6.8V dc at one side of R199 0V dc at the other side of R199 in ON
and 8.2V dc on one side of R199 and 0V dc in standby

0V dc at both sides of R188 in standby and ON.

Ok. A couple of things wrong here.
R199 appears to be blown open. Measure the resistance of R199. 10Ω expected.
D131 could be blown shorted.
Q137 could be blown. Not sure as yet. Still need investigating.

POWER_RLY from IC101 pin-26 to R188 does not seem correct on ON mode.
Edit: I just read your correction in post #20. That makes a huge difference now.

 

Measure the resistance of R199 with POWER OFF.
Taking a measurement with the resistor still in-circuit is ok in this case because the expected resistance is so low.
10Ω expected.

 

From your tests in post #12 it looks like the coil on the relay is being energised when in the ON state (Which is correct.)
With with the unit in the ON state and your meter set to the 200 volt AC range measure the voltage between pins 1 and 3 of the 3 pin connector CP108. (This is close to the two bridge rectifiers D134 and D135.) I expect a reading of between 60 and 90 volts. These are the two ends of the center tapped secondary of the large transformer.

Les.

0V ac between pins 1 and 3 of CP108.
I also checked pins 1/2 and 2/3. There's no ac voltage present.
If I connect the black multimeter lead to mains neutral and the red lead to any of the pins on CP108 I see 110V ac

 

Let us slow down and hold off for a bit until we get some concrete answers.
We want to know the status of R199. It appears to be blown.

 

Measure the resistance of R199 with POWER OFF.
Taking a measurement with the resistor still in-circuit is ok in this case because the expected resistance is so low.
10Ω expected.

R199 measures 10.2 Ohms

 

R199 measures 0.02 Ohms. When I try the meter in capacitance mode it looks shorted.

Forget the capacitance measurement.
Can you please post a photo of the meter (total meter, reading, range setting and jacks) while measuring R199?

 

Forget the capacitance measurement.
Can you please post a photo of the meter (total meter, reading, range setting and jacks) while measuring R199?

 

Thanks. Ok, I see 10.3Ω. That's better.

Please do not modify a previous post because this throws all subsequent posts out of context.
If you made a mistake, say so.
You can edit a post by adding an Edit: statement at the bottom of the post.

Moving on, we now have to go back and revisit voltage measurements surrounding R199, D131, RLY106, and Q137.
Wait for further instructions.

 

I'm very sorry.
Yes, I made a mistake before. I'm struggling to see my connections as the lighting where the amp is (in my conservatory) is great during daylight but not good now. I could move it to a better location.
I'll await instructions.

 

Your DMM does not have the ability to measure capacitance.
The battery in your DMM is running low. You want to attend to that at your earliest convenience.

 

I'll look at changing the battery now.
I do have a capacitance meter as well as the DMM.

 

I would recommend that you leave your DMM in the 200VDC measurement range for now.
We want to see the voltages on STANDBY and on ON for the following components, on both legs with respect to GND:

R199
D131

R199 will show us the voltage (and current) going to the relay.
D131 will show us the voltage across the relay.
Listen and tell us if you can hear the relay click when in the ON mode.

 

After we hear back from you we will take a break as it is getting dark.
I think we are making some progress. We will continue tomorrow.

 

New battery in DMM
R199 ON 9.0V dc one legs, 9.6V dc other leg
11.9V dc both legs standby

D131 ON 9.1V dc one leg 0Vdc other leg
11.9V dc on either leg standby

Yes, the relay clicks coming from standby to ON or back again

 

After we hear back from you we will take a break as it is getting dark.
I think we are making some progress. We will continue tomorrow.

Very grateful, thanks.

 

MrChips, Sean's tests in post #12 seem to suggest that the relay coil is being energised in the ON state.

Les.

 

MrChips, Sean's tests in post #12 seem to suggest that the relay coil is being energised in the ON state.

Les.

Thanks. I didn't catch that.
We'll continue with testing the AC mains side of the relay tomorrow.
110V is an anomaly since TS is in UK.

 

If I connect the black multimeter lead to mains neutral and the red lead to any of the pins on CP108 I see 110V ac

 

Sean, Re your post #23. In the last line that post you tested the voltage on the pins of CP108 WITH RESPECT TO MAINS NEUTRAL.
I can't understand the reasoning for doing that test. What was it supposed to show ?
Did you check the continuity of fuse FS101 ?
With the unit UNPUGGED FROM THE MAINS unplug the connector to CP110 and measure the resistance between the two pins of the plug that plugs into that connector. (The part with two wires going to it.) (These wires will connect to the primary of the large transformer.)

Les.

 

Two silly questions:

1) Is the POWER switch on the front panel pressed in?
2) Did you check fuse FS101?