Marantz 250 power board BWH resistor?

[R&B Stereo]

Greetings AK friends,

First time posting here, but longtime admirer of this site. I do have a side biz in vintage stereo repairs, and many years under my belt. And while constant learning is part of the process, sometimes one comes across a real head scratcher. I am restoring a Marantz model 250 (not the M) for a client and I came across a busted “what appears to be” a BWH resistor on the board. It’s not just a resistor but I would call it a “contraption” (has another resistor and capacitor in series and another capacitor in parallel attached to it). I say “appears to be” as the schematic only seems to refer to a 1ohm 2W BWH resistor. The “contraption”, which by the way appears from factory, from the good power board, has a ‘carbon’ resistor reading 100ohms, another 10ohms in series along with a 0.1uF capacitor, and a 6800pf capacitor in parallel. If you’re my age, it takes you right back to “the thing” horror movie. I have done some research and watched some YouTube on this model but I don’t recall coming across a suitable replacement for such. Would a 1ohm / 2W BWH resistor replacement be good enough, per the service manual? Many thanks in advance.

 

[dankik]

Did you check the two addendums to the 250 SM? Here are the 1st pages for each (10 pages & 14 pages).
What board is it on and any ref no.?

 

[ocdecio]

That "contraption" is 100% factory and is there to avoid oscillations and eventual destruction of the board - I've seen it burned down to a crisp before. It was eventually moved to the board layout itself on later versions and for example the 250M always had it in.

Change that back at your own peril.

 

[quadmatrix82]

That "contraption" is 100% factory and is there to avoid oscillations and eventual destruction of the board - I've seen it burned down to a crisp before. It was eventually moved to the board layout itself on later versions and for example the 250M always had it in.

Change that back at your own peril.

Agree with Otavio it’s factory try replicate as per original

 

[R&B Stereo]

That "contraption" is 100% factory and is there to avoid oscillations and eventual destruction of the board - I've seen it burned down to a crisp before. It was eventually moved to the board layout itself on later versions and for example the 250M always had it in.

Change that back at your own peril.

Much appreciated Ocdecio. Yep, I shall 'rebuild' it. My challenge here is to confirm the resistance of the resistors to use. From the 'good one' not busted on one channel, the carbon one tested 107 ohms (assuming 1W) but the color coding on it suggests 390. The little 1/4 ohm one tests 10ohms (need to have a look at color coding). I do have proper capacitance / V for the capacitors. Thoughts or suggestions?

 

[R&B Stereo]

Agree with Otavio it’s factory try replicate as per original

I shall !

 

[ocdecio]

Much appreciated Ocdecio. Yep, I shall 'rebuild' it. My challenge here is to confirm the resistance of the resistors to use. From the 'good one' not busted on one channel, the carbon one tested 107 ohms (assuming 1W) but the color coding on it suggests 390. The little 1/4 ohm one tests 10ohms (need to have a look at color coding). I do have proper capacitance / V for the capacitors. Thoughts or suggestions?

Here's the relevant circuit.

 

[R&B Stereo]

Here's the relevant circuit.

View attachment 3604681

Exactly what I needed. Thank you so much, Ocdecio.

 

[R&B Stereo]

Good afternoon y'all. Thought I would jump in to let you know this project is wrapped up. Was a labor of love alright! Rebuilt that 'contraption' (referred to above) successfully, recapped it fully, replaced some other resistors, etc... eventually still faced a dead short (nice bright DBT... ugh) but turned out to be two open IN4003 diodes on the power supply / protection board. It sounds great. Thank you for your assistance and caring.

 

[Jose Jimenez]

"but turned out to be two open IN4003 diodes on the power supply" How does this contribute to excessive current draw? There are six diodes on the
board and the bridge consist of four of them. Perhaps, do you mean shorted instead of open?