Difficulty

Moderate

Steps

4

Time Required

                          14 hours

Sections

1

  • Fuse, Diodes and switcher chip
  • 4 steps

Flags

2

Bullets!

Better coordination with markups and the color/type of bullets will help make this guide more clear!

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  • BackMarantz Receiver NR1604 Amp

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Introduction

Removing the cover, showed that the internal slow 1.5Amp fuse (labelled T1.5AL/250V) had blackened and was open circuit on a multimeter. This fuse was on the power (SMPS) board where the mains connector is plugged in.

It was therefore necessary to find out why the fuse had blown, so this printed circuit board was removed for inspection and showed a number of failed components. These were replaced and the the amplifier successfully worked again.

What you need

Step 1

              shows layout of printed circuit boards
  • With the casing removed to show inside of amp. The power board, at a rakish angle, has been partially removed, but still attached. see step 2 for more disassembly.

With the casing removed to show inside of amp. The power board, at a rakish angle, has been partially removed, but still attached. see step 2 for more disassembly.

1024

Step 2

              Further stripping of printed circuit boards
  • The largest board has been removed and shows the black and white ribbon cable wrapped around other cables. Now it can be untangled and the power board on the left can be removed.
  • To remove the largest board, I removed the back panel with numerous screws and other cables etc. Note the largest board which is horizontal is connected to two smaller vertical boards with rigid connectors which need to be eased apart. Take photos and note screw sizes as it could be days waiting for new components to arrive.

The largest board has been removed and shows the black and white ribbon cable wrapped around other cables. Now it can be untangled and the power board on the left can be removed.

To remove the largest board, I removed the back panel with numerous screws and other cables etc. Note the largest board which is horizontal is connected to two smaller vertical boards with rigid connectors which need to be eased apart. Take photos and note screw sizes as it could be days waiting for new components to arrive.

Step 3

              Shows extracted power board
  • The red square shows the location of the fuse which blew.
  • The blue square shows a ring of 7 zener diodes (MTZJ22B) which were all shorted. These were tested with a multimeter on diode setting.
  • The pink arrows show the approximate location of two silicon diodes (1N4007) which were shown to be shorted with a multimeter on diode setting.

The red square shows the location of the fuse which blew.

The blue square shows a ring of 7 zener diodes (MTZJ22B) which were all shorted. These were tested with a multimeter on diode setting.

The pink arrows show the approximate location of two silicon diodes (1N4007) which were shown to be shorted with a multimeter on diode setting.

Step 4

              damaged switcher chip
  • More careful inspection of the power board showed a discoloured ‘flare’ coming from the TOP258MG chip (arrowed red). This chip was therefore unsoldered from the board. (standard soldering iron and hand sprung pump)
  • The extracted chip (second image) indeed showed it had been holed and and cracked. A new one was ordered from ebay (5off £10 china).
  • Initially I didn’t realise the significance of the ‘flare’ mark on the circuit board. but when testing this board with only the new diodes and fuse, I noted this chip getting very hot.
  • Lesson: look for subtle damage to chips as not everyone has an infrared camera to spot chips overheating (50C in a few seconds) when testing a repaired board.
  • With the new components on the board, it was successfully giving a 5.2v output as stated next to the black and white ribbon cable.

More careful inspection of the power board showed a discoloured ‘flare’ coming from the TOP258MG chip (arrowed red). This chip was therefore unsoldered from the board. (standard soldering iron and hand sprung pump)

The extracted chip (second image) indeed showed it had been holed and and cracked. A new one was ordered from ebay (5off £10 china).

Initially I didn’t realise the significance of the ‘flare’ mark on the circuit board. but when testing this board with only the new diodes and fuse, I noted this chip getting very hot.

Lesson: look for subtle damage to chips as not everyone has an infrared camera to spot chips overheating (50C in a few seconds) when testing a repaired board.

With the new components on the board, it was successfully giving a 5.2v output as stated next to the black and white ribbon cable.

Soldering in the replacement diodes, integrated circuit and replacing the blown fuse got the amplifier working again.

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                                                                                      One other person completed this guide.

Author

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                    Dave Empson

Member since: 01/30/2017

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