Marantz 1152DC Integrated Amplifier Repair & Restoration

How’s this for a beautiful amplifier. I recently repaired and restored this absolutely stunning Marantz 1152DC integrated amplifier, let’s take a look.

The Marantz 1152DC is an integrated amplifier from the upper middle of Marantz’s range in the late 1970’s. The 1152DC and others from this series are very collectible now, thanks to their unique looks, great sound and Marantz’s famous build quality. They were quite expensive, but came with lots of great features and an excellent phono preamplifier.

This 1152DC was in almost perfect physical condition, but electrically it was different story. She was donated to me by her generous original owner, in dead condition. The unit had visited a well-known Perth electronics repairer at some point, and was worse off for it.

Specifications, courtesy of the HiFi Engine:

Power output: 76 watts per channel into 8Ω
Frequency response: 7Hz to 70kHz
Damping factor: 45
Input sensitivity: 1.8mV (MM), 180mV (line)
Signal to noise ratio: 78dB (MM), 91dB (line)
Output: 180mV (line), 1.5V (Pre out)
Semiconductors: 73 x transistors, 44 x diodes, 4 x FETs
Dimensions: 416 x 146 x 316mm
Weight: 14kg

You’ll find more about the Marantz 1152DC at Classic Audio.

Problems

The repairer who worked previously on this 1152DC, is well-known for taking shortcuts. Rather than take the time to clean boards, replace transistors as matched pairs, find parts that actually match those originally installed etc, this guy replaced just the bare minimum with poor substitutes, ‘made’ resistors, left charcoal on boards etc. Sound familiar..?

So, the 1152DC wouldn’t power on and showed some obvious signs of damage. Rather than risk more damage, I decided to completely overhaul her.

Initial Condition

I would describe this 1152DC as cosmetically very good, but electrically needing work.

Dirty, but otherwise pretty tidy.
Typical thermal paste / mica washer mess, but all original output devices. This is excellent news.
And lots of dust…

and flux…
Really? This is the best you could do..? Our creative technician ‘made’ these resistors from parts they had, because they didn’t have the specified value in the correct power rating. It’s a kludge and should never be done for anything other than testing purposes. It would have been nice if they’d cleaned the board under the vaporised part too… Note the two pairs of transistors – these should be two pairs of TO-92L packaged devices. Here, only one in each pair is an original TO-92L device. Q 408 for example is meant to be a complementary TO-92L device, but instead is a completely different TO-126 device. This is not good work, a recipe for bad sound and circuit instability.

Restoration

I use a similar restoration process for most amplifiers and preamplifiers. I start with a careful inspection before removing all the boards and separating the functional blocks. Then I focus on restoring each board or block, before reassembly, lubrication, adjustment and testing.

Cleaning the Chassis

This part is relatively straightforward, if it’s done right. Obviously, water and electronics can mix, but not when energised. Drying is a critical part of the process!

This looks much better. With a clean chassis, I can at least now see what I’m really working with.

After washing, the mess here is more obvious. Can you spot the three mismatched pairs of transistors? This 1152DC will never work properly like this.

Lots of heat damaged capacitors. In a unit like this, with lots of smaller capacitors that show signs of heat stress, it’s good policy to replace all of them.

Plenty of cheap, nasty flux from some past repair.
More stressed caps on this protection board.
Work needed, but at least the dust is gone.
Board Overhaul

As usual, I’ve used premium parts, including vintage resistors of the correct power rating, high-quality capacitors and NOS transistors that meet or exceed original spec. Output devices are factory original, contributing to the classic Marantz sound.

We will focus here mostly on the amplifier module.

Complete, original module. This tightly packed board will receive new capacitors, new thermal interfacing for the output transistors, everything will be cleaned and tidied.
Access is straightforward, thanks Marantz engineers.

The heatsink and transistors need cleaning to remove all traces of thermal grease. This is a good time to test output devices.

Time now to get to work on restoring this board.
Plenty of wiring on the back of the board. Not sure if these are kludges or as designed, but it’s hard to imagine Marantz would choose to do this.
Check out all the crusty old flux. You’d think that manufacturers would clean boards during manufacture, but in consumer-grade gear like this, they just don’t. I removed all this flux.
Like magic, here’s the finished board, complete will new caps.

High-spec Nichicons here, 105 degree rated, low ESR.
Here I’ve installed some vintage tantalums that sound great and look the part. Marantz used plenty of tants in their gear.
You can actually see all the traces now! What a difference de-fluxing makes, this looks 100% better and makes future fault-finding easier too.
Reassembled module.
I’ve mounted all devices on silpads…
They provide a low-maintenance, stable thermal interface.
They also make things much neater.

In the process of fixing that burned board you saw previously. Note the cool, vintage 1 watt, 56 Ohm metal film resistors.
Here it is, cleaned and with matched replacement transistors and new caps installed.
Here are the parts I replaced in this restoration.

The Finished Unit

I’m pleased to report that this overhauled 1152DC sounds great. Switches and controls are completely silent and the amplifier has a lovely warm sound you’d expect from a gorgeous vintage piece like this. Everything works as it should and, whilst I’d love to keep it, she needs a new home where she will become the centerpiece of a great vintage hi-fi system.

Since completing the restoration, I advertised this beautiful 1152DC for sale. She now has a new home in sunny Queensland!

Lots of sharp edges on these older Marantz components, but the styling is just classic.
Plenty of the slider-style potentiometers that Marantz and consumers seem to love!
I’ve never really known what a ‘console’ amplifier is, perhaps someone else knows..?!

If you would like me to look at your classic Marantz piece, don’t hesitate to get in touch.

4 thoughts on “Marantz 1152DC Integrated Amplifier Repair & Restoration”

  1. I realy like reading and also following you with your avesome work on this lovely gear. Best regards from Slovenia.. Zoran

  2. Another great look into proper restoration of some beautiful, classic vintage HiFi equipment.

    I always enjoy the journey you take us on with these blog reports and indeed the excellent photos that accompany it.

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