One for the electronics buffs…seemingly obscure 5v voltage regulators

[Johnnybravo]

What are your voltage readings on the input pins?

Will only probably get back on it two weekends time. Inundated with work

 

[skotl]

Having looked into this a bit further , I am not convinced this would be a straight swap with a normal 7805 in that if you Google that part number it seems to be bipolar and able to regulate both positive and negative 5v

I do suspect you’re making this more complicated than it needs to be. If you need to get some voltage down to 5V then a generic 7805 is a very easy way to do this.
As per my and other queries, what’s the readings at the pins?

 

[richie00boy]

Having looked into this a bit further , I am not convinced this would be a straight swap with a normal 7805 in that if you Google that part number it seems to be bipolar and able to regulate both positive and negative 5v

Bipolar is simply the technology used to make the regulator. As a 3 pin device it can only regulate one polarity.
LM7805 or uA7805 from TI should be a suitable replacement - having 7.5V input doesn't require a low dropout regulator (but it is close to the limit). LM2937-5 from TI is low dropout and might be a suitable replacement depending on the input and output capacitor values. It may be easier to find this part and change the capacitors if necessary.
You should check if there are capacitors close to the device on the input and output, if these are missing or faulty any replacement is likely to fail after a time. The low dropout regulators are less tolerant of this so I suspect may be the reason for failure (oscillation leading to overheating).

 

[Misterg]

It does seem a strange choice of component for the purpose,

If you need to get some voltage down to 5V then a generic 7805 is a very easy way to do this

The original 7805 would be marginal for producing 5V from 7.5V (2V dropout, so if the 7.5V supply dipped below 7V (due to loading, ripple, etc.) it would affect the 5V) so the DL version (0.6V dropout) seems a prudent choice to me. (That said, a 7805 would surely work for testing purposes.)

Note that a 78L05 isn't the same as a 78DL05 - the former is only a lower power version of the 7805, but with the same 2V dropout voltage.

 

[Johnnybravo]

Bipolar is simply the technology used to make the regulator. As a 3 pin device it can only regulate one polarity.
LM7805 or uA7805 from TI should be a suitable replacement - having 7.5V input doesn't require a low dropout regulator (but it is close to the limit). LM2973 from TI might be a suitable replacement depending on the input and output capacitor values. It may be easier to find this part and change the capacitors if necessary.
You should check if there are capacitors close to the device on the input and output, if these are missing or faulty any replacement is likely to fail after a time. The low dropout regulators are less tolerant of this so I suspect may be the reason for failure (oscillation leading to overheating).

Your comments tie in with what the technician said to me. Each voltage regulator has two capacitors close by. He suggested replacing both voltage regulators and all four capacitors. Probably for exactly the reason you mentioned

 

[Johnnybravo]

I do suspect you’re making this more complicated than it needs to be. If you need to get some voltage down to 5V then a generic 7805 is a very easy way to do this.
As per my and other queries, what’s the readings at the pins?

There must be a reason they chose to use the components they did. The Japanese are not stupid, and this machine was built to do a job. Not built to a price ! The very reason why they went bankrupt

Like I have said already, inundated with work so won’t be going back into this for two weekends. Want to have the necessary components to hand by then.

 

[ajlelectronics]

There must be a reason they chose to use the components they did. The Japanese are not stupid, and this machine was built to do a job. Not built to a price ! The very reason why they went bankrupt

Like I have said already, inundated with work so won’t be going back into this for two weekends. Want to have the necessary components to hand by then.

Not normally except for Sony's suicide missions, but that choice of component is peculiar, almost as if they found a problem and scratched around for a solution. TO-220 is not normally vertical either, the hole is for fastening it down.

 

[Johnnybravo]

Not normally except for Sony's suicide missions, but that choice of component is peculiar, almost as if they found a problem and scratched around for a solution. TO-220 is not normally vertical either, the hole is for fastening it down.

The next upgrade to that machine that distribution board was changed and powered by its own separate power supply that was piggybacked into the back of the main power supply’s heat sink.
So they were known to cause issues

 

[richie00boy]

Pretty common to stand TO-220 devices up like that. Once you get it sorted if you can hold your finger on the tab it is passable.

Does the unit experience any vibration? You might be able to find a small clip on heatsink which would help - often standup implementations like that are marginal for temperature. But additional measures might need to be taken if any vibration.

 

[ajlelectronics]

Pretty common to stand TO-220 devices up like that. Once you get it sorted if you can hold your finger on the tab it is passable.

Common yes, professional? No, but it saves a few pennies.