 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
198.50.63.15
In Reply to: RE: Need MCS 3245 power supply repair help/advice posted by Cougar on July 09, 2008 at 07:42:33
Hi Cougar,
Thanks for the help. I agree with you on the caps, I was figuring on just replacing all of the caps, they're cheap and after shipping it makes sense to buy everything you think you'll need once. I don't have a diode tester on my DMM, can I just test the voltage drop using the DMM ? Diode and the bridge rectifier are also fairly cheap. It seems to me that the most fool proof thig to do is just replace everything on the board. There are very small diodes and larger diodes can I just replace them all with the larger type for simplicity ? One last question, do you know what the thing is in the picture that I have circles and do you think that I should replace that as well ?
PJN
Follow Ups:
I see 4 caps that have boiled out, several "dry, overheated solder pads around some resistors, a chip off a high-temp power resistor, and a few other issues.. The devices you are wondering about are "transistors"... they are either NPN or PNP (pointless to go into a electronics lecture here..). They may be fine or not- you really need a "diode test" function on your DVM (I assume it's a digital tester), and the knowledge of how to interpret the readings. They are semi-conductor devices like diodes for testing purposes... In this portion of the circuit they will be common transistors, and very inexpensive (3904's or 3906's or something like that..)... you can replace everything if you wish, but something drew too much current from the power supply in the first place, and it may just smoke again... from your pic you have about $20 of parts to replace on this board (very approximately)... good luck...
Thanks for all the input. I've decided not to bother spending my time or my brother's money chasing repairs, there are to many unknowns and no guarantee of a good outcome. Besides as I recall I never was very impressed with the MCS, my old Kenwood and Sony recievers at the time sounded much nicer. I'll build a chip amp out of the parts instead.
Bad caps do not trip breakers or blow fuses except in the rare cases when they are shorted. That junk you see on the board is not cap crap, it is glue used during manufacturing. Sometimes when it turns color it becomes conductive but almost never enough to blow a breaker or fuse.
You don't want to give up yet ? Get a DVM and check the outputs. Doesn't matter what they read unless it is 0.000. That is a short when you use the -|> |- scale. You find that, remove them and the drivers. The other channel should work.
People always think caps, it ain't. Caps in the PS can cause hum and noise. Caps in the amp can cause loss of gain and response. I have only seen shorted big caps that break a breaker or blow a fuse in 40 years twice and one of those units was subjected to overvoltage, got 240 instead of 120.
I was the audio guy at three places I remember, and when I talked, they listened. We were always on a budget and that means not replacing $50 worth of parts when what it needs is fifty cents.
If it failed during a thunderstorm it could be the main rectifiers, get the DVM and I will tell you how to find out.
May I add? To spend ANY amount of money on this unit is of questionble merit, but I also understand FULLY the importance of "sentiment"- if it is THAT important, then spend as much as you can afford.... I suspect that you will smoke that same ps filter board instantly though... so get a variac and ramp up the 120 Vac slowly while monitoring the o/p voltage (speaker terminals) and stop the instant you see ANY increase in DC voltage- I'm betting the o/p transistors (one or both channels) or the driver transistors are shorted... so don't go too far down the trail unless it's that important....
I suppose those little diodes might be zener diodes, and I don't know what values they need to be. does anyone know where I might find a circuit diagram for a MCS 3245 ?
Thanks
PJN
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
