Linn LK-260 Owners manual

Service Manual for LK2 Series of Power Amps
Covering LK2(60), LK275 & LK280
For the purposes of this manual, we will refer to the three types as LK260,
LK275 & LK280. The term LK2 will be used as an “umbrella term”,
covering all three types, i.e. the LK2 series.
CONTENTS
INTRODUCTION ....................................................................................................................................	2
ABOUT THE LK2 SERIES .........................................................................................................................	2
HOW TO DIFFERENTIATE BETWEEN TYPES OF LK2.......................................................................................	2
ABOUT THIS MANUAL..............................................................................................................................	3
RETAILER & DISTRIBUTOR OBLIGATIONS ...................................................................................................	3
SPARE PARTS AVAILABILITY AND LK2 REPAIR ............................................................................................	3
HOW TO USE THIS MANUAL......................................................................................................................	3
IMPORTANT SAFETY INFORMATION & INSTALLATION ADVICE .........................................................	4
MAINS CONNECTIONS .............................................................................................................................	4
LETHAL VOLTAGES.................................................................................................................................	4
PLACEMENT..........................................................................................................................................	4
PROCEDURE FOR DISMANTLING AND RE-ASSEMBLING THE LK2.....................................................	5
FAULT FINDING ON THE LK2 – HINTS & TIPS ......................................................................................	9
POWER-UP PROBLEMS – FAULT TABLE............................................................................................	10
WON’T POWER UP.................................................................................................................................	10
WON’T SWITCH OFF...............................................................................................................................	10
FUSE BLOWING.....................................................................................................................................	11
AMPLIFIER PROBLEMS – FAULT TABLE ............................................................................................	13
NO OUTPUT .........................................................................................................................................	13
TRIP (PROTECTION) PROBLEMS ...............................................................................................................	15
DISTORTION / CRACKLING ETC ................................................................................................................	16
DC AT OUTPUT.....................................................................................................................................	17

Copyright © 2000 Linn Products Limited. All rights reserved. Paul O'Neill

LK2 Service Manual

Introduction

About the LK2 Series

There were three versions of the LK2:

• The first version was known at the time simply as the LK2. It gave an output of 60 watts per channel (into 8 ohm load) and used PCAS 003 type boards. For the purposes of this manual, we will refer to this version as the LK260.

• The second type was also usually known as the LK2 but was often called the LK275 to differentiate it from the 60-watt version, as it gave 75 watts per channel. Also used PCAS 003 type boards but with several improvements over the 60 watt version – the most obvious being the increased power output, but also had improved protection circuitry and better sound.

• The third and last type was known universally as the LK280. 80 watts per channel – used PCAS 020 boards. PCAS 020s, at first glance are similar to PCAS 003s, in that they are roughly the same size, shape and layout, but they are a completely different design of board (i.e. not just a modified version of PCAS 003) as a closer examination shows. The LK280 sounded considerably better than either of its predecessors.

How to differentiate between types of LK2

There are several methods of determining the specification of an LK2:

• Looking at the serial number of a unit and using the LK2 Product History (accessible via Linfo website – Product Information) will tell you which revision it was sold as. Since, however upgrade kits were sold by Linn in large quantities to allow customers to convert their early version LK2 into the latest spec, many units are not what they seem. The following information will help you to determine the specification of a unit if its exact history is unknown.

•LK280s had “LK280” printed on the facia – earlier units (LK2 & LK275) had “LK2” printed there, but beware – an earlier version may have been upgraded to LK280 spec.

•LK260s and LK275s had a red power LED and LK280s had a green LED. This is handy as a quick and easy indicator but is not 100% reliable (LEDs are easily changed)

•The best way to determine a unit’s spec is simply to remove the sleeve and look at the boards that are fitted (see below).

Distinguishing Features of Different Board Types

	PCAS 003 – used	60 watt type used same board
	in LK260/LK275	but with some differences, as
		shown below
	These diodes and	Capacitor &
	capacitors not fitted	resistor (bridged)
	to 60 watt boards	not fitted to 60
		watt board

PCAS 020 – used

in LK280

Small heatsink bar with transistors fitted to it – found on PCAS

020 only

Small “Hybrid” board fitted here at 90 degrees to main board – found on

PCAS 020 only

Page2	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill

LK2 Service Manual

About this manual

This manual deals effectively with three quite distinct amplifiers. The amps have enough in common to justify this approach and this avoids the confusion that might come with separate manuals. Any differences between the types will be dealt with in the “Circumstances” column – e.g. Applies to LK280 only.

This manual is designed to help you, as a Linn Retailer or Distributor, to repair as many LK2 faults at your repair centre as is practical and so provide the best possible service for your customer should a problem arise.

If you have any suggestions or comments regarding this manual, please contact Paul O’Neill at Linn

Products Ltd:	By E-mail	[e-mail]
	By Phone	++44 (0) 141 303 5005
	By Fax	++44 (0) 141 644 4262 Marked for attention of Paul O’Neill

Retailer & Distributor Obligations

Linn Specialist Retailers or Distributors are obliged to carry out the repairs in this manual under the terms of the contract & warranty agreements. You should return a faulty product to Linn for repair, only if the fault is not covered in this Service Manual. If a product, which is under warranty, is returned to Linn for repair and the fault is covered in the service manual, Linn may levy a charge and this charge should not be passed to the customer.

Spare Parts Availability and LK2 repair

Please note that the LK2 has been discontinued for some considerable time now and as such, we cannot guarantee the supply of spare parts – many are simply no longer available and some others are no longer in stock. Some part numbers are listed throughout this manual, but these are provided for information only and this does not imply that these parts will be available should you request them.

Linn guarantee that we will support a product until 5 years after the final build. We take this obligation very seriously and also go much further. Beyond this date, we will repair any Linn product that we possibly can, where it is within our power to do so. However, due to the difficulty with the availability of spare parts, as explained above, it is occasionally not possible to repair a product or supply parts for repair, if the necessary parts are not available.

How to use this manual

The main body of this manual, the fault table, is designed to be as quick and simple as possible to use when you are confronted with a faulty product and so it is arranged by fault symptom as the symptom is usually all that you will know about the fault.

Also read the “LK2 fault finding – Hints & Tips ” section below as the information contained there may save you a lot of time.

If you are unsure about the meaning of any words or phrases, look in the Glossary. (accessible via Linfo Website - Product Information)

Before embarking on any Service work, you should read the Service Procedures section (accessible via Linfo Website - Product Information), as there are certain procedures that must be followed in order to ensure the problem is resolved quickly and permanently

Table of contents & fault symptoms

Look firstly at the table of contents and find the category that covers the symptom you are seeing, then look down the list of faults in that section until you find the symptom or symptoms that best describe the problem.

Circumstances

Then simply follow the table along – the table specifies circumstances surrounding the fault symptom – e.g. whether the fault is likely to be intermittent or constant, if the fault only occurs within a range of serial numbers etc.

Possible causes

The next column details possible causes – this is effectively the most important section, probably the main reason you are looking at this manual at all. There may be several possible causes for the symptom you have – it is worth checking out all of these (and bear in mind that there may be more than one fault). For

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Contents	Paul O'Neill

LK2 Service Manual

some faults, simple checks are detailed that you can use to rule out the problem without replacing any parts, whereas for other faults, the simplest way to rule out the problem is to replace the component(s) listed

Cure

Quite simply the action that you must take to cure the problem.

Important Safety Information & Installation Advice

Mains connections

This appliance must be earthed – both for Safety and functional reasons.

Lethal Voltages

Inside the LK2, lethal voltages are present, avoid powering up an LK2 with the sleeve removed or with any live parts exposed. If you must work under such circumstances, DO NOT touch any part of the circuitry or any electrical connections and take great care to avoid electrocution.

Placement

Location & Environment

Do not locate near electronic products that may transmit RF, such as computers, fax machines, TVs etc, or connect them to the same mains socket as these devices. Also avoid close contact with the mains or signal leads of such products – careful routing of the cable may be required.

Although the LK2 can usually be stacked along with other products with no problem, it is better if possible to keep it apart from other products to prevent its operation being adversely affected by the heat and strong electrical field emitted by some products; also - since the LK2 can emit a considerable amount of heat and has a fairly strong electrical field, it is better to keep it away from other devices that may be adversely affected by this.

Avoid locations that have high humidity or the chance of the unit getting wet. Avoid locations where there is a lot of dust.

Handling & general maintenance.

Always handle the LK2 with great care – IT IS VERY HEAVY.

Always turn off the LK2 and wait at least 30 seconds before connecting or disconnecting any plugs to/from the sockets at the back of the unit to avoid damage to the speakers.

If you are carrying out any work on the LK2 with its’ sleeve removed, ALWAYS take anti-static precautions as tiny static discharges from your body, which you may be completely unaware of, can damage electronic circuitry and cause major problems. Anti-static earth mats & wrist straps must be used when handling any of the circuit boards or any spare parts.

Page4	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill

LK2 Service Manual

Procedure for Dismantling and Re-assembling the LK2

Step 1. Remove the boards from the LK2

Remember to keep all the screws and other parts that you remove from the LK2 in a safe place to re-use later.

1.Disconnect LK2 from everything and especially the mains (or Spark).

2.Place a soft cloth on the workbench & lie the LK2 upside down on the cloth. Using a No2 posidriv

screwdriver, remove the 4 screws that hold the sleeve on to the LK2. Stand the LK2 on its facia and slide the sleeve up and off. Carefully set it aside in a safe place where it will not get scratched or damaged.

3.Remove the 4 allen bolts or screws (older units used screws) holding the speaker sockets on to the back panel. Do this to both channels.

4.Disconnect both transformer connectors (the cables going from transformer to board) from the board

5.Lift the LK2 up so that it is standing on one of the heatsinks. Each channel is held into the tray by 2

countersunk screws that attach to the heatsink on the underside. Hold the channel that is now uppermost (to prevent it from falling once it has been freed) and remove the two screws from this channel only. Lie the LK2 down (correct way up) and remove the channel that you have just loosened – this can sometimes be tricky so follow these instructions:

• Pull the board slightly toward the front of the unit until the 3-pin cannon input socket at the rear is clear of the back panel – it may sometimes be necessary to push the back panel slightly in the opposite direction until the socket is completely clear.

• Lift the end of the board containing the 3-pin cannon socket upwards (see picture) until that end of the board is clear of the tray. Some delicate manoeuvring may be necessary, but don’t force it.

	2. Move the
			1. Lift this end up until
	entire board in
	this direction		clear of tray

•By carefully moving the board backwards & upwards, it should now be possible to lift it up and out of the tray.

•Repeat the above instruction for the other channel

Step 2/

Page5	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill

LK2 Service Manual

Step 2. Remove the heatsinks from the boards (if required)

1.Using the 5.5mm spanner or nut-runner, loosen the single nut/bolt found beside the 3-pin cannon socket (see picture below) – do not remove the nut completely, but loosen it to the point where only a very small amount of the bolt is protruding from one side of the nut.

2.The board is now held on to the heatsink by 4 allen screws or 4 nuts/bolts (see picture below).

•If nuts/bolts are fitted, loosen them but do not remove them (as with single bolt above), pull the board upwards until there is a gap between the board and the heatsink and then slide the board to one side. If the board will not move easily, check that you have loosened all 5 nuts/bolts. If all are loosened correctly and it is still not free, the board may be held on by the heatsink compound and will require some slight pressure to free it.

•If the board is held on by allen screws, completely remove all 4 screws, lift the board away from the heatsink and slide the single bolt beside the cannon socket sideways to free the board.

			Nuts & bolts or
			allen screws
			found at these 4
Loosen the
			locations
single bolt
found here
		Do not remove
		these two screws

3.Use a tissue or paper towel to clean the heatsink compound from the board and from the heatsink (if you don’t, you will find out very quickly that heatsink compound has a knack of ending up all over your clothes, hands, face etc)

Step 3/

Page6	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill

LK2 Service Manual

Step 3. Re-assemble the LK2

1.Re-attach the heatsink:

Apply heatsink compound in a single line along the centre of the coupling block as shown below

Heatsink compound here

If board was attached to heatsink by nuts & bolts – follow the instructions below:

•Remove all five bolts from the board and slide the bolts into the slots, arranged as shown below

Heatsink

Slide the bolts into the slots - positioned as shown

•Place the board onto the heatsink so that all the bolts pass through their respective holes on the board (some readjustment is usually necessary).

•Screw the nuts onto the bolts but do not tighten fully.

•Adjust the position of the board with respect to the heatsink so that the two are matched up – i.e. the two are parallel with each other and neither the board nor the heatsink are protruding at either side (see pictures below – exaggerated to show problems clearly)

				Heatsink					Heatsink
				protruding					not parallel
				from one side					to board

•Once heatsink and board are matched up, tighten bolts.

If heatsink was attached with allen screws:

Page7	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill

LK2 Service Manual

•Slide the single nut/bolt (still attached to board) into the middle of its slot – do not tighten

•Rest the board on the heatsink in a central position.

•Line up the screw holes in the board with those in the heatsink and screw in all four screws – but do not tighten fully.

•Line up the board and heatsink so that they are parallel and level with each other (as diagrams above) and then tighten the screws fully.

•Tighten the nut/bolt

2.Refit boards into tray – just do the reverse of the dismantling process described at the start of this document.

3.Refit sleeve

4.Test amp fully

Page8	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill

LK2 Service Manual

Fault Finding on the LK2 – hints & tips

The LK2 circuitry is notoriously difficult to fault-find on in the traditional way (tracing signals, measuring voltages etc), so this manual seeks to help you to avoid this ordeal. Check the fault tables below firstly, to see if your fault is included and if not, use the information in this section.

Trip

One issue that may prevent you from fault-finding is the inclusion of the “Trip” or protection circuitry which will shut down the entire board if it detects a problem that might cause damage to the amp or the speakers. If trip occurs, it makes fault finding very very difficult as no power reaches the amplifier section of the board. If this happens it is best to try to find the fault with the power off – use the information found in the Fault Tables below and in this section.

Isolating Faulty Components in the LK2 Circuit

Common Faults

Around 60-70% of faults in an LK260 or LK275 board only (i.e. not LK280) are attributable to just 4 components. See “LK2 Reliability Modifications” (accessible via Linfo – Product Information) for instructions on how to replace these components and prevent re-occurrence. This modification is a good first step for a faulty PCAS 003 board and should even be carried out to working boards as a preventative measure.

Transistors

The majority of remaining faults on an LK2 board are caused by faulty transistors, so this is a good place to start. If the transistors develop a fault, they normally develop a short circuit (zero ohms) or low impedance across one or more junctions, so it is usually quite a simple job to trace the faulty transistor by measuring across every junction of every transistor – while the transistor is still in circuit. This might seem daunting, given the number of transistors on each board, but it is definitely a worthwhile exercise as it may save you many hours of conventional fault–finding and does not take as long as you might think (about 20 minutes per board).

Just measure the impedance across all 3 junctions (Emitter – Bass; Emitter – Collector; Bass – Collector) of every transistor on the faulty board.

In general a working junction will measure many Kohms or even Megohms, whereas a faulty junction will tend to measure almost short circuit – perhaps a few ohms – possibly up to 500ohms at most. If in doubt, compare with the same junction on the good channel and replace transistor if you suspect faulty.

It is advised that you check every single transistor on the board, i.e. don’t stop if you find a faulty one, as quite often there is more than one faulty transistor on the board.

Remember to include the big transistors (the 4 that are clamped to the heatsink) when measuring.

The above test, while not absolutely guaranteed to find every faulty transistor, will find the vast majority. Remember that it is quite common for more than one component to be faulty, as often a faulty component will cause damage to others around it in the circuit. See below for advice on how to check for this.

Other components

Other components are slightly less straightforward. The same principles as with Transistors above can be applied (measure using an ohmmeter) but there is a lot more work involved and a lesser chance of success as these parts are less likely to go faulty and less likely to follow such a straightforward pattern as the transistors.

If you have a fault that is not caused by any of the faults listed in this manual – i.e. the fault tables and this section - then try to narrow the fault down to an area of the circuitry using conventional fault-finding and then measure and/or replace the components in that area.

Resistors can of course be easily measured for impedance but are very unlikely to go faulty unless another component failure has damaged them, so look for telltale signs like scorching etc on or around the resistor that might indicate this.

The Capacitors on this circuit can also be checked using an ohmmeter as above. Sometimes capacitors will internally short-circuit so worth a quick measurement.

Check the components (as transistors above) using an ohmmeter.

Page9	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill

LK2 Service Manual

Power-up problems – Fault Table
Won’t power up
Symptom	Circumstances	Possible Cause(s)	Cure
Won’t power up.	Constant	Fuse blown in unit and/or in	Replace fuse(s) with correct
Power LED dead		mains plug.	value & type.
& no function –			Fuse in mains lead should be 5A.
both channels			Fuse in LK2 should be “Slow
			Blow” – look for a ‘T’ before the
			rating on the fuse. Correct types
			are:
			100-115V	-	T3.15A antisurge
			220-240V	-	T6.3A antisurge
Won’t power up.	May be intermittent	Mains lead faulty	Replace faulty mains lead.
Power LED dead
& no function –
both channels
Won’t power up.	May be intermittent	Power switch faulty	Replace power switch – use Linn
Power LED dead			part no: SWRL 006
& no function –
both channels
Unit dies	At any time	Mains voltage dropping too	Consult an electrician or your
intermittently &		low for LK2 to function	electricity supply company.
stops working for		correctly (known as ‘Brown
a while – possible		outs’ as these voltage drops
distortion or		also sometimes cause the
reduction in		house lights to dim.)
sound quality -
both channels
Doesn’t power up	May be intermittent	Wrong mains voltage for LK2	Check voltage rating on
or		type – mains voltage is too	underside of LK2. If wrong,
Powers up		low. (e.g. 240V unit being	transformer will require
(display LED lit)		used with 115V mains	replacement. Correct part
but no function.		supply.)	numbers are:
or			MCAS 001/100 for 100V mains
Possible			MCAS 001/115 for 115V mains
distortion / poor			MCAS 001/220 for 220V mains
sound quality –			MCAS 001/240 for 240V mains
both channels			Our stock of these transformers is
			very limited, so it may not be
			possible to supply the part you
			require.
One channel	May be intermittent	Transformer cable not	Reconnect cable or repair if
dead		connected to board; may be	broken.
		broken or may have a bad
		connection
One channel	May be intermittent	Channel has “tripped”	See Trip Faults section below
dead
One channel	May be intermittent	Board is faulty	See Amplifier Faults section
dead			below
Won’t switch off
Amp will not	May be intermittent	Faulty power switch	Replace power switch – use Linn
switch off using			part no: SWRL 006
power switch
Page10		Copyright © 2000 Linn Products Limited. All rights reserved.
Contents				Paul O'Neill

LK2 Service Manual

Fuse blowing

Symptom	Circumstances	Possible Cause(s)	Cure
Fuse blowing	May be intermittent	Wrong type of fuse fitted	Replace fuse(s) with correct
			value & type.
			Fuse in mains lead should be 5A.
			Fuse in LK2 should be “Slow
			Blow” – look for a ‘T’ before the
			rating on the fuse. Correct types
			are:
			100-115V	-	T3.15A antisurge
			220-240V	-	T6.3A antisurge
Fuse blowing	May be intermittent	Mains surges	Consult an electrician or your
			electricity supply company..
Doesn’t power up	May be intermittent	Wrong mains voltage for LK2	Check voltage rating on
or		type – mains voltage is too	underside of LK2. If wrong,
Powers up		high (e.g. 115V unit being	transformer will require
(display LED lit)		used with 240V mains	replacement. Correct part
but no function.		supply.)	numbers are:
			MCAS 001/100 for 100V mains
Possible			MCAS 001/115 for 115V mains
distortion or poor			MCAS 001/220 for 220V mains
sound quality			MCAS 001/240 for 240V mains
			Our stock of these transformers is
			very limited, so it may not be
			possible to supply the part you
			require.
Fuse blowing	May be intermittent	Transformer faulty. To check	Replace transformer. Correct part
	but usually constant	if it is definitely the	numbers are:
		transformer, power down the	MCAS 002/100 for 100V mains
		unit, replace fuse, disconnect	MCAS 002/115 for 115V mains
		the transformer output from	MCAS 002/220 for 220V mains
		the Main board and power	MCAS 002/240 for 240V mains
		up. If the transformer IS the	Our stock of these transformers is
		cause, the fuse will continue	very limited, so it may not be
		to blow. If the fuse remains	possible to supply the part you
		intact, the fault is more likely	require.
		to be on the board.
Fuse blowing	Constant	Bridge rectifier diode on	Replace faulty bridge rectifier
		amplifier board faulty	diode(s)
		(probably internally short	Part details: MR752 6A 200V
		circuit). These are the four	Rectifier diode (Linn Part no:
		large diodes which can be	MISS 010)
		found on the underside of
		each amplifier board, under
		the big capacitors Try
		measuring across all four
		with an ohmmeter – if one
		has an internal short circuit, it
		should be quite obvious.

Page11	Copyright © 2000 Linn Products Limited. All rights reserved.
Contents	Paul O'Neill