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From: kvm on 17 Nov 2008 21:20
b wrote:
> On 16 nov, 16:50, kvm <k...(a)neo.rr.com> wrote:
>> b wrote:
>>> On 15 nov, 04:21, kvm <k...(a)neo.rr.com> wrote:
>>>> b wrote:
>>>>> these two vertical output ics seem almost identical, i think the 8170
>>>>> needs a ref voltage on pin 1. can they be interchanged? if so, what
>>>>> mods if any will be required.
>>>>> cheers. B
>>>> TDA8177 ICs are getting hard to find (discontinued).
>>>> Why not use it's smaller counterpart. The TDA8172 is a drop in
>>>> replacement that works for me. I have replaced 8177s with 8172s in
>>>> commercial 25" RGB monitors with no failures (2+ years) (Dotronix
>>>> DSV-25C video wall monitors). There should be a electrolytic capacitor
>>>> just off of the pins of this IC. It is usually a 100mfd with a voltage
>>>> rating between 35v and 50v. Replace this cap or you will be replacing
>>>> the IC again. (I use a 100mfd/63v which cuts down on failures).
>>>> No extra circuitry changes are needed if going from 8177s to 8172s. The
>>>> worst that can happen is the IC fails. I have used this IC in Toshiba
>>>> projection units also with no failures.
>>>> Good luck!
>>>> Dave
>>> Hi Dave
>>> thanks a lot for the info. I actually picked up a couple of TDA8177
>>> from my local supplier for about 2� each. Have yet to test the set
>>> extensively but I did replace the IC and cap you said, and two 1000uF
>>> 16v caps providing a +10v and -10v to the ic (used 35v 105� types).
>>> coincidentally I now have another set to fix, with a similar fault,
>>> only it uses a TDA8178S - do you think the TDA8172 would work there?
>>> the TDA 8178S is more expensive, at least in my local store. Ben
>> B,,
>> You might want to do a google search of TDA8170, 8172, 8177, 8178.
>> search as "TDA8172 pda" etc. You will find that the TDA8178 has a much
>> higher working voltage than TDA8170 and TDA8172 (90V) but lower current
>> handling (2A). There is a wealth of information available on the "net".
>> I think I'd spend the extra "pounds" and get the right IC as the working
>> voltage in the circuit would probably kill a lower voltage rated one.
>>
>> Lots of great info on the net... Just remember to replace the "pump-up"
>> capacitor (100mfd/63v) as this is usually what causes the death of
>> these ICs.
>>
>> Lots of luck!
>> Dave
>
> thanks again Dave. I have got the datasheets now. and will follow it
> up.
> I just checked the set in which I changed the TDA 8177F, the pumpup
> cap would appear to be 33uF. I suspect a slightly higher value may
> have been wise for reliability, who knows. reminds me of the vestel
> 11AK30 chassis line drive decoupler which is 10uF and many techs I
> have spoken to replace it with a 47uF, since things run cooler that
> way.
> -B
The difference in values may have to do with you being on the other side
of the pond. Our (USA) scanning frequencies are 60hz vertical and
15575hz horz.
I believe your vertical scan rate matches your AC line (mains) frequency
of 50hz (at least for analog TV). Check the pump-up caps in a few TVs
as this may be the case.
I'd be curious to see if they are different.
Dave.
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