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

[Berndt Josef Wulf]

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 _______________________________________________
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>> Email Help: paul at premium-rx.org
>
>
> =
>
> 

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