My Fm4 has a strange problem, I have replaced the back up battery and this
is working, if I store a station at 88.10 mhz when I switch it back on the
frequency comes up at 88.00 mhz for the first 5 - 10 minutes, it then slowly
creeps up to 88.5 then 88.10, it does this on all stations stored.

Does anyone have any ideas about this

Thanks
Gary

"gary" wrote in message
...
My Fm4 has a strange problem, I have replaced the back up battery and this
is working, if I store a station at 88.10 mhz when I switch it back on the
frequency comes up at 88.00 mhz for the first 5 - 10 minutes, it then
slowly
creeps up to 88.5 then 88.10, it does this on all stations stored.

Does anyone have any ideas about this

Thanks
Gary

Remove the MPA480 custom chip from its socket and re-insert it. This
sometimes cures spurious or erratic performance.
Considering the age of the Tuner, the socket contacts are likely not as good
as they should be and the process of removing & re-inserting the chip will
clean up the contacts. Personally I would replace the socket with a new one.
If this doesn't fix it, you are likely up for a new IC - which are available
from Quad at about UKP26.00
I had a strange fault on my FM4 a while back which I put down to a faulty
battery - the Tuner wouldn't hold stations in memory. I changed the battery,
but the fault remained. Further investigation showed that the IC had
developed an internal leak and was allowing the battery to drain very
quickly so I replaced the IC and that fixed the problem..
n.b. once the battery voltage drops under 4v then the memory goes AWOL.

"Mike Coatham" wrote in message
...

Oops... the IC is an MP4480

"Mike Coatham"

My Fm4 has a strange problem, I have replaced the back up battery and
this
is working, if I store a station at 88.10 mhz when I switch it back on
the
frequency comes up at 88.00 mhz for the first 5 - 10 minutes, it then
slowly creeps up to 88.5 then 88.10, it does this on all stations stored.


Remove the MP4480 custom chip from its socket and re-insert it. This
sometimes cures spurious or erratic performance.
Considering the age of the Tuner, the socket contacts are likely not as
good
as they should be and the process of removing & re-inserting the chip will
clean up the contacts. Personally I would replace the socket with a new
one.
If this doesn't fix it, you are likely up for a new IC - which are
available
from Quad at about UKP26.00



** After carefully examining the schematic of the FM4 - I reckon Mike is
pretty much right on the money here.

Your Quad tuner's problem is most likely some kind of corroded contact,
stray leakage or PCB dirt and dust contamination issue.

Just needs some TLC.






....... Phil

"gary"

My Fm4 has a strange problem, I have replaced the back up battery and this
is working, if I store a station at 88.10 mhz when I switch it back on the
frequency comes up at 88.00 mhz for the first 5 - 10 minutes, it then
slowly creeps up to 88.5 then 88.10, it does this on all stations stored.

Does anyone have any ideas about this


** I take 88.5 should be 88.05 ????

So the tuned frequency drifts up by only about 100 kHz as it warms up -
NOT 500 kHz.

Despite appearances, the FM4 is NOT frequency locked with a digital
frequency synthesiser, like most other tuners with a digital readout.

Tuning frequency is controlled by analogue circuitry via "varicaps " - so
cannot be entirely drift free.

However, the digital readout shows the ACTUAL operating frequency of the set
with high ( ie crystal ) accuracy.

There is likely NOTHING wrong with your FM4 - so leave it alone.

Please disregard my earlier post.




........ Phil

In article , Phil Allison
writes

"gary"

My Fm4 has a strange problem, I have replaced the back up battery and this
is working, if I store a station at 88.10 mhz when I switch it back on the
frequency comes up at 88.00 mhz for the first 5 - 10 minutes, it then
slowly creeps up to 88.5 then 88.10, it does this on all stations stored.

Does anyone have any ideas about this


** I take 88.5 should be 88.05 ????

So the tuned frequency drifts up by only about 100 kHz as it warms up -
NOT 500 kHz.

Despite appearances, the FM4 is NOT frequency locked with a digital
frequency synthesiser, like most other tuners with a digital readout.

Tuning frequency is controlled by analogue circuitry via "varicaps " - so
cannot be entirely drift free.

What is that locked to if anything, or is it free running with AFC?.

Doesn't seem to be an FM4 circuit in the web anywhere.....

However, the digital readout shows the ACTUAL operating frequency of the set
with high ( ie crystal ) accuracy.

There is likely NOTHING wrong with your FM4 - so leave it alone.

Please disregard my earlier post.




....... Phil

--
Tony Sayer

"tony sayer"


** I take 88.5 should be 88.05 ????

So the tuned frequency drifts up by only about 100 kHz as it warms up -
NOT 500 kHz.

Despite appearances, the FM4 is NOT frequency locked with a digital
frequency synthesiser, like most other tuners with a digital readout.

Tuning frequency is controlled by analogue circuitry via "varicaps " -
so
cannot be entirely drift free.

What is that locked to if anything, or is it free running with AFC?.


** Correct.

Just the DC bias voltage applied to the varicaps and internal temperature
set the frequency.

Likely some temperate compensation involved too.


Doesn't seem to be an FM4 circuit in the web anywhere.....


** Here's one:

http://www.dc-daylight.ltd.uk/Valve-...ic-circuit.pdf


The mysterious MP4480 uP ( a programmed Texas TMS1000 ? ) makes deciphering
it a bit interesting.




........ Phil

"tony sayer" wrote in message
news
In article , Phil Allison
writes

"gary"

My Fm4 has a strange problem, I have replaced the back up battery and
this
is working, if I store a station at 88.10 mhz when I switch it back on
the
frequency comes up at 88.00 mhz for the first 5 - 10 minutes, it then
slowly creeps up to 88.5 then 88.10, it does this on all stations
stored.

Does anyone have any ideas about this


** I take 88.5 should be 88.05 ????

So the tuned frequency drifts up by only about 100 kHz as it warms up -
NOT 500 kHz.

Despite appearances, the FM4 is NOT frequency locked with a digital
frequency synthesiser, like most other tuners with a digital readout.

Tuning frequency is controlled by analogue circuitry via "varicaps " -
so
cannot be entirely drift free.

What is that locked to if anything, or is it free running with AFC?.


The AFC operates on pre-set stations only and is derived from IC10 (4441)
the discriminator. The p.d across pins 6 and 10 is applied to the comparator
of IC14(TL092). The comparator amplifies the difference voltage via a
potential divider and an analogue switch and modifies the ref. voltage and
hence the tune volts.


Doesn't seem to be an FM4 circuit in the web anywhere.....

No...but I have the service manual which does

However, the digital readout shows the ACTUAL operating frequency of the
set
with high ( ie crystal ) accuracy.

There is likely NOTHING wrong with your FM4 - so leave it alone.

There IS something wrong - the set shouldn't drift.
But let's wait for the OP to come back and report on whether removing &
re-inserting the custom programmed microprocessor IC has fixed his problem.
Quad make special mention of this course of action in the service manual -
and suggest it as the first thing to try for faults with the symptoms
described. There are a couple of other components which could cause drift
but let's not go to Plan B until we know Plan A didn't work.

Hello Firstly Thanks to the guys who responded with their thoughts and
suggestions.

I did in fact take bull by the horns and remove the memory IC and its
socket, I then tossed the socket aside, cleaned up the pins on the IC and
soldered it directly into the PCB.

This so far seems to have stopped the problem, it is still a little twitchy
when I switch it on (Classic FM 100.00 Mhz) starts at 99.95 but within a
minute it changes to 100.00 Mhz and the same for the other stored stations.

So thanks again

Regards
Gary