My Little Dot MKIV died yesterday :(

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LittleRedRidingHood
Posts: 4
Joined: Jun 28th, '10, 09:25

My Little Dot MKIV died yesterday :(

Post by LittleRedRidingHood »

Since it's out of warranty I decided to take it apart.

The problem: Everything was working fine, and then the music faded out. I couldn't hear anything. No smoke that I could smell or anything.

What I saw was that two of the three resistors (I believe 160 Ohm / 3 Watt) behind the three big electrolytics, basically on the rear edge of the board, were completely burned out. When I removed the board, I got a shock.. then another shock.. from those resistors.

So I assume these are there to safely discharge the big electrolytics.

I took a new resistor and discharged the caps. Problem solved.

But now, I realize that the problem may be deeper than that. I don't think that having those two resistors out of order may make the amp mute. I can't hear anything other than a slight hum.

Anything else I should be checking?

Thanks for your help!

DavidZheZhe
Posts: 1718
Joined: Mar 14th, '06, 01:25

Re: My Little Dot MKIV died yesterday :(

Post by DavidZheZhe »

I'm sorry to hear that! So just to confirm, after replacing the resistors you have no sound? The three resistors are 2x 160 ohm / 3 W and 1 x 180 ohm / 3 W so you should make sure the impedance ratings of the new resistors are correct and all 3 should be replaced. If you cannot locate 3W resistors, any larger value will also be fine. If that does not help, I would recommend sending it back to us for repair/replacement. Even out of warranty, labor and parts are always covered (you'd just have to cover shipping).

LittleRedRidingHood
Posts: 4
Joined: Jun 28th, '10, 09:25

Re: My Little Dot MKIV died yesterday :(

Post by LittleRedRidingHood »

Hello David,

I need to buy the resistors, hopefully I'll get them either today or tomorrow. There are two issues - the board looks to have melted next to them so I'm not sure if the copper was affected (this may explain why I lost the music, right? I'd suppose that, even if both resistors burned out there shouldn't be any issue). The second is, should I change something else on the board to avoid frying the resistors? I read somewhere that if voltage was higher than 110 V you should add a small resistor somewhere in the circuit, but I can't remember where.

I'll probably be getting 5 Watt wirewound resistors, since I can't seem to find any smaller W value.

Thanks a lot for your help!

DavidZheZhe
Posts: 1718
Joined: Mar 14th, '06, 01:25

Re: My Little Dot MKIV died yesterday :(

Post by DavidZheZhe »

Generally this is caused by the power tubes starting to go out, but if you change to 5W versions you should be fine. This issue actually cropped up a few times in the past which is why we made some modifications to the Little Dot MK IV / SE circuit that handles unruly power tubes gracefully. If you get 5W resistors, you should be good to go.

LittleRedRidingHood
Posts: 4
Joined: Jun 28th, '10, 09:25

Re: My Little Dot MKIV died yesterday :(

Post by LittleRedRidingHood »

Hello David,

I just checked the values on the board, they are different from the ones you gave me. I see 180/3W, 180/3W, 150K/2W. Are those values OK? The ones that are burned are the 180 ones. SHould I replace them for the same values? Or should I use your values?

DavidZheZhe
Posts: 1718
Joined: Mar 14th, '06, 01:25

Re: My Little Dot MKIV died yesterday :(

Post by DavidZheZhe »

Ah you have a different circuit revision. In that case you should use the values noted on your PCB.

LittleRedRidingHood
Posts: 4
Joined: Jun 28th, '10, 09:25

Re: My Little Dot MKIV died yesterday :(

Post by LittleRedRidingHood »

Hello David!

Success! I found the 180 Ohm / 5W resistors and installed them yesterday. There had been so much heat next to the resistors, though, that the board actually sort of melted - so I had to hardwire the resistors to the caps. I then changed the coupling caps to a couple of Dayton precision polys I had around and everything turned on just fine :) I cleaned the amp and it looks brand new now.

One thing, though... There's something wrong with this picture.... can you find what it is? There's an error somewhere, and it's not the new resistors I installed! Did I get a Little Dot MKIII on an MKIV chassis???
la foto.JPG
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rudekolek
Posts: 1
Joined: Feb 23rd, '10, 20:15

Re: My Little Dot MKIV died yesterday :(

Post by rudekolek »

Hello Sword,
Power resistors died after couple of years in my Little Dot MKIV and burned out hole in PCB. One of those burned resistor but still alive and has 220Ohm, maybe because damaged. Should I use 180Ohm 5W resistor as described on PCB or bigger for my 230V version? I have 120Ohm cathode resistor for 6H30Pi-EH, is it correct for LDMKIV?

Thanks for your help!
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Robbie California
Posts: 59
Joined: Dec 30th, '08, 00:31

Re: My Little Dot MKIV died yesterday :(

Post by Robbie California »

Hey rudekolek ... any chance that you still have your MKIV open? I need to find out which APLS 27 is used in that model. All attempts to find out the answer using this forum or through David or Sword have remained unanswered.

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