The Work Bench



Cleaning circuit boards

If you have been following my Marantz 1200B rebuild you might have seen the early pictures which show a really grimy amplifier.  All of the circuit boards were coated with what seemed like a harden coating of oil or grease.

Part of the rebuild is to clean everything.  I have an ultrasonic cleaner but not everyone does, so what do you do? What do you clean boards with? Some people use alcohol, some use solvent based cleaners.  I use basically water.

Yeah Yeah, I know, not water on electronics ahhhhhhh!.  Relax it works really well.  Almost all ultrasonic cleaners use water with different types of cleaning agents added.  You can use a similar method on your own boards.

The at home version requires just a few items, orange based spray cleaner and a old tooth brush.  Spray the boards with the orange cleaner, let soak for a few minuets. Scrub lightly with the the tooth brush, spray orange cleaner again.  The final rinse is with warm water, being sure to get the board rinsed thoroughly.

Now for the really important part, you have to dry the board off.  Use some low PSI compressed air.  Blow all of the water off the board, blow all of the water from under the components.  The board should be 99% dry before you stop blowing it off.

Once you are sure that it dry, dry it again.  Now that it's really 99% dry the final step is to place it in a warm spot to finish drying.  You can put it outside in the sun or on a sunny window sill.  You can also place the board under a 100 watt desk lamp and let the heat from the lamp finish drying the board.  Leave the board under the heat for several hours to make sure it 100% dry.

Now you have a clean board to work on, it's so much easier to rebuild a clean board.





Calipers Can Be Your Friend

One of the tools on my bench is a digital caliper.  I use it all the time, especially when I'm measuring larger capacitors which are mounted in brackets on the chassis of an amplifier.  

Today i was putting together a parts order for an upcoming Marantz model 1040 integrated amplifier.  The 1040 has 2 main capacitors which are mounted in the center of the amp.  I know from experience that these caps are 35mm diameter but I used the calipers to measure the height, 50mm.  Sometimes the available space is very limited and if you buy parts that are to large, the will not fit into the chassis.  This is a problem with large value capacitors which can be much taller then the originals.

The calipers are also especially good for measuring the inside diameter of chassis mount holes, like the holes that switches or jacks fit through.  They are great for measuring the distance between mounting screws and in a pinch you can use them to measure the component mounting holes on a circuit board and then use them to bend the component leads to fit.

You can buy this exact set of calipers from Amazon for around $25.00.  Get a set, they will pay for themselves in just a few projects.


Replacement Lamps for your Vintage Marantz

As a regular part of every rebuild I do, I replace the miniature lamps in the unit.  My local source for lamps recently closed so I went looking for a good on-line source.  On the audio forum Audiokarma, memeber DGWOJO is the go to guy for vintage lamps.  I ordered the lamps and they arrived in just 4 days.  

The lamps are good quality and David even includes some solder and heat shrink tubing to cover the solder joints.

His web site is easy to use and David is a good resource to keep in your favorites list.

These lamp assemblies fit Marantz models 1030 and 1060.  One of these wil be going into the 1030 I have just finished rebuilding.



Rigol lowers their price

Rigol has just lowered the price on the DS1102E 100MHx 2 channel oscilloscope to $399.00.  There might be a new scope in my future.


New Bias & Offset Trimmers

One thing that really bugs me is when it's time to set the bias and offset adjusts on an amplifier and the trimmers are sloppy as hell. Sometimes the physical trimmer adjustment is so loose that it's almost impossible to make the smallest adjustment without over shooting it.

Also, for some reason it seems like the area in the trimmer right where it needs to be set is so over sensitive that it's almost impossible to get it set right on.

As one of the standard refurbish items I am adding to my ever growing list of mandatory parts to be replaced on every unit are theses trimmers. New Bourns trimmers are incredibly cheap and they offer so many different styles that find a replacement should be easy.


Of course you need to choose a trimmer of the right value and a style that works with the PCB it will be mounted on. Pay particular attention to the leg spacing for through hole mounting. Many older trimmers are larger than their modern replacements.

I decided to replace the bias trimmers on my Marantz 1090. I ordered two kinds, Bourns 3309 and Bourns 3329. Both will fit the PCB correctly, the 3309 are very similar to the originals, the 3329 will have the trimmer adjustment slot facing upwards which may make it easier to access.