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ShorBird 23rd January 2009 07:36 PM

Akai GX 265D line voltage on line outs?
When atempting to connect my akai reel to reel to my computer, I got some smoke from my reel to reel recorder. During the course of my investigation, it looks line there is a huge voltage difference between the line outs on the reel to reel and the line in's on the PC. I suspect this is AC coming through, but can't figure out how this can be since the Akai has a transformer based power supply and the PC line in's are supposed to be isolated from the AC line. Can anybody shed some light on this and direct me where to go or what to look at next? I do have service data on the akai which should help in any investigations.


SQLGuy 23rd January 2009 08:28 PM

First to check would probably be your household wiring. Make sure that hot is hot and neutral is neutral on the outlets used for both the PC and the reel to reel. Also make sure you have good, not floating, grounds on both outlets.

ShorBird 23rd January 2009 09:04 PM

Nope, wiring appears OK, passes test with one of those 3 prong testers. Have same issue at work as well, so probably not ac outlet wiring.

SQLGuy 23rd January 2009 09:08 PM

OK. One thing down, then.

Since you are aparently getting current flow between the two, they must share some common reference. Unless there is any other connection between the PC and the tape deck, the common reference should be AC ground.

With a meter, what do you measure, on AC and on DC, between the wall ground and the tape deck line outs, and also between the wall ground and the PC line in contacts?

jaycee 23rd January 2009 11:29 PM

Check your PC's case is connected to the ground pin on the IEC inlet of the power supply (with power off obviously).

Also, check that the chassis of your PC is not hot with respect to ground. If it is, then your PC's PSU has faulty Y capacitors to ground in it's input filter, and you should replace the PSU.

Also check your monitor, especially if it is a CRT type. I have seen instances of ungrounded CRT's leaking enough power through the VGA shield ground to cause nasty shocks. Never use a "cheater" plug on CRT's.

I hope i've used the right terminology - here in the UK, we call safety ground "Earth".

If its the Akai with the problem, check for a connection between it's PSU's 0V line and safety ground.

ShorBird 26th January 2009 03:18 PM

SQLGuy - Here are the results of my voltage tests on the reel to reel. FYI - this is a two-prong AAC connector without a key for polarization (both blades the same size.) I ran this test twice, swapping the plug around in the AC socket for the second set. All voltages are AC, using a Knight DVM.

Akai not powered up
Chan Connect Earth neutral hot
L shield 1.0 .5 115.3
L tip 1.0 .4 115.5
R shield 1.0 .4 115.1
R tip 1.0 .4 115.3
Chassis 1.0 .5 115.3

Akai powered up
L shield 42.6 42.9 73.1
L tip 42.6 42.8 73.1
R shield 42.6 42.9 73.1
R tip 42.6 42.9 72.9
Chassis 42.7 42.9 72.9


Akai not powered up
Chan Connect Earth neutral hot
L shield 112.5 113 2.9
L tip 112.8 112.9 2.9
R shield 112.6 113.1 2.9
R tip 112.8 113 2.9
Chassis 113.2 113.6 6

Akai powered up
L shield 70.9 71 44.7
L tip 70.8 71.1 44.7
R shield 70.9 71 44.7
R tip 70.8 71 44.7
Chassis 71.0 71.3 44.6

I assume since I'm not getting any tingle or zap when I operate the device (the front metal face plate is common with the chassis) that we are not taling any amps to speak of here. I also assume the minor differences in readings is due to technique and contact surface conditions.

I am perplexed as to what is happening. Any ideas based on the voltage data?


ShorBird 26th January 2009 03:20 PM

Forgot to add - don't see a DC component.

jaycee 26th January 2009 06:16 PM

Something is seriously wrong here.

At a guess, for some reason, what should be the neutral is also tied to the chassis somehow. You really need to open it up and find out where the connection is being made. If that's beyond your skill set then you need to take it to someone who can put it right.

ShorBird 26th January 2009 06:35 PM

Hi JayCee,

Using the ohmmeter, there is no indication of any connection between either of the two prongs of the AC line and the chassis, or the shield/hot lines of the line out. I used the ohmmeter scales from 200 to 200meg ohm and no indication of a path there. I got the same results regardless of whether the power switch was on or off.


jaycee 26th January 2009 07:38 PM

I guess it's capacitive coupling then, but even so, the cause should be found and fixed.

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