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Noisey Kaypro 2000 Plus power transformer

F

Fezzler

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Joined
Feb 3, 2008
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46
Location
USA
The power transformer for my old Kaypro 2000 Plus buzzes loudly when the transformer is place right side up as designed.
But if I place it on it's side, it goes silent.

Before I open it up, any ideas on what to check either visually or with a multimeter?

Specs:

CHARGER -- P/N 81-1190-1
INPUT: 115 VAC. 50/60 HZ. .24A
OUTPUT: 7.3 VDC. 2A

It has a 5-pin din power plug into the computer. (positive and negative to charge battery? Positive and negative to power pc when battery low? One ground?
 
The buzz, if position-dependent, is probably physical in nature, not electrical. Usually, transformers are coated in a fairly heavy varnish that "sticks" the laminations in the core together so they can't buzz. But first look for a loose screw or bit of metal...
 
Chuck(G) said:
The buzz, if position-dependent, is probably physical in nature, not electrical. Usually, transformers are coated in a fairly heavy varnish that "sticks" the laminations in the core together so they can't buzz. But first look for a loose screw or bit of metal...
Click to expand...

Great news! I disassemble the transformer and in inspecting it, I found that a solder to one side of a very large capacitor was dried up and not making a good connection. I am not even an amateur electrical engineer. Just a home hobbyist with an interest in old computers. I can not tell you how many times I have brought back to life old computers and their peripherals due to simply a broken solder point.

Two seconds with the soldering iron and the rare Kaypro 2000 Plus is back to life. Battery is charging. Disks work. Screen looks great. Yea!
 
I'm surprised that a solder connection would fix a mechanical buzz, unless that's all that's holding the transformer still. If it is, it will likely fall again unless you stabilise that transformer otherwise.

I wonder if cold solder joints are typical for Kaypro. (My only experience is with my II, which had many.) Where was this charger made?
 
KC9UDX said:
I'm surprised that a solder connection would fix a mechanical buzz, unless that's all that's holding the transformer still. If it is, it will likely fall again unless you stabilise that transformer otherwise.

I wonder if cold solder joints are typical for Kaypro. (My only experience is with my II, which had many.) Where was this charger made?
Click to expand...

Let me ask you this. With the very large capacitor suffering from a cold solder joint, is it possible the sound was coming not from the transformer as I originally suspected but rather from the internal modem? That is a possibility? Or, simply the speaker reacting to improper voltage?

It was made in Solana Beach, Ca.

The computer now boot, screen looks great, loads BIOS, asks for boot disk and will boot off of A:. It will run programs, etc. but occasionally when accessing the disk freeze and display random ASCII codes. I suspect either a bad disk, bad disk drive or perhaps even a power issue that occurs when the drive need a spike in power for longer disk activity. But it did successfully run Poly Windows and some other small applications.
 
A filter capacitor (not working correctly) certainly could cause a hum at any speaker, and possibly (but highly unlikely at this frequency) from ceramic disc capacitors.

Don't forget to include RAM and address bus paths in your diagnostics. But do try to narrow it down starting with the simplest things. If you can get a program to prove out the RAM, that might be the easiest thing to do first.
 
KC9UDX said:
A filter capacitor (not working correctly) certainly could cause a hum at any speaker, and possibly (but highly unlikely at this frequency) from ceramic disc capacitors.

Don't forget to include RAM and address bus paths in your diagnostics. But do try to narrow it down starting with the simplest things. If you can get a program to prove out the RAM, that might be the easiest thing to do first.
Click to expand...

I am no expert, but doesn't the BIOS boot check and verify the ram? 640k good! (Has extended ram too.)
 
I don't know what kind of test that is. A lot of power on RAM detection schemes that I am familiar with don't do a rigourous error detection; they only test for the presence of RAM. Whether this one does one or the other, I don't know.
 
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