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Rabbit 16v 21st November 2020 11:19 PM

So, connect speaker to speaker connections, power up amp, make sure neither output ICs are installed and see what I get? Ive powered it up with both ICs removed and rail voltage lines connected from power supply board to audio board and one second tick still happens. Would connecting a speaker to the output side have any change in effect here?

When the amp is ticking (I suspect this is protection mode?), the amp just mutes. I have not put a meter on the rail voltage when its doing this though. I can certainly do that if needed!

Perry Babin 21st November 2020 11:41 PM

Do you have a scope?

I don't have the exact diagram for this amp so I don't know what sort of protection it has (we don't even know if it's actually going into protection). Having a load connected to the output terminals may stop it from going into DC offset protection.

Rabbit 16v 22nd November 2020 12:29 AM

I do have a couple scopes. Ive just been using a Fluke 97 scopemeter for now. I have a Lectrotech single channel scops, but no scale as its missing.

I only have one speaker that I have been using on each channel when testing, but I cant see if everything was fine not having the other channel not connected creating this symptom.

any thoughts on what I might check with the scope?

Perry Babin 22nd November 2020 12:39 AM

If the modules are out, just jump the terminals of each channel with a wire.

A scope will tell you far more than a multimeter. For example, you could immediately tell if the supply was shutting down by looking at the waveform on the primary or secondary windings. Looking at the rail voltage may be misleading because the rail caps could remain charged after the supply shuts down.

Please (and this applies to anyone who needs repair help) use your sig line to list all equipment you have, editing it as equipment changes. Include the model numbers.

Top of page, menu USER CP >> EDIT SIGNATURE

Oscilloscope (yes or no)
Type of signal source (grounded RCA shields preferred).
Soldering iron
Desoldering pump
Power supply
2 ohm current limiting resistor (hollow cylindrical ceramic 100w preferred)

Rabbit 16v 22nd November 2020 01:11 AM

Thanks, will edit. Sorry, Im all new to this. Also, I do appreciate your time and I have been reading your website as well. Seems this IC setup is a bit unique for older amps.

I will try that with ICs out and rails still connected and report back.

also will update with what I have for test equipment. Probably going to get a current limiter of some type so I dont melt anything. That 24a spike after I replaced the transistors threw me for a scare.

Rabbit 16v 23rd November 2020 11:06 PM

Ok, both ICs removed and now for some reason I only have 33V neg on one side. The pos side is at about 1v. Possibly an issue with the cap on the pos side? Or maybe an issue with the rectifier?

Rabbit 16v 23rd November 2020 11:13 PM

No ticking though!

Perry Babin 23rd November 2020 11:23 PM

It's not likely to be a shorted cap. That would cause excessive current draw.

It could be a bad solder joint, open trace, or a defective rectifier (if there is input to the rectifier but nothing on it's output terminal).

Side note, you rarely need a precisely accurate amp meter on your 12v power supply. For the most part, you only need to be able to see movement and be able to see if the change in current is minor or excessive.

Rabbit 16v 24th November 2020 12:02 AM

Ok more testing shows that input to rectifier with rectifier remove is 33vac. still only getting on leg of rail voltage at this point. Swapped in another rectifier just to see, and same result.

Perry Babin 24th November 2020 12:04 AM

What signal are you seeing on the two input legs of the rectifier (rectifier installed)?

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