Re: Hello from newcomer Fabio Trevisan - My first Tek Scope 464 + DM44
On 13 Sep 2016 08:46:02 -0700, you wrote:
Sorry Dave, My reply to you ended up with the formatting completely screwed up.It was no problem; many replies on the list get mangled for whatever
On 13 Sep 2016 08:42:37 -0700, you wrote:
Hi Dave, Thanks a lot for your comments (so promptly!!)I had a general idea about how the DM44 delta delayed sweep function
should work but I found the description in the manual was ambiguous so
I wanted to find an example on video. I suspect most users who pick
up a DM44 have no idea what delta delayed sweep is.
You're also right about the ALT mode switch. I wasn't sure of its upper side,which actually has its "pushed" contact connected to +5V and therefore could be very well being used for something else in the scope, but one way or the other, having +5 on the pushed position is the opposite than what the DM44 requires, so I knew that the DM44 no matter what would need to be connected to the lower side of the switch (which, apart from the wire going to the DM44, seemed to be completely unused).I was surprised that the ALT switch is not used except as a
placeholder in these oscilloscopes. The late 466 manual does not show
it at all and the 464 and early 466 manuals show it but with no
The DM44 is suppose to be a factory installed option so it does not
quite surprise me that the DM44 service manual does not cover the
needed modification to the ALT switch.
Then, after checking it thoroughly, I connected the wiper of the lower side to the +5V and voilá, I can see two intensified "marks" in all vertical modes. That part of the problem was fixed already when I wrote yesterday but thanks for your comments as they helped me validate my conclusions.The DM44 has a toggle set/reset flip-flop which determines if the
delayed or delta delayed sweep control is used but it was not
immediately clear to me from only the DM44 schematic under which
conditions it toggles. I would have to study the oscilloscope
schematics as well to figure it out.
I remember that story about Jim Williams. They also had differentialThe ALT mode switch in the 464/466 is the default position for theOnce again, you are "on the spot" about the retrofitting... Today I found the ultimate proof of that!
diagnostic competitions where the objective was to figure out the
problem with a minimum number of tests.
I do not think soldering the ICs or other socketted parts in isI would reseat all of the ICs and anything else in a socket. I do notI shall reseat the ICs when I have some time... I already reseat most transistors. Once I`m done with the DM44 and know it works in all functions and ranges (when I know I won't have to replace anything else), I`m even thinking of soldering them all to the board...
warranted. If you remove the sockets, they can be replaced with
better sockets. Machined collet pin sockets are very reliable and if
you want to spend a little extra time on it, the collect pins can be
cut out of the replacement sockets and used individually:
Some people put a 1 ohm resistor in series with the fuse F1487 toYep, that is a drop in the CRT acceleration voltage.I`m thinking of monitoring the current drawn by the inverter, as it heats-up , to see if there's any noticeable bump or dip when it reaches the "dropout". I have a DMM with RS232 logging that will fit this bill.
monitor the collector current of the output transistor.
If you want to monitor the error amplifier, I think the voltage at the
collector of Q1476 is the best spot.
Another failure mode has occurred to me; Q1486 could be failing as it
heats up which is something I have seen before in transistors.