also give any switches a good clean.

Andy.
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Old 27th Aug 2020, 8:50 am   #31
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Default Re: Dynamco D7100 restoration

Always worth following the instructions in the operator's manual to the letter when it comes to triggering although many older scopes struggle with certain signals.

Alan
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Old 27th Aug 2020, 10:12 pm   #32
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Default Re: Dynamco D7100 restoration

In post 22 you referred to the "HF stability" control. The HF stab should be either switched of, or minimum effect if input signals are lower frequency than say 5MHz. I don't have any info on this scope to hand, but that is my understanding from what you wrote. I am assuming you are not referring to a "Stability" control. Not sure I would expect there to be one on a scope of this era.
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Old 27th Aug 2020, 10:34 pm   #33
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Default Re: Dynamco D7100 restoration

Thanks again for the help & advice all.

The manual does have a calibration procedure which I've completed and aside from the trace not quite being parallel to the graticule everything is set up as it should be.

Les, I read in the manual that the HF Stab should be set to auto for low frequencies but it doesn't mention a frequency to enable it at so thank you for the 5MHz ballpark. It mentions it has little effect at low repetition rates but with it making the trace disappear I thought that might be a malfunction.
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Old 28th Aug 2020, 7:42 am   #34
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Default Re: Dynamco D7100 restoration

Show us a pic of the Y amp front panel in detail please, it might help.

Andy.
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Old 28th Aug 2020, 6:24 pm   #35
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Default Re: Dynamco D7100 restoration

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Originally Posted by Diabolical Artificer View Post
Show us a pic of the Y amp front panel in detail please, it might help.

Andy.
I've taken a high-quality pic of the front of the scope here, you should be able to see all the controls and what they do from it.
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