Mesa dc-5 LDR's

[Andy Le Blanc]

I have a Mesa on the bench with a channel switching fault.

Is there a "better" way to check LDR function in circuit?

Are all LDR's the same?

This is one part that I haven't had to replace yet.

[dehughes]

I have a Mesa on the bench with a channel switching fault.

Is there a "better" way to check LDR function in circuit?

Are all LDR's the same?

This is one part that I haven't had to replace yet.

I have no idea what an LDR even is, but I am amused that you've had to replace every other part but that. I wager it's hyperbole, but still...

[funkmeblue]

the "LDR" is a boogs weekest link. Aren't they light dependent relays? Have you called boogie? They have always been helpful with all my questions.

[Andy Le Blanc]

Haven't contacted mesa yet, the channel lights say its switching but the lead
channel controls are still functioning. There are LDRs at the input and a
relay after the master volumes, its one or the other. But replacement and service means
major dis assembly to access the solder joins under the PCB. I'm rather put out.
Nice amp, all around, quality and parts, but you have to bend over and take
it if it ever needs service. The investment of time to service this product
is prohibitive.

[Phil_S]

Andy,
I believe the messy booger is the Jaguar of amps.
Regards,
Phil

[Andy Le Blanc]

Ah-men..........

I've had to go thru a few mark 2 boogies, they do hold up ok , they was rode hard.

Just pounded, spk hanging, large components floating inside the chassis,
one looked like it had tried to start a fire.......

They're not un-fixable.... I found a new focus with this DC-5. Its starting to look
like it may be a relay, I cant get some sort of reading on whether the relay
that selects channel, after the channel masters, is functioning. Which may mean that its not.
I still have to poke around back to the power side to see if there's
another cause
These are not as "messy" as the old ones appeared, but the PCb board has to
be flipped to service, and dis assembly and re assembly of the dashboard
controls is time consuming. This why you see those big ribbon cables and
PCb interconnects.

I haven't found a PCb layout yet...... and I still need to get after relays.....

Good thing is thats not a tube issue, everything else is ahead at full thrusters.

[mhuss]

LDR = Light Dependent Resistor, the Vactrol is the common example. There's a light of some sort in the same package, usually an LED, and basically the 'resistor' part is used as an open/closed switch. Typically, the resistor part will measure 'open circuit' when the LED is dark, and a few dozen ohms when the light is on.

Check that the light/LED side is getting the voltage change when the channel is switched, and check that the resistor side is shorting the appropriate point in the circuit when the LED is getting voltage.

--mark