I'm not necessarily convinced Q504 is good - try the multimeter on C-E (E-C) again, now that you have it out. E-C should measure open. And Q507 seems to have been accidentially inserted into pins 3-3-1 on the transistor tester (i.e. E+C connected together!), no wonder it registers as a diode - try again one row to the right.
If Q504 does test good, try between where its collector was and the +50V rail. If this test still shows a nice short, that does not bode well for the STK.
EDIT: So pin 6-9 would show pretty much that. Yeah, a C-B short on the npn driver transistor in the STK is what I suspected all along. If it was associated with static discharge, the resulting signal spike may have sent this transistor into secondary breakdown... or possibly it already was marginal in C-E breakdown before and could have died at any time that close to full power was demanded from the unit.
Has anyone ever repaired such an STK? Aside from the questions of hacking it open and obtaining bare die transistors of the right kind in the first place, I guess it's a rather hairy process... so probably not altogether unfeasible, just impractical.
If Q504 does test good, try between where its collector was and the +50V rail. If this test still shows a nice short, that does not bode well for the STK.
EDIT: So pin 6-9 would show pretty much that. Yeah, a C-B short on the npn driver transistor in the STK is what I suspected all along. If it was associated with static discharge, the resulting signal spike may have sent this transistor into secondary breakdown... or possibly it already was marginal in C-E breakdown before and could have died at any time that close to full power was demanded from the unit.
Has anyone ever repaired such an STK? Aside from the questions of hacking it open and obtaining bare die transistors of the right kind in the first place, I guess it's a rather hairy process... so probably not altogether unfeasible, just impractical.
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Agreed, but this shouldnt have happened. The case should have protected the circuit. Did he loose a ground somwhere?
When a 10kV transient is applied to a consumer product, everything is up for grabs. Certainly some
of the semiconductors could be damaged or weakened.
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"while I had it playing some music, I scooted across the carpet to adjust a dial and had nice static shock
jump from my finger to unit. It just so happened to go silent at that moment."
Arghh. Well, 507 is definitely dead. Figures the STK 1060 looks that way too. Crappy luck.
SK3931 data sheet here:
SK3931
Datasheet, Equivalent, Cross Reference Search. Transistor Catalog
STK1060 replacement options?
SK3931 data sheet here:
SK3931
Datasheet, Equivalent, Cross Reference Search. Transistor Catalog
STK1060 replacement options?
Yeah, that's why i didn't mention it earlier. I've shocked my other receivers many times without incident. But, it's probably too much of a coincidence...
And I also thought about the ground issue. But other than recapping, I did not remove anything else. I left all the boards connected as I had full access to the bottom of the pcb. But it certainly could have had a ground issue since that seems to make since with the static shock.
The question now is it practical/possible to save it?
@sgrossklass - I am certain that the 507 pins were inserted correctly. I removed it and tried it again with the same result just to be sure and I took the time to align the pins properly so it would insert correctly.
And I also thought about the ground issue. But other than recapping, I did not remove anything else. I left all the boards connected as I had full access to the bottom of the pcb. But it certainly could have had a ground issue since that seems to make since with the static shock.
The question now is it practical/possible to save it?
@sgrossklass - I am certain that the 507 pins were inserted correctly. I removed it and tried it again with the same result just to be sure and I took the time to align the pins properly so it would insert correctly.
C2E and E2C both measure .447v on 504. Thats the outer pin to the middle pin and vice versa (according to the data sheet it's ECB.
@sgrossklass - great catch sir! You were indeed correct. 507 appears to be fine.
Q507_good.jpg - Google Drive
Q507_good.jpg - Google Drive
Oh, and would a 2SB716A be ok as a replacement for 2SB716? The only differences are the Vcb an Vce. 716 is both 120 and the 716A is stating 140. All other numbers are the same.
Bipolar Transistor Cross-reference Search | Equivalent Transistors
Bipolar Transistor Cross-reference Search | Equivalent Transistors
I think I found a suitable replacement.
2SB716 --> KSA992
And it's NPN complement
2SD756 --> KSC1845
The only diff I can see on the spec sheet is the collector power dissipation. The B716 is spec'd at 750mW and the A992 is spec'd at 500mW. All other specs look the same to me.
Would this be a suitable replacement pair for Q507 and 504?
When looking for transistor replacements, which of the common spec's are the most important to look out for when matching?
Thanks guys!
2SB716 --> KSA992
And it's NPN complement
2SD756 --> KSC1845
The only diff I can see on the spec sheet is the collector power dissipation. The B716 is spec'd at 750mW and the A992 is spec'd at 500mW. All other specs look the same to me.
Would this be a suitable replacement pair for Q507 and 504?
When looking for transistor replacements, which of the common spec's are the most important to look out for when matching?
Thanks guys!
DC values in general, absolute max ratings for sure
Vce: same or higher
Ic: ditto
P: ditto
(500mW instead of 750mW means do recalculate if within 80% of power limit, otherwise no go)
Hfe: comparable, -50% max for low power, -20% med, -10% high
Ft/ccb if possible.
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