First Kenwood on the bench in ten years for me, was given this one for free as it sort was in a basket during a visit to a fellow AK'r residence last week. Anyways, the back story was his friend tried to repair it, was un-successful and thats how the journey started. Hmmm, dual mono block 75wpc integrated for free, lets get her running and compare it to my 717.
The left side rectifier diodes were both missing which led me to eye the non nos output transistors, both tested dead shorted so replaced both sides with Sanken 2sa747 and 2sc1116's. Worked backwards towards the beginning of the amplifier stage installing new caps, any 2sc2089's I came across with ksc1845's and the 10 and 14v zeners. Replaced those missing power supply diodes with a couple of 1n4007's I had along with a new transistor and relay just for good measure.
On the dbt she went with the pre main jumpers pulled, no fireworks and a nice relay click after three seconds, both channel bias levels were under 10mv (on a 60w bulb) so went after the offset. Those dual FET pairs do wander around a bit but got them both to settle down +/-10 mv or so. Brought the unit up on mains and set the bias to 14mv and went after the pre-amp.
Now, that board is nice to work on after you take the whole front apart. Spent a lot of time getting the three filter buttons to pass a resistance test, dang fussy things, was tempted to take them all the way apart but D5 finally cleaned them up. The rest was straightforward r&r and buttoned everything back up again.
Replaced the covers after some tidying up, hooked it up to a set of HPM 100's I finished repairing recently and gave a listen. Very responsive tone controls, I like the multi level loudness settings too. Fun little project, easy to work on and a nice piece to add to the collection.
The left side rectifier diodes were both missing which led me to eye the non nos output transistors, both tested dead shorted so replaced both sides with Sanken 2sa747 and 2sc1116's. Worked backwards towards the beginning of the amplifier stage installing new caps, any 2sc2089's I came across with ksc1845's and the 10 and 14v zeners. Replaced those missing power supply diodes with a couple of 1n4007's I had along with a new transistor and relay just for good measure.
On the dbt she went with the pre main jumpers pulled, no fireworks and a nice relay click after three seconds, both channel bias levels were under 10mv (on a 60w bulb) so went after the offset. Those dual FET pairs do wander around a bit but got them both to settle down +/-10 mv or so. Brought the unit up on mains and set the bias to 14mv and went after the pre-amp.
Now, that board is nice to work on after you take the whole front apart. Spent a lot of time getting the three filter buttons to pass a resistance test, dang fussy things, was tempted to take them all the way apart but D5 finally cleaned them up. The rest was straightforward r&r and buttoned everything back up again.
Replaced the covers after some tidying up, hooked it up to a set of HPM 100's I finished repairing recently and gave a listen. Very responsive tone controls, I like the multi level loudness settings too. Fun little project, easy to work on and a nice piece to add to the collection.