vinstersroc
New Member
Hi Everyone,
I am resurrecting a 7070. Basket case but complete, i.e., all parts are there. With the help of many contributors to AK, i.e., reading the pertinent threads regarding 7070s etal, I have sound coming out of the speakers! Thank you to everyone that helped!
Replaced the infamous "fuseable"? resistors, R34,33 R41,42, 43 and 44 resistors on board F-2624 (Driver Circuit Board). Replaced R04 in the Regulated Power Supply Circuit Board (F-2626) and R04 on the motherboard, F-2625. Replacing R04 on F-2625 started the sound coming from the speakers. Checked DC offset and have managed 2-3 mV on both channels.
Problem is the DC bias current. I am measuring 11 mA on the left channel and 18 mA on the right channel when taking the readings from pins 05, 06 and 07 of F-2625. Spec is 30 mA+/- 1 mA. Adjusting VR03 and VR04 has no effect on the bias current readings.
(While I'm on the subject of DC bias current, why are some posters listing their DC bias current readings in mVs? This is a current measurement not a voltage measurement, correct? Back to the story...unsuccessful in changing the bias current values using the techniques described in the SM. Have distortion in both channels, all volume levels. Have cleaned all of the pots including VR01,02,03 and 04 and all switches with CRC QD, some benefit. Interesting observation, while I was in the process of discovering the faulty components, during the process of turning the unit on and off and exercising the controls, there were sporadic moments (seconds) when the output seemed to be accurate, i.e., little or no distortion and clean sound (around 9-10 o'clock for volume control). That's what made me think the controls were dirty so I continued spraying QD into them. Controls are insitu however so I'm not confident they are seeing contact cleaner the way they should for a thorough cleaning. Checked output transistors and others on driver, regulated power supply and motherboard using "diode test technique", appear to be OK. Have not replaced any capacitors anywhere. Any advice would be greatly appreciated because she's almost there...
Thanks.
Paul
I am resurrecting a 7070. Basket case but complete, i.e., all parts are there. With the help of many contributors to AK, i.e., reading the pertinent threads regarding 7070s etal, I have sound coming out of the speakers! Thank you to everyone that helped!
Replaced the infamous "fuseable"? resistors, R34,33 R41,42, 43 and 44 resistors on board F-2624 (Driver Circuit Board). Replaced R04 in the Regulated Power Supply Circuit Board (F-2626) and R04 on the motherboard, F-2625. Replacing R04 on F-2625 started the sound coming from the speakers. Checked DC offset and have managed 2-3 mV on both channels.
Problem is the DC bias current. I am measuring 11 mA on the left channel and 18 mA on the right channel when taking the readings from pins 05, 06 and 07 of F-2625. Spec is 30 mA+/- 1 mA. Adjusting VR03 and VR04 has no effect on the bias current readings.
(While I'm on the subject of DC bias current, why are some posters listing their DC bias current readings in mVs? This is a current measurement not a voltage measurement, correct? Back to the story...unsuccessful in changing the bias current values using the techniques described in the SM. Have distortion in both channels, all volume levels. Have cleaned all of the pots including VR01,02,03 and 04 and all switches with CRC QD, some benefit. Interesting observation, while I was in the process of discovering the faulty components, during the process of turning the unit on and off and exercising the controls, there were sporadic moments (seconds) when the output seemed to be accurate, i.e., little or no distortion and clean sound (around 9-10 o'clock for volume control). That's what made me think the controls were dirty so I continued spraying QD into them. Controls are insitu however so I'm not confident they are seeing contact cleaner the way they should for a thorough cleaning. Checked output transistors and others on driver, regulated power supply and motherboard using "diode test technique", appear to be OK. Have not replaced any capacitors anywhere. Any advice would be greatly appreciated because she's almost there...
Thanks.
Paul
