REL T5 Main Amplifier Power Resistors Replacement

Place the subwoofer on it legs to protect the driver. Be careful not to touch the driver/speaker on the bottom when you handle the case.

Using the 3mm hex tool, remove only the outer rim of screws, starting from the bottom.

Make sure to support the plate amp by gripping the heat sink.

Remove the top screws. Be aware: the heavy transformer is located at the top. Removing the top screws will probably make the plate amp tilt out of the case.

Using the heatsink, carefully lift the plate amp out of the case. Again: it's heavier than you might expect!

The plate amp is still connected to the driver via faston connectors. I found it easiest to disconnect the driver connectors, but removing them from the amplifier side works equally well.

You've now removed the plate amp. Set it aside on the heatsink side. The height of the heatsink will make sure that the controls are not damaged.

Now is a good time to check the voltage rails for residual voltage. Everything after the rectifier bridge should be <45V, but always take appropriate precautions when it comes to mains powered devices.

Snip all tywraps, such that all cables can be manipulated freely.

Disconnect all connectors that tie to the transformer

Make sure that all leads can be manipulated freely.

Start loosening the screws on the back using the m3 hex tool

Don't remove them fully, yet though.

Turn the amp on it's back.

Remove the nuts from the screws that where loosened on the back.

Remove the philips screws using a #2.

Loosen the dampening rubber by running a Halberd Spudger underneath it.

The rubber is not adhered to the aluminium and is pretty tough, so a moderate amount of force is allowed.

You can now remove the transformer from the plate. Be careful not to damage the controls on the plate now that the assembly is a lot lighter.

Remove the connectors to the amp board.

Discharge the capacitor e.g. using a replacement 1k3 power resistor.

Carefully bridge the resistor across the + and - legs of the recifier, but don't touch anything else.

Verify that the voltage is near zero. 0.2V or so is fine.

The voltage starts at around 100V, so be careful.

Remove the screws to the thermistor.

Remove the screws to the transistors.

Store them in a separate baggy.

Remove screws for four corners.

Store them in or on their posts.

Gently lift up the PCB. The transistors might be held down by thermal paste, so use a spudger to release them.

Carefully remove silica pads, take note: they are very fragile!

Remove excessive black putty where needed.

Thoroughly clean back plate with Isopropyl Alcohol (IPA).

Clean silica pads as well and store them.

Cover the electronics with paper and tape.

This reduces the risk of drilling chips ending up in the electronics.

(Please excuse the dirty plate. If only my repair went as linear as this guide)

At this point you have some options:

Tapping

Bolting

Adhering

I don't trust adhesives, and I do not have a tap, so bolting was the only option. I salvaged the M2 screws and nuts from the housing of an old laptop.

Mark the positions in between the heatsink fins.

This allows for nuts to be inserted later.

Place the transformer back on the plate, and align the resistors in the available space.

Drill the holes. Aluminum is very grippy, so make sure to use an appropriate cutting oil. I drilled at 2.5mm.

Drill the counter holes on the heatsink side to seat the nuts. Make sure not to get any chips or oil in the process! I drilled these holes at 3.5.

Deburr the holes so the resistors lie flat on the plate. This improves thermal coupling.

Test fit the resistors and the nuts to make sure everything fits as intended before committing to permanent mounting.

I had to tweak the rubber damper under the transformer a bit.

Attach wires to the resistors.

Ensure adequate length for installation (you can snip off the excess; adding is harder).

Clean the nut and the heatsink hole thoroughly with IPA.

Using epoxy and a toothpick, apply a little on the inside of the screwhole.

Fix one nut at a time to preserve alignment.

Once dry, remove all screws.

Solder the resistors into place, shorten the wires to fit.

Apply thermal paste and mount to the backplate.

Apply loctite to the threads.

Hook the amp up to a Dim Bulb Tester. I used a halogen bulb, it works the same.

Make sure the light flashes when you turn the amp on, but then dims down.

Optionally use this cover on the mains pins, to reduce the risk of electrical shock.

Test the voltage on pin 4 and pin 7

Use ground from the speaker connector

Voltages should be around:

pin4: -14.5V

pin 7: 14.5V

Final test before disconnecting the dim-bulb: check that the DC offset on the speaker terminals is zero (or else yuor buying a new driver

You're now ready to hook the amp up directly to mains and listen to your music. Enjoy your upgrade!

Don't forget to reassemble first ;-)

Optional, but highly recommended for longevity

Apply electronics glue to all protruding elements (wires, capacitors, ...)

I took a gamble and used Bison PolyMax, since I have no further use for electronics glue. It should be applicable, although impossible to remove. I'll worry about that later.

Make sure all tie wraps are in place, so everything is nice and tight.

Add some thread locker to the resistors screws.