SB 104A probblems

[Vin]

Thanks for your very generous reponses.  Your information has helped me greatly.  First of all, I've determined that I have a 104 updated to a 104A.  The front panel was upgraded with a new bottom strip with the nomenclature SB-104A but the 100 HZ button exists which tells me it must have been the original 104.  

The unit was very sick when I got it.  Turns out that most of the problems were associated with pulling the boaards and cleaning contacts.  The rcvr now works pretty well but has low audio and audio is distorted on USB.  Checked the BFO injection on a scope and the VRF is 4 volts on LSB and 2 volts on USB (will look into this) I suspect however that the IF filter may have shifted.  

On low power the rig was not generating any output.  Checking, I found that a mod had been made to the IC 1350 circuit on the transmitter board , someone substituted a  pot for the 1200 ohm supply resistor (poorly)  I removed this and put a 1200 ohm resistor back and bingo - good low power.  When going to high power the transmitter drew 25 amps with no drive!  (Only for a couple seconds _ I turned it off).  I removed the PA and check the transistors and they appear OK  (following Kee Talen's procedures).  I now need to sniff around and see what's missing to the PA board,  might be to do with the alc.

I had another SB 104A about ten years ago and am sorry I let it go.  It worked flawlessly and as I remember the rcvr was excellent. (never went under the hood with it).  I hope to get this one up snuff.  Regards  Vin  W1TUJ

-----------------------------------------------------------
Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/HEATH.html