ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Wow! I'm impressed! Congratulations!
To be honest, I wasn't very hopeful after having seen what you allowed your soldering iron do to the original board and after seeing some blatant mistakes in your "latest draft" in the post above (sorry for not posting when I saw it;I had 2 hectic weeks).
I was actually hoping that you'd take up Martin's offer of getting your hands on a proven working board..But now that you've managed to make a new board from scratch, all I can say is: Chapeau!
Blood, sweat and tears at its best! .
Thanks for the ‘Hats off’ manfy, i admit to being quite chuffed to have a working 1700. A few beers have met their demise in celebration but I know my efforts have not achieved the quality and attention to detail of enthusiastic others residing here
To add to my story: The two aluminium capacitors on the power supply have now been replaced (par for the cause) without problems but am now hesitant to unwire the 40 watt bulb before connecting to my uncles (inherited) “Mission” speakers
Q; Will the “idle current” on the power amp board need adjusting after removal of 40 watt tungsten bulb? - Maybe fear after success is cutting in!
You mention that there were “blatant mistakes” in my latest draft. I’m curious to know what they are ? always willing learn..
A ‘shielded’ 5pin din to 3.5m jack lead is next on the list to connect B&O to iMac - hope to avoid the hum on tape input.
Will post images of complete shiny closed lid unit when wired up to speakers
Beocord 1200 and Beomaster 1700 type 1701
Pete: To add to my story: The two aluminium capacitors on the power supply have now been replaced (par for the cause) without problems but am now hesitant to unwire the 40 watt bulb before connecting to my uncles (inherited) “Mission” speakers Q; Will the “idle current” on the power amp board need adjusting after removal of 40 watt tungsten bulb? - Maybe fear after success is cutting in!
Good that you ask. Yes, it probably will change - not excessively but it will be a bit off and that's because the light bulb in the mains line acts as a cheap power resistor, which in turn has the function of a current limiter. According to Ohm's law there will be a voltage drop across the bulb: V=R*I and that means that the voltage at the transformer is lower than normal.
That dim bulb tester is normally only intended to be used in the early stages of repair. Once you know that the tested circuits are basically ok, you'd remove the light bulb and do all further testing and adjudtment in the normal condition of the device, i.e. connected directly to mains. I'd say you can remove the light bulb now and measure/readjust the idle currents as per service manual. Once that is done, all should be good.
Pete:You mention that there were “blatant mistakes” in my latest draft. I’m curious to know what they are ? always willing learn..
Well, "blatant" was maybe too strong a word. Let's call it obvious mistakes. The first thing I noticed was that the output caps had the wrong polarity (I guess that happened because you drew those schematics based on the board and not based on the schematics in the service manual. Second thing was the transistor on the left marked with "05". It shows a 37pF capacitor connected to the collector but no other connection - and that can't be right.I didn't look any further because I was quite busy that day, and unfortunately I never got around to post my concerns. On the other hand, I was quite certain that you would recognize the mistake in the diagram once you carefully started comparing your own diagram with the diagram in the service manual -- and you did. Else your self-made circuit woudn't play music now.