I'm trying to trouble shoot this amp . No output at all after Led Zep.
Left to cool off (I was sweaty) during which time the amp shoulda too.
Turned on - relay clicks away after playing ok for a few minutes. Does this repeatedly so gets put in garage.
Months and months later nothing from amp at all. Also no schematic from manufacturers of amp or relay. How helpful.
The second picture is flipped for your convenience hopefully.
The relay has 6 pins 2 to speaker outs (white conn. top Left). headphones (from cntre pins) and the lower two pins go to the large smoothings caps via some diodes transistors etc. I measure 31.2v at both of these with respect to chassis ground.
I have been signal tracing using the rather excellent non propriety Rolson 6mm Titanium Injector. At the relay I can hear the headphone tone and the speaker tone.

On power up I hesitantly touched my Rolson to these pins in turn whereupon the relay clicked in on one side only. No audible tone (or programme material in a later test) The Rolson produces a rough 1kHz tone and the signal is at 3.8V (amplitude?)

I'm purely guessing but probably the relay switches between amp output and headphones. Is the extra voltage enough to click in and hold the relay?
Am I barking up the wrong tree?

it may take me ages to draw a schematic so hopefully I can get a prod in the right direction.

Thanks

 

What is the part number of the power amp devices?

The relay probably is an output disconnect to prevent a loud thump when the amp powers up. It might also disconnect the speakers when the chips or power supply detect an overcurrent. That is common in my audio gear.

Start at the power supply. You have no output coupling capacitors so I'm guessing bipolar source voltages. They might be unregulated but there are three power components in the upper right corner. You can measure across the large filter caps to see if there are equal opposite voltages. Next get a datasheet for the power amp device and measure its power pins.

ak

 

What is the part number of the power amp devices?

The relay probably is an output disconnect to prevent a loud thump when the amp powers up. It might also disconnect the speakers when the chips or power supply detect an overcurrent. That is common in my audio gear.

Start at the power supply. You have no output coupling capacitors so I'm guessing bipolar source voltages. They might be unregulated but there are three power components in the upper right corner. You can measure across the large filter caps to see if there are equal opposite voltages. Next get a datasheet for the power amp device and measure its power pins.

ak

Thjanks AK will do tomorrow. I thnk over current sounds likely due to all the clicking and no sound. It was on 11 for a while . 20 watts into 150 which having googled I still don't know if is bad or good! My laymans hunch is the speakers being big try to drive the amp too hard, amp distorts and being harmonically rich are worked to death so relay cuts in . but WTFDIK?
I didn't think signal tracing the power supply was a sensible move or would achieve anything. I'll get the voltmeter out tomorrow and the pencil and paper.
It is bipolar and there are 3 regulators.

Thanks for solving the relay puzzle. Sometimes trying to find something that seems relevant is very hard esp. when you can buy stuff and not have any clue from the manufacturer what it is - only what it does.

 

Since you don't have a schematic, I think a plan is to start where something works (the power supply, hopefully), and follow along until something doesn't work.

ak

 

Basically good advice. I was curious as to the device numbers. I would also measure the DC voltage across the diodes bridge outputs (going to the caps) to see what they are.

I was figuring out how to straighten out the images with GIMP and MS Paint.

 

A side shot showing the parts on the heat sink might be useful.

 

Ok guys thanks. I tested a few diodes in circuit but I guess that was no good as they are paralleled.
Bill I tried to download some photo packages to do so but then spent 30 mins getting all the secret spam off.
It was my only 1/2 hour of the day!!!!!!!!!!!!!!!

Will do better over weekend.

 

Look for Gimp under a reputable download site. Major Geeks is another forum I used to be fond of, they have a terrific DL section.

Gimp is a major pain in the assets to learn, but it is a complete package. I also use it to make PCBs, it will print to scale accurately. I make toner transfers with it.

If you can you need to power the circuit up and look at the DC out. You might have a bad cap, for example. This will show as around 10mv AC riding on the DC values. If you were to look at it with a oscope you would see the DC dipping all the way to zero volts with narrow spikes.

 

Hello,

The gimp can be found here:
http://www.gimp.org/

If you like photoshop better, but don't want to pay for it, there is GIMPSHOP.
GIMPSHOP is the gimp with a layer on top to have it look like photoshop:
http://www.gimpshop.com/

Bertus

 

I am wearing the Gimp Mask now. thanks guys

 

I went through something similar as you yesterday. I went for Photoshop, and picked up a nasty. So I spent the next couple of hours cleaning them (multiple). A friend reminded me about Gimp, which I already had (Ver. 2.8). It did the trick!

 

Ok Bill here is layered image. any advice on how to best present it?

 

PDF is a pain to work with, so I use the <PrtScn> key to copy the screen, and paste it to a M/S Paint .png file. I manually crop it, and end up with this...

 

Being an old grunt tech I have a lot of experience matching the PCB side to the component side real world.

 

I meant more - is the level of transparency useable - I guess that's quite rhetorical !
reason I use pdf is to upload. Last time I zipped I was zapped. Compression has always been an issue for me - LOL

Well challenge accepted - I'll draw up a schematic.

cheers

 

At this point we don't need a schematic, part numbers would be nice. We also need the voltages across all the big caps, both DC and AC. Schematics might be needed, but one of the basics of troubleshooting is go through the easy stuff first.

 

so I've had some fun this morning:

Primary 0 115 230
Sec 24 0 24 11 0 11 0-3 6 ( I don't get the 0-3 marking)
V Ac 24.2 24.2 10.8 10.8 0 0 (but measured -15.9 Dc on last two wires??)

All secondary wires have cont. with like colour except the two black (??)

Regs.   Vin   Vout
LM7805  14.3   5
LM7808  14.3   7.99
LM7908 -14.56 -8.01

IC LM3886
                             [IC1       IC2 ] All DC
Pin 1                        [33V       32.9] 
Pin 3out                     [-2.7mV    -3.4mV] 
Pin 4V-                      [-32.4 V  -32.4]
Pin 5V+                      [32.9V     32.9V]
Pin 9Vin-                    [-6.3mV    -7.5mV]
Pin10Vin+                    [-3.3mv    -3.4mV]

Same readings as Pin 3 at end of inductors. I can signal inject at pin3 and hear on phones both sides.

No Ac output from IC's (I imagine music is AC!) - conclusion dodgy Chips?

If yes then why is the next problem to solve.

Could be up the wrong tree though - happened b4! Sorry madam.

 

sorry wont let me line up info better.

 

Hello,

You could try to use the code tags.
Then the text is in monospaced font and the spaces are preserved.
I have edited your post using the code tags.
Here I descibed how to use the code tags:
Use of CODE tags

There are more bb-codes available:
bbcode

Not all may work, as the administrator can set if they may be used or not.

Bertus

 

Ok I see - type between the parenthesis not inside. Doh!