Hi

Just attempted to repair a 1987 vintage2m handheld. Replaced NiCads and
they charge ..trouble is the PLL keeps unlocking. Replaced the lithium
memory battery as well ... no change. This doesn't happen all the time
....set operates as normal for hours on end and then this happens (U shows on
display) Good audio etc reported ... anybody any idea where to look for
this fault???

Stumped!

Steve

VK3CAX

Stephen;
The most likely place to start is to adjust the VCO capacitor or coil so
that the steering line voltage is within the correct range, usually 1.7
to 2.5 volts depending on the design and frequency of operation. If you
can find a schematic, their should be notes regarding this adjustment.
You might try tuning the radio from one end of the band to the other, if
it relocks, say on the low end and not on the high end (or vice versa)
you can pretty much count on it being a VCO adjustment. Bear in mind
that as the radio ages, the tuning capacitor or other components can get
contaminated especially if the VCO circuit is potted in paraffin as many
are.

Joe

Stephen Curtis wrote:

Hi

Just attempted to repair a 1987 vintage2m handheld. Replaced NiCads and
they charge ..trouble is the PLL keeps unlocking. Replaced the lithium
memory battery as well ... no change. This doesn't happen all the time
...set operates as normal for hours on end and then this happens (U shows on
display) Good audio etc reported ... anybody any idea where to look for
this fault???

Stumped!

Steve

VK3CAX





--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

"Jazz is not dead, It just smells funny" F.Z

Stephen;
The most likely place to start is to adjust the VCO capacitor or coil so
that the steering line voltage is within the correct range, usually 1.7
to 2.5 volts depending on the design and frequency of operation. If you
can find a schematic, their should be notes regarding this adjustment.
You might try tuning the radio from one end of the band to the other, if
it relocks, say on the low end and not on the high end (or vice versa)
you can pretty much count on it being a VCO adjustment. Bear in mind
that as the radio ages, the tuning capacitor or other components can get
contaminated especially if the VCO circuit is potted in paraffin as many
are.

Joe

Stephen Curtis wrote:

Hi

Just attempted to repair a 1987 vintage2m handheld. Replaced NiCads and
they charge ..trouble is the PLL keeps unlocking. Replaced the lithium
memory battery as well ... no change. This doesn't happen all the time
...set operates as normal for hours on end and then this happens (U shows on
display) Good audio etc reported ... anybody any idea where to look for
this fault???

Stumped!

Steve

VK3CAX





--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

"Jazz is not dead, It just smells funny" F.Z

Stephen;
The most likely place to start is to adjust the VCO capacitor or coil so
that the steering line voltage is within the correct range, usually 1.7
to 2.5 volts depending on the design and frequency of operation. If you
can find a schematic, their should be notes regarding this adjustment.
You might try tuning the radio from one end of the band to the other, if
it relocks, say on the low end and not on the high end (or vice versa)
you can pretty much count on it being a VCO adjustment. Bear in mind
that as the radio ages, the tuning capacitor or other components can get
contaminated especially if the VCO circuit is potted in paraffin as many
are.

Joe

Stephen Curtis wrote:

Hi

Just attempted to repair a 1987 vintage2m handheld. Replaced NiCads and
they charge ..trouble is the PLL keeps unlocking. Replaced the lithium
memory battery as well ... no change. This doesn't happen all the time
...set operates as normal for hours on end and then this happens (U shows on
display) Good audio etc reported ... anybody any idea where to look for
this fault???

Stumped!

Steve

VK3CAX





--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

"Jazz is not dead, It just smells funny" F.Z