Teac receiver-amplifiers - UK Vintage Radio Repair and Restoration Discussion Forum

allan · 4th Dec 2020, 5:55 pm

My Teac AG15D, bought new many years ago gave sterling service until I needed to fit a few new electolytics to restore power rails. Then it started to overheat and cut out so I fitted a computer fan to keep it cool (running at 6 volts to keep noise low), that works fine, but it now it needs a good thump to get it started and my XYL is complaining.
I now have a Teac AG-D200 bought cheap with "static in speakers" which I'm assuming is dry joints. Although I have the User Manual I can't find a repair manual (which might help in its repair). Does anyone know of such a thing or corrected dry joints in the AG-D200?
Allan G3PIY

allan · 21st Dec 2020, 10:31 am

I took the AG- D200 amplifier apart, finding it was fairly similar in construction to the older AG-15D. Plugged onto the main circuit board was a circuit board carrying a set of 7 preamp and driver circuits. Hundreds and hundreds of solder joints with 50% cracked. Either it's poor solder or a poor soldering machine but anyone with an AG-D200 may also suffer from crackly audio.
Another problem was dry-jointed audio output relays. Not the switched connections, but the coil pins.
Allan G3PIY

Radio Wrangler · 21st Dec 2020, 11:57 am

I've seen bad joints in quantity produced in wave-solder machines if the solder gets contaminated (it was gold dissolution in this case - unlikely in consumer goods!) and when the acid flux foamer stopped but the rest of the machine ran on.

For some years Icom was notorious for bad joints in bulk. They obviously hadn't got their process under control. If it ain't workin' STOP! but sometimes production schedules are allowed to override common sense.

It's a lot of work refluxing and resoldering everything.

David

SiriusHardware · 21st Dec 2020, 12:07 pm

Allan, it's a little bit difficult to untangle the exact sequence of events from your OP but one possible reading is that replacing the electrolytics fixed one problem but brought on another?

I don't know these units at all but is it possible that you have replaced electrolytics which were originally 'special' low-ESR types (as typically used in switch-mode power supplies) with common or garden electrolytics?. If so, what typically happens is that they work, but not for very long.

stevehertz · 21st Dec 2020, 2:06 pm

As someone who collects and restores vintage hifi, I often find myself going over virtually all of the PCB solder joints in a set, yes that's hundreds of joints. But it's worth it, often the bad joints are not viewable as such with the naked eye, so I just go over them all. A classic is the thin ghostly grey ring around a component lead that otherwise looks like a good joint. Dry joints and copious cleaning of switches and pots generally cures most of the 'faults' in vintage hifi. I've had sets that are barely working, channels down, all kinds of things, but once the previous procedures have been carried out, all is fine, fully working!

allan · 27th Dec 2020, 5:33 pm

I tackled the AG-15D again and found I'd helped make it worse by connecting the new cooling fan to the supply delivered by the hottest regulator, so instead. I used one of the unregulated supplies powering the PA transistors and used a larger resistor to keep the 12 volt fan at about 4 volts (to keep it quiet).
The replacement capacitor was actually three new 2000uF in parallel so they would be OK ESR-wise.
The cutting out was due to dry joints at the relays used to switch on the output circuits.
The amp is now working perfectly.
The newer D200 is also OK now. I resoldered 700 bad joints on the circuit board driving the 7 output transistor-pairs. That amp also had dry joints at all its relays.
I think the bad board must have been in a Friday afternoon batch with rubbish flow solder. I now suspect the D200 had been through the hands of a previous repairer judging from lots of red & blue marks on various solder joints, pins etc and lots of resoldering at the power output transistors. Alas he'd missed the board with the 7 preamps and the bad soldering at the relays. Oddly in both amps it was the coil pins that were bad. The changeover connections had large pads with more solder and were blameless.
Allan

stevehertz · 27th Dec 2020, 6:46 pm

Quote:

Originally Posted by allan

I tackled the AG-15D again and found I'd helped make it worse by connecting the new cooling fan to the supply delivered by the hottest regulator, so instead. I used one of the unregulated supplies powering the PA transistors and used a larger resistor to keep the 12 volt fan at about 4 volts (to keep it quiet).
The replacement capacitor was actually three new 2000uF in parallel so they would be OK ESR-wise.
The cutting out was due to dry joints at the relays used to switch on the output circuits.
The amp is now working perfectly.
The newer D200 is also OK now. I resoldered 700 bad joints on the circuit board driving the 7 output transistor-pairs. That amp also had dry joints at all its relays.
I think the bad board must have been in a Friday afternoon batch with rubbish flow solder. I now suspect the D200 had been through the hands of a previous repairer judging from lots of red & blue marks on various solder joints, pins etc and lots of resoldering at the power output transistors. Alas he'd missed the board with the 7 preamps and the bad soldering at the relays. Oddly in both amps it was the coil pins that were bad. The changeover connections had large pads with more solder and were blameless.
Allan

Inspectors use red felt tip pen to identify potential dry joints. Usually these are then re-soldered by hand before the set is finally tested and shipped. If you look at that nearest red marked joint in your photo you can see the tell take ghostly grey ring around the component lead. But it has not been re-soldered at the factory!

paulsherwin · 27th Dec 2020, 6:47 pm

You really shouldn't have to add an aftermarket fan unless you're using the amp in extreme conditions. It suggests you still have an undiagnosed fault there.

Bad solder joints in the speaker protection circuitry seem to be very common for some reason. I had to reflow them in my Marantz amp a couple of years ago.

allan · 29th Dec 2020, 4:44 pm

You're right Paul
It was cutting out and I suspected overheating, because the low voltage regulators use a common heatsink which was getting very warm, but probably normal. It was probably just the relay coil pins dry-jointed.
I left the fan in place and the heatsink runs cool so I left it in place after I'd resoldered the relays.
All's well now
Allan

4th Dec 2020, 5:55 pm	#1
allan Pentode Join Date: Oct 2005 Location: South coast near Ringwood/Christchurch, Dorset, UK. Posts: 230	Teac receiver-amplifiers My Teac AG15D, bought new many years ago gave sterling service until I needed to fit a few new electolytics to restore power rails. Then it started to overheat and cut out so I fitted a computer fan to keep it cool (running at 6 volts to keep noise low), that works fine, but it now it needs a good thump to get it started and my XYL is complaining. I now have a Teac AG-D200 bought cheap with "static in speakers" which I'm assuming is dry joints. Although I have the User Manual I can't find a repair manual (which might help in its repair). Does anyone know of such a thing or corrected dry joints in the AG-D200? Allan G3PIY Attached Thumbnails

21st Dec 2020, 10:31 am	#2
allan Pentode Join Date: Oct 2005 Location: South coast near Ringwood/Christchurch, Dorset, UK. Posts: 230	Re: Teac receiver-amplifiers I took the AG- D200 amplifier apart, finding it was fairly similar in construction to the older AG-15D. Plugged onto the main circuit board was a circuit board carrying a set of 7 preamp and driver circuits. Hundreds and hundreds of solder joints with 50% cracked. Either it's poor solder or a poor soldering machine but anyone with an AG-D200 may also suffer from crackly audio. Another problem was dry-jointed audio output relays. Not the switched connections, but the coil pins. Allan G3PIY Last edited by allan; 21st Dec 2020 at 10:36 am.

21st Dec 2020, 11:57 am	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,858	Re: Teac receiver-amplifiers I've seen bad joints in quantity produced in wave-solder machines if the solder gets contaminated (it was gold dissolution in this case - unlikely in consumer goods!) and when the acid flux foamer stopped but the rest of the machine ran on. For some years Icom was notorious for bad joints in bulk. They obviously hadn't got their process under control. If it ain't workin' STOP! but sometimes production schedules are allowed to override common sense. It's a lot of work refluxing and resoldering everything. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

21st Dec 2020, 12:07 pm	#4
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,548	Re: Teac receiver-amplifiers Allan, it's a little bit difficult to untangle the exact sequence of events from your OP but one possible reading is that replacing the electrolytics fixed one problem but brought on another? I don't know these units at all but is it possible that you have replaced electrolytics which were originally 'special' low-ESR types (as typically used in switch-mode power supplies) with common or garden electrolytics?. If so, what typically happens is that they work, but not for very long.

21st Dec 2020, 2:06 pm	#5
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,830	Re: Teac receiver-amplifiers As someone who collects and restores vintage hifi, I often find myself going over virtually all of the PCB solder joints in a set, yes that's hundreds of joints. But it's worth it, often the bad joints are not viewable as such with the naked eye, so I just go over them all. A classic is the thin ghostly grey ring around a component lead that otherwise looks like a good joint. Dry joints and copious cleaning of switches and pots generally cures most of the 'faults' in vintage hifi. I've had sets that are barely working, channels down, all kinds of things, but once the previous procedures have been carried out, all is fine, fully working! __________________ A digital radio is the latest thing, but a vintage wireless is forever..

27th Dec 2020, 5:33 pm	#6
allan Pentode Join Date: Oct 2005 Location: South coast near Ringwood/Christchurch, Dorset, UK. Posts: 230	Re: Teac receiver-amplifiers I tackled the AG-15D again and found I'd helped make it worse by connecting the new cooling fan to the supply delivered by the hottest regulator, so instead. I used one of the unregulated supplies powering the PA transistors and used a larger resistor to keep the 12 volt fan at about 4 volts (to keep it quiet). The replacement capacitor was actually three new 2000uF in parallel so they would be OK ESR-wise. The cutting out was due to dry joints at the relays used to switch on the output circuits. The amp is now working perfectly. The newer D200 is also OK now. I resoldered 700 bad joints on the circuit board driving the 7 output transistor-pairs. That amp also had dry joints at all its relays. I think the bad board must have been in a Friday afternoon batch with rubbish flow solder. I now suspect the D200 had been through the hands of a previous repairer judging from lots of red & blue marks on various solder joints, pins etc and lots of resoldering at the power output transistors. Alas he'd missed the board with the 7 preamps and the bad soldering at the relays. Oddly in both amps it was the coil pins that were bad. The changeover connections had large pads with more solder and were blameless. Allan Attached Thumbnails

27th Dec 2020, 6:47 pm	#8
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,934	Re: Teac receiver-amplifiers You really shouldn't have to add an aftermarket fan unless you're using the amp in extreme conditions. It suggests you still have an undiagnosed fault there. Bad solder joints in the speaker protection circuitry seem to be very common for some reason. I had to reflow them in my Marantz amp a couple of years ago.

29th Dec 2020, 4:44 pm	#9
allan Pentode Join Date: Oct 2005 Location: South coast near Ringwood/Christchurch, Dorset, UK. Posts: 230	Re: Teac receiver-amplifiers You're right Paul It was cutting out and I suspected overheating, because the low voltage regulators use a common heatsink which was getting very warm, but probably normal. It was probably just the relay coil pins dry-jointed. I left the fan in place and the heatsink runs cool so I left it in place after I'd resoldered the relays. All's well now Allan