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Old 27th Mar 2017, 7:11 pm   #1
delaitt
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Default Deciphering resistor value in McMichael 365

Evening All

I'm repairing a McMichael 365.

Some of the resistor values have drifted by 50 to 80%.

In addition, a few resistor values are a bit hard to decipher from their colour code. For example, the one on the first picture is meant to be a 500K according to the schematic and manual?

In addition, this is not helped by the fact that some of the actual wiring around the detection diode resistor load appears to differ from the schematic. It seems i'm experiencing exactly the same anomaly (or feature!) as mentioned in the following post. I'm wondering if McMichael had actually made a revision to their original schematic drawing ?

https://www.vintage-radio.net/forum/...d.php?t=105570

Would you know how to decode the resistor values on these pictures?

The dog bone resistor of 2.2K also seems of a different value compared to the cathode bias resistor R5 of V3 which is meant to be 1350 ohm. The photos of the above post also appear to be using the same original component which re-inforces the fact there may have been a second revision of the schematic/manual?

Thanks

Thierry
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Old 27th Mar 2017, 7:18 pm   #2
Andrewausfa
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Default Re: Deciphering resistor value in McMichael 365

Thierry,

They look like body/tip/spot resistors (even though this one is banded) - so your body green 5, tip black 0, yellow spot multiplier 0000 = 500K.

Andrew
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Old 27th Mar 2017, 7:18 pm   #3
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Default Re: Deciphering resistor value in McMichael 365

As a guess:

1st pic 500k.
2nd pic, not sure about the dogbone but possibly 2.5k if there's no body dot, the other two, 120k
3rd pic, 3 meg ohm.

Lawrence.
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Old 27th Mar 2017, 7:43 pm   #4
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Default Re: Deciphering resistor value in McMichael 365

What Lawrence said
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Old 27th Mar 2017, 9:22 pm   #5
delaitt
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Default Re: Deciphering resistor value in McMichael 365

Great, thank you.

Something else i would like to ask regarding this set. Does the motor or its mechanical parts require any particular maintenance e.g. oiling, etc ?

Thierry
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Old 27th Mar 2017, 10:31 pm   #6
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Default Re: Deciphering resistor value in McMichael 365

The two similar ones look more like 12K to me, but if 120K makes sense in the circuit then OK. Check them?
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Old 27th Mar 2017, 11:15 pm   #7
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Default Re: Deciphering resistor value in McMichael 365

Quote:
Originally Posted by Herald1360 View Post
The two similar ones look more like 12K to me, but if 120K makes sense in the circuit then OK. Check them?
Their colours are brown (1), red (2), yellow (0000), = 120000 ohms = 120K.

Regards,

Dave.
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Old 28th Mar 2017, 9:37 pm   #8
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Default Re: Deciphering resistor value in McMichael 365

Hmmm... let's put it down to my monitor- they looked more like brown red orange to me.

Would yellow fade to orange or vice versa I wonder?
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Old 31st Mar 2017, 9:28 am   #9
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Default Re: Deciphering resistor value in McMichael 365

I put mine back to the configuration according to the circuit diagram and it works well now if maybe a little lacking in bass response. I eventually cleared up the hum from the smaller speaker by substituting a 10H inductor.

I completely stripped the motor and deck as the original lubrication had gone solid. Fortunately, being a single play unit, it is very simple. The rubbers in the pickup head were also solid. There is lots of information here about this. For the pivot rubbers I discovered that you can still get bicycle valve rubber tube on ebay if required, but in the meantime I had bought some Fladen traditional float rubbers which were recommended and they also work well.
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