[Shop-talk] Help identifying a chip

Mon Feb 25 06:51:06 MST 2019

 All good stuff but a few points of clarification.  The LM in LM7805CT will change depending on the manufacturer.  You can find L7805 or MC7805 or NCP7805 and others.  They will all work.  The CT indicates the package, TO220 in this case.  You want the same package as what is in there now to avoid some cludge job hooking up a different style part.  Also, these parts are current limited.  If there is a short down stream the part will not fail, it will limit the current to the short until the die temperature reaches 150 deg C at which point it will reduce the output current and continue in this mode indefinitely.  These parts are pretty bullet-proof.  About the only way they will fail is too much voltage is applied.  As stated the input voltage can be as high as 35 volts but if it is much higher the part will fail.  Typical failure mode is a short input to output and this will pass this high voltage on to the rest of the circuit and may cause other failures.
I say may because it depends on what else is in the circuit.  If there are voltage suppressors and current limiters (fuses) they may protect the rest of the circuit.  It depends on what the designer put in there.
We design and manufacture industrial products that are designed to operate from a 24 Vdc supply.  It is not uncommon for users to try to power them off of 120 Vac because that is what the old part being replaced used.  It was common enough that I designed a protection circuit that would monitor the input power and only pass it on to the device if it was within the acceptable range.  So, instead of getting a room full of smoke the user will find the part not working.  When they call in to complain we tell them to use the right power.  They do so and the part works as advertised.  Result: happy customer.  

Dave 

-----Original Message-----
From: Trevor Boicey via Shop-talk <shop-talk at autox.team.net>
To: Battmain <battmain at yahoo.com>
Cc: shop-talk at autox.team.net <shop-talk at autox.team.net>
Sent: Mon, Feb 25, 2019 12:31 am
Subject: Re: [Shop-talk] Help identifying a chip

There are a lot of parts that will work there. As previously mentioned it's a 1 amp 5 volt regulator in a TO220 case. (TO220 is the case style with three pins and a heat sink tab with hole for a bolt to attach it to something metal to keep it cool)
Extremely common and extremely cheap part. Makes nice clean 5V from any input voltage from about 6V to about 35V. Three pins are just "input voltage 6V-35V", "output voltage 5V", and ground.
Digikey for that voltage and case shows the ubiquitous 7805 as well as compatible variations up to 5A:
https://www.digikey.com/products/en/integrated-circuits-ics/pmic-voltage-regulators-linear/699?k=&pkeyword=7805&sv=0&pv1779=56&sf=0&FV=40203a%2Cffe002bb&quantity=&ColumnSort=0&page=1&stock=1&pageSize=25

Any part designated 7805-anything should work.
It likely blew up because something else shorted, but if the shorting was temporary then it might just need replacing.
Suggestion: Buy a few because they are much cheaper than postage will be, about 50 cents each at Digikey in quantity <10. Solder in a new one and see if it works or blows up again.
If it blows up again, look for shorts around the device and fix those before blowing up another one.

Repeat until it's working or you lose interest.
On Sat, Feb 23, 2019 at 11:01 AM Battmain via Shop-talk <shop-talk at autox.team.net> wrote:

 Could I use *any* MC7805CT as a replacement, as the first link shows different models of that regulator? Some models of the regulator have variable output as listed in the second link. I suspect the output should stay constant for power, but since the amp output section has the pot on it, was wondering if I should go with the adjustable output regulator or just stick with a fixed output?

Brian

    On Saturday, February 23, 2019, 9:37:17 AM EST, Pat Horne <patintexas at icloud.com> wrote:  

 This chip is a voltage regulator, not the audio amplifier. The part number indicates that it is a 5v fixed regulator. 
Peace, Pat

Pat Horne We support Habitat for Humanity

On Feb 23, 2019, at 7:35 AM, Battmain via Shop-talk <shop-talk at autox.team.net> wrote:

 I did look up that model, however, here is an example from this site...MC7805CT Datasheet, PDF - Alldatasheet

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MC7805CT Datasheet, PDF - Alldatasheet
alldatasheet.comMC7805CT Datasheet, MC7805CT PDF, MC7805CT Data sheet, MC7805CT manual, MC7805CT pdf, MC7805CT, datenblatt, Elec... |

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They list multiple models of that chip. The one I think is closest is...http://pdf1.alldatasheet.com/datasheet-pdf/view/82852/FAIRCHILD/MC7805CT.html
because of the variable output.  The amp does have level/volume pot on it. The other datasheets in the list do not show a variable output.
Brian

    On Saturday, February 23, 2019, 6:30:21 AM EST, Jeff Scarbrough <fishplate at gmail.com> wrote:  

 How about LM7805CT?

On Sat, Feb 23, 2019 at 2:16 AM Battmain via Shop-talk
<shop-talk at autox.team.net> wrote:
>
> Finally got around to installing an amplified speaker I had sitting around for years.  It was supposed to be a simple install, but looks like I fried something in the haste.
>
> I already picked up the capacitor in the picture,  but I think the regulator might be fried also based on the burn marks.Seems there are different models of that regulator.  The amp is in a 12v application.  Anybody have any ideas as to what model regulator it is? (or what I could substitute it with? Will be getting it from that auction site. :) )
> Picture in the link...(that's the best I could get) https://i.imgur.com/FIfJA4O.jpg
>
> I figure if I throw $5 at it in parts, it wouldn't hurt to try.
>
>
> Brian

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