Service Manual for Palomar SSB-500?

[loosecannon]

well darn it Robb, i do think you are right. i guess i got excited when i saw that different path to the collectors of the driver and final in AM mode and traced it back to that relay.LOL

however, while looking at the block diagram i did see something interesting!

notice how X6 the 11.2850 crystal is used for AM receive, but not for AM transmit!

the USB crystal is used for AM transmit.

you might check that crystal as well as D45 and TR39.

still just guessing here, but maybe getting closer?

i also agree with Andy that TR22 could be suspect.
LC

 

[Handy Andy]

Not from my point of view...

The "SSB" side of things - if power applied in SSB mode to power the IF 7.8MHz doesn't get thru - there are several mods on the CB Tricks Website that feature D30 as well as "swing kit" installs - if the power to TR39 falls - TR41 or Clariifer may have no voltage on it to make the AM 11.285 Oscillator work when in AM RX mode for it sources from another part of the board in TX or RX mode - if it's not done right - AM (TR39) will only see TX mode...

TR22 still stands though - it's the easiest as well as a simple voltage check of Clarifier in nRX TX mode in AM

 

[Robb]

TR22 tested OK.

Took out the relay and cleaned the contacts; they were only a little dirty. But since this thing is old (~40 years), I thought it would be best to eliminate it as a problem and clean it. Broke off the tip of a q-tip and used the paper stick with some straight contact cleaner until they were shiny as a new penny. Reassembled/installed/tested OK.

Removed ground side of clarifier and put it back to thru the resistor to ground on the board, in order to change the clarifier center back closer.

Gonna get back to the radio in a while when I get some time for it.

 

[Handy Andy]

Just don't give up -

You may need some type of noise maker to trace signal back from Volume onto the Detector and work your way back.

Heck, could be something as simple as Squelch control - for they do have two settings one for SSB another for AM...VR2 (FET Gain) and VR3 SQ trim.

TR10 also retrieves 8V from the MODE switch to affect the gain for S/RF VR1 and AGC "drive" for AM off of TR11 - TR11 affects the RF input thru D1 and TR4 (Think Pin diode attenuation)

You know, a lot of people get mad at me (flambe'd evenly roasted and seasoned) at times for my approach.

Well, look at it from the aspect of a tech that had to learn the ropes without a bunch of lecture hall verbosity - I approach this with a guess as to the reason they post out here. I see this as; because they've tried the usual suspects and run out of ideas - so sorry for Left Field approaches but please understand that I see these radios with some "bizzare" stuff done to them that I had to sort out and redo for a customer.

I never get rich from that effort but boy have I learned a lot of "what not to do"...

 

[Robb]

Well, it's been a while since I had the chance to get back to this radio and work on it. The same customer also brought me a second Palomar SSB-500. I never have been able to find any of these radios before, but now I have two to work on. The second radio is otherwise OK and just needs alignment.

Recapped the entire radio - first.

So, I went thru A.T.E. with this radio with the bad receiver ('Always Test Everything') to find the fault. Actually, I ended finding more than I thought was at fault using the 'ATE' method. Since it was only the receiver strip, I just went down the chain from in to out - given. Took more time to locate the parts on the board than to test them - lol. At first, I found two leaky diodes (D-1 and D-2) and replaced them with 1N4148's. Replaced TR-5 (2SC1730) with another since the part in there wasn't a 1730 and I had some.

When I worked all of the way down to TR-11, I noticed when checking it (on one of those cheap $7 component testers from ebay) that the hfE was low. At first, I didn't really pay attention to that reading on that meter since it isn't exactly known for being accurate in that regard. Even tho the transistor was otherwise OK when tested; not shorted.
I then wondered: gee; maybe it really is leaky?

Sure enough, it was.
Replaced that 2SC710 with a 2SC945 - and - BINGO - receive is now working like a mad dog.

In addition, I found that two tantalum caps were bad (C-49 and C-52 - with bad ESRs); they were also different values than the schemo called for. Someone had been trying to fix this radio before I got it.

I must wonder as to what caused those part failures?

Those little $7 component testers from ebay are just xlnt for working on radios with.
Worth every penny!

Thanks to all that chimed in - too!

'Gotta love it when a plan comes together' -nomadradio . . .

 

[loosecannon]

nice job Rob!

man i hate 'weak' problems in radios. they are always more complicated than 'doesn't work' problems.

the fact that you found a weak transistor that would have tested good doing a diode test just goes to show that we really can't assume anything until we've tested it.

Im sure you have a very impressed customer right now.
LC

 

[Robb]

Thank You, LC, for helping me out with this one.

I dunno if the customer will be impressed, as he wasn't even aware that AM receive was poor. I had to bring it up to him after a cursory check of the radio before starting work on it. He's gotta like it now, as this radio is anything but deaf. Since this chassis is basically the same as the 858 chassis, the receive is sooo sensitive now, he will have to notice.

Those little component testers are kinduva marvel IMO. David Jones/EEV Blog pointed out in his video review of them saying they weren't accurate for the cap % loss and hfE values; but it still showed me enough of a difference to be noticed and take a second look. Which turned out to be right. Great tool for the beginner and I reckon that pros will need to give them a second glance/chance too.

Now, if I can just build a capacitor leakage tester from Paul Carlson's Lab, I will have another inexpensive but cheap piece of gear in order to keep my bench on top of things when troubleshooting.

Thanks again, LC!

 

[loosecannon]

i love mr. Carlson's youtube channel.

I actually started watching it before i ever knew he was a ham.
that is one smart dude.

I think im going to pick up one of those testers finally, just to have on hand.
I use an old heathkit transistor tester these days but i still want to have one.
LC