The pre-amp out/line out is a jack on the panel.

 

You can get some Android phone based test equipment. On my phone I have a sign gen, oscope, and spectrum analyzer. Unfortunately the scope and spectrum use the microphone so, I have to use headphones or speaker.

Plug a headphone in the line out jack .... Use the master volume control to set the volume. See attached manual.

 

Can you inject a signal to the Line In and check if there is audio out from the speakers?

Line out and line in are about the halfway points in audio systems.

Make sure all controls are about mid position.

 

Can you inject a signal to the Line In and check if there is audio out from the speakers?

Line out and line in are about the halfway points in audio systems.

Make sure all controls are about mid position.

No audio out with signal at Line In, nothing from the speaker out or Line out. When I inject audio into the Instrument input I get audio to the Line In jack so its after that

 

What should I expect where, at the Base of Q10 I have audio and when I check it at the emitter of Q9 it blew my ear drums!! At the speaker jack I'm barely getting anything

 

On your schematic, you have voltage levels listed. Can you compile a list of locations you tested and the voltage you observed there? In case you haven't realized it yet ... I like copious notes.

Since you injected a line level signal at the Line In Jack and you had NO audio at the speaker, we can work on that problem first. Or if you prefer, you can inject a signal at the instrument in ... which is probably around 10 mV rms ... and repair it till you get the LINE Out.

Which one do you want to start the effort ... Line IN to speaker or Instrument IN to Line Out?

 

On your schematic, you have voltage levels listed. Can you compile a list of locations you tested and the voltage you observed there? In case you haven't realized it yet ... I like copious notes.

Since you injected a line level signal at the Line In Jack and you had NO audio at the speaker, we can work on that problem first. Or if you prefer, you can inject a signal at the instrument in ... which is probably around 10 mV rms ... and repair it till you get the LINE Out.

Which one do you want to start the effort ... Line IN to speaker or Instrument IN to Line Out?

I think the Line In makes more sense, I'll start going through the voltages my biggest issue is figuring out which component is which, I'll pull the board and map it as best I can, I do have an O'Scope so I can see those P-P voltages now. I really appreciate the help.

 

Ok ... we can do that.

Attached is a better image of the CR-280 series PA schematic.

Take copious notes.

Let me know the value you read on the + and - 45 volt lines.

 

When I was first taught troubleshooting, I was taught this method. A few things one should remember is they need to review the user manuals to glean some information on they system. Granted, most audio amplifiers follow a similar process and once you realize it, a mental block diagram will develop.

Ok, upon review of the available schematics and the user manual, I drew this block diagram:



When you use that method I linked to above, you would use this diagram after you compiled a description of the problem from a functional test. That means all functions, not just signal in and no signal out.

The power amplifier is basically x50. So, if you put .1 V rms into the Line In jack expect 5 V rms at a 4 ohm load.

 

Awesome that is definitely helpful!
The fun I'm having is finding everything, since the board is mounted face down and uses the chassis as ground I need to map where everything is looking at the back of the board, and on the front a large heat sink covers 3/4 of the components so it's interesting but I started working on it last night and it's getting there, it makes it a lot easier having part numbers so I'm just starting at the transistors and going out to the points that need to be measured. Thank you the block diagram definitely helps make sense of what I'm actually looking at and why!

 

Haven't got everything but I think I've found a suspect, here is what I have so far with 1vrms audio into the Line In jack
J1-1 45.4v
J1-5 -45.4
Q1 base -.32v
Q1 Collector -44.4v
R9 .55v / -16.24v
Q3 Collector -43.1
Q8 base 5.7v
Q8 collector -45.4
c16 5.7v
Q9 base -1.5v
Q9 collector 45.3 v
c17 6.8v

so Q8,9 are confusing me, how am I reading 7v at C17 then -1.5v at the base of Q9 they are tied directly, then C16 and Q8 seem to act as expected except I should be getting -1.1v. Both emitters are reading around .04v and 25vac. So on the surface it looks like at the very least C16 and 17 could be bad, the voltage getting to them is correct but coming from both is not. I checked the collector voltages on Q10-13 and they are all at 45.4 +/- as should be, which makes sense since the collectors of Q8,9 are good.

 

Based on what you measures and what is posted on that power amp schematic, what areas should you be addressing.

I will look your info over when I get home in a couple of hours.

 

I hate for you to duplicate efforts, but, according to the schematic (pre-amp) notes, the DC voltages are measures at quiescent conditions. In other words, no input signal.

Make your list to include all the voltages listed on the schematic. The format should be:
Test point. Expected. Measured.

The problem could be further back, closer to the input.

Once you get all the readings, grab the schematic, your test results, and the beverage of your choice, then step away from the gear to look at what you have and plan you next move.

 

When you measure the voltage across C17 or C16, your meter will display the difference between the base and collector voltages. depending on where you placed the meter leads, black and red, you will read a positive or negative number.

using the figures from the schematic and (simulation)
Q8 base -1.1 (-1.2)
Q8 collector -44.7 (-45)
difference 43.6 (43.8)

 

Part of the problem was probably the way I was reading them, had the neg lead sitting on a common ground for the board. I can't express how much I appreciate the help, and it turns out I found the problem!!
I decided to do another audio probe and just follow the audio to see if I could find something obvious so I plugged into the instrument input cranked the 1khz tone up and started at the Line In, the Power transistors were pumping the audio big time so I knew it had to be after those, I made it all the way to the speaker outs and still had amplified audio!!! soooo checked my test speaker and yep you guessed it wide open, I did blow another component it was my speaker!! Unfortunately all I have is low power Alnicos and I really don't want to blow those so I need to get a high power speaker to truly test but it appears to have been fixed all along.

The good news is I really learned a lot mostly stuff I forgot 20+ years ago since everything I do now is RF I don't get the opportunity to actually play with circuits so this was awesome, again thank you for the assist, I'll let you know if testing goes well once I hook to a speaker!

 

When you do a quiesent test, the base of Q8 and Q9 should be the same, only opposite polarity. If they are not, adj the potentiometer till they are. But do that only with an appropriate load.

You probably took out the speaker when you injected the 1v signal at the emitter.

To refresh your working knowledge, stuffed into the abyss of your brain, get a simulation program. I use TINA, and the free version is tini-ti at ti.

Others use LTSpice.

You could make quite the service manual for yourself. Some circuits are good for associative learning, you know, applying previously learned material in new situations.

I never seen the amp before. I'm glad you got it done.

 

Piggybacking on this thread -- I want to use just the preamp section(s) and ditch the power amp section (I feed the pre into a different power amp). What boards do I retain? It looks like one board is the threshold, which I don't need...would that bring me down to one board? with a 12v supply need?