Rowe cd 100a

[mcarlo1117]

ftp://Rowe
I bought a rowe cd 100a and I am having amp issues. One side of the amp has alot of static and sounds terible. I checked all speaker and they work fine, I took amp out and found 1 bad 8 amp fuse. I changed all 4 resistors and I still have the same problem.

So confused..

Mike

[ami-man]

Hello Mike,

You say you have replaced 4 x resistors? was one of the bias restistors blown? usually you test/replace the transistor at the fuse location or replace the pair of matched transistors.

Regards
Alan

Alan Hood
ami-man
UK

[mcarlo1117]

Hi Ami-Man,

Not sure how to test the resistors. I was going by some other post that I saw on here and just changed all 4 of them. When i first started looking for the problem is when I found 1 blown fuse on driver board.

Mike

[jdemarti]

Hello Mike,

I assume you are talking about the 4 Darlington transistors (not resistors), correct?   The transistors are the four components that mount on top of the amp's large heatsink.  The transistors plug in, not soldered.

If that is the case, are you still blowing a fuse? If so, did you reuse the plastic MICA wafer (the plastic gasket looking piece between the transistor and the heatsink). Check for rips or damage on the wafer. There can't be any metal to metal contact as the mica wafer keeps the transistor from shorting out on the heatsink.

Lastly, where did you get the transistors, Ebay?  Caution when buying ones from China. Some of the transistors may be counterfeit and will blow resistors on the driver board.

John

[ami-man]

Hello John,

It is not only the transistors from China that are a problem, the add that is currently on Ebay by an USA dealer for a two sets of matched darlingtons very cheap! this is one to be avoided.
A well known engineer in the USA told me he had bought some and had been conned; he found these transistors to be no use at all.

Regards
Alan

Alan Hood
ami-man
UK

[jdemarti]

Good point, Alan.  I guess the the lesson is "Beware anywhere".  I would suggest that people stick to buying from reputable companies such as Future Electronics, Mouser, etc.

John

[du24pont24]

I am having the the same problem with mine!   I replaced all transistors and fuses (but 7.5 amp not 8 amp), and worked great for a month.   I just added a preamp board so I could hook up a MP3 player to it, and it worked maybe 8 times fine.    Then one side of speakers went out, now both sides?  Is it my preamp???   If I did blow fuses, does that mean my new transistors are screwed up too???   I did use the old wafers, plus added heat sink compound!  How do you check transistors without taking them out???

[jdemarti]

The easiest way is to take the transistors out and check if any of them are shorted.  You have to undo the connectors going to the transistors anyway in order to properly test for a short. May as well take them out.  If you blew another fuse, I would guess that a transistor went bad/shorted.

[ami-man]

Hello du24pont24,

Sorry you do not give your name.

I have to agree with John if you have blown another fuse then more than likelt you will have that transistor down.
You do have to check that any of the large resistors on the driver board effected do not show signs of overheating or have not split apart (or swelling). Have you checked the driver boards for dry joints (cold joints USA) to the connection pins?

Regards
Alan

Alan Hood
ami-man
UK

[du24pont24]

I am sorry, my name is Derek.    I don't even know what to look for when you say cold joints??  Yes I am in the USA.    I didn't know if the pre amp board may have screwed something up in the amp!?


Derek

[jdemarti]

A cold joint just means an inadequately heated solder connection. The solder is not making a good connection between the pin and the board. When you say preamp and mp3 I assume you mean the rowe preamp accessory board. I doubt that is causing your issue unless you have it hooked up wrong. My guess is you may have gotten a bad set of transistors or they are being shorted on the heatsink. Also, check the two driver boards for any blown resistors; especially if you happened to smell something burning when the transistors popped.

[ami-man]

Hello Derek,

Being as you are in the USA, I suggest that you send your amplifier to Bruce Wentworth of AB Leisure for testing/repair. Just search on google for Bruce Wentworth jukebox.

With regards to dry joints (cold joints USA) on Rowe Ami this is usually only on the connections pins and John is correct in his explanation. You see this easily by looking for a crack in the solder around the connection pin.
This needs fully desoldering, cleaning of the joint and resoldering in order to make a good mechanical and electroinc joint, if you can not solder correctly it should be left alone and be done by an engineer who can solder. In addition it is best policy to only solder the connection pins do not start going over other joints on the board as it is a pain for an engineer to make sence of any past work and increases the costs of repairs.

Regards
Alan

Alan Hood
ami-man
UK