[R-390] R-390A Cosmos PTO has erratic linearity

[Roger Ruszkowski]

Larry,
 
Read all the mail on the topic before you  jump in.
 
I propose a bad cap with a couple PF shift
on temperature or voltage or vibration.
Also consider a cold solder joint.
 
For the cold solder joint I would go through the connections on the 
tube base outside the PTO can.
Then do the inside of the can.
 
Isolating an offending cap will be a shotgun approach.
Eye ball for likely suspects. If it looks like it has been run over it may be unstable.


Cold air may not be real diagnostic as changing the temp of any cap may pull the 
frequency as far as it is drifting. But you could get lucky.  The bad cap may go real
off the reservation for you and give its self away.

Good luck the problem is very fixable

Any mechanical slop can be taken into consideration when doing the measurements.

Always come up on the way point from the same direction.
Get close and roll slowly up to the point from the same side.
Roll up to or down to the point you want to measure.

It when you find the difference between points keep moving or
the frequency counter keeps drifting around as the PTO is left setting still.

You will have to get the PTO stable first. Then you can try and trim it up.
Do set the end to end span before you work on the mid point linearity.

Roger AI4NI
 
 
-----Original Message-----
From: Larry H <dinlarh at att.net>
To: r-390 <r-390 at mailman.qth.net>
Sent: Sat, Jun 14, 2014 6:35 am
Subject: [R-390] R-390A Cosmos PTO has erratic linearity


I'm restoring a Stewart Warner R390A with a cosmos pto type 136-1. Although I've 
had to fix a number of problems on the R390A, it looks and operates well now 
except for 1 issue (or I think it's an issue). I've graphed the linearity of the 
pto numerous times every 25 KC, and it tracks mostly +/- 100 - 200 cycles (with 
a few exceptions up to 300 cycles), but after adjusting the linearity bad spots 
numerous times, different ones keep popping up.  IE, the measurement 
repeatability is poor, but still mostly with in +/- 300 cycles.  This is after 
letting it warm up for 2 hours.  The frequency stability is very good.  Also, if 
I graph the pto linearity, use it for a few minutes, and graph the linearity 
again (without making any adjustments to the pto) its different than the 
previous graph.  Everything inside the pto seems tight and the gear train to the 
readout is tight (IE: very little slack). I have cleaned the pto shaft grounding 
contact and checked
 the contact pressure.  The endpoint also varies about +/- 100 cycles. I have 
the prescribed spacing in the oldham coupler (its in very good condition) and it 
is ligned up very closely with the KC shaft and the spring is installed 
correctly. The gear train and the pto operate very smoothly.

Should this be better or is this normal?  Any suggestions would be most welcome. 
 Thanks.

Regards, Larry
______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html