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crackle · 6th Feb 2017, 5:51 pm

Hi Steve
I have found that the two 50 ohm bias setting trim pots very often go out of spec. They always seem to go high.
The service manual says use 2 ammeters, one across link A and one across link B.

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Then adjust each for 2.5mA on both meters.
I strongly suggest using 2 meters as adjusting one trim pot alters the value on both.

An alternative way is use 2 DMM set to mV range and measure the voltage across the two 4.7 ohm resistors R22 & R23. This should be approximately 12mV when the current is set correct. Using this method helps prevent the coper track lifting from repeated removal of the wire links.

see also https://www.vintage-radio.net/forum/...6&postcount=30

Mike

p.s. correction of the link to the KB / STC service data; http://kbmuseum.org.uk/other_service...2_3_4_crts.pdf

6th Feb 2017, 5:51 pm	#3
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: RGD RP231 Transistor record player Hi Steve I have found that the two 50 ohm bias setting trim pots very often go out of spec. They always seem to go high. The service manual says use 2 ammeters, one across link A and one across link B. Then adjust each for 2.5mA on both meters. I strongly suggest using 2 meters as adjusting one trim pot alters the value on both. An alternative way is use 2 DMM set to mV range and measure the voltage across the two 4.7 ohm resistors R22 & R23. This should be approximately 12mV when the current is set correct. Using this method helps prevent the coper track lifting from repeated removal of the wire links. see also https://www.vintage-radio.net/forum/...6&postcount=30 Mike p.s. correction of the link to the KB / STC service data; http://kbmuseum.org.uk/other_service...2_3_4_crts.pdf Last edited by crackle; 6th Feb 2017 at 5:56 pm.