The AM Forum

I'm attempting to bring back to life a Heath HO-10 (I know, HO-HO!)  Power supply and the two .15 caps have been replaced.  I get a nice bright trace, H and V position controls work, H and V gain controls work, BUT - I can't get the trace down to a dot.  With both gain controls at minimum, I get a bar about one screen gradient high, by three wide.  Pots have been cleaned and tubes checked.  Your thoughts?

Have you gone through and measured every resistor and cap? Replaced every paper and electrolytic cap?   That is what I would do before even thinking about troubleshooting.

This is reportedly the best way to clear up the trace on the Ho-Ho-10.....

And John knows what he is doing!

The scope shouldn't be able to reduce to a dot.  I'm not familiar with the HO-10 but no scope will reduce the horizontal trace to a dot.  Unless you have the horizontal in external input mode.

Fred

Just covering all the bases...This is a Heathkit, and they won't let you fail....

Are you using the Heathkit manual?

http://www.vintagemanuals.com/search.php?find=ho-10
$22

http://www.manualman.com/index.cfm?v_link=product_detail&v_key=74554&v_manufacturer_id=255
$20

All the specs and alignment procedures should be there!  :)

Thanks for the tips! I do have a manual, and the initial checkout described on p. 37 and 38 says the scope should produce a dot with h and v gain controls fully counterclockwise.  Then it takes the builder through use of the focus and positioning controls.  Advancing the h gain produces a horizontal line - but mine is a thick "bar."  I'm not quite ready to use the centrifugal force remedy, but who knows?  Actually, I'm making progress with the critter, since I couldn't get a trace at all until this morning.  Checking components, solder connections (some were big blobs), and grounds.  Will keep everyone posted, and thanks for any more thoughts or ideas. :-\

Best tip:  see Todd's post above

Seriously, I'm betting the filter cap is bad, you're getting 60 hz hum on that thing.

Even more seriously take my advice, swing it by its line cord against the concrete so you're never tempted to fix it, and buy a good triggered sweep scope for $50

Success! :D  Measuring individual resistors revealed the 3.3 meg resistor that goes from the cold side of the focus pot to ground measured 5.4 meg.  I wondered if the focus control just couldn't bring the beam into sharp resolution.  The junque box revealed a 1 meg resistor that I tacked in parallel to the original resistor.  Ohm's law says the new resistance will be about .85 meg, which it was.
Going from way high value to way low, but I gave it a try.  Sharp focus in the control's center range!

Yes, I know there are better scopes out there for practically peanuts, but this was a hamfest find from years ago that I'm just getting into now.  It's a great winter project (we've broken a record for below zero days in one winter season that went back to 1917.)

My HO-10 has all new electrolytics, and I added a three wire AC plug with a fuse holder mounted on the chassis.  It does display the famous AC ripple this model is so famous for, so maybe I'll add some extra filtering.  And if I do decide to upgrade some day, I can sell this one at a hamfest with a clear conscience that it DOES work!

Again, thanks for all the help.  The next project up is the DX-100 I've used for a door stop for the last 17 years.  Hey, I've got it making power - but the speech amp section really needs love, so I may have more questions to come.  It's going to be a long winter, but I'm trying to make the best of it!

When replacing those electrolytics, all the resistors in the focus and positioning areas should be checked and/or replaced. I wrapped aluminum foil around the CRT to cure the horizontal line ripple.

Thanks, Pete.  I was wondering about the aluminum foil trick, will give it a try.  If nothing else, it will help protect my Ho-Ho from alien thought control! 

Just read the thread, was going to post "check the focus voltage"... :D

I to have an old hamfest Ho-Ho, it had bad HV caps... other than that it worked last time I looked at it. I was going to put it on top of my Apache, but I never finished working on the Apache. I use a Tek 24XX 300mhz scope off epay for monitoring the receiver and the xmit...

                  _-_-

Thanks for the note, Bear.  The problems with my scope are solved, for now at least.
73, Jim