Mark IV Channel LED problem

[vhyken]

While I was playing this morning, i noticed my lead channel drop its power and LED light seem to die. And now. when Im on Channel 1 or 2. THe Lead channel's LED light is still lit on. Btw when i turn on the amp once in awhile my footswitch for the LEAD+EQ channel doesnt work but I here a boosted channel 1 sound.. Does anybody experience this?

 

[GD_NC]

Yep. Sounds like your LDRs are going bad. Take it to a Mesa tech and get it checked out. Many mid-90's Mesa amps (especially Mark IVs, DCs & T-verbs) suffer from this.

Typical issues caused by this are ...
1. blinking/dim/not working LEDs (#1 sign)
2. Footswitch not working correctly
3. Odd noises - popping, "wurring", or it sounds like an open mic in the wind.
4. Volume drops/swell

My Mark IV had nearly identical symptoms before I got it fixed.

 

[McBarry]

Up front, I've never been inside a MkIV..but if the channel is losing power (I assume U mean volume) AND the LED is dimming, I'd have expected the cause was further up the power supply chain, given I would not imagine the LDR to switch audio and LED power.. Could be wrong of course..

 

[GD_NC]

Search these "LDR Problem", "LDR Mark IV", or "LDR Tremoverb" and you'll get a ton of info. (google advanced search works much better than the search engine on the board)

You might want to peek in your amp and see if you have Silonix LDRs. This came from an earlier post. It's an excerpt from a Mesa technical notice...

*NOTE: LDR's manufactured by "VACTEC"
(has 3 lines of print on top) are more reliable
than LDR's made by "SILONIX" (has single 4-
digit number). If you encounter an amp having
several "SILONIX" LDR's, please call
Mesa/Boogie to arrange a factory repair

 

[vhyken]

Yep. Sounds like your LDRs are going bad. Take it to a Mesa tech and get it checked out. Many mid-90's Mesa amps (especially Mark IVs, DCs & T-verbs) suffer from this.

Typical issues caused by this are ...
1. blinking/dim/not working LEDs (#1 sign)
2. Footswitch not working correctly
3. Odd noises - popping, "wurring", or it sounds like an open mic in the wind.
4. Volume drops/swell

My Mark IV had nearly identical symptoms before I got it fixed.

This!!.. thats all the symptoms!..and in proper order which i've experienced haha.. will bring it tomorrow to my local amp tech.. does Mesa sell those LDR's for my mark iv?.. I also remembered changing my speakers to a vintage 30. I thought that was the culprit but i think is far off to be the cause. Might contact Mesa for now. Thanks GD_NC!.

btw last time my DC-3's LDR also failed. But sold it for the Mark IV.

 

[GD_NC]

If you have Silonix LDRs have your tech call Mesa and they might replace the parts for free. I think there's something like 27 LDR's in a Mark IV so even though they are cheap (~$8) it can add up. I don't recall the labor being all that much. It was under $200 for me. I had all of them replaced just to be sure I don't have to deal with that again.

I also saw on another post about a T-verbs with Silonix LDRs that Mesa will provide the labor if you ship it back to them. I'm not sure about that but it's worth asking. If you have an older Mark IV it my be a good idea to send it back home for a complete checkup anyway.

Note that other LDRs can fail too. They don't last forever. However the Silonix ones have been known to have unusually high failure rates.

 

[vhyken]

I see. I hope thats the case. Just waiting for my tech's call. Thanks so much GD_NC

 

[GD_NC]

Good Luck! I hope it works out for you.

 

[vhyken]

Yeah! My mark iv is in great condition again. My tech checked all the LDR and all are working just fine. The problem seem to came from the switching matrix. My tech just pulled the 2 small thingy's out and cleaned the contact parts.. and it was good to go.. my tech told me that if there was wromg in the sound. then the LDRs wOuld be the problem.