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

  • From: "Leonard Caillouet" <lcaillo@xxxxxxxxxxxx>
  • To: <techassist@xxxxxxxxxxxxx>
  • Date: Fri, 7 Nov 2003 22:15:39 -0500

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" <teltek3@xxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
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)
>
> ************************************************************************
> *****
> Classifieds! Buy or Sell!
> http://sell.tech-assist.org
> The Tech Address Book:
> http://www.tech-assist.org/secure/tip/contact.htm
> Add a Repair Tip Here, or Change/Remove your Email Address:
> http://www.tech-assist.org/secure/tip/main.htm
> Lost Password:
> http://www.tech-assist.org  and select "Lost your Login Info?".
> Email Archives:
> //www.freelists.org/archives/techassist/
>
>
****************************************************************************
*
> Classifieds! Buy or Sell!
> http://sell.tech-assist.org
> The Tech Address Book:
> http://www.tech-assist.org/secure/tip/contact.htm
> Add a Repair Tip Here, or Change/Remove your Email Address:
> http://www.tech-assist.org/secure/tip/main.htm
> Lost Password:
> http://www.tech-assist.org  and select "Lost your Login Info?".
> Email Archives:
> //www.freelists.org/archives/techassist/


*****************************************************************************
Classifieds! Buy or Sell!
http://sell.tech-assist.org
The Tech Address Book:
http://www.tech-assist.org/secure/tip/contact.htm
Add a Repair Tip Here, or Change/Remove your Email Address:
http://www.tech-assist.org/secure/tip/main.htm
Lost Password:
http://www.tech-assist.org  and select "Lost your Login Info?".
Email Archives:
//www.freelists.org/archives/techassist/

Other related posts:

  1. Home
  2. techassist
  3. Archive
  4. 11-2003