Tektronix SG 503 - works but can't shift range

[ajhalls]

I just got a Tektronix SG 503 250MHz pulse generator, but when I adjust the range selector down to anything but 250MHz it doesn't work, so the lowest I can get is about 115MHz. I have tried pulling and reseating all the IC chips but it still doesn't help. Anything else I should try on this so I can use it with a 100MHz scope?

Alan

[Bhannis]

ajhalls

The signal generator SG503 is a leveled signal generator with 50kHz to 250MHz range.
The oscillator part is divided in two main circuits. One for the 50kHz to 100MHz and one for the 100MHz to 250MHz. I suspect the Q130 (151-0211-xx og 151-0451-xx) transistor in the 50kHz to 100MHz range to be blown. it is possible to find replacement but try swapping the Q140 and Q130 transistors first to check if it is the transistor. These transistors can be found on the "B" side of the generator (right side looking at the front) and are the two TO-39 transistors with heat sink. These transistors are not soldered and can be pulled and out and inserted carefully.
The swap will give you the 50kHz-100MHz and your 100-250MHz range will be dead

But of course, first of all, check the power supply voltages and check Q130 circuit for shorts

If you don't have the manual this can be downloaded from http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Tektronix/Tektronix_-_TM-500_Series/Tektronix_-_SG-503 or http://w140.com/tekwiki/wiki/SG503

B

[Neomys Sapiens]

@Bhannis
Newbie at the forum, but no newbie in respect to the TM500-series, obviously!?
You are not alone here - more operators and threads on those!
Here for example:
https://www.eevblog.com/forum/testgear/tektronix-tm-series-test-equipment/msg1252616/#msg1252616

[Bhannis]

@Neomys Sapiens
You're right. I'm a newbie at the forum but have been playing with the old tektronix stuff for some time, just for fun.
I simply love these old TM500 units. They do what they are suppose to and are quite easy to work on
I have a small collection now and all from broken, none-functional, cheap ebay units. I can almost smell the burned tant when I see picture of one of these units 

[ajhalls]

Thank you very much, I swapped them and got it working differently, the range is now around 90k-260k which should get me working again. I will see if I can buy a few more and change them out.
Alan