Just got a Au x1 and of coarse need info

[Harolda]

View attachment 989509 Yes, I will be using the phono mm section. It sounds excellent. The left channel still has a problem on phono 1 or 2 unless I HIT it hard on the side then everything works perfect.

The phone boards are recapped and waiting for the order to come in with trimmer pots to replace.

I have adjusted all of the amp, but have the infamous "unable to get -10.5 volts from trimmer" it runs out of adjustment. It's also waiting on that shipment for the grounding capacitors mod.

Here are some pictures so farView attachment 989504View attachment 989505

Make sure to clean all switches, that could solve your issue with the phono. Also the small relays might be the problem.
Good job on the recap, did you also replace the double diodes on the phono boards and on the power supply? The last mod is sometimes questionable, but I replaced those, just like John.
To get the desired -10.5v you would have to replace two resistors r73 and r74 from 5.6k to 3.9k to reduce the voltage drop over the trimmer circuit and so to increase your output voltage. Look at John's posts about this.

 

[Bigdrive]

Resistors, yes I have switched them to 3.9k. Trimmers are installed on power supply board, vr1-vr4.

I will be cleaning switches tonight. I believe it's the switches causing the problem, so they will all be cleaned. If that does not fix it, I will replace relays.

Just want to verify the v1212 should be replaced with 1n4148 general purpose diodes as discussed in several places on the forum and does the final product look like picture above?

 

[Harolda]

Yes your replacement is correct

 

[Bigdrive]

Update....

The good news,

1)Trim pots, V1212's and resistor value changed from 5.6k to 3.9k all changed on regulated PSB.
2)Switches all disassembled and cleaned.
3)Molex connectors all de-pinned inspected and retensioned.
3)Installed grounding caps mod on flat amp.
4)Replaced all four Phono relays so it was all done.
5)Lamps all replaced

The bad news,

Started it up with phono boards removed to get a basic reading from regulated PSB. Nothing on TP1 and TP2 and -50 ish on TP3 and TP4. Started to adjust TP4 and thought I seen some smoke.....the loud bang confirmed I had seen smoke! 1000uf@16 on regulated PSB exploded on left mc power supply.

Upon checking found I had crossed a yellow and white coming off of the power supply to the regulated PSB. I will provide pictures of it next post. Corrected the crossed wires and replaced cap. Adjusted TP1-4 with no problems. With the change of resistor I had -11.5 on TP1 and TP2 before adjusting down.

Ran it for several hours to ensure voltages are stable. Phono cards still have not been installed yet. Replaced the trimpot on mc 2770 and 2771 and installed card. Relays work OK. I had had a problem on L/H phono going in and out and it is now all gone

BUT, here is my problem.

Both l/h and r/h voltages are not steady. The l/h is worse than the r/h. They drift .001 of a volt every 3 seconds. in other words if l/h is at 0mv when you start and you listen to an album at the end it will be -.243v The r/h does it also but about 1/2 as bad. It seems to be temp orientated. Regulated power supply is rock steady at -10.5 both channels.

Any suggestions?

 

[Bigdrive]

Here are the pics

 

[Harolda]

You are talking about drift in dc voltage on the mc and mm boards? There has been discussion about dc drift on the Mc boards on this forum in the past. There was also a solution presented to this somewhere. I am currently also installing my phono boards and I still have to check wether there is an issue with this dc drift.

i did a complete upgrade of the boards to a later version and I removed the ceramic cap to chassis on the mc boards as advised by some. Later versions also do not have this cap. I hope to get an idea today on where I stand with the dc stability

 

[Bigdrive]

I will some searching.

When you say you upgraded yours to the latest version do you have a list of changes you made?

 

[Bigdrive]

I have beefed up the grounding on the 2771 card and removed the ceramic capacitor as per attached pics

 

[Bigdrive]

I put one card in and checked voltages.

It turned on at -.220v and within two minutes increased to .020v. From there it slowly cycled to .000 then up to .010.

Is it fixed, I don't think so. I did not have the player connected for obvious reasons, but tomorrow I will finish the other card and do some more reading. Then work the amp with some vinyle.

It has the 4 relay, first version, would it help going to the six relay board?

 

[Willy6]

View attachment 993145 I put one card in and checked voltages.

It turned on at -.220v and within two minutes increased to .020v. From there it slowly cycled to .000 then up to .010.

Is it fixed, I don't think so. I did not have the player connected for obvious reasons, but tomorrow I will finish the other card and do some more reading. Then work the amp with some vinyle.

It has the 4 relay, first version, would it help going to the six relay board? View attachment 993145

Did you apply the Martin Kuehne grounding modification?I'm still running the first version with his mod with zero problems..

 

[Bigdrive]

Yes, the flat amp has had the 10mkt grounding mod and the MM board f-2771/70 have had the grounding paths increased and ceramic cap on the back removed. No mods done to MC cards as they will not be used and are not installed during the voltage checks.

It has not had the cap and resistor added to the double FET on the flat amp, but I think that is for a different problem.

Does the shield need to be installed to get a better ground when taking the measurement?

Sorry if its a stupid question, I was up until 2am reading your 34 page fight you had with

 

[Bigdrive]

dame enter button!!!!

you had with your beauty. Well done

 

[Bigdrive]

I think I found the problem.

I was using a chassis ground instead of star ground. When I switched to star both channels were adjustable to within limits. The hint was entries made about bias adjusting and using emitter output instead of the pins.

Although I have been paying close attention to grounds, there still maybe a problem . I will look closer at this when the drivers come out again next week for trimmer replacement and diode replacements and pin repairs, someone just cut the wires off rather then desoulder!!! They were nice enough to leave the pins

Question, should not all points on chassis be as good as the star ground?

 

[Willy6]

dame enter button!!!!

you had with your beauty. Well done

I was learning along the way on mine and I found out later that I had everything right the first time but kept second guessing myself and making things more difficult then they really were..

 

[Willy6]

I think I found the problem.

I was using a chassis ground instead of star ground. When I switched to star both channels were adjustable to within limits. The hint was entries made about bias adjusting and using emitter output instead of the pins.

Although I have been paying close attention to grounds, there still maybe a problem . I will look closer at this when the drivers come out again next week for trimmer replacement and diode replacements and pin repairs, someone just cut the wires off rather then desoulder!!! They were nice enough to leave the pins

Question, should not all points on chassis be as good as the star ground?

I found out later that the wires from the test point pins are soldered to the wrong spot on the outputs I'll take pic of the change I made and post it here soon.

 

[Willy6]

On board F-2772 If you follow the traces from the tps they lead to 17 and 18 on the other side of the board and there are two wires one black (17) and one white (18) the factory made a mistake and put the white wire (18) on the wrong side of the op transistor. As you can see with these pics I moved the white wire to the other side of the op and now the test points work like they should..

 

[Bigdrive]

Thanks, just getting ready to put amp back in. I made the correction.

Had to remove and clean the outputs! This is in the middle of cleaning, paste was all over pins, in socket, everywhere.

 

[Bigdrive]

Does anybody have a part number for these?

 

[Bigdrive]

I was going to order these from digikey but want to be sure.

A111033CT-ND

 

[Bigdrive]

Got second driver amp out and was labelling output transistors positions and realized that if the amp is rotated 180 degrees, #1 would be on the other side.

Better check pictures of first amp to be sure, like it's been said check, check and check ten more times.
Transistors were in backwards

I took them out to switch them around and noticed that the thermal grease was not contacting as much as 50% of some transistors
When I put a straight edge across the fastening points a piece of paper could be pulled through.
I also realized that the insulators were trashed and where the legs go through were signifantly higher than the .0028 of the rest of the insulator to the tune of .006

The screws are all just about striped because of what I call valve cover syndrome. If they leak oil just tighten the shit out the screws
Bottom line the transistors are bent about .0025. So on a flat surface and 400 grit sandpaper I have taken some of it out. Not all, just some. The material on the bottom is thin and then goes to copper. I have not gone down to the copper.
The new insulators are .0028 and I will check the grease footprint on all before assembly.
Here is a picture of one done. Disregard insulator, it will be replaced before installation.