Sharp XL-HP500 help - UK Vintage Radio Repair and Restoration Discussion Forum

Deltatango · 9th Mar 2019, 7:50 pm

I wonder if anyone can give me some help with an old Sharp XL-500 which has blown its output amplifier again.

It uses a STK402-071 module which blew the original part, this was changed along with power supply and other electrolytic capacitors as some of its small ones had puffed up, I thought it best to change the power supply caps to ensure even + and - rail charge up.

Just hope now if anyone has ideas on this problem

Many thanks from Davidt

tri-comp · 9th Mar 2019, 9:41 pm

Davidt,

Did you replace ALL electrolytic cap's around the chip ?
They are:
C901, C902, C909, C910, C913, C914, C915, C916, & C925.

And then there's the obvious:
Did you check your speakers ?
A shorted out tweeter or two will put a heavy load on the IC when the volume is turned up.
Shorted speaker cables will also make the life difficult for an output-IC.

The less obvious:
Due to insufficient mechanical cooling of the chip,
Sharp installed a volume-level dependent blower circuit to cool the IC when under high volume load.
Technics did the same in some of their receivers and the motor faulted.
Possibly because a parallel electrolytic cap. across the motor became defective.
The Sharp-circuit, even if a lot simpler, works in the same fashion.
Here the parallel-cap. is of course C930.

Rgds,

/Torben

Deltatango · 21st Mar 2019, 12:57 am

Sorry for my late response but those capacitors were changed with its original fault as some had puffed up plus diodes and transistors in that area.

Got a better spec sheet detail on that range of IC and it shows a curious shift in supply voltage +/- 50v maximum, +/- 44v with 6 ohm load, then recommended voltage of +/- 30v for 6 ohm load. Well this unit has a 37v +/- supply line, I found some engineers who made the comment that they got fed up at times if these IC's popped a bit often (playing loudly) so changed it for the next module IC up.

I intend to get that cooling fan more involved on a constant level setting it to spin at some speed that cools without making too much noise but allowing it to speed up if required.

Many thanks so far from davidt

9th Mar 2019, 7:50 pm	#1
Deltatango Triode Join Date: May 2018 Location: Tonbridge, Kent, UK. Posts: 41	Sharp XL-HP500 help I wonder if anyone can give me some help with an old Sharp XL-500 which has blown its output amplifier again. It uses a STK402-071 module which blew the original part, this was changed along with power supply and other electrolytic capacitors as some of its small ones had puffed up, I thought it best to change the power supply caps to ensure even + and - rail charge up. Just hope now if anyone has ideas on this problem Many thanks from Davidt Attached Thumbnails

9th Mar 2019, 9:41 pm	#2
tri-comp Heptode Join Date: Oct 2008 Location: Aalborg, Denmark Posts: 903	Re: Sharp XL-HP500 help Davidt, Did you replace ALL electrolytic cap's around the chip ? They are: C901, C902, C909, C910, C913, C914, C915, C916, & C925. And then there's the obvious: Did you check your speakers ? A shorted out tweeter or two will put a heavy load on the IC when the volume is turned up. Shorted speaker cables will also make the life difficult for an output-IC. The less obvious: Due to insufficient mechanical cooling of the chip, Sharp installed a volume-level dependent blower circuit to cool the IC when under high volume load. Technics did the same in some of their receivers and the motor faulted. Possibly because a parallel electrolytic cap. across the motor became defective. The Sharp-circuit, even if a lot simpler, works in the same fashion. Here the parallel-cap. is of course C930. Rgds, /Torben

21st Mar 2019, 12:57 am	#3
Deltatango Triode Join Date: May 2018 Location: Tonbridge, Kent, UK. Posts: 41	Re: Sharp XL-HP500 help Sorry for my late response but those capacitors were changed with its original fault as some had puffed up plus diodes and transistors in that area. Got a better spec sheet detail on that range of IC and it shows a curious shift in supply voltage +/- 50v maximum, +/- 44v with 6 ohm load, then recommended voltage of +/- 30v for 6 ohm load. Well this unit has a 37v +/- supply line, I found some engineers who made the comment that they got fed up at times if these IC's popped a bit often (playing loudly) so changed it for the next module IC up. I intend to get that cooling fan more involved on a constant level setting it to spin at some speed that cools without making too much noise but allowing it to speed up if required. Many thanks so far from davidt