AW: [Premium-Rx] URR-74/WJ8718 help

[Ahmet G.]

DS8857J is in a ceramic pkg. It is built to operate up to INDustrial
temp ranges of +105 C.

there is a copper finger attached to the front panel and it touches 
the IC when the board is installed, whereby providing heat sinking.

regards
ahmet
> 
> G'day,
> 
> I'm not surprised that the device gets hot as there is a fair bit of
> current going through it.
> 
> 73, Berndt
> VK5ABN
> 
> -----Ursprüngliche Nachricht-----
> Von: premium-rx-bounces at mailman.qth.net
> [mailto:premium-rx-bounces at mailman.qth.net] Im Auftrag von L D Ritta
> Gesendet: Saturday, 11 October 2008 10:11 PM
> An: Ahmet G.; premium-rx at mailman.qth.net
> Betreff: Re: [Premium-Rx] URR-74/WJ8718 help
> 
> 
> Howdy Ahmet
> In the WJ 8718/URR-74  on the display board there is a bcd to decimal
> decode
> and
> a bcd to 7 segment decoder. there are no transistors between the DS8857
> and
> the displays.
> so that is not the problem. unless you can prove otherwise.
> The only other chip is a  MOS to LED 8 digit driver which goes between
> the
> cathode of the displays
> and 4028 bcd to decimal decoder.
> BTW is the running time meter supposted to be noisy, it goes tic tic tic
> it
> is very annoying.
> and I noticed the DS8857J is very hot I mean you could burn your self.
> 
> 
> 
> 
> Lee
> ----- Original Message -----
> From: "Ahmet G." <ahmet-m at usa.com>
> To: "L D Ritta" <ufp at optusnet.com.au>; <premium-rx at mailman.qth.net>
> Sent: Saturday, October 11, 2008 8:33 PM
> Subject: Re: [Premium-Rx] URR-74/WJ8718 help
> 
> 
> >
> > Hello
> >
> > DS8857 is an IC made by National Semiconductor
> > It is a BCD to 7 Segment display driver, Decoder.
> > Current: 60mA
> > Type: CA Common Anode
> >
> > I believe you can replace this with a similar driver IC from the 74xxx
> 
> > series drivers that you can find easier in the market. Such as: 
> > 7446, 7447, 74247 which are CA types
> >
> > They have same connection diagrams and functions, each one with 
> > an additional function such as Ripple Blanking on the DS8857.
> >
> > Usually there are power transistors that regulate the higher 
> > currents on the display boards ( they are usually attached to 
> > heat sinks) and these transistors tend to burn out before the 
> > driver ICs. One of the main reasons is the fact the heat sink 
> > connection is lose or accumulated dust thereby blocking heat 
> > flow. So you may want to check to see if the transistors are ok 
> > before replacing the driver IC.
> >
> > Hope this helps.
> >
> > Ahmet Gundes
> >
> >>
> >> Hello Everyone
> >> Well I got my my URR-74 working after I changed my back panel for one
> 
> >> from a WJ-8718. However the display does not work, the f and b 
> >> segments are out on all displays. This looks like
> >> the U8 on the display board which is a DS8857 however I can not
> >> find any data on it on google.
> >>
> >> Am I correct in my logic and someone know what I can use to 
> >> replace it. your ideas please.
> >>
> >> 73 Lee _______________________________________________
> >> Premium-Rx Mailing List
> >> To Post: premium-rx at mailman.qth.net
> >> For Info: http://mailman.qth.net/mailman/listinfo/premium-rx
> >> Visit the Website: http://www.premium-rx.org
> >> Email Help: paul at premium-rx.org
> >



=
Macarthur Place Napa Valley hotel
Beautiful AAA 4-Diamond Napa Valley hotel.Luxurious rooms; spa.
http://a8-asy.a8ww.net/a8-ads/adftrclick?redirectid=cc60bdd02dc4b334d36888a7feee727e