Trying to repair Yaesu FP-707 power supply

[Cartel]

I'm trying to fix this for my buddy. The power supply would power up, put out 13.8v but drop to 0v with any load.
He tried to fix it by replacing 3 caps in the "AVR" board, that didnt work.
I fired the parts cannon and replaced 3 "10D1" diodes with 3 "sk3081" diodes I had, a new 35 amp bridge rectifier, I tested all the other components and for the "2SA1012" was subed with a ECG "TIP53" and I replaced that with a "D45H8G" and same results, 13.8 and 0v under load.

I pulled the 2SD717 regulators and they all tested as 2 resistors so I assumed they were dead.
I replaced those with 3 "2STW100" parts and now I did a quick pulse of 120v and its putting out 22VDC

Is it because I used 2STW100 which is darlington type?

I'm out of ideas.

thanks

[Cartel]

Re: Trying to repair Yaesu FP-707 power supply

false alarm I'm sorry.
The voltage adjust was cranked, its working fine.

whew!

[Cartel]

Re: Trying to repair Yaesu FP-707 power supply

Might not be out of the woods yet.
It doesnt seem to be regulating very well.

[redwire]

Re: Trying to repair Yaesu FP-707 power supply

When it craters, can you measure the voltages on the error amplifier Q103 and maybe Q102.

Be careful it's got huge filter caps 99,000uF which can hold a big charge. I would make sure they are discharged through a say 1k resistor before going in there.

[R_J]

Re: Trying to repair Yaesu FP-707 power supply

Install the proper transistors for Q1~Q3, I don't think those 2STW100 will work.

[redwire]

Re: Trying to repair Yaesu FP-707 power supply

Yeah the PSU will have too much gain and would oscillate with the Darlington pass transistors...
The JFET current-source is interesting in that it gets a -ve voltage supplied.

There was a day when people would troubleshoot and test transistors. There's only 6 in the Yaesu.
I think the cannon got fired too quickly, might be best to aim it first lol.

[eccerr0r]

Re: Trying to repair Yaesu FP-707 power supply

easier to just swap and hope it fixes the problem instead of thinking...
May even be faster too unfortunately, but that's the case with most modern equipment.

Dang... if that's being paired with a FT-707 I hope a ham isn't actually asking a non-ham to fix PSUs... or at least I hope that any ham would know not to replace a singleton BJT with a Darlington pair.

[CapLeaker]

Re: Trying to repair Yaesu FP-707 power supply

In that style PSU most of the time the problem are the pass transistors (2SD717). I’ve repaired tons of these.

[redwire]

Re: Trying to repair Yaesu FP-707 power supply

What are you using as a substitute for 2SD717?
I think I'd use (real not Ali/eBay) 2N3055G or 2N3772 but TO-3 package parts are quickly being discontinued.

[R_J]

Re: Trying to repair Yaesu FP-707 power supply

Maybe a TIP3055 TO-247-3 case available from digikey

[Cartel]

Re: Trying to repair Yaesu FP-707 power supply

Thanks for all the replies.
I never really worked on power supplies too much.
I was hoping for a "quick fix". I did test each part and just replaced the diodes just because I had new ones in stock.

Well the darlingtons came up on a substitute list and digikey had plenty for cheap: https://alltransistors.com/crsearch....ps=TO247&cf=on

Digikey has 0 stock on most items and 1 source never got back to me and ebay is a joke.
And yes Redwire I hooked up a car tire pump and it was oscillating up and down. So I guess thats a fail.

R_J yes TIP3055 are $1.50 and in stock. Guess Ill grab them

thank you all for your tips I appreciate it.

[CapLeaker]

Re: Trying to repair Yaesu FP-707 power supply

The SD717's are not darlington's. The TIP3055's are a good replacement fit.

[Cartel]

Re: Trying to repair Yaesu FP-707 power supply

The SD717's are not darlington's. The TIP3055's are a good replacement fit.

ya I seen it say darlington and I just chose to ignore it. Live and learn but now I know to avoid them. Problem solved I hope

[Cartel]

Re: Trying to repair Yaesu FP-707 power supply

Maybe a TIP3055 TO-247-3 case available from digikey

I just finished installing ST tip3055 (3) and its working great. Thank you for the tip on the tip.