Wavetek Model 130 Function Generator - Power supply problem

[Dgtech]

Re: Wavetek Model 130 Function Generator - Power supply problem

Just for the hell of it, I double checked the voltage on TP 2 and it shows .85 volts to TP1. Should be +15.

[Dgtech]

Re: Wavetek Model 130 Function Generator - Power supply problem

I measured wrong. I measured from the positive side of C48 instead of C49. Sorry, I was rushing. OK I have 6.1 volts on the cathode of CR19 to TP1.

[redwire]

Re: Wavetek Model 130 Function Generator - Power supply problem

That reading doesn't make sense to me;
-ve voltage at CR19-K and TP1(GND) would make filter cap C48 blow up.
Unless the xfmer center tap/rectifier is wonky.

Do you have the +/-22VDC rails at least?

Measure the voltages on Q17, Q19 and across R96 and post.
That will show what the vreg is doing I think.

[Dgtech]

Re: Wavetek Model 130 Function Generator - Power supply problem

Sorry guys that I took so long to get back to this.

So... on the cathode of CR19 with respect to TP1 there is -23Vdc using the correct polarity. Black on TP1

[redwire]

Re: Wavetek Model 130 Function Generator - Power supply problem

I thought either the vreg is bad or there is an overload between the +15 to -15V rails.

Q17 and Q18 are normally on full-tilt (from R88) and then IC6 turns them off to set +15V. Backwards from most designs. I think the lowest it could then go is CR19, so this means the two transistors are probably not working or overloaded.

I would solder in two reverse diodes like 1N4001 across the +15V to GND, and -15V to GND to stop the +15V rail going to -V can damage IC's and capacitors. Try not to run it like this.
Maybe you can open both TP2 and TP3 (jumper) and see if the +15V comes up, for troubleshooting.

If IC6 is dead I worry the +15V goes to 22V.
You can use LM741's to sub for the uA709's; Still available in the cans wow.

Check for shorted transistors Q1, Q2. They could overload those rails.

[budm]

Re: Wavetek Model 130 Function Generator - Power supply problem

Did you already test the Q17,and Q18 (they are the pass transistors setup as Darlington), Q19 (is for Over current protection)?
Check the DCV between TP1 and Cathode of Zener CR19.
Right now Q17/18 are not being turned on.

[Dgtech]

I have this old function generator that I got recently and it has a power supply issue that I cant quit lock down.

Please view the schematic.

Incoming voltages 120VAC = OK
Fuse = OK
Using TP 1 as GND in this section;
TP2 = -2.7 to -4.8 varying with frequency knob\potentiometer. (Bad should be +15VDC
TP3 = -15VDC (Good)
Top of R116 = 26VDC
Bottom of R117 = -26VDC

I dont really know how to disect further to pinpoint the bad component. At this point I'd guess and just change out IC6 maybe?