Pls help in 9260: noisy/hum

G'day,

first of all, your description shows that the receiver must have been in
a repair shop at least once ... and one power transistor seems to be missing,
as 5 + 2 is seven, not eight ... --- or is there yet another type used ?
No -- I see 3 from TI. Wild combination ...

Clearly, mixing different types of power devices is not a good idea (to put it
mildly ...), and should be changed. But there will be other problems hidden,
such as bad contacts (are all modules still secured with the extra screw in the
bottom ?), faulty capacitors, possibly semiconductors as well.

Do you have any knowledge of when and how the repair was done ?
Do you have basic knowledge of electronics, and can you work with the
service manual and read the diagrams ?

I'll take a look at the images -- maybe I see more then ...

Best regards,

Michael

p.s.: I see that there are 8 power transistors on the aluminium bar, but the different
types are mixed even among the two npn or pnp pairs -- very bad ! This looks like
a receiver that might need a complete revision, not just a quick fix. Nothing that can
be done at a distance, unless you are experienced or have an experienced friend.

Hi,

both have been used. Here, it is quite clear that the BD 245 were the original
ones, and the BDV must have been put in later. If you change them, you best get
yourself a set of BD 245 C (not B), and check that they match (similar beta).

Also, at least the PNP driver was changed -- there should be a BD 318, and I
cannot see what is in that position now (leftmost on the PCB). I can provide
the transistors if you can't find them -- where are you located ?

Before you rush off and buy -- are you familiar with the work that has to be done ?
Your problem is unlikely to go away after just changing the power transistors ... there
is definitely more to be done.

BTW: Philips or TI -- that does not matter. Mostly the TI were used, as far as I
can tell (I have seen some 30 or so, and only met the BDV once ...). It also does
not matter which receiver it is -- the power amp section is the same (7140, 9140, 92xx),
though they run with different voltages. In the 9260, you have (at 230 Volt AC)
around 41 ... 42 V DC. This is why, when getting new transistors, you better take
the C type. It is for 100 Volt, while the B type is for 80 (which is a bit tight).

Often, also the driver PCBs have problems (see some of the other threads, all this
is well documented here). The one-sided hum will be somewhere else, I think.

Best regards,

Michael

Fine -- the BD 418 is then no problem. It seemed replaced, but because it was
on the edge of the images, I could not see that for sure.

As to the other issue: The BDV on your image are _definitely_ the ones that
were put in later, not originally. You can see that from the fact that they are
from different series. So, the TI must have been the original set.

But this really does not matter -- you can use either, but not MIXED. I prefer
the BD 245 C / BD 246 C, as they are easier to obtain. If you want to use
the BDV, you can do that -- but then better the BDV 95 / BDV 96 (they
are the 100 V versions, which is needed for the 9260).

In fact, the BD 245 B / BD 246 B is sometimes specified for 90 V, and sometimes
for 80 V -- I suspect there are differences depending on the manufacturer. The
version from TI seems to have 90 Volts, but I would not want to depend on this
for the modern version from ISC etc. So, if you have original TI, you can use
BD 245 B / BD 246 B. If you buy modern remakes (from ISC or similar), make
sure you get BD 245 C / BD 246 C.


Also, to clarify one thing: The BDV 93/94 appear in several service manuals,
e.g. for an amplifier that run with just +- 38 Volts DC. For them, the 80 V of the BDV
are (just) sufficient. When Saba introduced the 92xx series, the voltage was increased
to a bit over +- 40 Volts, and the BDV 93/94 were no longer sufficient. I do not
know why they appear in the manuals for 9250 and 9260. As I said,
I have only once so far seen the BDV in an 92xx (and I'm not even sure that
was original, or a replaced set of power amp boards). I would NOT advise to use
them (or if you do, go for BDV 95/96).

Electrically, there is very little difference between the two types. The slightly
higher power capability of the BDV seems irrelevant here. So, any
claim that BDV is better than BD is most likely unwarranted. It might very well be
that the BDV from Philips were a European version of the BD from TI. But
there will be small differences in the precise behaviour, which is why they should
not be mixed. I would strongly doubt that there are sonic differences -- other
parts in the 9260 are more critical.

Good luck with the replacement -- the real hunt for the problems will start
afterwards ...

Michael

p.s.: Some corrections worked in above.

G'day,

the BD 245 C is NPN, the BD 246 C is PNP. I'm not sure whether you should attempt
a repair if this is new to you ... do you have a friend who knows all this and
can help you ? Note that after a change (which has to observe various points,
including proper isolation etc.) the amp has to be adjusted again. There is
absolutely NO POINT in making a modification without proper knowledge of
the basics of electronics !!

Best regards,

Michael

I would prefer BD245C/246C as you, too!

Andreas

And please check the other parts on the final stage and driver pcb's too. Only replacement of the BD245/246 mostly will not do the trick. But if you have a technician who is skilled in electronics, he will check for sure.
If you buy the transistors, prefer a good brand, not the cheapest offer from china.