I was able to get the amp to a stable power-on state with a 30a fuse - all I really did was change the orientation of the POS card. The center leg of the power fets are showing this on the oScope (10 v/div @ 5uS).
I'm also getting some very strange voltage readings from the transformer coil. ~40vAC from bottom left to bottom right 'outside' pads sound right? (Referenced picture) I thought this should be up to ~80vAC.
I'm also getting some very strange voltage readings from the transformer coil. ~40vAC from bottom left to bottom right 'outside' pads sound right? (Referenced picture) I thought this should be up to ~80vAC.
Yup that fixed it. I've got sound from both channels using the frequency generator. Thats a first for this amp in awhile! At this point I wouldnt say the sound is very clean as the bias pots are all the way counter-clockwise but the amp is definately able to produce audio from RCA.
Now, how can I make this amplifier naturally turn on? Im jumping pin 16 of the 494 to ground.
Now, how can I make this amplifier naturally turn on? Im jumping pin 16 of the 494 to ground.
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Just confirmed a 10A will allow the amp to power and play. I think this POS or MOS card whatever you call it when installed in some other direction this amp wants to pop 30A fuses. That being said, im starting to think resistor install must have shorted out some of the protection circuit as the power and output transistors are checking out OK. I wonder why Steve said I needed new power fets...
I really wish I knew how to install this card. I found an original manual online and it was no help. Its like the card can be installed rightside-up or upside-down as well as frontwards and backwards - 4 ways total. Which way is the "Front" of the amplifier?
I really wish I knew how to install this card. I found an original manual online and it was no help. Its like the card can be installed rightside-up or upside-down as well as frontwards and backwards - 4 ways total. Which way is the "Front" of the amplifier?
You may want to take a pencil eraser or a fiberglass scratch brush and clean the fingers in that card.
I think the top photo would be the way to install it for normal operation. Does it blow the fuse when installed that way?
Does the POS light come on when you install it facing the opposite direction?
I think the front would be the front panel with the controls.
I think the top photo would be the way to install it for normal operation. Does it blow the fuse when installed that way?
Does the POS light come on when you install it facing the opposite direction?
I think the front would be the front panel with the controls.
As pictured, the amp powers and plays with a 10A fuse (as long as I ground pin 16 of the 494). The way I have the card installed is with the "Stereo / Bridged" facing the amp controls. It seems like that is how it is running - L and R RCAs coorespond to what is being outputted at the speaker terminals.
Unfortunatly all but one incandecent bulbs on this amp are burnt out so i cant really tell if the amp is going into POS mode. I do want to replace these bulbs eventually. I'll try testing if POS enables with my DVM. Can I use LEDs to replace these bulbs?
Unfortunatly all but one incandecent bulbs on this amp are burnt out so i cant really tell if the amp is going into POS mode. I do want to replace these bulbs eventually. I'll try testing if POS enables with my DVM. Can I use LEDs to replace these bulbs?
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If you install the card so that it doesn't blow the fuse, will it work if you reconnect pin 16 to it's proper place on the board?
You should be able to replace them. If the original lamps were in series, it will be simple. You'll only need to insert a single current limiting resistor.
If they are in parallel, you'll have to insert a resistor in series with each one or modify the circuit board to allow you to connect them in series.
I'm assuming that they all work together and are not independent indicators.
Are you 100% sure that this module is supposed to work in all 4 orientations with this amp. Maybe it's only supposed to work with the text right side up.
You should be able to replace them. If the original lamps were in series, it will be simple. You'll only need to insert a single current limiting resistor.
If they are in parallel, you'll have to insert a resistor in series with each one or modify the circuit board to allow you to connect them in series.
I'm assuming that they all work together and are not independent indicators.
Are you 100% sure that this module is supposed to work in all 4 orientations with this amp. Maybe it's only supposed to work with the text right side up.
I'm not 100% sure about anything with the POS module. The only thing I'm sure of is the designer called it a POS for a reason lol. it seems that one way the module shorts out almost half the pins. I wonder if in that direction the module is designed to put the amp into test/diagnostic mode.
I'm going to leave it exactly the way it is pictured i nthe above shots.
I tried jumping the 494's ping 16 back to its intended pad but the amp wont power up.
I'm going to leave it exactly the way it is pictured i nthe above shots.
I tried jumping the 494's ping 16 back to its intended pad but the amp wont power up.
Now that you know that the amp is working as it should and there is no reason for it to shut down, you can go back to trying to determine why the LM339 doesn't have power. Have you tried feeding the 339 12v through a 1 amp fuse or through a 1 ohm 1/4w resistor to see if that would allow the amp to power up with pin 16 connected to the board?
I believe that's what you should have. You can check for continuity from pin 12 to ground. I doubt that the IC would be fed with 5v. It's likely that it's supposed to be fed with 12v. In some of the older Autotek amps, the remote fed the comparator (LM393, not LM339) via a diode in one of the modules.
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