[TechAssist] Re: FYI 2SC4834 Sony power supply transistors Q601,Q602

  • From: "majorthom@xxxxxxxxxxxxx" <majorthom@xxxxxxxxxxxxx>
  • To: techassist@xxxxxxxxxxxxx
  • Date: Sat, 8 Nov 2003 19:57:19 -0800 (PST)

I want to jump in on this while it's being discussed.I want to check my p/s 
alone and need a suggested load for the 135vdc.I tried two 60w light bulbs in 
series but think the impedance was too low as the 4834's ran too hot.Also I 
wasn't aware of the hdt soldering or connection problem....................Any 
tips?.Pete
Kevin <kevintv@xxxxxxx> wrote:I have seen quite a number of Sony's that have 
the bad VDR and the
shorted C4834's. When the HOT goes (not as common), then the VDR is not
involved--only the transistors and resistors in the P/S. I live in an
area where there are a lot of power outages and possible surges. I
believe that the power surges damage the VDR(s) over time. 

Kevin Wilks
Kevin's TV & Video Repair
Penticton BC Canada
kevintv@xxxxxxx 


-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of Phillip R. Hull
Sent: Saturday, November 08, 2003 7:04 AM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Re: FYI 2SC4834 Sony power supply transistors
Q601,Q602

I repair a few of the Sonys and never found one bad. They all checked
infinite.
Phillip R. Hull STET
phil245@xxxxxxxxxxxxx
FAX 517-569-2242
----- Original Message ----- 
From: "Leonard Caillouet" 
To: 
Sent: Friday, November 07, 2003 10:15 PM
Subject: [TechAssist] Re: FYI 2SC4834 Sony power supply transistors
Q601,Q602


> I never replace the MOVs (VDR) unless they are bad. When they are
they
will
> generally show something less than infinite resistance. I use the
drive
> test on the Sencore with a horizontal key pulse and watch where they
clamp
> if I suspect them. It only goes up to 300 vpp so I don't get a full
voltage
> test on some of them, but I shouldn't see any clamping at all at that
level
> on the higher voltage ones. With the lower voltage ratings I just
turn up
> the drive signal until I see it clamping on the scope. If the source
of
the
> problem is the HDT solder connections and a shorted HOT, the MOVs are
almost
> never a problem. I have found that the more likely cause of problems
in
> these circuits are the caps. You have to check them all. I have seen
some
> that were just off value by 30-40%, but usually they are cracked or
shorted.
>
> As for the time it takes to match them, I have found that I get good
matches
> by buying lots of 10 and sorting them by forward bias voltage on the
> junctions. Takes just a few minutes on each batch. Then if I get a
pair
> with a duty cycle off by more than a few percent I reverse them and
that
> almost always corrects it. Time is money, and recalls waste time.
More
> importantly, reputation is money and I hate having recalls, so it is
worth
> my time to make sure it is right. Besides, we mark up the parts
enough to
> cover the effort in getting it right.
>
> Leonard Caillouet
> Electronics World
> Gainesville, FL
>
> ----- Original Message ----- 
> From: "Tel-Tek Electronics" 
> To: 
> Sent: Friday, November 07, 2003 6:45 PM
> Subject: [TechAssist] Re: FYI 2SC4834 Sony power supply transistors
> Q601,Q602
>
>
> > Would almost call for a "matched pair", since this duty cycle is so
> > critical.
> > I'm getting the Sony kit from Global, and I doubt they are trying to
> > match them up, even though it's suppose to be a kit.
> > Just had one of those sets a couple of days ago...very important to
> > change those VDR's. VDR601 and VDR602.
> > BTW...that Sony-SPKIT sells at Global for $9.95..which includes the
601
> > and 602...the H/O transistor and a .1 ohm resistor. That $9.95 Can.
> > Which is probably about $7 US.
> >
> > -Ed-
> >
> > Ed Gaidies
> > Tel-Tek Electronics
> > Ontario-Canada
> >
> > teltek3@xxxxxxxxxxxx
> >
> > -----Original Message-----
> > From: techassist-bounce@xxxxxxxxxxxxx
> > [mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of Leonard G.
> > Caillouet
> > Sent: Friday, November 07, 2003 6:01 PM
> > To: techassist@xxxxxxxxxxxxx
> > Subject: [TechAssist] FYI 2SC4834 Sony power supply transistors
> > Q601,Q602
> >
> > Just a few notes on these transistors and the results of some
> > experimenting.
> > I had a KV27ts32 and a KV32s25 in the shop with the classic HOT
shorted
> > and
> > Q601,602 shorted. I had some 2SC4834M in stock and ordered some
plain
> > 2SC4834 from Tritronics and some 2SC4834P from Acme Enterprises
> > (Orlando).
> > I tried each type in both sets and found that the higher rank
(letter)
> > transistors ran progressively cooler. I matched the transistors
from
> > batches of 10 by forward bias voltage on the junctions then in
circuit
> > for
> > nearest to 50% duty cylce. I have found that swapping pairs or
swapping
> > the
> > caps on Q601,602 can often improve the ratio to closer to 50%.
> >
> > Interestingly, the higher gain transistors ran cooler by 10-20
degrees,
> > depending on the set, but the overall current drawn by the set was
> > virtually
> > the same(~60-70 mA with & without a signal)
> >
> > Summing up, it appears that the higher rank transistors are the
better
> > choice. Acme has them at a great price(10 for $15.95) and has free
> > shipping
> > for the time being on orders over $25. They are a new operation but
> > Glen,
> > the main contact there was a manager for MCM at one time and seems
> > veryinterested in winning over the business of shops like us. So
far
> > they
> > seem to be good to work with.
> >
> > BTW, the KV32S25 was a bit atypical in that the HOT failure was due
to a
> > bad
> > FBT. The price was pretty steep and the customer did not want to
fix
> > it, so
> > I gambled and tried an aftermarket transformer from HR. It seems
fine
> > so
> > far and at the lower price the customer went for the fix. We'll see
if
> > it
> > holds up. I don't like subbing flybacks but these have had a good
rep.
> >
> > Leonard G. Caillouet
> > Electronics World
> > Gainesville, FL
> > 352-332-5608
> > 352-332-5668 (fax)
> >
> >
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