LDII+ capacitors

Oct 1, 2007 at 9:37 PM Thread Starter Post #1 of 10
Dept_of_Alchemy

Dept_of_Alchemy

Headphoneus Supremus
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I dusted up my malfunctioning LDII+ last weekend to have a look inside with a multimeter, hoping to discover the reason why the left channel is dead and why it was arching before it was dead. I came away with more questions about the LDII+ design than ever before.

First of all, when I measured the capacitance of the two circled capacitors, I found the R cap to be 209uF and the L cap to be 668uF. Strangly, I can get the exact same capacitance values by measuring the leads of the red caps just to the right of the two circled ones. I figured that the problem is in one of the caps, so I desoldered the four of them off the board and measured 205uF for both the blue ones and 680uF for both the red ones and they seemed to be perfectly fine. So my questions is, if the capacitors are alright, then why do I get strange values when they're on the board? And why is my left channel dead if the capacitors are alright? And does any of this have to do with the famed arching on the LDII+?

By the way, does anyone know why there are two transistors in the design and what they are for? Also, what brand of capacitor are the blue ones I circled?

1469986322_ef383592d0_o.jpg
 
Oct 1, 2007 at 9:47 PM Post #2 of 10
when measuring the capacitance on the boards, you are measuring the total capacitance between those two nodes. It's not possible to just single out one component on the node. Looks like the problem isn't with the capacitors...

edit:

The "transistors" you are wanted to know about are in fact voltage regulators. The 7805s are a 5 volt regulators.
 
Oct 1, 2007 at 9:47 PM Post #3 of 10
What happened initially? Playing one day, went out the next? Was it transitional? List the phases if so...

From looking at that board, I would suspect one of the voltage regulators or tubes has gone haywire. Is the PSU integrated or a separate unit?

Take voltage measurements from key points on the working channel and then compare them with the faulty. If voltage looks good, chances are a tube has gone bad. Try swapping the tubes around. This will tell you pretty quick what is going on. I wouldn't do the swap right away, you may risk damaging the good tube. Wait till the proper voltages have been verified.

~Zip
 
Oct 1, 2007 at 11:32 PM Post #4 of 10
Quote:

Originally Posted by ziplock /img/forum/go_quote.gif
What happened initially? Playing one day, went out the next? Was it transitional? List the phases if so...

From looking at that board, I would suspect one of the voltage regulators or tubes has gone haywire. Is the PSU integrated or a separate unit?


How do I check if the voltage regulator is good or bad using a multimeter? Is it the same as checking a transistor? And are all 7805's the same or if not how do I find replacements?

The way it died was pretty sudden, one day I turned it on and the left channel just wasn't working. I do suspect that the failure was something heat-related because the day before it died I left it on for about 12 hours straight and I don't usually do that.

The tubes are fine, I know because the first diagnostic I did was swap the tubes and the left channel was still dead (I can hear a faint sound coming from the left channel if I turn the source up, though).

The LDII+ has a built-in transformer PSU on top of the unit.
 
Oct 2, 2007 at 12:42 AM Post #5 of 10
Quote:

Originally Posted by Dept_of_Alchemy /img/forum/go_quote.gif
How do I check if the voltage regulator is good or bad using a multimeter? Is it the same as checking a transistor? And are all 7805's the same or if not how do I find replacements?

The way it died was pretty sudden, one day I turned it on and the left channel just wasn't working. I do suspect that the failure was something heat-related because the day before it died I left it on for about 12 hours straight and I don't usually do that.

The tubes are fine, I know because the first diagnostic I did was swap the tubes and the left channel was still dead (I can hear a faint sound coming from the left channel if I turn the source up, though).

The LDII+ has a built-in transformer PSU on top of the unit.


OK, the 7805s are the voltage regulators. Each channel has it's own. The configuration is as follows:

From left to right, facing the front of the transistor.

Pin 1: Voltage in
Pin 2: Ground
Pin 3: Voltage out

Set your multimeter to read DC with a minimum setting of 20v or higher.

Take the negative lead (black) and place it on the metal backing (not the heatsink) of the 7805. This is also considered Pin 2.

Take the positive lead (red) and measure the voltage coming from Pin 1 and then Pin 2. Write down the values. Repeat this process for the other regulator.

This will tell you that the transformer and voltage regulators are doing their job properly. Obviously if one side is way off, you have a faulty component.

Example, if both of the input voltages are the same, but one of the output voltages is different, this would indicate a possible bad transistor.

Be careful not to short anything while probing around. You could cause further damage or shock yourself.

See what you can come up with... report back.

This thread should probably be moved over to DIY. This is pretty techy stuff and outside the scope of typical amp discussion.

~Zip

Edit: It's entirely possible we are getting ahead of ourselves. Double check and make sure your source is putting out the proper line levels. Make sure the balance in windows mixer is not way off!
tongue.gif
 
Oct 2, 2007 at 4:55 AM Post #6 of 10
The 7805's are the DC filament regulators and they carry some current so it's possible one died. Without 5 volts on the filament, the tube isnt going to work.
The regulators are a common part, not hard to get. An easy fix.

Be careful in there, you are right next to 220vdc keep one hand behind your back. Seriously, if you hit high voltage with one hand and the other is grounded the voltage runs right across your heart and it can stop. 'Killed by Head-fi' on your headstone.
 
Oct 3, 2007 at 4:49 AM Post #8 of 10
Quote:

Originally Posted by Dept_of_Alchemy /img/forum/go_quote.gif
Where can I find the heat sink for the 7805's?


They are the black finned things they are screwed to.
 
Oct 3, 2007 at 6:37 AM Post #10 of 10
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