Tremoverb LDR dating "problem" era

from what i understand, there was a certain batch of tremoverbs that were made with the problematic/bad batch of LDR's. was wondering if anyone knew, either by year of build or serial number range, which t-verbs were affected by this. i've got a '99 that's been pretty solid w/no issues except for the fact that the tremolo depth knob does pretty much nothing these days. not sure if it's an LDR thing, or maybe just a bad pot or something else?

I have an early Mark IVb (w/attached power cord) that was made with the bad LDRs. I'm not sure of the exact time frame. I'm guessing it's roughly around 1995 based on the serial # of my amp. I had to have all the relays replaced.

If your amp is from 1999, I think you are ok.

I'm not sure if my TOV's problems are the LDR (orange channel fades in and out and then cuts out completely) My TOV is a 1999, when I opened it up, it had LDR's with just four numbers on them, which I think is supposed to be, the bad ones. Not sure about any of this yet, still at the tech. I too thought a 1999 model would be fine. I think your trem problem is normal, depth doesn't do much.

You can always call Mesa tech support and ask.

I had to have all the relays replaced

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did you mean the LDR's, or relays? i thought that all those LDR's were substitutes for having relays, which all the newer mesa's now have from what i understand.

thinskin57 said:

I had to have all the relays replaced

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did you mean the LDR's, or relays? i thought that all those LDR's were substitutes for having relays, which all the newer mesa's now have from what i understand.

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I'm have no electonics background but I thought LDR stood for "Light Dependant Relay" or "Light/Dark Relay". At any rate I'm looking at the repair bill and it says...

"Replaced 27 factory Silonix LDRs with 27 Vactec LDRs"

Mine is number R-002900. I'm pretty sure it's in a 93 or 94. I had to take it in last year because it was having channel dropout, the red channel if I remember correctly. They replaced the LDR's, and told me about the bad batch issues. I don't think your 99 is subject to the same probs, so I would call Mesa directly.

Hope that helps a bit,
Mike

GD_NC said:

thinskin57 said:

I had to have all the relays replaced

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did you mean the LDR's, or relays? i thought that all those LDR's were substitutes for having relays, which all the newer mesa's now have from what i understand.

Click to expand...

I'm have no electonics background but I thought LDR stood for "Light Dependant Relay" or "Light/Dark Relay". At any rate I'm looking at the repair bill and it says...

"Replaced 27 factory Silonix LDRs with 27 Vactec LDRs"

Click to expand...

i'm nearly positive it stands for Light Dependent RESISTOR.

I found this from Mesa boogie about the LDR's

TECH BULLETIN: "Tremoverb" Update
*NOTE: This update does not apply to very early units
having a 120ohm, 10W sandblock resistor near pwr transformer.
The "Tremoverb" amplifier has two 47-ohm, 1/4-watt resistors
(one is located mext to the pair of relays and is connected
to LDR #3 - Location 26-E on diagram below. The other is
next to and connected to LDR #13 - location 14-B below).
Please replace both of these 47-ohm resistors with 220-ohm, 1/2 watt resistors.
Also, the 68-ohm resistor that is connected to LDR's 11 & 12
(location 14-C below) should be increased to 360-ohms.
Finally, please REPLACE LDR's #3 (type 5C4/2), #11 (5C9), #12 (5C9) and #13 (5C4).

*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

I think your trem problem is normal, depth doesn't do much.

you may have the same problem as me then, because i've owned 3 of these and on the other two tverbs i had the depth worked as you would expect it to.

jamme61 said:

I found this from Mesa boogie about the LDR's

TECH BULLETIN: "Tremoverb" Update
*NOTE: This update does not apply to very early units
having a 120ohm, 10W sandblock resistor near pwr transformer.
The "Tremoverb" amplifier has two 47-ohm, 1/4-watt resistors
(one is located mext to the pair of relays and is connected
to LDR #3 - Location 26-E on diagram below. The other is
next to and connected to LDR #13 - location 14-B below).
Please replace both of these 47-ohm resistors with 220-ohm, 1/2 watt resistors.
Also, the 68-ohm resistor that is connected to LDR's 11 & 12
(location 14-C below) should be increased to 360-ohms.
Finally, please REPLACE LDR's #3 (type 5C4/2), #11 (5C9), #12 (5C9) and #13 (5C4).

*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

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hey, thanks for that Jamme61! i just referenced some high-res pic i took of the inside of my tverb chassis and was relieved to see that i do indeed have the VACTEC type. (3 lines of print on top) good to know. thanks again. steve.

cool beans! you should be good.

Not necessarily. The Vactecs are *more* reliable, not perfectly reliable. I'm almost 100% certain (without pulling the chassis again) that my '94 has Vactecs, but two were gone when I got it.

The faults you're experiencing *could* certainly all be due to faulty LDRs - although they could be due to other things too.

thinskin57 said:

i'm nearly positive it stands for Light Dependent RESISTOR.

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Correct.

Each LDR consists of a photocell (basically a switch which opens or closes depending on the presence of light) and an LED in a lightproof housing. When the LED turns on, the photocell turns off and blocks the flow of current, which allows for the various settings.

One would think using a multi-pole relay would be easier, but with that comes an audible click from the contacts mating. LDRs don't make that noise, which accounts for why the 3 channel Rectos pop when changing channels, and the 2 channels don't. They started using relays in the 3 channel heads instead of LDRs.

Some other observation concerning LDRs vs Relays. To replicate the function of a single relay requires four LDRs. Relays cost about 3-5 dollars a piece. The LDRs used in the rectifiers cost about the same, but require four of them to duplicate the function of the relay, meaning 20 dollars. Relays are also more dependable. So dependability and costs influenced the change from LDRs to relays. Also, about the time mesa switched from LDRs to relays vactrol production from being switched from Vactec to Perkin/Elmer so I'm sure supply concerns influenced the change as well. LDRs have the benefit of being four individual pieces when being used like a relay. The benefit is when a wire goes to the front panel, it doesn't have to return to the same spot like it does on a relay. It makes designing a PCB board a lot simpler.

You only need four LDRs to replace one relay if the full DPDT switching of the relay is used - often it isn't, and you only need two LDRs to do the same job if both sides are used single-throw, which many are. Relays introduce a little of their own extra complexity too because to suppress the pops requires a timed muting circuit which can also occasionally cause trouble - as well as that annoying brief signal drop-out when switching. LDRs also allow more options, because the four separate switches can be used in *any* combination at the same time, whereas a relay is limited to just two mutually exclusive ones - which I think would prevent some of the channel cloning, one of the cleverest and most useful features of these amps. (I'd need to check the switching matrix schematic to be sure.)

I don't think anyone should be scared of the LDRs, it's no worse a problem than some other age and use-related service issues on other amps. All amps are going to need maintenance eventually, and the actual rate of LDR failure is really pretty low. Relays aren't immune from failure either, and are much more of a pain to change - they're one of the very few components that require board removal on a Mesa, because they entirely cover their own pin connections, which then can't be accessed from the top. At least the LDRs are easier to change, and don't need the board out, even if in some cases you have to remove other ones that are stacked over the top first...

Yes, I had also thought about adding that to my previous post but decided my post was getting wordy. The current production LDRs from Perkin/Elmer are good quality. Like I said previously I think the reason for the switch was the cost of LDRs and the possibility that they would be in short supply at the time the switch from LDR to relays were made. I also think the supply issue was why Mesa tried another brand of LDRs in the first tremoverbs, and realized the quality issue with the other brand.

I don't think anyone should be scared of the LDRs, it's no worse a problem than some other age and use-related service issues on other amps. All amps are going to need maintenance eventually, and the actual rate of LDR failure is really pretty low. Relays aren't immune from failure either, and are much more of a pain to change - they're one of the very few components that require board removal on a Mesa, because they entirely cover their own pin connections, which then can't be accessed from the top. At least the LDRs are easier to change, and don't need the board out, even if in some cases you have to remove other ones that are stacked over the top first...

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Very true about the maintenance! I've had older DC's that have had every LDR fried, but this is a power supply issue.
As for replacing relays, I break them off from the top. Then you can get to the solder connections.
I usually replace the relay with an IC socket, just cut off the legs of the socket that you won't be using. Then, you can snap a new relay into place easily.
I also add just a dab of silicone so that it will stay put. Saves a butt load of time!

Now *that* is genius! I never thought of doing that...

Thank you .

After removing the board from a DC-3, I had to get really inventive! It takes so long to get them out that I just can't charge for all of the time.

So far, it's worked pretty well!