Picked up an old Adcom GFT-1A with no FM

Picked up an old Adcom GFT-1A with no FM. The AM works great. I have looked around for a schematic but no luck. Has anyone had any experience with this model and problem..
The tuner scans fine and memory is also fine. I checked a few caps and so far they are all a bit over value (good). Any suggestions?
Best regards,
My 1st post here.
Soundtec
 
Add a FM module, after checking the schematic.
FM decoder or discriminator chip may be faulty, difficult to find.

You will get remote, and USB / SD as well.
Cost is like $2 here.
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Random net image, no ties to seller.
Needs 5V + Ground, 7805 works.

Reception is better than most old sets.
 
A lot of old sets with working amps have been converted here, the cassette is no longer used, or the tuner...the technicians charge about $5 to install one of these, everybody is happy that there is new life in the old double cassette / radio / amp unit.
The old tuners were gang type, the digital conversion with this FM module gives terrific clarity, sounds much crisper, more dynamic range.
And you can switch inputs, Bluetooth, SD card, USB stick also works.
I use a similar one in my car, all the music is on a 32 GB stick, and FM also works. No cassette or disk drive to get bumped and damaged by our potholes.
 
Check the antenna input from back panel to FM side through the switches in the signal path.
Spray contact cleaner in all the switches if it is an old set, cleans them and prevents oxidation.
Some sets have decoders that will not work under marginal signal level.
And check the supply voltages on that board as well. Particularly signal chips.

Try and see what happens.
 
I have verified the caps and all were ok. I also cleaned switches but I did not see any issues. What is strange is on FM all I hear is noise. The signal strength is showing maximum. When I scan it just runs continuously with no channels locking in.
I really need a service manual.
 
Disconnect the antenna, see the signal level.
If is still shows full...I don't know.
Could be PLL issue if signal goes to zero. It is not able to lock, and synthesizer tuner chip may be at fault, or the signal connections.
You need signal generator, may be scope to restore alignment.
 
That can mean a short or faulty chip.
Try and find a manual, and see if spare chips are available.
Trace the signal from socket to board.
Sometimes a disc Capacitor is faulty.

Which is one of the reasons I said put a new module...sometimes the parts are simply not available, you use what is a good substitute.
 
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You definitely need a circuit diagram. There is a GFT1 on HiFi Engine but the diagram is unreadable (really poor scanned copy).

Tuner faults are tough at the best of times. Working on why the meter shows full strength might be a way into the fault but you need diagrams...

Other ways are to look at the RF chipset and work from data sheets and also other tuners using similar chips. It can give clues sometimes.
 
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Hi Soundtec,
I am familiar with those. I was authorized warranty for Adcom for years and still fix them.

These are not bad tuners to begin with. All kinds of people write things and say things without any actual experience.

These have normal circuits. First, check the FM B+ regulator, then the Vt voltage and also the frequency output from the tuner to the tuner controller. Normally it will go through a prescaler IC first as the input frequency will run from approx 90 Mhz to 120 MHz.

I still do tuner alignments and have more than enough equipment for the job, including a new Keysight RF generator (pricey as hell).

-Chris
 
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Hi Soundtec,
STOP! Do not replace anything!!! Please!

Please check these things first! The first rule of service is to change as little as possible before reaching for a soldering iron. The most common failures will be the small ceramic capacitors and polystyrene caps. Those are extremely heat sensitive. You can short them with too much heat for too long with a soldering iron.

I've been doing this for over 45 years professionally, and am known for tuner service and alignment. I trained technicians for decades. Please, listen to me. Even if you bought the ICs, I have trouble with defective and fake parts. Do not change anything. We know for certain the original parts are real, that's one issue. The other is that changing some ICs forces realignment. You do not have the equipment or experience. Also, it is not adjustment. The tuner worked then didn't. Either a part failed, or it was "struck by technician".

May I ask where you are located? If you're close I'll look at it for free. Just please, do not replace parts or start adjusting things! You can PM me.

-Chris
 
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If you knock it out of alignment, you need a signal generator.
It is most likely a bad supply or capacitor.
If the original ICs are not sold at the famous suppliers, you are taking a chance.

By the way, that FM module is also sold ready in a box, with power supply, as a pre amplifier. $5 here.
Just connect as an external source.

So if your amp is otherwise working, I would send it to a very experienced service engineer like Chris, or leave it alone after checking for minor stuff as above.
You will end up spending a lot on signal generators and so on, and you must be prepared to invest much more than $1000 if you buy new equipment, which may be justified only if it is routinely in use.
Otherwise, leave it to the experts.
 
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Hi NareshBrd,
Thanks. One note though. I have found that tuner paks are generally not aligned well, and those were for production. After-market units have even less quality control.

I really can't stress enough how important it is to keep the original parts installed until you know for certain one is bad. To do that you have to really understand how these things work. This goes for repairing anything, amplifiers included. "shot gunning" a piece of equipment often leads to more problems and sometimes economically unfeasible repairs. Real substitutes can make an amplifier unstable, fakes cause issues that are more fun to deal with. Often too, a part can "work", but not properly. This is very true of after-market ICs.

I needed some uPc1225H (or uPc1270H) driver ICs. From three "good" suppliers, I received three large lots of ICs that were no good. Still need them but I gave up on getting real ones. I'll redesign the equipment using current ICs from authorized distributors. I only needed 4 pieces, and simply could not get any.

I think the best way to sum up a repair / service job is simply to avoid introducing any variables. Follow the clues to the reason it isn't working. However, today I get almost 100% of repairs suffering from T.I.M.. (Technician Induced Malfunction). Those are very hard to find and fix because there is no causal relationship to anything. Everyone's an expert it seems, especially if they haven't any real training in the subject.

-Chris
 
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My Kenwood set from the same era would lose memory if not connected to mains all the time.
Similar fluorescent display, but white.
I got used to keeping it on for three hours a day, rest of the time disconnected from mains.

Does it hold memory on AM?
If yes, fine.
If not, there should be a low voltage (below 25V, more like 16 or lower), high value capacitor near the RF chips which may be leaky. Like 6800 uF or even higher.
Those are sometimes seen as memory backup sources.

And do try a circuit trace from antenna connector to the tuner section.
Check the antenna with another tuner, if possible.
 
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Hi NareshBrd,
Yes, it should hold memory on AM and FM both. Same chip, same memory array.

It will either have a memory backup capacitor or battery (I can't remember which). The capacitor is rated at 5.5 VDC, anywhere from 0.022F to 0.47F (yes, that's farads). Otherwise it will be a coin cell with tabs spot welded on it. Some earlier ones use NiCad batteries. They leak, so you really want to get those replaced even if the memory is still holding. Approx 3 VDC or higher with almost no current draw. Sometimes there will be a normal capacitor across it that may go leaky and kill the battery / capacitor.

The tuner circuit will run on +12 VDC, or something close. They all do. Check for ripple on that supply. It is also common (in all brands) for the 12 VDC regulator to fail as they tend to run hot. The logic will run on + 5 VDC. Again, check for ripple. Obviously you need an oscilloscope to do that.

Often times Vt will range between 2.8 to 22 or 28 VDC, so there is a charge pump that may fail and also a higher voltage supply. This is used on varactor tuners (the ones that are electronically tuned, no big tuning capacitor and no dial pointer). When replacing a solid state tuner you must make sure you have the tuning voltage range the same. I have seen a couple that use a 12 VDC supply for the tuning voltage, different tuner pack or custom type.

You do need to adjust the tracking so that the station you want appears in the capture range so it can lock on and fine tune the station the rest of the way for you.

-Chris
 
He said above that AM memory works.
So, FM side problem.
On an old (and here in India, obscure) set with parts that are not made for 30+ years.

For me, unless the set had sentimental value, I would not try to repair it, as the substitute parts will mostly be dubious, and even if genuine, need equipment that I do not have.
And that will be expensive in time and money.

So my short and sweet answer was to put a new FM module, as in Post # 2 above.