[sdiy] HP130C scope issue

[Ullrich Peter]

Hi Bob!

Do you have the Service Manual for it?

If not then you can load it from here for free (2 manuals per day for free)

http://elektrotanya.com/hp_130c.pdf/download.html
http://elektrotanya.com/hp_130c_sm2.pdf/download.html

Maybe you can find some hints there...

Ciao
Peter

http://www.ullrich.at.tt
________________________________________
Von: synth-diy-bounces at dropmix.xs4all.nl [synth-diy-bounces at dropmix.xs4all.nl] im Auftrag von Bob Weigel [sounddoctorin at imt.net]
Gesendet: Sonntag, 14. April 2013 13:19
An: synthdiy
Betreff: [sdiy] HP130C scope issue

Gotta love me still using a 1962 HP scope...but..This is so strange.  My
scope I'm so used to I refuse to ditch it..lol... besides it's full of
telefunken EC88 tubes.  ... I have had it out of cal for a while and a
JITTER in the trigger.  I mean you can trigger if you get right on the
edge but anywhere between it's bouncing around from some 60hz
modulation.  Oh and I opened it because an electrolytic was
smelling...found that and replaced it..the final one that has the 250
and 100V filters to ground on it.  Replaced with an 80uF since I had a
can NOS in a box.

ANyway the jitter was still there sadly.  But I found with another scope
that there is signal on the 250V that rises WITH the jitter..(Initially
there is no perceivable jitter..but after a few minutes it's quite bad.
Typically seeing three waveforms offset by a few mm when it's in it's
warmed up mode)

The 250V comes right off a diode from a xformer winding... with a 150uF
cap between it and the regulator feed for the 100V  (There are two
transformer windings stacked with a regulator for the 100V between..then
ground..then another similar circuit for -100V below that)...and
initially it was more like almost 300V!  And again..no adjustment for
that.  I probably should have just made a regulator and the issue might
be gone.

Instead I assume it was the other cap. I replaced the 150 with a 470uF
.  THE MAGNITUDE dropped..but otherwise it basically went through the
same routine.  So strange... with the simple nature of the circuit I
just can't see another contributor.  The waveform is certainly smoother
now... but it's got a rounded saw wave that's near what it was before
when it warms up a few minutes!

Then I put in a 10W zener at 33V with a 10Ohm inrush limit to drop the
voltage down to near spec at 261V.  Now I've got some jitter all the
time probably from the 10ohm resistor though I thought it probably
wouldn't introduce enough ripple..I'm too tired to think.  If anyone has
another idea who's maybe seen this kind of thing in the past.... I can't
believe I spent that much time on this relic.  I sure must love it
dearly.  lol

--
Check out sounddoctorin.com for songs, a studio tour, help
repairing old synthesizers and parts or thought provoking
articles that could help make your eternity!

_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
The information contained in this e-mail message is privileged and
confidential and is for the exclusive use of the addressee. The person
who receives this message and who is not the addressee, one of his
employees or an agent entitled to hand it over to the addressee, is
informed that he may not use, disclose or reproduce the contents
thereof, and is kindly asked to notify the sender and delete the e-mail
immediately.