Rebuilds & Repairs: A section that covers ongoing work and projects.


Work Begins on the 1200B

After my brief initial testing of the 1200B I wanted to get some parts ordered from Mouser. I pulled the rectifier – relay and the power supply boards and mad up a list of the components I need to rebuild them.

Inside the 1200B is so dirty and grungy that it's hard imagine where this unit has been. Everything is coated with a sticky brown substance. I had to use Goof Off on the chassis and a citrus orange cleaner on all of the cabling.

I spent about four hours scrubbing and cleaning. In the end I did get it to shine and now its clean enough to work on.  

See all of the 1200B pictures


Rebuild of a Marantz 1030 Integrated Amplifier

I have to many amplifiers and I'm running out of space to display them all properly. Two weeks ago I spent some time rearranging everything and I found places for all but a few. It's time to thin things out a bit and let some models find new homes.

There are some models that while I really enjoy having them, I really don't use them much. The Marantz model 1030 Integrated Amplifier is one of those. The 1030 has a truly clean Marantz sound, but at 15 WPC it's a little under powered for my use. If I needed another bedroom system it would be perfect, but I don't.

I bought this 1030 a few years ago and if I remember correctly it was the first of this model I have had. When I received it there was a pleasant surprise, it's an early Engraved, Gold-Toned model, serial number 2411. If you look in the original owners manual you will find a picture showing the back of an amplifier and its shows a serial number of 1084.

These early 1030's also have Pre-Amp output and Main-Amp input jacks with the typical Marantz jumpers. Later versions did not have this feature.

I decided to rebuild this 1030 before sending it on its way. Upon close inspection I found that while it's all original, several of the power supply capacitors have failed and a total recap is in order.

I carefully made a complete list of the capacitors I would need,. I did a visual inspection of each board and then compared that to the service manual. There were some discrepancy's between the two lists but since the amp is all original what I saw on each board overrides what the manual lists.

Dis-assembly is simple with this model, the cover is held in place with four screws and the bottom is held on with eight more screws. The board layout is simple and access is great for all of the boards.

I took the knobs and face plate off and set them aside. You have to work from both the top and bottom side of these little integrated amplifiers, so standing them up on their ends works well but you do have to roll them back and forth and you don't want to risk that special face plate.


I did the P800 power supply board first. There's just four capacitors to replace. I found the two 100uF 50 volt caps had both vented through their bottoms.

One major difference between capacitors back in 1973 and today are their size. Modern capacitors are very much smaller than the originals. Most of the time this isn't a problem but you do need to take the lead spacing into account on the large caps.

I like to use Nichicon FG and KW series capacitors when possible.  These audio grade caps are probably a better quality than the originals and in this appilaction the end result will be good. 

Next: Tone and Phono Boards

See all of the 1030 pictures



Super Bright Fuse LED's

I recently bought a Marantz 170DC Power Amplifier because I've always want a DC Amplifier in my collection. I probably paid a little more than I wanted too, but this amp is in really good condition. The face plate is ultra clean and has no damage and the amp itself is all original and untouched.

When I got it home I gave it a good look over and found that two of the meter bulbs were burnt out. The 170DC uses original fuse style bulbs that are used in a lot of 70's equipment. Since I don't have any of these laying around I started looking for some replacements. I ran across a discussion on Audio Karma about a company, Super Bright LED's which makes direct replacement fuse style LED lamps.

They offer both 6 and 12 volt models and the cost is only $2.49 per bulb. I order four LED lamps and they showed up in five days. The LED lamps are well made, however I was somewhat surprise that the LED wasn't encased inside glass. I guess I just assumed they would have a glass tube like the originals even though it's not necessary with an LED.

The meter lamps on the 170DC are powered directly from the power transformer and I measured 7.5 AC volts to the lamp sockets. I bought the 6 volt lamps for the 170DC because I figured that it would be easy enough to drop the voltage a little with a couple of diodes in line. Since LED's prefer DC to AC I will probably add a rectifier to the circuit before I'm done.

So, the real question is how do the LED's look in comparison to the original bulbs? The original bulbs look like they had a blue tinting over the glass, perhaps to add some additional color to the meters. The LED's have a very bright white colored light compared to the yellowish color of the incandescent bulbs. After install two LED's in the left meter and comparing them to the right meter with original bulbs, the LED lit meter has richer color and the blues and reds are deeper. In the right meter the blues look somewhat greenish and the red is lighter and more pinkish.

The lamp housing on the 170DC have several opening in them, probably to let the heat from the bulbs out. Since heat is not an issue with the LED's I may cover over these openings for two reasons. Firstly to make sure that all of those photons are shinning through the meters and it will eliminate the light that shines through the top of the vented cover.

See all of the Super Bright LED photos 


Marantz 1090 "The Lost Episodes"

Parts 2-4 

This is the last and final installment of my Marantz 1090 rebuild. I should title it “When a simple repair goes bad”.

I posted the original segment of this repair back on June 20th 2011, at that time the actual rebuild of the 1090 was well under way and it was almost completed by the end of June. Then several events happened all at the same time delaying the completion of the rebuild. The biggest event was the decision to move my business into a new location. I had been in the original location for 21 years, so moving was no small task.

Without any real time to work on this web site I attempted to hurry through the 1090 rebuild and get it posted on this site. Before the move I had the recap completed and final adjustments were done. The 1090 was in daily testing mode to make sure that it had turned out as I expected and there were no problems with the rebuild. I noticed after a few days that the left channel output transistors were running hotter than the right.

I rechecked the bias and DC offset and both channels were spot on, so I decided to take look at why this was happening. One thing I hate more than anything else is having to redo a project that I have just completed, it's a total waste of time. I disassembled the amp and starting checking voltages.

As they say in the movies “this is when tragedy struck”. The 1090 is awkward to work on because there's not much slack in the interconnecting wires, so when its disassembled everything is sort of floating loose in the case. This includes the rectifier, which accidentally had one terminal touching the power transformer case. Then accidentally the metal bat-wing of the right channel output transistor got bumped into the transformer case. Flash – Spark, oh cr*p.

At this point I was completely out of time and the 1090 was set aside to be completed later.

Later became December 5th 2011. I stole a few minuets out of one day and pulled the output transistors to check them. What I found was surprising, they all tested good but they were all the wrong part numbers and not even the same wrong parts on each side. Mystery solved in regards to the heat issue.

I order new outputs from Little Diode in England. These are the original style Bat Wing outputs and they're not cheap. I also order new bias transistors while I was at it. Altogether about $124.00

Finally on December 28th I had time enough to get the 1090 finished. I hate any project that sits untouched for months and months, you really can't just jump into where you left off. I started from the beginning check everything and installed the new transistors.

With the 1090 mostly reassembled I powered it on and initial checks showed no bias adjustment on the left channel and almost 40 volts DC at the left channel speaker connections. Ugggh. At least the right channel was fine.

More voltage checking turned up Q709 as bad, I robbed a replacement form another unit and kept my fingers crossed, everything seemed correct. I had the proper bias voltage (12mA) and -9mV offset on the left channel.

With a pair of Pioneer HPM100's and a Sony CD player connected it was time to give this 1090 a real test. I choose Bad Company's “Bad Company” as my test CD. So how did it sound? Well the right channel sounded great, the left channel was silent............

Double check speaker connections, input connections and flipped connections around just to make sure. . . nothing. Double checked left channel voltages, everything was spot on. In the back on my mind I had a feeling that this was some reassembly error, so I got to take the 1090 apart again.....

I found that I had re soldered the input cable to the volume control pot to the wrong terminals. A quick redo, an even quicker reassembly and folks we had music out of both channels!

I really put the 1090 through its paces with music I love to play loud, ending up with Motley Crue's Girls, Girls, Girls. I watched the watt meter and kept track of the heat being dissipated from the outputs, finally everything was on track and working correctly. I left the 1090 at idle for about 5 hours and rechecked and readjusted the bis just a little.

The next day I worked through the performance verification as outlined in the service manual. I measured 47 watts of output on the oscilloscope and 0.0878 of THD. These tested were made with an 8 ohm load. The 1090 has been in daily testing mode for over a week and everything sound great.

I work on and repair equipment everyday in my business and for the most part this daily work is uneventful and completed in a timely manner. The primary problem with the 1090 was not the unit itself, it was the lack of time I had to put into it. Starting and stopping a project over many months is just asking for trouble. The lack on continuity in the project is just a recipe for disaster.

I have so many units I really want to work on and my time is still limited. With this new year my biggest challenge will be making time to work on my hobby in a proper manner.

See all of the final 1090 pictures. 


Marantz 1090 Intergrated Amplifier Rebuild, part 1 of 4

Part 1: The acquisition, Initial Impressions

I found this Marantz 1090 integrated amplifier during one of my morning on-line searches. The seller had set a low starting bid of $49.00 and the auction was for 7 days. I was hoping that I might this unit for the opening price, there were no bids at all until two days before the auction ended.  I waited until in at the last minuet and got the amplifier for $56.00 plus $27.00 shipping.  A great deal I think.

The seller described the only problem with the amplifier was that it would take 5-10 minuets once it was turned on before any sound came out.  This sounded unusual and I was thinking it would  probably be something that would be straight forward to repair.  A week later the unit showed up, well packaged and in very nice cosmetic condition.

The first thing I like to do with a new piece of equipment is remove the cover and take a look around.  What you find under the cover can tell you a lot about the life story of a unit.  This 1090 had a nice even coat of slightly sticky, brownish dust covering everything inside.  This is just what I like to see, a genuine “original condition” unit that has not been messed around with.

As a precaution I used my Variac and Simpson 390-2 watt meter to power up the 1090 for the first time.  This allows me to monitor the current as I turn up voltage up to power the unit.  At 120 volts the 1090 was drawing 10 watts, just what I would expect for this type of design.

I did a quick check for DC voltages at the speaker terminals: Right Channel 11mv  Left Channel 9mv, both well within proper settings.  The 1090 doesn't have any DC offset adjustments.  I didn’t observe any problem with the unit working correctly at all.  This model doesn’t have a protection relay, however there is a 2-3 second delay once the unit is turned on.

Initial Impressions:

The Marantz 1090 was manufactured during 1977 and 1978 and some where between 600 and 900 units were produced.  Since 1090 is a physically larger than say a model 1060, you find a lot of free space inside the unit.  There are really just two main circuit boards plus the tone control board and input board on the back of the chassis.  This type of design is very different than older Marantz models that share a similar size.  If you look inside a model 1200, you will find almost no free space, it’s just packed with circuit boards.  All of the free space in the 1090 tends to leave the impression that this is a “cheaper” model.

The faceplate on the 1090 is large and so are the knobs.  In comparison to a 1060, the 1090 looks sparse and simple. One of the features I do like about the 1090 are the tone controls.  The faders are a detent style, so you get that light click as they move through their range.  I also like the fact that there is a mid level tone control. After having the 1090 sitting on my desk for a week the look did grow on me.

How dose it sound:

I think it’s important to listen to every unit before jumping into a rebuild.  I decided to use my Pioneer HPM100’s and give the 1090 a test listen.  My first selection was from Peter Frampton Comes Alive this is one of my favorite albums and I know it so very well that I can easily compare how it sounds with the 1090 compared to my daily system.  The 1090 has lots of power, much more that I was expecting for 45 WPC. My second selection was from Motley Crue's Girls, Girls, Girls, there's an instrumental version of Girls, Girls, Girls that will give any amp a real workout. Paired with the HPM100's the 1090 didn't disappoint me.

The 1090 is rated at 45 WPC and it sound like a lot more, I'll be testing the output on the bench before starting the rebuild.  The HPM100’s tend to be base heavy and mid range forward and the 1090 seems to be a base heavy amplifier, so this proved to be a strong combination, no need for use of the loudness control with this setup.   I found that having the tone controls set to mid level produced a good amount of base and mids.  As usual for me I had the highs down a notch or two.

All in all the 1090 surprised me, it sounds better that I expected. I’m not sure exactly why I expected less of the model, but I was happy with its sound.

Click to View all of the 1090 pictures

Next up: Parts 2-4 consolidated into one post.

See all of the Final 1090 Pictures Here



Page 1 2