Beomaster 1600 Type17XX Capacitor Polariy

[jfrancis49]

Hello All,

I have re-capped the larger board of a Beogram 1600 and when I was checking against a second duplicate parts board I have, I saw that the electrolytic capacitor on C110 is reversed from the parts board. The board symbol indicates I have put it in correctly on teh recapped board. The negative polarity of C110 connects with R110 according to the printed board symbol and the schematic in the service manual. The spare parts board has the positive polarity connected to R110 but the symbol indicates that it should be the negative. Should I go by the mounted capacitor on the parts board and assume the symbols on the board and schematic of the manual are both wrong.

I don’t want to plug this in until I know what is correct. Any help would be appreciated.

John

[Glitch]

The order that I use for a conflicting polarity situation:

1) Do a quick analysis and install the capacitor such that it is forward biased.

2) Verify the forward bias by taking a voltage reading right when the device is powered up

3) Install in the same polarity as the original part (taking pictures of the board before the recap can help here)

4) Install per the schematic (errors are easy to fix/update on schematics)

5) Install per the markings on the board (boards are often not scrapped due to printing errors)

Glitch

 

[Dillen]

C110 (2,2uF series coupling capacitor for phono right channel input) should have
positive pin towards TR100/R111.

Martin

[jfrancis49]

Hello Martin,

I am hopefully tracing from TR100/R111 correctly and the circuit goes through R110 to C110. I have your capacitor replacement kit for the 1600 and the photo for that looks like the positive end of C110 goes to the outside of the board. It is the capacitor that is furthest top right and is 2.2uf. Does that sound correct?

Ps. Thanks Glitch!

[Glitch]

Dillen wrote:

C110 (2,2uF series coupling capacitor for phono right channel input) should have positive pin towards TR100/R111

Martin: For a low level (<2v) audio signal coupling capacitor, isn’t the polarity somewhat arbitrary since the DC voltage is zero?  Would this explain the inconsistencies that jfrancis49 is seeing?

Sorry if my questions or explanations don’t make sense as I’m not looking at the schematic.

Glitch

[Dillen]

The series of capacitor and resistor can be in either order.
One end of the capacitor carries a known DC level ~ the base voltage of the first transistor.
Seeing as this is an input, we don’t know the level of any DC content of the incoming signal.
It’s a general handrule to make the positive lead face inwards.

This also goes for line-level outputs. Positive inwards.
So when coupling an input to an output, it will be negative pin facing negative pin = bipolar capacitance.

Martin

[jfrancis49]

Sorry to sound so dense, but can someone tell me if the positive polarity of C110 is then correctly connected to R110 as is on the parts board?

Thanks!

[Dillen]

Look  at the series of components; DIN socket, resistor, capacitor and transistor.

If the resistor is nearest TR100 (and the capacitor is nearest the DIN socket), the caps positive pin should go towards the resistor.
If the capacitor is nearest TR100 (and the resistor is nearest the DIN socket), the caps negative pin should go towards the resistor.

Martin

[Die_Bogener]

Make it easy. Put a voltmeter in the circuit and measure it.

Or replace the cap with a bipolar cap. There is no need to use a bipolar elko, it can be a nice Wima MKS foil cap, making better sound and they are non polarized. Wimas fit in both directions…

[Dillen]

A bit difficult to measure.
As long as one end of the capacitor is not connected to anything, only the voltage at the other end is known.
And noone knows what it will be connected to in the future.

A foil cap would be a good solution as well – but completely out of proportions quality-wise.
Looking at the rest of the construction there will be other limitations playing in long before any difference from electrolytics to foil caps come into view.
This Beomaster is not an audiophile unit in any way, – never will be and never was intended to be.

Martin

[jfrancis49]

Thanks to all of you for the advice and feedback. I went ahead and placed the capacitor according to the spare parts board, I think that placement was consistent with Martin’s advice. I had some confusion tracing the circuit.

The receiver is now working, and I am not connecting a turntable to it anyway so maybe the polarity is immaterial.

Not an audiophile receiver as Martin pointed out, but a nice unit to have as a secondary sound system.

Happy Holdays!

[Author]

Posts