Re: A slightly sick SG505


Hi Eric,
I can't help you directly but you might be interested in a SG505 I inherited that is incomplete. It probably came from the Tek Country Store. I have no use for it but you might be able to use it as a "parts mule" or for locating the problem with your SG505 by substituting parts from this one.

It is missing the Output Level rotary switch, Source R switch, and Intermod Test Sig pushbutton. All of the other front panel pushbuttons and knobs are there including the Frequency dial and that very interesting pot it turns. All of the ICs, transistors, caps, transformers, fuses, and even a small lightbulb appear to be there.
There are two 1" high standoffs about 2/3 0f the way towards the back of the plugin that may have held a small PC board (just a guess). Whatever they were holding is gone.

If you are interested please contact me off list at dennis at ridesoft dot com.

Dennis Tillman W7PF

-----Original Message-----
From: [] On Behalf Of Eric
Sent: Wednesday, January 29, 2020 7:03 PM
Subject: [TekScopes] A slightly sick SG505

I am hoping the wonderful minds here can help me with a sick SG505. The main output is working and the distortion is good. They Sync output is not working correctly. I have checked U1300 and Q1300 and 1301 off the board and they seem to be behaving like they should. For U 1300 the resistance between pins 4 and 5 goes down when power is applied to pin 1 and 2 with a bench power supply. I can see signal at the base of Q1301 but the signal seems to die in the optoisolater probing 5 or 4 with a scope shows dc only. Q1301 and 1300 both pass a diode test off the board as transistors of their respective types. I suspect U1300 but what is odd it seemed to work off the board. Not sure what I am missing.

Dennis Tillman W7PF
TekScopes Moderator

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