autotek model 44 repair help

[grandam88]

Alright I have a autotek model 44 previously had issues with powering into protect mode. Replaced n4751 @zd1 next to ohm load switch. Switch selects between 1 and 2 ohms. Amp powers up now with input level turned down to lowest level if you turn of all the way up it goes to protect with no speakers or RCA cables connected. Connected RCA cables and a 3 ohm speaker up to channel 1with audio playing. No sound at all but speakers does full excursion in then out then rests. Does repeatedly. Does this on both channels. When speaker is bridged does nothing.

Tested all output fets all test fine.

[timwebb]

u check the output driver transistors?

[grandam88]

if your talking about the output fets.transistors, yes i did. If not, please inform me of what they look like.

thanks

[Perry Babin]

Can you post a photo of the board so I can see precisely which amp this is?

[grandam88]

as you can see the board got kind of "crispy" where the diode i guess it is blew. previous owner said he ran it below 1 ohm maybe even with switch in 2 ohm position. the amp is an autotek 44 revision d.

[Perry Babin]

What's the resistance between the RCA shields and the non-bridging speaker terminals?

If you place the black probe on one of the non-bridging speaker terminals, what is the DC voltage on pins 4 and 11 of the 14-pin op-amps?

With no speakers connected, what's the DC voltage measured directly across the speaker terminals for each channel? Place the black probe on the non-bridging speaker terminal when reading the voltage on both channels.

[grandam88]

alright, resistance between rca shields and non bridging terminals is .4 on both terminals and both shields, which is the resistance of my probes touching, so 0 ohms.

secondly, i assumed when you said 14 pin op-amps, you meant the 3 14-pin ic chips.

if so then here are the measurements. as labeled on board.

ic-101
pin 4(19.55)
pin 11(11.67)

ic-201
pin4(19.63)
pin11(11.26)

ic-3
pin4(11.45)
pin11(11.09)

lastly w/no speakers connected the dc voltage measured directly across speaker terminals on each channel was

ch.1(.17)
ch.2(.15) fluctuating to (-.20)

If i a wrong about the op amps, please let me know what they look like. thanks

[Perry Babin]

What were you using for a signal source when the speaker was pulsing in and out?

[grandam88]

Car radio. RCA s and radio work fine on another amp

[Perry Babin]

Are the RCA shields on the head unit OK (0 ohms to the case of the head unit)?

Is the head unit ground connected to the amp ground?