Good stuff Jamie, so now you can go over the complete circuit and measure the voltages to see they agree with the diagram.
To understand the black art of electronics is to understand witchcraft. Andrew.
Good stuff Jamie, so now you can go over the complete circuit and measure the voltages to see they agree with the diagram.
The biggest issue still seems to be that 7.25V Missing from LH and RH VT1.
And yet the base and emitter voltages are correct?
Is R29 ok?
To understand the black art of electronics is to understand witchcraft. Andrew.
Looking at the map, I'd hope to see about 16-17V across C9, the decoupling electrolytic. Ohms Law says the transistors should be passing about 400µA of emitter current - if the two 10µF caps that bypass the emitter bias resistors are going s/c under volts then that would upset the DC conditions somewhat. Similarly, if they went o/c they'd reduce the gain of the stage somewhat as then extra negative feedback would be introduced across the emitter load.
And yet the base and emitter voltages are correct?
Is R29 ok?
Brand New
Looking at the map, I'd hope to see about 16-17V across C9, the decoupling electrolytic. Ohms Law says the transistors should be passing about 400µA of emitter current - if the two 10µF caps that bypass the emitter bias resistors are going s/c under volts then that would upset the DC conditions somewhat. Similarly, if they went o/c they'd reduce the gain of the stage somewhat as then extra negative feedback would be introduced across the emitter load.
Also brand new..... eurghhhhhhhh
Hmmm, Might check R3 & R4. They LOOK to be replacements based on the photo of an "unspoiled" chassis Chris shared a while back...
EDIT: 11k and 12.7k so they're ok too!
@jskinner97 Okay, so... what're the voltages on VT1, the voltage across C9 and what type is VT1 - I don't speak Thorn 😉
R1 & R2 are fine too! 😥 😥 😥 😥 😥 😥 😥
@jskinner97 Okay, so... what're the voltages on VT1, the voltage across C9 and what type is VT1 - I don't speak Thorn 😉
The data is in an image a few posts back lol, the main thing missing is 7.25V on the detector of both VT1's which is a BC186
One other thing - can you connect an AC voltmeter across the loudspeakers with no signal applied to the input? Turn the volume up too.
@jskinner97 Okay, so... what're the voltages on VT1, the voltage across C9 and what type is VT1 - I don't speak Thorn 😉
The data is in an image a few posts back lol, the main thing missing is 7.25V on the detector of both VT1's which is a BC186
And you are measuring these actual voltages on your amplifier, yes?
3.6V AC across c9
LH speaker 0.023V AC
RH Speaker 0.018V AC
No input vol on full
the right channel is virtually non existant
All other voltages on all other transistors are fine/ Only problem is that missing 7.25V DC on both VT1 its way down to about 2.3V
OK. I changed a resistor and we have about 5.6V on LH VT1.... RH VT1 is missing the 7.25V
3.6V AC across c9
Sorry, my mistake Jamie - in this instance I'm interested in the DC voltage.
So you've changed a resistor - which one? An absence of collector volts is pretty fundamental, it points to the collector load being o/c, or a very dead transistor!
R9 and R10 changed…
C9 DCV 18.59V
What state are R7/8/11/12 in?
7 in tolerance
8 new
11 & 12 in tolerance
they’re being checked on my Chinese tester which applies 5V to them
