Design flaw for Line Magnetic's LM-508IA.

There is a design flaw on the Line Magnetic LM-508IA involving the cap under the right output transformer which can eventually implode. In my case, smoke even came out of the amp after a *very* loud POP! So far, I have been able to verify 3 people experienced this problem ; myself, @dianos and @J.D.80

The Nichicon cap in question is rated for a mere 450V at 85 degrees Celcius (185 F) and low ripple current capacity. On an aired-out simple circuit, that might be OK, but with the heat inside the amp as it sits directly under a hot transformer, it can possibly blow. This implosion affects a couple of other caps directly connected to it so those also need to be changed. In my case, a resistor also died.



We can see the burn marks and the bulging top of the cap. Fortunately, the X slits allow the cap to simply expand instead of explode.

As a sidenote, this and the adjacent caps apparently do not affect the tone so feel free to buy any reputed brand as replacements as long as they're from an authorized dealer. There are fakes on eBay and elsewhere so it is not recommended to source them from such platforms.

My replacement cap is also from Nichicon but rated at 500V and 105 degrees C (221 F). My tech added protection by soldering a diode across this new cap to prevent this problem from happening again. The diode also has no affect on the tone.



According to my tech, "the problem originates for two reasons. Insufficient ripple current in the original cap and the polarized capacitor is seeing a small but significant reverse voltage until the high-voltage relay trips. At most times only around -25V, but it did spike up to about -70 at one point. The diode shunts that away without affecting anything else. Once the high voltage kicks in, the diode does nothing."

Credit goes to Dan Santoni of DTS Electronics located in Hamilton, Ontario ; Audio Repairs

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We now at least know the reason why this became an issue and how to prevent it. Due to my experience and after reading that of others, I highly recommend current and future owners of this amp proactively replace the aforementioned cap and add the diode to prevent this issue from occurring.

The newer version of this amp, the LM-805IA, uses very similar circuitry but I'm unable to find images of the insides to confirm whether the same values are used for that cap. In the event the values are identical, I urge all LM-805IA owners to follow suit.

EDIT : I've posted the same thing in the thread dedicated to the 508IA but I believe this problem warrants its own thread to ensure this important message isn't lost in its 46 pages.

 

Dan is a great tech. Used his services before a few times. Always gets the job done. Glad to see you got the amp fixed at hopefully little cost overall.

 

This is the repair? That's an ugly gloppy mess.

 

I'm no tech but can state he comes highly recommended and he put a lot of time and research into this problem. Plus, he was able to diagnose a nagging channel imbalance I had experienced for a long while. He was also able to squeeze me in right before he went on vacation. He went above and beyond on my behalf. Won't hesitate to use him again in the future.

No idea how it's supposed to look but I can assure you that my ears don't much care either way. As long as it sounds glorious, that's all that matters.

 

Thanks for sharing this. So I received my LM508 back in March, new from a US dealer. I noticed the buzz/hum and tried various fixes but nothing really helped. I posted about this in the LM508 thread and most people, including the dealer, said that it's normal for these amps and its basically just going to have a slight buzz/hum. There were times it didn't bother me much, but it was always there. However, there were times it seemed excessive and then I had a couple of times where after listening to music for 2-3 hours the buzz would get extremely noticeable. It also came primarily from the right transformer. I took a video and sent it to my dealer. He told me to send it to his tech in Arizona. The amp has been there since May. I was told its a bad transformer and they're waiting for a part from LM. I'm going to contact him tomorrow and try and get more details. The dealer has been responsive and nice, but it seems likely this issue is what may be going on with my unit?

 

I hope this problem gets escalated to LM HQ. I've experienced red-plating tubes which caused me many hours of anxiety, I can only imagine what you went through with the popping sound and smoke coming from your amplifier. I understand these issues are inherent to owning tube gear but still scary nonetheless. Thanks for sharing this and glad you had a competent tech nearby to help you sort it out.

 

How many caps do you have to replace and how much each? I am planning to get the 508 but I’m worried about it.

 

It might be good to make sure the amps are UL certified or something as well because if the problem causes a house fire you may not be covered under your insurance. For those people who leave their amp on when they go to restroom or are in the kitchen etc.

 

If it is a design flaw then the company should fix it even if it's 10 years out of warranty. This is is not a wear and tear thing.

 

What troubleshooting did you do prior to bringing it to a tech? Did you swap tubes for the Right and Left channels? Doing so would illustrate whether it's a tube-related issue as the problem would likely migrate from one channel to the other. If the problem persists in remaining on one channel, it could technically be a transformer problem.

However, I am quite shocked about the length of time this is taking. Is it High End Repair in Phoenix? If so, I was in communication with James Koch who assured me that although ordering an output transformer (assuming that is the culprit) would take months, one could be sent by air to speed up the process and estimated the shipping costs to be $70 extra.

If what you say is true, I'd suggest picking up the phone and getting a detailed report on what is going on. In the event it is the OT that is defective, ask that they ship the part by air so you can get your amp back in this lifetime.

I believe 3. The one which caused the problem and two others which were connected to it and were simply victims.

The victims were replaced with identical ones. IIRC, these caps were pretty cheap. The amp is easy to work on and that part of it is completely open anyway so labor shouldn't be time-consuming either.

 

My tech solved transformer hum from the right transformer by just tighten the screws. Total silence since then.

 

Are all 508ia amps experiencing this? or is it the gray market amps? I know that my 518ia had different caps than what the grey market 518`s had, i saw this with my own eyes.

I have owned various LM amps over the last decade and have had zero issues with any of them.

 

There is no such thing as a gray market unit. Aside from the power transformer's voltage handling (240V vs 120V), there's zero difference.

The issue isn't occurring for everyone but there's a definite pattern. Some of the units experiencing the problem were the 120V version while others were 240V.

Since I compiled all the info, my recommendation is to proactively prevent the issue from occurring. Up to the individual to do it or not. The amp worked great until it didn't.

 

I tried swapping tubes in channels plus using different tubes. I made sure my outlet was grounded. I tried different pc's and tried going direct to the wall outlet and using various power products including ac offset power strips (emotiva and van alstine). Nothing worked or made an improvement. The noise was all on the right and the right transformer got hotter and vibrated quite a bit more than the left. It is High End Repair in PHX. My dealer told me it is the transformer and it is almost ready. He said it is not related to this issue. I'd hate to get it back and have another issue. Not sure what to do at this point because if I get it back and have the issue you're describing, after I've alerted them, I will be pissed. I've been really patient but this was a big purchase for me and I feel like I haven't had a working product that I paid for 6+ months ago.

 

LM, HER, and/or your dealer are bound to deny this defect for many reasons. You could try applying some pressure but it's up to you to take the time and trouble to go through this. The tubes and caps plus the diode and labor cost me a total of about $135 US by a very competent tech.

You might never encounter the issue or you may. It's a coin toss. Since it's already in the bench, replacing one cap and inserting a diode wouldn't take only a very short time. The diode is even optional but my tech wanted to make *sure* it'd never happen again. Even just upgrading the cap will seriously decrease the chances of encountering the problem. Changing a single easily accessible cap is child's play and could be done in 5 min.

 

How much high end audio equipment is UL certified? Think I have read that the vast majority isn't, as that's a costly process. Or maybe that was CSA approved...something to look into I guess.

I will check all the amps I currently own (two SS, one tube; one Cdn, one UK, one Chinese). Not holding my breath for any of them!

 

Surprised no one mentioned this. Buy a high temperature replacement capacitor. High temperature electrolytic capacitors are rated at 105C vs standard 85C temperature.

 

You clearly didn't read the OP.

 

You are right, I missed text below picture.

 

Hello guys
Im a happy owner of a LM-508IA and I've just read your posts about the caps failure and I've got worried.

Can you please give us more information about how do you use yours LM-508IA?

I mean, average hours per listening section, average volume levels, how many months it took to fail, ventilation of the rack holding the amp, are they 120V or 240V versions (mine is 240V), and any other information you consider important.

I bought mine from a chinese LM authorized dealer as I live in Argentina and there´s no LM dealer here. I will ask the chinese dealer who sold it to me, nevertheless I would appreciate your experience feedback.

Thank you!

PS: by the way, I've used mine with several different tubes for about six months with out issues. I use it three or four times a week and my listening sessions are about 5 to 8 hours at low to moderate volume levels.

 

Hello Strat-Mangler
Looking at my amp, I just discovered a ventilation grill on the right side, right next to the cap you mentioned, as it is also shown on your first picture. That grill its not on the other side of the amp, only on the right side.

Some thoughts:

1. It seems that LM designers have thought about the heat as they have placed the cap right next to a grill.

2. Just in case, did you placed the amp with enough space for ventilation?

3. Is this blowing cap failure a massive issue or just two or three cases?

3. There's also a grill below the amp. Did you have the amp standing on its original feet or did you use any aditional feet, or antivibration suplement, that could rise the amp a little bit and make the lower grill work better?

Kind regards

 

2. Yes.
3. Few people reporting so tough to say.
4. Original feet.

 

My chinese dealer, who I believe is quite professional (I bought several items from him) and is posted on LM chinese website as an official dealer, told me that he has sold more than 100 units of the LM-508IA and he has never got this problem.

Nevertheless, I told him to ask Line Magnetic factory for an opinion on the subject, as I believe your dealer, and the ones who sold the other amps with the same problem, should have contacted the factory.

What was your dealer's response to the problem? What service or answer did he give you? If he's an official dealer, did he contact LM factory for this?

 

Good for him and those owners. Still happened to at least 3 members of this board which is too many to be a coincidence.

What is your agenda, here?

I bought mine used.

 

Yikes that’s some nasty soldering. Looks like something I’d do!