Marantz 2270 Power Amplifier Board Parts BOM

[PhilInAudio]

Here is some data that some of you may find helpful, especially when trouble shooting a board. Below is the voltage-across-resistors data that I measured from my properly functioning right channel Power Amplifier Board (P750) prior to the new parts being installed.





I hope this helps.

Phil

 

[catrafter]

I think you may need to use a bias transistor with a higher Vbe.

Tom

 

[PhilInAudio]

Tom thanks for the idea. I did buy the OnSemi MJE243G for H760, but haven't installed it yet given the notes on my BOM. Perhaps I should have read my note again. LOL

OK...I'll install it and see what happens. I'll try to do it this weekend.

By the way, I have jumpers on R784 and R785. The Service Manual calls for 3.9 Ohm resistors to be used in these locations. Why are jumpers used there instead?

After listening to my 2270 for an extended period of time, as of right now, I really love the sound of my 2270!!! I still love the 250M, but the 2270 is just as wonderful! I have owned a lot of great stereo gear in my time, but there is something about the Marantz sound that I just can't put my finger on...it just blows me away!

Again...thanks for the idea and please share any thoughts that you have on the jumpers question.

Phil

 

[catrafter]

I'm glad you are enjoying your Marantz gear.
The resistors in R784 and R785 can be used to control the output bias current. With jumpers in place (zero Ohms resistance) the bias current will be highest.
Not in your case, but if the bias current is too high you could add resistors to decrease the bias current.
Ecluser's case study in this thread covers most everything one needs to know about 2270 power amp bias.

Tom

 

[PhilInAudio]

Tom...thanks for your response.

I have studied Ecluser's case study on biasing the 2270 Power Amp Board (P750). What a fantastic explanation! What caught my attention was the 1,257 mV test point between each of the bases of H758 and H759. This is a fast and easy test point to check and it should render some good insight as to why my bias current is so low. (I'm getting 0.00 mV between J754 and J756 instead of the 5.0 mV specified by the Service Manual.)

I also understand your point about the jumpers at, R784 and R785, that came stock with my 2270. Clearly if resistance is added at these points, the voltage generated from the current passing through the resistors would start to reverse bias the emitter junctions of the transistors, which, as a result, would decrease the bias current. So, in short, adding resistance at R784 and R785 is only good if you need to decrease the bias current. My problem is that I need to increase the bias current so changing the jumpers to any level of resistance would work completely against what I am trying to achieve! Tom, thanks for clarifying this.

I'm still planning on changing out H760 and putting in the brand new OnSemi MJE243G part as you suggested and...if necessary, tinkering with the bias circuit resistance values. Unfortunately, I couldn't do it this weekend. I'll try to get to it tomorrow or Tuesday.

I'll post the results.

Phil

 

[PhilInAudio]

OK..I have time this weekend to work on the 2270's bias issue in the left channel. I'll update everyone shortly.

 

[Aaron99]

OK..I have time this weekend to work on the 2270's bias issue in the left channel. I'll update everyone shortly.

Update?

 

[Steven Tate]

(I'm getting 0.00 mV between J754 and J756 instead of the 5.0 mV specified by the Service Manual.)

Just wanted to make sure you had noticed the test points in the SM are only correct for very early units. For most 2270’s, measure bias between J754 and J760 and adjust to 10mV. This is discussed a couple of times in the Marantz Service Manual error thread.

 

[PhilInAudio]

Sorry, I've been extremely busy for the past year and have been out of touch. Steven Tate...thanks for your last message! I'll recheck my 2270 when I get the chance. The good news is that my 2270 has been running absolutely perfectly since the amplifier section rebuild back at the end of 2017. I would say that the parts identified in my BOM worked perfectly well and I would highly recommend them for any 2270 rebuilding project.

 

[jjsxr9]

This thread is a wealth of information! I am about to begin a restore on my 2270 and have been trying to sponge up as much info as I can. Are you planning on restoring the preamp board?
Thanks for your hard work!

 

[virgilvdog]

can you send me a diagram on how you connected wire to board thank you very much for your idea

 

[JJCalvillo]

I did something to my Marantz 2270 that I'd like to share. At the very beginning of this project, I modified my Power Amplifier Boards (P750) and 2270 chassis by adding connectors to the boards and chassis so that I can easily connect or disconnect the Power Amplifier Boards from my 2270 receiver chassis. There are major benefits to adding these connectors: 1) From a completely assembled 2270, with the connectors, I can disassemble and remove both Power Amplifier Boards in less than 5 minutes! 2) With the connectors, I can easily connect a board, power it up and test it without having to reinstall it! 3) Adding the connectors makes servicing the 2270 relatively pain free.

Here are some pictures of the connectors that I used. Note the boards still have their original Marantz parts on them:

View attachment 1005309

View attachment 1005310

View attachment 1005311

If you are interested in adding the connectors I used, below is a picture of the connector packaging that includes the brand and sku#:

View attachment 1005312


You'll need 16 gauge wire in 6 colors: Red, White, Blue, Green, Yellow and Black. AutoZone has the perfect 16 gauge wire for this application. Their 16 gauge wire is not stiff like so many others. The AutoZone links for 30 foot rolls are:

Red - http://www.autozone.com/miscellaneo...-wire/electrical-wire-primary-wire/163444_0_0
White - http://www.autozone.com/miscellaneo...-wire/electrical-wire-primary-wire/768395_0_0
Blue - http://www.autozone.com/miscellaneo...-wire/electrical-wire-primary-wire/163410_0_0
Green - http://www.autozone.com/miscellaneo...-wire/electrical-wire-primary-wire/150807_0_0
Yellow - http://www.autozone.com/miscellaneo...-wire/electrical-wire-primary-wire/163428_0_0
Black - http://www.autozone.com/miscellaneo...-wire/electrical-wire-primary-wire/163451_0_0

Marantz built my 2270 with 18 gauge wire. I don't know if this was standard practice, but I like using the thicker 16 gauge. The 16 gauge wire just simply has better conducting capability than the 18 gauge and it worked extremely well for me.

Regarding the connectors, the connector contacts have crimp tabs. I used the crimp tabs and then soldered the wire, which resulted in really solid wire connections to the contacts.

If someone else has worked on your 2270, expect that you'll need to rewire a part of the chassis' power lines because you'll find that the previous person had burned too much insulation exposing wires and/or created very tight wire connections by cutting wires too short and re-soldered them to their terminals anyway.

If done properly, it will take you about 2 hours to make the necessary modifications to add the connectors.

If you are not very experienced in electronics and soldering or don't know what you are doing...do not attempt to do this or anything else in this thread. Hire a professional!

Good luck all...please feel free to comment.

Phil

PhilDaMAN!

 

[Steven Tate]

I have thought about putting connectors on my 2270 to make the amp boards removable. The reason I haven't yet is that many of the problems I encountered in my 2275 and 2325 traced back to a bad connection in one of those multiple terminal connectors. I may still do it, but I just have a feeling I'm introducing another place for a connection problem.

 

[JJCalvillo]

Get good connectors and pay attention when you do it.

IMO the benefit is massive. So much easier to access and test the boards. Also if you're worried about connection problems you aren't stressing any wires if they're disconnected.