Possible damage from reversed DC power?
 

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I accidentally reversed the polarity of my DC power supply. I blew
the fuse in my TNC, but I can't find a fuse in my TR-7400A and the
only fuse I see in my TS-520 appears to be for the AC power supply.

What sort of damage could these radios have suffered?

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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In message , Jack Twilley
writes
I accidentally reversed the polarity of my DC power supply. I blew
the fuse in my TNC, but I can't find a fuse in my TR-7400A and the
only fuse I see in my TS-520 appears to be for the AC power supply.

What sort of damage could these radios have suffered?

You may have blown the 'idiot diode' as well as the fuse..

Mike
--
M.J.Powell

"Jack Twilley" wrote in message
...
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I accidentally reversed the polarity of my DC power supply. I blew
the fuse in my TNC, but I can't find a fuse in my TR-7400A and the
only fuse I see in my TS-520 appears to be for the AC power supply.

What sort of damage could these radios have suffered?

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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There is a diode on the 7400a that is there to stop damage in such an thing
happens.

It is either in parallel to ground off the 12v lead in in the rig , or it
may be in series. But most likely it will be in parallel.

It will be easy to see as it will be burnt and probably busted open. It is
also shorted. Hopefully it went before the rest of the radio did. But if
it did not stop there, look at the Voltage regulator (s) chip (s) and you
probably blew out the rcve audio stages also.

Why was there no fuse is my question on the 7400A line?

As to the TS-520, it runs on AC. Why is there a DC power supply on it?

Dan/W4NTI

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"Mike" == M J Powell writes:

Jack I accidentally reversed the polarity of my DC power supply. I
Jack blew the fuse in my TNC, but I can't find a fuse in my TR-7400A
Jack and the only fuse I see in my TS-520 appears to be for the AC
Jack power supply.

Jack What sort of damage could these radios have suffered?

Mike You may have blown the 'idiot diode' as well as the fuse..

I have the schematic to the TS-520, so I can look for an obvious diode
near the power connector but I don't have the schematic for the
TR-7400A. If anyone out there has the schematic and knows where this
idiot diode is, let me know.

Mike Mike -- M.J.Powell

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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"W4NTI" == w4nti Dan writes:

Jack I accidentally reversed the polarity of my DC power supply. I
Jack blew the fuse in my TNC, but I can't find a fuse in my TR-7400A
Jack and the only fuse I see in my TS-520 appears to be for the AC
Jack power supply.

Jack What sort of damage could these radios have suffered?

Jack Jack.

W4NTI There is a diode on the 7400a that is there to stop damage in
W4NTI such an thing happens.

The aforementioned "idiot diode".

W4NTI It is either in parallel to ground off the 12v lead in in the
W4NTI rig , or it may be in series. But most likely it will be in
W4NTI parallel.

W4NTI It will be easy to see as it will be burnt and probably busted
W4NTI open. It is also shorted. Hopefully it went before the rest
W4NTI of the radio did. But if it did not stop there, look at the
W4NTI Voltage regulator (s) chip (s) and you probably blew out the
W4NTI rcve audio stages also.

I'll look for a smoky component then.

W4NTI Why was there no fuse is my question on the 7400A line?

There was. It blew, but when I replaced that fuse, the radio still
didn't turn on, so I suspected an internal fuse.

W4NTI As to the TS-520, it runs on AC. Why is there a DC power
W4NTI supply on it?

The TS-520 can run on AC or DC, depending on what power cable is
attached to the rig. Mine has the DC power cable attached (it
connects to different pins) so it can run directly off DC.

W4NTI Dan/W4NTI

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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In message , Jack Twilley
writes
"Mike" == M J Powell writes:

Jack I accidentally reversed the polarity of my DC power supply. I
Jack blew the fuse in my TNC, but I can't find a fuse in my TR-7400A
Jack and the only fuse I see in my TS-520 appears to be for the AC
Jack power supply.

Jack What sort of damage could these radios have suffered?

Mike You may have blown the 'idiot diode' as well as the fuse..

I have the schematic to the TS-520, so I can look for an obvious diode
near the power connector but I don't have the schematic for the
TR-7400A. If anyone out there has the schematic and knows where this
idiot diode is, let me know.

If you have an ohmmeter you could clip it across the DC input pins and
start unsoldering various connections etc.

By the way - have you measured ohms across the DC input? Clip leads both
ways round?

Mike
--
M.J.Powell