DR #57 - Turntable Repair - Kenwood KD-850

this is a Kenwood model KD 850 turntable I've been told that it started off by blowing fuses and then eventually wouldn't power on at all there's been a little bit of work done to this already before me but not much the owner would really like to get this running as would I so let's see if we can make it happen rule number one when something's blowing fuses let's not power it back on till we open it up and take a look let's take a quick look at inside before I get started up to this point in my life I've worked on precisely zero turntables so my ignorance will be pretty obvious when it comes to terminology and the way these work but I do know that since it's not powering on the first place to look is the power supply board so I'll rotate this take a closer look at that there are a few components Under The Shield so let's get that removed we now have access to the power supply board the owner did mention that the main capacitor was cut and removed for troubleshooting we'll fix that later other than that everything appears to be intact even the fuse is in place intact and correct 2 amps at 250 volts let's review the schematic and try and figure out how this power supply Works here's the power supply board on the schematic AC enters the board from the Transformer via pins three and four it's rectified via this bridge rectifier D1 it's then smoothed out via this capacitor C2 this big one right here and then we have three output rails rail number one is 14.2 volts via pin 13 and that's regulated by this ic1 which I believe is just a 15vol regulator rail number two is 23.5 volts via pin 14 and that is unregulated it comes directly after the bridge rectifier rail number three is 22 Vols via pin 15 that is regulated via q1 and xener diode D2 so what to test on the power supply well this unit's decades old so regardless of how they test I'm going to replace both electrolytics I'll measure both resistors make sure those are what they need to be my main suspects are the semiconductors I'm going to pull those and test those individually that's going to be the bridge rectifier here the 15vol regulator ic1 here and the transistor q1 here the resistor closest to us should be 470 ohms reading 463 seems okay and the other one should be 100 ohms 98.1 those are fine let's check for dead shorts we'll start with ic1 the 15 volt regulator that looks good move on to transistor q1 that looks good as well and our Bridge rectifier D1 that is shorted all the way around definitely bad now due to their age I'm going to replace ic1 transistor q1 anyway as well as brid director D1 I'll order replacements for this and this capacitor and I also noticed that one of the tabs for the fuse holder is pretty flimsy it's not providing a lot of support tension on the fuse so I'll try and replace that as well all the replacement parts have arrived time to rebuild the power supply the power supply rebuild is complete looks very nice time to to reinstall and test I've reconnected the power supply it's test time I haven't connected anything to the outputs yet I want to verify proper functionality of the power supply before moving on it's all powered on as a reminder pin 13 should be somewhere around 15 volts the schematic has it labeled as 14.2 that doesn't make any sense to me this is being regulated by a 15v regulator so 15.2 volts makes more sense to me I'm happy with that PIN 14 schematic has it labeled as 23.5 volts but this is completely dependent on your incoming ac voltage and there's no adjustment for this so 27.6 volts looks fine to me and pin 15 should be right around 22 volts 22.3 looks great so I'd say the power supply is back that was a successful repair of the power supply board for this Kenwood KD 850 turntable but there's quite a bit of work yet to be done if you're interested in seeing how this turns out I will post a follow-up video on my patreon page a link to that page will be in the description for this video thanks for watching