Harman Kardon PM660

Hamstall called by. I've got this 'arman Kardon, can you give it the once-over?

Yeah, why not.

It a nice early 80's integrated amplifier. Spec recons on about 80 watts per channel into 8 Ohms. No spec is given for power into 4 ohms. It's a completely discrete design. Not an op-amp in sight.



Nicely laid out...











A good-sized transformer and rectifiers... and plenty of smoothing caps.










10,000 uF , and there's 4 of 'em....













... and that "Sony" on//off switch .... (it all looks a bit Sony to be honest)











Super phono pre-amp, MC and MM....












... fitting with a smattering of ELNA "for audio" capacitors, so you know where your money went....











... and four position, front panel adjustable, capacitance loading for your odd-ball cartridge....


















Underneath reveals, well, not a lot really. 4 pairs of Toshiba 2SB775/2SD845 output transistors. Cleverly mounted through holes in the PCB, straight onto those gargantuan heatsinks....

Speaker wiring takes a bit of a long route home....











... and through some rather flimsy looking speaker select switches. I don't think I'd want to be switching speakers whilst playing....

























Two tape loops, two phono inputs (with short circuit plugs if you're not using one to keep the noise out), an aux and a tuner input....









So ... set the bias up (a blissfully easy procedure, thanks to a great service manual), a clean up of the pots and switches, all the caps look in great condition, and testing the ESR of a good few proves this to be the case.

The tuner indicator lamp is open-circuit...

Diminutive little lamp, so we'll replace it with a warm-white wide-angle LED...










The holder had to be drilled out slightly to enable the slightly fatter legs of the LED to pass through, and a 10K currently limiting resistor is fitted, to run the LED at a low ~1mA.









Not a bad colour match....

It plays effortlessly. I've no idea on it's output power as it easily over-ranges my audio wattmeter at 50 watts, with no sign of distress.

The phono stage is a delight. Nice and quiet.

Tone controls have a lot more range than is probably required...

There... another repair done...

Linn Axis (of evil) repair

Belated happy new year readers!

Been a really busy January, and I've not had much time in the workshop. I've completely moved a radio station for a charity, and it's been stressful! (more on that in a forthcoming post)

Anyway, Jon rang. A fine cycling chap from Bristol. Got an Linn Axis that won't run....

Can you take a look?

Yeah, why not...

It duly arrives sans platter and stylus.

I plug it in , and sure enough the motor just stutters... which is pretty usual for one of these.

The motor drive board will be faulty. Now there's much BS on the interwebs that these boards aren't repairable as "the programmable parts are no longer available" .... which is rubbish, as there aren't any.... someone's probably just trying to flog you an upgrade ... and Linn ownership is all about upgrades , right?

It's just a bunch of logic, and some op-amps...

This board is quite an early one, as it's got a ribbon cable to the speed/on/off switch which is soldered straight into the board...


So. Remove the sub platter and belt. Clean up the inevitable oil spill from the bearing. Now move the turntable to the edge of the bench, and remove the three large suspension screws holding the top plate to the rubber suspension mounts. If you're doing this with the arm attached, remove the cable strain relief first. Lift up the front edge of the top plate a bit and have a peep underneath. If your switch is attached by a coloured ribbon cable, then you'll need to pop the switch out, and slide it back inside. If it's a copper coloured flexi, (like Jon's below) just disconnect it from the motor drive board. Lift the top plate clear and put it out of reach of the cat.


Now remove the 6 small screws indicated by the red arrows, and the mains lead from the terminal block on the bottom right.

With a bit of jiggling, you should now be able to extract the board. You may need to squash one of the suspension mounts a bit to extract it.






Now change every last damn electrolytic on the board, even the high voltage ones.

Here's the shopping list:
2 x 33uF 350V axial
2 x 47uF 250V axial
2x 220uF 16V axial
7x 22uF 50V radial.





Now a word of warning.... this board is "live" when it's connected. So use an isolation transformer when doing any fault finding on it. With a bit of luck, you should now have a running board.. however, I have seen turntables with D2 & D3 open circuit, BR1 short circuit. A real head scratcher was one which intermittently blew fuses, which was one of the BUX85F output transistors!

Now if you switch the motor on without a platter and belt on, it will spin up, and then stall a few seconds later. This is usual. Once the platter is on, it should work fine.

.... of course Jon's wasn't going to be so easy, and also needed an LM324 quad op-amp replaced to finally restore operation....

I've seen forum posts saying just change the small caps....... change 'em all. These had been in there since 1989 and were shot away!











Once it's all happy, put the top plate back on, do up the suspension screws (not too tight) and replace the strain-relief on the tone arm wires and check the speed (you really need the top platter on when doing this)

Speed is adjusted using an INSULATED screw driver through two holes on the underside. They have bungs in them, you'll need to just pop those out, and replace them once happy.


Now Jon ... where's your stylus?

UPDATE March 2019! ...

Colin's just popped round with another Axis with a common problem after recapping .... motor spins backwards or not at all or just sits there vibrating. Usual causes are the two HEF4013 flip-flops hanging a line up. Change 'em both. They're just by the switch cable, and are U1 and U2.

Other frequent flyers are the two watty 15K resistors, R2 & R3. With these faulty, there won't be 35V across C5.

Have fun all!

It's an Arduino Christmas!

It's that time of the year again... and the workshop was bereft of Christmas decorations...

So something was quickly conjured up.

My colleagues, Laura and William, fashioned a cardboard christmas tree. Ryan wired up 6 LED's and some current limiting resistors up to the 6 "Analog in" ports on an Arduino board, and I wrote the world's shortest sketch...

void setup() {

DDRC = 0B00111111;

}

void loop() {

PORTC = int(random(63));

delay (10);

}

How's that?

Minimalist!

The Mini 1275GT gets paint!

After a year of languishing in the garage again, I finally managed to find somewhere to paint it!

The story so far is here, here, and here.

Now, my friend Matt is building a drag racing car, and a while back I volunteered to do the electrical bits for him. I was happy to help. The car is insane. It's a Vauxhall Chevette, fitted with a 7.5 litre Chevrolet Big block motor !!!!

Rather you than me Matt!




Anyway, Matt very kindly offered the use of his painting skills and garage to paint the Mini.

So, I set to preparing the car in my garage...

First thing was to sort the awful bulkhead ...














... wet flatting the panels...

Julian lends a hand sorting out the repaired rear quarter...














Outside to blow all the dust off...

... and on the trailer to Matt's!








In double-quick time, Matt has painted the car in etch-primer...




































and then 2 coats of a white primer base coat, which is rubbed down with scotchbrite...





















Matt prepares the Jade green paint. It's the car's original colour....



















Matt expertly applies the first coat....

It was about this point that I started to feel a bit emotional... I blame it on the paint fumes ;)

After two coats, Matt is feeling rather proud of his great work, and justifiably so.

After allowing the paint to harden overnight, it's back on the trailer....

.... and home again... 

Now the paint must be wet flatted with very fine wet and dry paper, and polished up. I'm going to let the paint harden off for a few weeks....

Huge thanks go to my great friends, Matt and Julian, without whom I'd never be able to realise this dream....