I have a cheap little radio that runs on AC or batteries, a Jensen
MR-550, fwiw. The voltage coming out of the power transformer is zero. >Between the prongs on the AC plug it has 580 ohms. It also says it has
a "thermal fuse fitted D 125 0" (I think the last digit is a zero.) But
I haven't foudn the fuse yet. Would the fuse be in the secondary
circuit? I thought it would be in the primary but there is ocntinuity
there, 580 ohms. My friend says it wroked fine for the first 2 months
and then went dead.
On Thu, 12 Mar 2026 01:00:56 -0400, micky <NONONOmisc07@fmguy.com>
wrote:
I have a cheap little radio that runs on AC or batteries, a Jensen
MR-550, fwiw. The voltage coming out of the power transformer is zero. >>Between the prongs on the AC plug it has 580 ohms. It also says it has
a "thermal fuse fitted D 125 0" (I think the last digit is a zero.) But
I haven't foudn the fuse yet. Would the fuse be in the secondary
circuit? I thought it would be in the primary but there is ocntinuity >>there, 580 ohms. My friend says it wroked fine for the first 2 months
and then went dead.
You can measure the impedance of the transformer output,
but thermal
fuses are normally placed in the primary.
Check for dry solder joints on the transformer pins.
RL
In sci.electronics.repair, on Thu, 12 Mar 2026 09:24:59 -0400, legg ><legg@nospam.magma.ca> wrote:
On Thu, 12 Mar 2026 01:00:56 -0400, micky <NONONOmisc07@fmguy.com>
wrote:
I have a cheap little radio that runs on AC or batteries, a Jensen >>>MR-550, fwiw. The voltage coming out of the power transformer is zero. >>>Between the prongs on the AC plug it has 580 ohms. It also says it has
a "thermal fuse fitted D 125 0" (I think the last digit is a zero.) But >>>I haven't foudn the fuse yet. Would the fuse be in the secondary >>>circuit? I thought it would be in the primary but there is ocntinuity >>>there, 580 ohms. My friend says it wroked fine for the first 2 months >>>and then went dead.
I'm making progress.
You can measure the impedance of the transformer output,
It is infinite.
but thermal
fuses are normally placed in the primary.
That's what I thought.
Check for dry solder joints on the transformer pins.
No pins. Primary wires connected to line cord and covered with
heatshink tubing. 580 ohma between them.
Secondary wire straight to little circuit board, which has diodes on it.
I took out the transformer and I don't see where the fuse would be.
Maybe next to the windings.
It also runs on 4 C-batteries. My friend says that doesn't work either,
but things don't usually break in two ways at once, especially a Jensen >radio, even if cheap. Maybe one of his batteries was dead. If the 4 >batteries put out 6v DC, what should the AC output voltage of the
transformer be to get 6 volts for the radio?
Or I could assume it's the fuse, take the current one apart, find the
fuse, bypass it, on the theory that the fuse should have been in the
primary anyhow. ??????
RL
In sci.electronics.repair, on Fri, 13 Mar 2026 22:44:36 -0400, micky ><NONONOmisc07@fmguy.com> wrote:
In sci.electronics.repair, on Thu, 12 Mar 2026 09:24:59 -0400, legg >><legg@nospam.magma.ca> wrote:
On Thu, 12 Mar 2026 01:00:56 -0400, micky <NONONOmisc07@fmguy.com>
wrote:
I have a cheap little radio that runs on AC or batteries, a Jensen >>>>MR-550, fwiw. The voltage coming out of the power transformer is zero. >>>>Between the prongs on the AC plug it has 580 ohms. It also says it has >>>>a "thermal fuse fitted D 125 0" (I think the last digit is a zero.) But >>>>I haven't foudn the fuse yet. Would the fuse be in the secondary >>>>circuit? I thought it would be in the primary but there is ocntinuity >>>>there, 580 ohms. My friend says it wroked fine for the first 2 months >>>>and then went dead.
I'm making progress.
You can measure the impedance of the transformer output,
It is infinite.
but thermal
fuses are normally placed in the primary.
That's what I thought.
Check for dry solder joints on the transformer pins.
No pins. Primary wires connected to line cord and covered with
heatshink tubing. 580 ohma between them.
Secondary wire straight to little circuit board, which has diodes on it.
I took out the transformer and I don't see where the fuse would be.
Maybe next to the windings.
It also runs on 4 C-batteries. My friend says that doesn't work either,
And when I tried it with a universal charger, set to 6v, it didn't work,
nor with the polarity reversed. Not a peep out of it on AM or FM across
the whole dial.
Oops. should I have tried 7.5 and 9 volts too?
but things don't usually break in two ways at once, especially a Jensen >>radio, even if cheap. Maybe one of his batteries was dead. If the 4 >>batteries put out 6v DC, what should the AC output voltage of the >>transformer be to get 6 volts for the radio?
Or I could assume it's the fuse, take the current one apart, find the
fuse, bypass it, on the theory that the fuse should have been in the >>primary anyhow. ??????
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