Quad FM 4 tuner problems

[alanworland]

Just aquired an FM 4 tuner which is a fairly early model but with the retrofitted PCB that looks like it was fitted by Quad as there is a service sticker dated March 1983. It is in super condition, however It has had a problem with the battery as there is discolouration on the main circuit board and some minor corrosion on a diode, nothing major at all. The present battery is also expired and showing signs of leaking.
It seems to work although obviously none of the presets retain any stations but the display appears to have all the segments powered and lit? tuning can still be performed as some segments are brighter than others so a frequency can be 'made out' Also the second digit is brighter than all the others?
I've not inspected this electronically yet with a meter. Once I have replaced the existing battery any pointers as to where I should start looking?

Alan

[nutteronthebus]

I have 4 faulty FM4's all with various faults ( no display unable to tune etc ) the main problem is with the caps and diodes around the battery the Zener for tuning voltage or go down the QF4PCB7 chip that removes the battery
Dave

[alanworland]

Thanks, and sorry you have so many!
I think get the meter out check supplies etc then attack the electrolytic caps.
Having searched for the service manuals/schematics it seems these underwent quite a few changes since introduction.
Battery elimination sounds good but a cheaper solution would be to mount the battery on the rear panel for easy access and it's non destructive leak potential! although I don't really have a problem with retuning to be honest.

Alan

[Jon_G4MDC]

On the wonky display digits also perhaps check the segment multiplexing.

I had a Kenwood which did what you describe due to blocking diodes which had become leaky in the reverse direction.

[nutteronthebus]

There is a fix for the battery where it is mounted in a leek proof box on the PCB. I have the full service manual for the FM4 if you need any info

Dave

[Ted Kendall]

Probably the best way to sort this out is to fit Quad's replacement microprocessor which does not need a backup battery and offers seven more presets to boot. A complete kit is available direct from Quad.

[alanworland]

Thanks for the service manual offer, I did manage to find and download it.
Quite a neat idea with the battery box, keeps all the leaked corrosive contents in one place! I have a battery on the way and may try and find a 'container' for it.
List of replacement components next.

Alan

[nutteronthebus]

There are a lot of videos on youtube with FM4 repairs https://www.youtube.com/results?search_query=quad+FM4

Dave

[Craig Sawyers]

Originally Posted by Ted Kendall

Probably the best way to sort this out is to fit Quad's replacement microprocessor which does not need a backup battery and offers seven more presets to boot. A complete kit is available direct from Quad.

Good shout! I replaced the (leaking) battery a few years ago - but after your post ordered a microprocessor kit from Quad just now.

Even though they are owned by the Chinese (IAG) their customer service out of Huntingdon is still second to none.

Craig

[turretslug]

I'm most impressed- when a common gripe on the forum is the short-lived nature of modern consumer goods, I'm quite taken aback that a 40-odd year-old product has this sort of upgrade revision available for it! It makes a change from "Sorry sir, but we regret that support for this product is no longer available. You may be interested in our 2020 model line-up"....

[nutteronthebus]

The fitting instructions are on the DADA web page in the download section for the QF4PCB7 chip and the chip at 92 euros

Dave

[alanworland]

Sounds like the way to go, unfortunately my new battery turned up today! Must admit I have been in touch with Quad a few times recently regarding my (also old) 405-2 power amp and have found them quite helpful and more than willing to service their products at a very reasonable cost.

Alan

[chartz2]

Hi everyone,

I'm looking for a good soul that would be able to take photos of the QF4PCB7 (based on a PIC chip, but which one?) module that Quad used to make, both sides of course. I intend to develop one in house.

Thanks!

[Ted Kendall]

Why don't you just buy one?

[chartz2]

Originally Posted by Ted Kendall

Why don't you just buy one?

There's none available, plus they were circa € 100 when available. The PIC chips are very very cheap, a few quid.

And I like retro-engineering for fun

[Ted Kendall]

Do you mean the processor chip? These, or an updated version thereof, are still available - I bought one a few months ago. If a manufacturer is prepared to swim against the tide to the extent of supporting, and indeed upgrading, a thirty year old design at reasonable cost, I think it's positively churlish not to support them.

[chartz2]

Right. I’ve dropped Rob Flain an email, but I’m not holding my breath.

[alanworland]

As this popped again up I thought I would bring my original starter post up to date!
Changed all electrolytic capacitors and a couple of diodes that showed signs of corrosion due to battery leaks and the unit was still not right, also changed one of the big IC's (no diagram with me so can't say which!) although voltages were correct.
Decided rather than just replace components I'd send it to Quad!
Excellent turnaround with a fixed charge of £55 (+vat) came back working beautifully with a list and charge also for the components used.
Indeed they also replaced the battery and leakproof box for which there was no charge.
All in all I was well pleased and with a years warranty and it performs really well.
Mine still has 'only' the 8 presets, but I find that more than enough? and if not it's no big deal to tune in another transmission?
As you say, what service on a 40 year old product - can't beat it!

Alan

[turretslug]

That gets a 'like' from me!

[Ted Kendall]

Can't complain about that cost of ownership!