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Yulong Sabre D18 thread: reviews, impressions, discussion (full review added 2/5) - Page 69

post #1021 of 1024

A ways back (on page 58) in this blog there's some discussion about modifications to a component - transistor Q3. Some models of the D18 have a heatsink attached, whereas some didn't. Mine has no heatsink. After 3 years of reliable use and good performance component Q3 smoked itself. After a brief smell of baking bakerlite and a whiff of smoke from the ventilation slots the sound became quieter, so I turned it off. After inspecting the PCB I noticed Q3 was cooked to the point it had turned to white, friable ash - to the extent I'm unable to read the part number. I'd guess its been on the way out for a while. Further, I think Yulong probably realised it was prone to overheating since they put a heatsink on (maybe) later models.

 

I contacted Yulong who haven't been particularly helpful, requesting the entire unit be sent back to them. Me, I'd rather take a punt and just change the component, but Yulong appear exceptionally reluctant to divulge what type of transistor it is.

 

I'm humbly requesting that any Head Hi-Fier who's got their D18 open and can see what breed the transistor is could tell me ? Thanking that kind person in advance.

 

 

 

post #1022 of 1024

I just checked mine and it has Q3 heatsinked.  This looks like a factory patch since the lead of R53 has been soldered directly to Q3's emitter, replacing the board trace.  The heatsink and glue though prevents telling what Q3 is, but it looks like some jellybean NPN BJT (2N3904 or BC5xx, BC377, or whatever) used as an emitter follower with R53.  I suspect you can use pretty much anything in its place.  I'd try a 2N3904; they're pretty low noise.  I don't see a base resistor off hand near its base, so it's probably not a low Vce(sat) device.  Since there's only one Q3 my guess is it's used as an EF to power something.

 

BTW, mine also has a big patch of flux around U11... looks like it was reflowed and not fully cleaned up afterwards.  Ewww.

 

Edit: it could also be a low-power regulator (akin to a 78L05)... but the board silkscreen has BCE for the pins, and I doubt any of them are grounded (didn't run a continuity check).


Edited by sandab - 7/19/15 at 11:13am
post #1023 of 1024

BTW, wear a wrist strap when poking around; the OPA604 op-amp next to Q3 is a FET device so is very ESD sensitive.  A wild guess would be the follower powers the OPA604 which amplifies or buffers the IIS input bitstream and the use of a FET op-amp powered by a follower is for noise isolation purposes.  They haven't connected the trim pins of the op-amp, but I guess for this purpose a bit of input offset doesn't matter.


Edited by sandab - 7/19/15 at 11:25am
post #1024 of 1024

Thanks for your prompt response, its greatly appreciated. I'll have a crack with a 2N3904.

 

Cheers - Ian.

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