Luxman L-80V repairs and renovations.

The ever-cheerful Martin called ...

"I'm chuffed with the R-1040 you did, can you do my other one?"

Yeah ... why not. 

.. and he brings me another R-1040 to do, and also a rather nice L-80V (which was unexpected, as somewhere our wires had got crossed!)

Luxman do make some nice looking kit.

Martin wants the amp serviced and re-capped. It's got a low-level hum to it.

Anyway , off with the wooden sleeve (in the same manner as the R-1040) and I'm greeted with a very familiar sight...

... it's the same as the L&G L2800 I did here all those years ago, or at least the main PCB is. 

It's also suffering with the same leakage... Let's get re-capping the thing. 

Almost as much of a slog as the R1040....

Most of the electrolytic capacitors are in a woeful state...

Much in the same way as the L&G 2800, output transistors are a mix of manufacturers, this time on the same channels!

To get at the capacitors on the tone control and loudness control boards, first remove the knobs.. 

Then remove the screws securing the front panel, both the aluminium and plastic sections. Theses are
located on the top and bottom of the front panel. 

With the front panel removed...

... undo the securing nuts holding the two tone control pots to the front panel. 

... and, whilst access is still limited, you can now get at the caps on the tone control board

Similar process with the loudness board. Remove the four securing screws... 

... and re-cap the board.

The main smoothing caps, whilst looking in good condition, are both reading low in value. This is probably the cause of the hum. Sadly the caps I used in Martin's R-1040 are now on a long back-order time. Some other Nichicon caps are in stock, so these are ordered, but are of smaller diameter than the originals, so some sleeves are 3D printed, and the caps replaced. I've printed four, because I'm going to need 4 for Martin's other R-1040

Snug...

With the re-cap complete, the bias is set, and the amplifier is a stunning performer. 

It's given a good soak test with the most excellent International Teachers of Pop 

https://www.youtube.com/watch?v=9r_Gqx_GFEg

Now to do Martin's other R-1040 !

Sinclair ZX Spectrum repair

George rang... 

"Got a ZX Spectrum here that doesn't work. Care to have a quick look?"

Yeah... why not?

It duly arrives in the post. 

I have to be honest, and say I haven't so much as seen one since the 90's... and only fixed very few back then. 

It's the earlier sort, with the rubber keyboard. 

The power supply is tested (Centre negative!) and it's output is around 14V DC off-load, so that's OK. The supply is put to one side, and the unit is powered up from the workshop supply. Something is loading the supply heavily.

Five screws in the bottom of the case gives us access to the PCB. 

Carefully remove the two keyboard ribbons, and remove the single screw in the middle of the board, to remove the PCB. 

This machine is fitted with a version 4 PCB, and the chips are all dated around 1984. 

Attention is focussed on the power supply. 

It consists of an LM340TS (7805) linear regulator, and a small self-oscillating supply, which provides + & - 12V, -5V (not at 20 amps!!) and a 12V "AC" rail

A few cursory checks, and it looks like our 7805 has failed, thankfully short circuit to ground, rather than short circuit from input to output... having ~14V on something that's expecting 5V can really ruin your day.

The heatsink and offending part are removed from the board (carefully, the double sided print is fragile) and a Traco TSR1-2450 switched mode IC fitted in it's place. This is pin-for-pin compatible with the 7805 it replaces, but barely gets warm to the touch, and requires no heatsink. 

The rest of the board is in really nice condition. The modulator's a bit rusty, but it's getting on! 

Powering up the unit, and we have life.. but just a black screen with a white boarder. No copyright message, no keyboard clicks... Removal of the socketed IC's, and a quick clean up with some servisol contact cleaner .. and we can try again.

Bingo, the familiar (C) 1982 Sinclair Research Ltd message appears on my (rather small) workshop test monitor!

The obligatory test programme is typed in ... 

... and it runs, but all is not quite right ... 

Keys 1 to 5 don't work. :( It'll need a new keyboard membrane. 

Never mind, we can at least play Manic Miner... 

So a .wav is obtained of Manic Miner, and loaded onto my aging MP3 player, and connected to the Spectrum's EAR socket... 

LOAD ""

The boarder changes colour as it's supposed to, but no amount of amplification persuades it to pick up the pilot tone, nor can I hear the tone through the speaker. My heart sinks at the thought of a faulty ULA ... 

The tape and sound interface all share a common pin on the ULA (28) ... audio comes in to our EAR socket, is loaded by R37, fed via R36 and C32, with a bit of filtration by C35. D13 Clamps the signal, and it's passed to pin 28 of the ULA. Also hanging on pin 28, is an output to the MIC socket for saving programs, and, via D9 & TR7 out to the speaker. Possible candidates for failure are R36 & C32 open circuit (unlikely), C35 & D13 short circuit. D9/TR7 and possibly even the speaker faulty, or, of course the EAR socket itself. The ULA could be faulty, and loading the whole thing down. So, we have key clicks, which shows that the speaker and TR7/D9 are working, and that the ULA is at least outputting something (whether it can input, is undecided at present.) and that it isn't being loaded down by a short circuit D13 or C35. We also can't hear the signal through the speaker, so that leaves us C32 or R36 open, a duff EAR socket, or a ULA that goes into a low-impedance situation when it's set to receive audio. What's the betting it's the socket ... after-all, that's the bit that had all the abuse in the 80's! 

After tracing the audio through the circuit, it's not the EAR socket! It is in fact, and open circuit C32! 

As an aside, it appear my 4B board differs from this circuit diagram, as TR7 is fed from the 12V rail, rather than 5V as shown. 

LOAD ""  


Bingo! 

Now onto the keyboard. Yesterday I ordered a replacement membrane from the fabulous  https://www.retroleum.co.uk/  . It arrived this morning. What fantastic service! Phil who owns the store also manufactures a replacement ULA, called a Nebula for sensible money, although stocks are short at the time of writing.

The kit comes well packed, with detailed instructions, and a plastic razor blade tool.

Changing the membrane is simplicity itself... 

Flip over the keyboard, and carefully bend the brass tags straight. Later computers apparently have the front plate stuck down with some double sided tape, which the plastic razor blade will assist in removing.

The plate can then be lifted off. Some wiggling and tweaking of the brass tags was required...

The old membrane can now be lifted out, and the new one slots right in. I have to say I'm now a bit worried, as the numbers 1 to 5 have a conductor in common... what happens if I've missed a broken connector, and the membrane's not at fault? I suppose I've just spent a few pounds for nothing...

Thankfully, my diagnosis of a faulty membrane was spot on..

Another saved from landfill!

Luxman R-1040 Repairs and restoration.

 Look at it..... 

...Just look at it...

What a thing of beauty. A joy to behold. 

It's a Luxman R-1040 receiver, dating from 1978.

I'm somewhat jealous. A quote from Hifi Engine "It has a genuine output of at least 40 watts continuous per channel into 8 ohms from 20Hz to 20,000Hz with no more than 0.05% total harmonic distortion." That's a very fine spec today, let alone 1978.

This one belongs to cheerful Martin, and has issues. It makes a noise like the tide going out when it's first switched on, some of the lamps have failed, the pots and switches are all scratchy, and Martin would like it re-capped. No mean feat. 

Right, let's crack on... 

There are 6 fittings, which look like they'd be perfectly at home on some Ikea furniture underneath. Remove them with the receiver on it's side, and simple slide the whole chassis out. Put the wooden cover somewhere out of the way, where the cat won't use it as a scratching post.

... it's almost as good looking on the inside as it is on the outside... look at all the space (are you listening Aurex!) 

Access is generally easy. We're going to need to remove the power amp board from the output transistors, and the volume control board to gain access to some of the caps thereon, but it's all very nice.

It appears a cap has let go in the past, as there's some debris... 

A quick look at the service manual and some nice Nichicon caps are on there way. (I would have gone with OE Nippon's, but the price!! I'm damned if I'll pay over £50+VAT each for some of them!) 

You've got to love the march of technology! The new cap on the left, which has a better specification than the old on the right...

The output transistor's heatsink is removed to facilitate change of capacitors, and the output transistors marked up, so they go back in the same order, and the old heatsink grease cleaned off and replaced with thermpath. 

There's a considerable number of caps in this unit, so it takes some number of evenings to complete.

Martin mentioned he wanted the dial lamps replaced, as one had failed... 

This necessitated removal of the front panel...  

.. and the dial glass. 

Despite the remaining dial lamp shining a white light, when it was disassembled, There were two green caps, which had faded / melted with the heat. The original illumination would have been green.

The white wire is disconnected from the power supply tag pin 10, and a 1N4007 diode and a 470uF capacitor are fitted to switch the supply to DC, so we can fit some appropriate LEDs easily...

... nice...

Bias is set for 45mA (after a minute or so's warm up), DC offset nulled out and the pots and switches cleaned.

And finally all buttoned up and tested. 

Leak Varislope II.

Ian's last piece of kit is a Varislope 2 (technically a late Varislope II Stereo) to match the Stereo 20.

On thing I find a little odd about the Varislope, is it's use of EF86 pentodes instead of, say ECC83's.... anyway. 

One EF86 has been changed in the past. If Ian can detect one side souds a little "different" to the other, I'll find 2 new matching valves.

It's chock full of horrible, sticky visconal capacitors. On with the gloves!

One cap has been replaced in the past, and it's the same vintage to those in the Stereo 20, 1979.

The preamp consists of an EF86 gain stage, followed by a Baxandall tone control, and another EF86 stage, where you can vary the response of the tone controls, and negative feedback.

After the capacitors are evicted, I check through all the resistors. Unbelievably, only two cathode resistors are outside of specification. 

Studying the circuit further, it appears the EF86's are run close to starvation mode at around 250uA, great for gain, not so great for distortion. 

Does this matter? Nah, on test it sounds great... :)