Need some help on a Kenwood KA 405

[Ornon Shaw]

Bought a Kenwood KA 405 when I hooked it up noticed the right channel was very weak. I went head and Deoxit all my POTS but it didn't make a difference. Figured I would go ahead and do a complete recap on it. I ordered a upgrade recap kit for it from High end audio online. I also ordered the upgrades for the power supply caps. Though the orginals were 7500uf 50v I found out they dont make them anymore so went up to 8200uf 50v caps. I also figured while it was apart and after reading all the problems that other folks were having that I would change out the HA1457 IC on the preamp board with some replacements I found on EBAY, the NJM4458D with the TI NE5532P on the controll board, and the OPamps on the poweramp board 2SA1105 &2SC2580 TO-3P with the 2SA1695 & 2SC4468 TO-3P Transistors. Figured I just upgrade everything. While I was recapping I found a burnt out resistor on either R29 or R30 on the preamp board so just replaced both of them with a new resistor carbon film 100ohm 5% instead of the 10%. I removed out the relay switch on the power amp board and checked the relays as well as cleaned them they were not pitted or dirty at all in fact they look brand new shiney gold. After I had done all the work I went ahead and tripled checked my placement of Caps making sure I had not reversed polarity, and fired it up. The power came on but no click from relay. I shut it back down and realized the I had reversed the yellow, orange, red, and brown wires on the Preamp board, and the brown, red, orange, yellow, green, blue, and violet wires on the X11-1570-10(b/2) board volume pot. Once I put the wires back into the right order. I went ahead and turned the amp back on and heard the speaker relay switch kick in. I left it on for a few minutes watching for and checking to see if I had any burning, smoking, overheat of components all seemed fine. I turned it back off decided to put a phono as input and wired up some speakers to it. Turned it back powers up but, no relay click no sound from either channels, tried a tuner as well . Seems like it went from bad to worse looking for any Ideas, suggestions or thoughts as to what I might of done wrong? So I'm wondering if maybe I had gotten some bad preamp IC? When I wired it up wrong could I have burnt out the Dual amp IC on the controll board, or should I have gotten Driver Transistors when I replaced out the OPAMP MOSFET TO-3P. A little help as to which way to go would really be appreciated. Oh little bit about me I actually went to school back in 1999-2001 to be a CET finished up the schooling actually never got my CET, just couldn't find any jobs around where I live so literall I haven't done anything on electronics since I graduated from school. So please little patience here with as I'm having to try to refresh myself and remember what the heck I'm doing!

Thanks so much for any help you could offer me!


Thanks

 

[Ornon Shaw]

Out of curiosity is anyone familar enough with Ka 405 to know if this cut on the foil side of my preamp PCB is factory cut or someone modifing the board. I am getting high Voltage readings off pin number 4 and 8 on my IC-3. I am wondering if this cut is the cause of it as I can't seem to find any other reason as to why the voltage is high on IC 3 when it isn't on the other two IC on this board. They all feed by the same rail.

Thanks

 

[Ornon Shaw]

The speaker relay switch is still in protection mode. I have voltage 4.4v at pin3 and 5.2v at pin 4 and of course 44.5v on Pin 1. I pulled C1&C2 out of circuit to bypass the tone board and still in protection mode. Yesterday I had Pulled pin 3 and pin 4 out of circuit to see if I could trick it out of protection mode, it worked but as I was checking voltages on just pin 3 my probe slipped and touch both pin3 and the PCB pad and instantly put it back into protection mode. While it was in Protection mode I measured voltage on both 3&4 and found 0v on pin 4 but pin3 had 3.2v while the actual pad -5.7v. So whatever the problem is with the DC offset its carry thru both Direct and tone on!

 

[slimecity]

This might be a pretty good lesson in positively identifying an issue first, before doing wholesale upgrading.

You shoud be using a dim bulb tester to fire the unit up, for safety.

I would start by checking all your voltages from the powersupply and then as per the schematic.

 

[Ornon Shaw]

Yea I have DBT. When I first started this amp, it was very low to almost not audio output on right channel. So I started reading the different forums and other peoples problem. Figured what the heck I'll just replace the caps and while I'm out it I'll replace all the other parts that people seemed to have problems with the shotgun approach. Didn't work very well, LOL the HA1457's(3 of them) I bought to replace the original ones with turned out to be fake. Once the preamp board was finally up and running correctly still had the problem with protection relay. So as of right now and with great amount of help from another person we're trying to figure out where the problem lies. I'm pretty confident that a plain recap would not of solved the problems though, at this point of the game it is just one thing that I can rule out. I just hope we can figure this out before I go bald from pulling my hair out!!!!