Maybe a little off topic, but I have been contemplating buying a cheap (<$150) portable oscilloscope to mess around trying to fix a pile (read 10 and growing) of Disk II drives I have accumulated which seem to have various curious problems (6 of them pass speed tests, but won't work properly). I have received alot of great advice in the past from people here to fix these, but I think to get under the skin of them, I will have a go with the Disk II trouble shooting guide and see what I can achieve following that through.
My question is, are these cheap devices good enough to cope with this sort of work. Its been 30 years since I last used a scope, so I am green when it comes to this sort of work (but keen to have a go, if its not too expensive).
Atomtan,
lol, I know the feeling.
I also have not used a scope in a long time.
Last year I was considering the same avenue you are, and have continuously put it off.
Of course, not having employment right now has helped with that decision, but after I get back to work, getting a scope of my own and re-learning how to use it is one of the things on my list.
In the case you posted - it might be a good idea to use a scope due to the fact that speedtest itself doesn´t give any real judgement to the quality of the signals themself...
but for good diagnostic a good but simple scope wiil be needed -
the minimum limits should be set to 20 Mhz like the common old fashioned ones, that were used as equipment in school-labs.
there is rather good chance to get them as used devices or to probably borrow one from a friend ?
If you want to buy a used one you shouldn´t do that at ebay unless it´s equipped with a take-back-guarantee from a professional-seller. And i guess that the idea to buy one is that you probably guess the need also in future for other repairs ?
regards speedyG
The minimum scope I would recommend for retro computing is 100MHZ, 2channel. The base timing frequency of an Apple II is 14MHZ, which a 20MHZ scope will not be able to handle (google Nyquist, if you don't believe me).
Check out my Blog post on the topic and also check out Dave L. Jones wonderful eevblog which has many reviews and equipment recomemendations.
http://www.willegal.net/blog/?p=952
http://www.eevblog.com
regards,
Mike W.
Hello Mike,
allthough several guys believe that a 20 Mhz scope can´t handle that - believe me one thing: i own a Hameg 20 Mhz 2 Channel scope and it handles 14 Mhz.... the only point is that it will display not one cycle but minmum of 10 cycles but with the spread function it is possible to expand that to a fair view of three cycles....
i´ve been using this scope for more than 30 years and never had problems to examine all functions at an apple... the only expansion to that was a 16 channel chopper built by myself to also display 16 pin of a chip at one time in 16 lines above each other with a offset voltage.... by that way i realized the function of an logic analyzer....
but at least for the HAMEG 205 i can guarantee that it handles 14 Mhz with clear sharp display....
and therefor at least i don´t care what other guys might try to tell in other internet blogs - its my experience, that i have seen it by myself, that it works proper...
regards speedyG
I agree with Mike, if you can get a 100mhz that would be cover you in most vintage computer situations. I actually got an Instek GOS-653G dual trace 50mhz w/sweep delay brand spanking new off of ebay for $169. For me it covers everything and it was new in the box so I didn't have to do anything but plug it in. I wanted a 100mhz, but couldn't find one for a decent price at the time.
There is a used 100mhz Instek on ebay with only one bid at about 100 bucks with a day to go, it also says guaranted to work...
http://www.ebay.com/itm/GW-INSTEK-GOS-6112-2-CHANNEL-100MHZ-OSCILLOSCOPE-2CH-W-LF-210E-PROBE-MANUAL-/330682105380?pt=BI_Oscilloscopes&hash=item4cfe307e24
I'm sure that 20MHZ would be more than adequate the majority of the time, maybe all the time, for a large number of retro-computer folks. On the other hand, I've encountered an occasional case where 20MHZ was not enough. I even had one case where I had the bandwidth cranked all the way up to 100MHZ to get a good look at a glitch on the Mimeo 1 and I wished I had more bandwidth. In the end, everyone has to make their own call as to what they can afford and/or justify. When I made my choice, I prioritized bandwidth and cost over features and ease of use. For a lot of people, this could be the wrong choice.
Regards,
Mike W.
Thanks for the useful tips, time to set a budget and venture into the world of scopes...! My desire to fix up an Apple II continues to take me on a wide and varied journey, frustating at times, but most of it has been rewarding and suprising in equal doses.