The reason I asked about replacing the two 0.47uF electrolytic caps with polypropylene was because I had read that the poly caps don't wear out. They also usually have high voltage limits so can take a lot of punishment. Aren't the poly caps generally used in small capacitance values because they are affordable at those values?  Is the reason there are polarized electrolytic caps in the circuit because they are most cost effective for those capacitance values?  I know people talk about using certain type of electrolytics in the signal path because it affects the sound but if it were possible (cost and size availability) wouldn't it be ideal to just have polypropylene caps instead of the polarized electrolytics?  I have often Googled and searched about the use of capacitors and I don't really have a good feel about why there are electrolytic caps (especially polorized e-caps) in these circuits except for the fact that they are the types of caps that have the capacitance values needed at a reasonable cost.  Is that the case? Or is it also because of electrical characteristics provided by the electrolytic caps that are favorable to audio signals?   

I am not seriously looking at changing the way I recap my audio equipment but I was just wondering why we replace the parts with the shortest life span with the same type.

sonavor:

The reason I asked about replacing the two 0.47uF electrolytic caps with polypropylene was because I had read that the poly caps don't wear out. They also usually have high voltage limits so can take a lot of punishment. Aren't the poly caps generally used in small capacitance values because they are affordable at those values?  Is the reason there are polarized electrolytic caps in the circuit because they are most cost effective for those capacitance values?

Basically you're right there. However, neither of these two particular caps are on the audio signal path, and neither of them is in a position where they could easily die prematurely (8C2 stabilizes the tuning voltage, which is essentially DC, while 8C46 filters the AFC signal coming out of the FM detector - again, rather stable and it even has a small ceramic by its side to help).

You can of course replace them, but it's not going to affect anything unless the old caps are outright faulty, which they most probably are not. Increased ESR of aging caps doesn't really matter at these positions.

Generally B&O receivers, which used electronic switching and tone controls very early compared to most other manufactures, usually have a lot of capacitors on the signal path. Above 1 µF, plastic film capacitors were physically large and quite expensive back then, and both reasons probably contribute to why B&O used so many electrolytics on the signal path - and tantalums when the space was tight.

These can be replaced and it may alter the sound audibly (sometimes even to the better...), but it takes some experience and understanding of the circuits to judge when it might be useful and when it will be just wasted time & money. I've installed MKS2 caps instead of tantalums here and there in kit that I use myself, but mostly I just use the same kind of components that were there originally. Even bog standard aluminum electrolytics have improved a lot in quality during the last 30 years. Not to mention in physical size!

Thanks for the reply Mika.  The experience and understanding of the circuits part is what I would like to get to.  Until then I play it safe and try to match what was existing.

-sonavor

Hi sonavor, great project you're working on. I'm following this closely, last week I bought a BM6000 locally. The only issue I've found so far is a slipping volume control belt. It's time to place another order with Dillen.

Thanks

John

Great, thanks.

I will be changing my belt too with one I got from Dillen.  I am almost done with the base PCB recaps.  Then I will start on the PCBs under the lid. 

I think I have found my favorite module to recap - 07 - RIAA Amplifier

Here is the 07 module with the electrolytic caps removed and the replacements.  I forgot to take a picture after I soldered in the new caps so I'll have to show a picture of the finished board re-installed in the chassis.

The 14 Module - Remote Receiver was a little tricky to remove.  This board isn't mounted to the chassis with screws like the other boards.  It is held in place with plastic tabs.  I wanted to make sure I didn't break any of the tabs and the IR receiver piece fits over a tab that is hard to get to as seen in the picture below.  After loosening the board from the main tabs I used a small, thin screw driver to gently push the front tab back as I pulled the board up so the IR receiver cleared (the front tab).

Here is Module 14 front and back before the recap.

If you want to replace all of the electrolytic caps on the 14 Module you have to open up the metal box.  The picture here shows the 14 module before and after the caps were replaced.  One cap - C7, 3.3nF, 63V - was not replaced.

I'm getting close to the halfway point I think.  I will reinstall the recapped bottom chassis boards then start on the boards under the top cover.  That is where the display IC replacement, the volume control belt replacement, switch deoxidation and some more recaps will take place.

Recapped Modules 07 and 14 reinstalled

Recapped 08 and 09 modules reinstalled

Here is the recapped 06 Motor Control Module reinstalled.  I forgot to mention during the recap that the C7 electrolytic capacitor in the back (10uF, 63V) was not recapped.  I did measure it and it was between 10uF and 11uF.  There wasn't a replacement for it in the upgrade kit.

Not to leave any of the lower chassis recapped boards out - here is the 16 Power Supply Module

Tommorrow I will start looking at how to dissassemble the components under the top cover.

I realized it is already tomorrow so here are some pictures of my start on the front cover components.  I am starting with looking at the switch button assembly.  The instructions I had were pretty clear but until you actually attempt to take these things apart in person it always seems tricky.  The pictures here show the plastic tabs (be careful with them) on the bottom, right, front of the BM6000 that release the front edge of the switch assembly.  Once you have that released where the front edge comes up (see the second picture), you can slide the whole switch assembly forward (green arrows).

You done a long shift :) While you have that keypad off it is a good oppertunity to remove all the keys and stick 'em in the sink with some detergent! Also clean all the dust and gunk off round the edges of the buttons it is amazing how nice this keypad can shine after a deep clean :)

I did do some cleaning...in the following pictures of the push button assembly apart I used the green goopy stuff to remove dirt and dust.  I'm trying to determine if I am brave enough to peel back and mess with the little pop buttons. If I do, are there exposed areas to use Deoxit on?  After the buttons are cleaned will the black sticky tape be used again to cover them or do you lay down new tape?

Is that silly putty? Get the whole lot (minus the electronics lol) in the sink as there will be some scummy stuff that only a mild detergent can remove!

The black stuff peels off and I normally sitck to a clean plastic surface and reuse, as there is usually enough sticky to put it back! BTW it would have been easier to unplug the keypad first and work on things seperately!

The green goop is something I picked up at a RadioShack store.  It is called CyberClean.  I remember something like it back in the eighties (I think) that was sold as a toy....called Green Slime or something.  It does a good job.  I had been using it to clean keyboards as it isn't a liquid and picks up pretty much everything it touches.  I don't see any residue afterwards either.  I tried my ohmmeter after rubbing it on a plastic surface to see if it left anything conductive and I got nothing.  So far it hasn't given me any problems and it works good on cleaning boards and other parts. It is realitively cheap too, about $4 US. This is the first one I have tried so I don't know how long it lasts before you have to throw it away.

As Olly suggested, the keypad panel can be disconnected and removed.  This picture shows that.  The two connectors have to be unplugged with the Beomaster lid opened up.  The connectors can then be reached without too much diffuculty from the other side (of what this picture shows).  Once disconnected, the wires and plugs can be navigated through the slot where the wires come out of (top picture).  Note that the little copper tabs coming through the keypad board secure the pop buttons to their locations and provide the spring to the pushbutton.

I decided to be brave and expose the actual keypad button as Olly suggested....just one button though - the standby button.  I figured it was probably used quite a bit.  I peeled back the tape that covers the keypad buttons from the corner where the standby is.  Using some tweezers I gently eased the top of the button out.  I made sure not to disturb the tabs much.  The contact side of the button didn't look too bad.  It's hard to tell from the picture.  The bottom right picture is after I swabbed the underside of the button with some deoxit gold (applied it to a swab, then to the button).  That is all I think I will do right now on the keypad.  I checked each button for feel and they all feel like they work good. 

I am going to continue on.  I need to figure out how to get to the 02 Module (Microcomputer) and 03 Module (Volume and Tone Control) so I can finish the recap and replace the IC for the frequency display.

I figured that the next steps will be to remove everything on the front of the top/lid to get to the boards and controls underneath.  The boards I need to get to for some recapping and the IC8 replacement (on the 02 Module).  The volume and tone controls so I can deox the controls.

So starting with the volume and tone control cover assembly - there are three tabs accessible from the inside of the lid when it is tilted open (like a car hood).  Carefully pressing the tabs and pulling the top of the cover will allow it to release out from the lid.  Once it is free it will lift out.  The plug I show must be unplugged so the assembly can be fully removed.

With the cover removed you can access the volume and tone control switches to deox them and clean out any dust.