Tuesday, 21 April 2020

Dual PA5030 Integrated amplifier faults and fixes.

The famous George rang...

"Got this amplifier with a crackle... can you have a look?"

Yeah ... why not.

It's a Dual PA5030, a good quality hifi amp from around 1988.

Off with the lid, and a few issues are immediately apparent....

... leaking capacitors ...

... so they're evicted, the board cleaned up with some IPA, and the caps replaced with some nice new ones ...

Thankfully Dual provided us with a nice access panel on the bottom, making repair a breeze...

Switches and pots are duly clean ed up, the bias set, and the amp put on test. After a few minutes, the bias is checked, all is not well. The left channel's bias is moving about. It's set again, and something's obviously wrong. A low rumble is apparent in the left hand channel. Out with some freezer-spray-on- the-cheap. Spraying the Left hand output transistors restores operation. Damn. They're obsolete...

At this point I'm gifted another identical Dual amp with a fault! The output transistors are swapped out of this amp, and set up again. The fault remains....

Some head-scratching and a quick perusal of the manual is required...

The voltage on the emittor of Q617, a 2SB631 is wobbling about as the amp warms up. Replacement provides a cure.

The amp is a really impressive performer. The moving-coil input is a touch noisy, but looking at it's topology, not surprising. It's better than my Rotel. MM is very quiet, as is everything else.

Another saved from landfill!

Sunday, 19 April 2020

Garrard Zero 100 from Hero to Zero (and back again) - Arm re-wire.

After successfully overhauling the mechanics of the Zero 100, I carted it in the lounge for a proper test.

All good ... a couple of LP's in and it loses the left channel. It comes back again.

Sunday morning, bacon sandwich. Beatles Rubber Soul. I return from the kitchen, coffee and sandwich in hand, and sit on the sofa, listening to the Beatles....

Funny, didn't think I had the mono press of this....

... and I don't.

Damn. Arm wiring.

Now I'm one of those odd people who actually enjoy arm wiring, but this could be a little daunting.
A quick google search chucks up loads of people who say it can be done, but it's very difficult neigh on impossible etc etc etc .....

Good, I like a challenge.

Cartridge Slide out first, and put it to one side, so we don't damage it.

Undo the gimbal housing screw and slide the gimbal housing down the arm and put that somewhere safe.

As there was no doubt in my mind that the wiring was at fault, I just cut it off ...

Slacken the arm bearing off, this will allow extraction of the arm.

OK so far ....

Removal of two screws allow the separation of the arm tube from the bearing support. There's a small grub screw at an angle, losen this to remove the plastic insulation "top hat" which the wiring passes through. I didn't do this at this time, and broke the wiring, not that that mattered.

I spent a few minutes looking at this, trying to work out how to get the headshell pivot apart.

Get a piece of blu-tak, and stick it over the pivot...

... and pull. Bingo, the small silver cover pops out, and reveals a small black plastic nut. Undo this, and don't lose the washer underneath it.

... And there's the wiring :)

The headshell is then removed, and four lengths of Litz wire prepared. Always allow for much more than you think you'll need. It easier to make it shorter ;)

A piece of teflon wire is used to pull the new new wire through the arm tube.

Out with the old ...

In with the new.

This is the angled grub screw I talked about earlier. Loosen this to remove that white plastic insulating "top hat".

Pass the new wiring through the insulator, and refit. The bearing support can now be re-attached to the arm tube.

My teflon wire is once again employed to pull the wiring through the centre of the gimbal.

Refit the arm, and nip the bearing up just enough to remove any play.

Refit the cartridge slide, with three wires diconnected, and, using a multimeter, identify each conductor. I use a coloured sharpie to mark each one.

and finally trim the leads, and solder them to the output connector.

The Beatles are now back in stereo (which is a pity tbh, the mono mix is far superior.)

Feet up, Sunday afternoon listening to The Blossoms.

Now, what about that plinth?

Friday, 17 April 2020

Garrard Zero 100. From Zero to Hero.

Many moons ago, I was seduced by this oddball Garrard turntable.

It's that weird pantograph arm. It should track perfectly. I spotted this one, at one of those audio jumble meets. It's missing a lever or two, and the selector switches are sort of hanging there, the plinth battered and bruised.. £18 and it followed me home, much to the delight of the long and suffering Mrs Doz.

It's seen a bit of action. There's the usual "Garrard glue" to deal with, but the main issues are with the control switches...

There's some sort of mounting bracket missing or broken.

A quick look at the exploding diagram shows it's no 126...

I managed to score a few parts on eBay, but sadly not the bracket. Those levers are in better nick than mine though...

So a suitable bit of steel was cut and filed to shape...

That looks like it should do the job. There's an issue though. The screws originally fitted into the plastic top plate, where there's a reinforced bit. It's broken off...
I removed the levers (I wanted to change them anyway), and put some epoxy down to build up a layer to support the screws. 
and while that's going off, I swap the levers over, and sort out removing the sticky grease from the rest of the mechanism.. 
The speed change detent arm was exceptionally seized up, and required plenty of heat to get it to free up.

Once the epoxy had cured it was flattened off, and it was at this point I realised that the top plate was no longer secured to the chassis. as again there were sheered off screw fittings... a change of tack was required, there just isn't enough strength here......

The bracket is reversed, and bonded to the chassis with some of the UV cure adhesive I've tried before... now I take it the UV has only cured the outside part, but it seems to be holding. Where the plastic top plate is broken off, I used the glue gun to fill the void, and fit a screw through my previous epoxy repair to secure the top plate at the other side. The clamp is simply holding the top plate flush.

... and the following morning, all the gluing seems to be very strong... good. Pretty it isn't, but it's now at least functional.

The deck is flipped back over, and the platter removed, by removing the rubber mat, and removing the wire clip securing the centre spindle.

The platter itself has the strobe markings on it's underside...

... which are viewed via a mirror in the "subterranian" strobe housing. It'll need removing to clean the mirror.

Two screws either side, and it drops down...

 ... and we can clean the mirror. The small plastic window can also be removed and cleaned.

A quick note on how the speed adjust works.
The manual speed adjustment knob under the speed selector operates a lever, which moves the idler up and down a tapered section on the motor drive shaft, thus changing the speed. A bit "lenco" really...

There's more grease to be cleaned up and replaced on the top. This lever is seized solid, and, once again, needed a bit of hot air to tempt it off.

The motor mounts are still supple, as is the idler, so that's good news.

Now to the Zero 100's arm. This is what interests me about this turntable ... it gives it it's name, Zero tracking error. The headshell actually moves as the arm moves across the record, removing the error. This one is horribly wobbly. Now because the headshell is articulated, it's never going to be the stiffest tonearm, but this is wobbling around from the pivot end.

One screw removes the perspex gimbal surround, allowing a better view.

Sure enough a tiny screw is missing, which secures the arm tube to the bearing. A replacement is found, dropped, lost and found again before being fitted.

Now the arm is given a quick buff up to remove the worst of the corrosion on it's surface, and the brass cover on the counterweight is treated likewise.. Looking quite smart now :)

Fitting a cartridge. Now the Zero 100, in common with a few other Garrard decks of the time uses a convenient cartridge slide. Convenient that is, if you happen to have one... I knew mine was missing, so I'd previously stopped into my favourite purveyor of Garrard bits, and managed to procure a new-old-stock slide. The contacts are a bit tarnished, but that'll soon clean up.

My friend John had sent me a previously enjoyed AT95 a while back, so that was mounted onto the slide...

Normally the Zero 100 came with a perspex alignment gauge, that slid over the slider, and you just set your stylus onto the cross-hairs, and all is done. Obviously this was long-gone. As our arm compensates for any tracking error, using a conventional protractor and setting Stevenson, Baerwald etc is irrelevant.  After nearly starting a fight on a Garrard forum (some people eh?)  I hatched a plan... the arm should track something near parallel, so all I need is a line from the centre spindle out, move it about until our cartridge is on the line, move the arm in and out, and set the cartridge position so the line is followed.

A piece of cotton is pressed into service, and the cartridge position set. There is a light curve to the track, however.

Tracking weight and anti-skate are set up as per the manual.

And successfully plays through the workshop test LP, scratched and warped though it may be.

Now to think about doing something to tidy up the plinth.