Need help with Marantz 1060 dead amplifier section

[Bajanbmw]

Hello AKers
I have read almost all the wonderful postings on the Marantz 1060 but would still appreciate some specific input. I bought a 1060 unit many years ago and used it as a preamp only since the power amp section was completely dead on both channels. The preamp section is still very strong and sounds wonderful but I now want to use it as a stand alone integrated so I recapped the board, also upgraded the three big caps with Nichicon caps and installed 4 new MJ21194 transistors all from digikey. Its not completely dead now but I can barely hear that it's coming to life...(extremely weak attempt at sound output) and if I turn volume up slightly it dies. Since both channels are affected I checked voltage at J709 and its about 72 volts. DBT lights up slightly at start up and then goes out. What's my next step short of rebuilding the entire board?
Thanks in advance!

 

[ivandezande]

Hello AKers
I have read almost all the wonderful postings on the Marantz 1060 but would still appreciate some specific input. I bought a 1060 unit many years ago and used it as a preamp only since the power amp section was completely dead on both channels. The preamp section is still very strong and sounds wonderful but I now want to use it as a stand alone integrated so I recapped the board, also upgraded the three big caps with Nichicon caps and installed 4 new MJ21194 transistors all from digikey. Its not completely dead now but I can barely hear that it's coming to life...(extremely weak attempt at sound output) and if I turn volume up slightly it dies. Since both channels are affected I checked voltage at J709 and its about 72 volts. DBT lights up slightly at start up and then goes out. What's my next step short of rebuilding the entire board?
Thanks in advance!

Start checking voltages and transistors on the entire board. Is it biasing? Did you install things correctly?

It was a bad idea to recap it and replace the output transistors before troubleshooting....

 

[Bajanbmw]

Correct...Hindsight is 20/20. I haven't tried biasing since I didn't want to go any further before getting ideas. However I was extremely careful installing the caps and output transistors and did them meticulously. I will continue with your suggestions.

 

[Tubologic]

The voltage at J709 is the main (unregulated) power amp supply voltage rail and anything between 70 and 80VDC is correct, thus your measured voltage is within specs.
The first thing to check are the voltages at J715 and J716 which must be about the half of the supply rail (35 to 40 VDC) and adjustable with the R723/R724 trimpots respectively. CAUTION! if the measured voltages at J715/716 are stuck at full supply voltage (70VDC or more) your speaker output coupling caps C006/C007 (only rated for 55V) are in danger and may leak or explode ! If you can't adjust half supply voltage at J715/716 something is wrong in the amp which must be debugged. Don't forget to check the output stage 0.24 ohms wirewound resistors (R747,748,749,750) which are often found open after power transistors failure.
Then you should check the bias (idle current), the easiest way is to clip a DC voltmeter across J713/J717 (L channel) and J714/718 (R channel) and adjust the bias pots R729/R730 for a reading of 15 mV (0.015 VDC) , a final touch up will be needed after a warmup period of 5 to 10 minutes. It is also recommended to replace all the small electrolytic caps on the power amp PC board, with a special attention to the NFB coupling caps C709/710 which are know to be failure prone in the 1060.

And also don't forget to check if the pre out/main in bridges are present at the back of the amp, I know this is obvious but since you have used the 1060 as a preamp previously and have no sound now on both channels maybe the bridges are simply missing... the 1060 doesn't have automatic pre/main switching phono connectors and external bridges MUST be present for normal use.

 

[Bajanbmw]

Thanks for the suggestions. I checked the voltages and found out there were a few transistors out of spec and also pots that were non functional... I guess from many years of non use. I just went ahead and wiped the board clean and replaced all parts based on information from the many rebuilds on AK. It was not as intimidating as I thought it would be because of all the good documentation available here. The amp section now works for the first time in many years and to my surprise sounds pretty damn good driving a pair of DQ10's. AK rocks!!