Hi,
My son purchased a known faulty Quad FM4.
The battery had leaked over a wide area of the LH side.
Initially after a clean up and replacement battery the memory and tuning worked well. the problem now, is that when switched on, the RH display digits flicker until the unit drifts up into tune. this also happens on the memory presets also. I have changed C11 and C12 which were found to be low capacity.
I have also changed various diodes and including the 6.2v zener. I am not at all familiar with this set and am at a loss as what to do next. Whether it is a psu, digital or afc problem, I have no idea...
The memory led's also seem to not light up , particularly at switch on.
Your help would be greatly appreciated.
Mick
My son purchased a known faulty Quad FM4.
The battery had leaked over a wide area of the LH side.
Initially after a clean up and replacement battery the memory and tuning worked well. the problem now, is that when switched on, the RH display digits flicker until the unit drifts up into tune. this also happens on the memory presets also. I have changed C11 and C12 which were found to be low capacity.
I have also changed various diodes and including the 6.2v zener. I am not at all familiar with this set and am at a loss as what to do next. Whether it is a psu, digital or afc problem, I have no idea...
The memory led's also seem to not light up , particularly at switch on.
Your help would be greatly appreciated.
Mick
The FM4 starts up with the top left station preselected, so this is one symptom, not two. Have a look at the 100uF capacitor(s?) that stabilize the Ref + and - voltages. Top left of the schematic, under IC1. Also observe these voltages during startup, and the tuning voltage at the tuning pot wiper. They should not drift.
LEDs not lighting could be the LED itself or the corresponding driver transistor in the row of 8.
LEDs not lighting could be the LED itself or the corresponding driver transistor in the row of 8.
hi, ejp,
thanks for the prompt reply...
i have changed c11 and C12. They were both very low capacitance (60uf and 50uf)
I have also changed the green led, which was not lit.
I put a 3mm green one in. Volt drop across it is 1.8v and it is now lit faintly. Initially, I had no idea whether it should be on or off. I have also changed D23/24 although they did not read faulty but were mentioned somewhere in a thread as causing problems.
ihave also changed the 6.2v zenner because if signs of corrosion on the lead wires.
the new zener reads 6.12v across it (?). I wonder how critical this is. the voltage across the tuner pot is constant on my meter at the same value. My meter has only decimal two digits and the last one flutters a bit.
One thing is clear, at switch on, the frequency scale is off tune on all tuning buttons
and the longer the rx is off the longer it takes to creep up to frequency.
This to me looks like some psu etc., component or other creeping up to full value.
The 12v regulator is very, very hot to the touch , by the way.
thanks for the prompt reply...
i have changed c11 and C12. They were both very low capacitance (60uf and 50uf)
I have also changed the green led, which was not lit.
I put a 3mm green one in. Volt drop across it is 1.8v and it is now lit faintly. Initially, I had no idea whether it should be on or off. I have also changed D23/24 although they did not read faulty but were mentioned somewhere in a thread as causing problems.
ihave also changed the 6.2v zenner because if signs of corrosion on the lead wires.
the new zener reads 6.12v across it (?). I wonder how critical this is. the voltage across the tuner pot is constant on my meter at the same value. My meter has only decimal two digits and the last one flutters a bit.
One thing is clear, at switch on, the frequency scale is off tune on all tuning buttons
and the longer the rx is off the longer it takes to creep up to frequency.
This to me looks like some psu etc., component or other creeping up to full value.
The 12v regulator is very, very hot to the touch , by the way.
Change C4, C5 and C6, and C57. Fit a heatsink to the 7812. Green LED should be lit. Check the behaviour of the 12V rail voltage, the 4.8V battery voltage, and the voltage at the tuning knob wiper during startup. Investigate the LM334 and R21,22,23.
Hi all,
Old(ish) thread but I have a query too.
No news from original OP, as usual 🙁
On my latest example (brown, sn circa 5000), the yellow buttons wouldn't trigger the TMS1000 at all, or erratically so. Sometimes one button would work, just like that, and one moment later it would do nothing.
I realized that when I touched pins 2 and 3 with my finger, while looking for bad solder joints, everything worked as it should. New joints did nothing, unfortunately.
Then I tried to spray a little contact cleaner over those pins and it worked fine until the liquid had evaporated (repeatedly).
I therefore connected two small caps (330 pF) between pin two and GND and pin 3 and GND.
Now stations can be selected and memorized fine as they should.
Every single cap was replaced, new battery.
As an aside, when cold, the frequency is a bit flickery on the last digit only, then after 30 sec or so, it is dead stable. And yes I've replaced the AFC cap too. All voltages as per SM right after power-up.
Explanation(s) please? 🙂
Thank you!
Old(ish) thread but I have a query too.
No news from original OP, as usual 🙁
On my latest example (brown, sn circa 5000), the yellow buttons wouldn't trigger the TMS1000 at all, or erratically so. Sometimes one button would work, just like that, and one moment later it would do nothing.
I realized that when I touched pins 2 and 3 with my finger, while looking for bad solder joints, everything worked as it should. New joints did nothing, unfortunately.
Then I tried to spray a little contact cleaner over those pins and it worked fine until the liquid had evaporated (repeatedly).
I therefore connected two small caps (330 pF) between pin two and GND and pin 3 and GND.
Now stations can be selected and memorized fine as they should.
Every single cap was replaced, new battery.
As an aside, when cold, the frequency is a bit flickery on the last digit only, then after 30 sec or so, it is dead stable. And yes I've replaced the AFC cap too. All voltages as per SM right after power-up.
Explanation(s) please? 🙂
Thank you!
Last edited:
To avoid thread-jacking (sorry Mick if you ever read this, please give some news), new thread here:
https://www.diyaudio.com/forums/analogue-source/349076-quad-fm4-issues.html#post6069696
https://www.diyaudio.com/forums/analogue-source/349076-quad-fm4-issues.html#post6069696
As the OP for this thread,
My apologise for my unforgivable rudeness in not replying.
None of the things suggested worked in my case and after changing some items many times I started to loose heart in the item.
after a while i went back to it and noticed that if I got all the preset buttons on to a station, and left it on a preset at switch off. it always came back on station at switch on but never on station in manual mode - flickering last digit - an drifted into tune eventually...
After several weeks I found a service manual and observed that there is no AFC on manual. So, that's as far as I have got.
My apologise for my unforgivable rudeness in not replying.
None of the things suggested worked in my case and after changing some items many times I started to loose heart in the item.
after a while i went back to it and noticed that if I got all the preset buttons on to a station, and left it on a preset at switch off. it always came back on station at switch on but never on station in manual mode - flickering last digit - an drifted into tune eventually...
After several weeks I found a service manual and observed that there is no AFC on manual. So, that's as far as I have got.
I should belatedly correct what I wrote above. The FM4 should come up tuned to the station it was on when powered off, or Manual if that was in effect then, and if so, near the same frequency unless the tuning knob has been moved,
So can we assume it's an FM4 thing? I've done two some time ago, replaced the battery and the caps that were off-spec but it still tends to drift on the last .05MHz, also on saved presets. Sometimes it stays stable for a few hours, then after another hour it's off by .05 again...
Yes it’s a feature of my two FM4s, an early brown one and a late green. You need fairly a strong signal for this to disappear in my experience.
Yes they all do that. Mine has been doing it for 35 years. I suspect it's more a display issue rather than actual mistuning.