Marantz 250M

[hedroom]

Unlike the US/European models, those 250M Japanese versions are factory modified, attached some pics of the power board. When I got the first one, I thought some tech had modified only to realize these are factory mods, when I received 2 more of the same, all from serials 30,000+ and above. I restored the first 2 back to the original design, as I could not find any information on these mods. These power boards also have a standard BJT 2SA1124 in place of the PNP Darlington at location Q503. I did a full restore on the first 2, Pics of the first unit.
View attachment 2424590 View attachment 2424591View attachment 2424593View attachment 2424595 View attachment 2424596

GRonald, I love the way your amp boards turned out... Can you tell me the transistors you used for the pre-drivers and drivers? Also, did you use standard electrolytics to replace the tantalums? I'm in the middle of my restore and any info like that would be greatly appreciated.

Wade

 

[GRonald]

Sure. I will look at my notes.
Can you post a picture of your board as there are four different versions, assuming it is the same as the attachments in your first post. A picture will help too.

Ronnie

 

[GRonald]

The board in my earlier post has the following parts:

C502 - Tantalum to bipolar electrolytic Capacitor. Mouser part 598-106BPA050M
Alternately I have also used Panasonic MPR Film Capacitor with Mouser part 667-ECW-FD2J225J
C503 and C504 - Tantalum to electrolytic Capacitor Mouser part 594-2222-021-27479
PreDrivers (Q510/511) - Omsemi MJE15032/MJE15033 with heat Sinks part numbers 532-577002B00 and 490-HSE-B2111-038
The above requires some additional work, On other boards I have used
PreDrivers (Q510/511) Microchip 2N3440/2N5416 Part No 494-2N3440 and 494-2N5416 Please use the Microchip transistors for this location the other ones at Mouser do not work well.

Drivers: Q516/Q517 I used MJE15032/15033.

Hope that helps.

 

[hedroom]

Here are all of my pictures so far... Marantz 250M Pictures

I'm bringing this thing up to the finish line and my last decisions on components are the drivers everything else is in the works...

I've removed every transistor and cap and most of the resistors and replaced everything that was out of spec and then some

Just looking for someone that has had success with particular components so, any InSite you would have about the model / version or other components would be greatly appreciated.

Wade

 

[hedroom]

The board in my earlier post has the following parts:

C502 - Tantalum to bipolar electrolytic Capacitor. Mouser part 598-106BPA050M
Alternately I have also used Panasonic MPR Film Capacitor with Mouser part 667-ECW-FD2J225J
C503 and C504 - Tantalum to electrolytic Capacitor Mouser part 594-2222-021-27479
PreDrivers (Q510/511) - Omsemi MJE15032/MJE15033 with heat Sinks part numbers 532-577002B00 and 490-HSE-B2111-038
The above requires some additional work, On other boards I have used
PreDrivers (Q510/511) Microchip 2N3440/2N5416 Part No 494-2N3440 and 494-2N5416 Please use the Microchip transistors for this location the other ones at Mouser do not work well.

Drivers: Q516/Q517 I used MJE15032/15033.

Hope that helps.

It Helps a lot! I really like the way you mounted the pre-drivers and driver with the heat sinks. It's making me reconsider that "look"...

 

[GRonald]

It Helps a lot! I really like the way you mounted the pre-drivers and driver with the heat sinks. It's making me reconsider that "look"...

I prefer those as well, and yes, please replace those bias/Dc offset pots; the originals clean well but will cause a lot of intermittent problems down the line.

 

[GRonald]

I am all about the 250/250M and own quite a few units. I prefer to do a full restore as I run them all day and, in the man-cave with no AC most of the times. Since I started doing full restore none of the units have given any problems and I run them hard. The Marantz 2330 is my all-time favorite receiver, but I just keep going back to the 125/7T/33/250M combos. Currently got a custom relay board which I will use to replace the old board don't like bending pins or mounting on top that way it ends up and last but not least a toroidal transformer to kick things up.
Also fixing my 43/4400 units, I eventually plan to run a 43/4400 as a tuner, preamp connected to a 250M and a 500 as a permanent unit in the listening room. Hopefully soon.

 

[hedroom]

In contrast, this 250m project is a "one off" for me... I just want to have a cool system in my music room. found the amp with a Model 3200 pre amp, 150 Tuner and SLT12 turntable, all for $80. All need work but I only want to have to fix them once correctly and get back to collecting and listening to vinyl. I like the fact that you have not had any problems since restoring... That's where I want to be...

 

[hedroom]

I am all about the 250/250M and own quite a few units. I prefer to do a full restore as I run them all day and, in the man-cave with no AC most of the times. Since I started doing full restore none of the units have given any problems and I run them hard. The Marantz 2330 is my all-time favorite receiver, but I just keep going back to the 125/7T/33/250M combos. Currently got a custom relay board which I will use to replace the old board don't like bending pins or mounting on top that way it ends up and last but not least a toroidal transformer to kick things up.
Also fixing my 43/4400 units, I eventually plan to run a 43/4400 as a tuner, preamp connected to a 250M and a 500 as a permanent unit in the listening room. Hopefully soon.

Is your custom relay board something that you make yourself or do you have it made someplace like PCBway?

I fabricated an adapter board for my relay and it works but is a bit unsightly...

 

[ocdecio]

I much rather prefer to reroute the wires on a LY2 type relay:

 

[hedroom]

I prefer those as well, and yes, please replace those bias/Dc offset pots; the originals clean well but will cause a lot of intermittent problems down the line.

So, let me send you back to your notes... What are the specs on the pots you use for your rebuilds? i.e. the ones in your pictures look quite nice. Although adjusting while the board is in place might be a problem...

W

 

[GRonald]

Is your custom relay board something that you make yourself or do you have it made someplace like PCBway?

I fabricated an adapter board for my relay and it works but is a bit unsightly...

I am in the process of getting a board with two separate relay circuits and Ly2 relays.
Have a look here https://audiokarma.org/forums/index.php?threads/marantz-2385-l-channel-out.993203/
This is a smaller board we made to fit in the 2500/2600/2385 with LY2 relays. Its available from AudioKarma Member George (@ton4eff) on request.
You can do what @ocdecio has mentioned in his post, you have to open the relay and rewire, or you can rewire the board. There are quite a few good posts on doing the same.

 

[GRonald]

So, let me send you back to your notes... What are the specs on the pots you use for your rebuilds? i.e. the ones in your pictures look quite nice. Although adjusting while the board is in place might be a problem...

W

Look at this at Mouser, 858-93PR100LF (for bias)
I have these type.

 

[hedroom]

The board in my earlier post has the following parts:

C502 - Tantalum to bipolar electrolytic Capacitor. Mouser part 598-106BPA050M
Alternately I have also used Panasonic MPR Film Capacitor with Mouser part 667-ECW-FD2J225J
C503 and C504 - Tantalum to electrolytic Capacitor Mouser part 594-2222-021-27479
PreDrivers (Q510/511) - Omsemi MJE15032/MJE15033 with heat Sinks part numbers 532-577002B00 and 490-HSE-B2111-038
The above requires some additional work, On other boards I have used
PreDrivers (Q510/511) Microchip 2N3440/2N5416 Part No 494-2N3440 and 494-2N5416 Please use the Microchip transistors for this location the other ones at Mouser do not work well.

Drivers: Q516/Q517 I used MJE15032/15033.

Hope that helps.

So, why do you have different values for C502 vs C503 & C504? My parts list and schematic show all three to be 10 MFD.
Also, what about the weird electrolytic C527? I don't see it on your rebuild... Looks like a jumper is there.

Once again, thanks for the help. I'm really feeling good about the outcome and I'm getting close (Kinda)...

W

 

[GRonald]

So, why do you have different values for C502 vs C503 & C504? My parts list and schematic show all three to be 10 MFD.
Also, what about the weird electrolytic C527? I don't see it on your rebuild... Looks like a jumper is there.

Once again, thanks for the help. I'm really feeling good about the outcome and I'm getting close (Kinda)...

W

Different function. C502 vs C503 & C504?.

electrolytic C527

Use a standard radial electrolytic low impedance capacitor, this one is in parallel with a 10 ohms resistor and is used for noise reduction from source (explanation will be lengthy). In my humble onion it causes more issues than resolves them. So, I bypass it with a jumper. You don't have to do the same unless your amp is oscillating.

 

[hedroom]

So here's where I am with my Marantz 250M.

I've rebuilt the relay board with a new relay, caps and resistors. It's tested and is working properly.

The power supply board was in good shape but I did replace the 2 bleeder resistors.

I have replaced all of the resistors on the right channel board with the exception of R513 & R519 both of which are precision resistors that I don't have replacements for yet.

I've replaced some of the mica caps that were out of spec but most of those were dead on within spec...

Replaced the electrolytic cap C507, still deciding on the tants but I have electrolytic replacements for them if I need them (I do plan to change these out). I did not change any of the yellow Philips caps they were all good and the way I understand it, they very rarely go bad.

The only semiconductors I've replaced are the pre-drivers the drivers and the outputs. I have replacements for all of the others but I'm reluctant to wholesale change out the transistors before I put it on the bench for testing. I have removed all of the transistors individually and tested them. They all tested within their datasheet specs.

I put power to the right channel using a DBT and it seems that I was successful with getting it back together correctly. I was able to set DC offset and bias current as per the service manual. I also injects a 1kHZ/1V signal at the input and received a very clean sine wave at the output of about 19V. This was just a "smoke" test for now more testing to come after the other channel is complete.

Still deciding on the DC offset and bias pots. They are difficult to adjust in that they are very sensitive. Does replacing these pots improve the adjustability or is that just the nature of the beast? I've seen them replaced with 1-watt trimmers (as in GRonald's excellent example). I'm wondering if anyone who has done that can speak to the "adjustability" of these settings. I did pull one of the pots from my board and had a difficult time with it so if I don't need to pull them that would be ok with me.

I'm wondering is anyone has used the 2N3904/2N3906 as replacements for 2N4123/2N4125? The gain on my new components is so much higher than the old.

I've attached before and after pics...

Here is my semiconductor list:

Q507	TRANSISTOR, PNP, 2N3931	2N5415
Q508	TRANSISTOR, NPN, S40447	2N3440
Q510	TRANSISTOR, NPN, S40445	2SC783
Q511	TRANSISTOR, PNP, S40446	2SA483
Q501	TRANSISTOR, NPN, 2N5961	Still Available
Q502	TRANSISTOR, NPN, 2N5961	Still Available
Q503	TRANSISTOR, PNP, MPSA65	Still Available
Q504	TRANSISTOR, NPN, SPS1951	BC547B
Q505	TRANSISTOR, PNP, 2N4125	2N3906
Q506	TRANSISTOR, NPN, 2N4123	2N3904
Q516	TRANSISTOR, NPN, MPSA43	NTE287
Q517	TRANSISTOR, PNP, MPSA93	Still Available
Q518	TRANSISTOR, PNP, MPS6519	BC557
Q519	TRANSISTOR, NPN, SPS1928	BC550C
Q520	TRANSISTOR, NPN, 2N4123	2N3904
Q521	TRANSISTOR, PNP, MPS6519	BC557
Q801	TRANSISTOR, NPN, MJE180	Still Available
Q803	TRANSISTOR, NPN, SJ2519	MJ21194G
Q805	TRANSISTOR, NPN, SJ2519	MJ21194G
Q802	TRANSISTOR, PNP, SJ2520	MJ21193G
Q804	TRANSISTOR, PNP, SJ2520	MJ21193G

 

[hedroom]

I've made quite a bit of progress on this project. I have completed both boards and have them reassembled. I've run them up to full voltage without an input load and checked all of the voltages listed on the "Component Side" figure on page 22. I started with the bottom right -14.3 volt at R510 and moved counterclockwise around the board and checked all 30 points. (see attached PDF). Both channels run very stable with idle current and the bias holds steady at 12mV and the DC offset remains right at 0V. An 8 Ohm dummy speaker load was attached.

Having done that I have some questions.

The DC voltage at the C1/C2 caps is 60.3 VDC as opposed to the specified 58.5 VDC. All if the measurements that I've taken (see attached voltages PDF) are close but a little off. I'm suspecting the mains line voltage...

The line voltage at my residence is 121.5 VAC (a little high). The Transformer secondary measures 88.2/43.9/4.9 VAC (I did not see a spec for this).

The C1 & C2 caps are 20,000/100 as opposed to the original 22,000/60. Is that a factor?

The bleeder resistors R601/R602 were changed out to 3 watt components. They seem to run hot. I this normal? Along with the R517/R518... They get rather warm also... My heat gun puts them in 150-170 deg range. Just wondering if this is correct behavior?

So is this close enough or is there some adjustment that I can make?

Also, when a single channel is powered up, it will draw ~41.3 watts. Does that sound about right?

I've also attached a new transistor substitution list. The one I attached in the previous post had some mistakes...

Cheers,

Wade

 

[GRonald]

I've made quite a bit of progress on this project. I have completed both boards and have them reassembled. I've run them up to full voltage without an input load and checked all of the voltages listed on the "Component Side" figure on page 22. I started with the bottom right -14.3 volt at R510 and moved counterclockwise around the board and checked all 30 points. (see attached PDF). Both channels run very stable with idle current and the bias holds steady at 12mV and the DC offset remains right at 0V. An 8 Ohm dummy speaker load was attached.

Having done that I have some questions.

The DC voltage at the C1/C2 caps is 60.3 VDC as opposed to the specified 58.5 VDC. All if the measurements that I've taken (see attached voltages PDF) are close but a little off. I'm suspecting the mains line voltage...

This is normal with most 250M units, the voltage will drop to 57.5 volts as you drive the amp above 10 watts. The exception here is the Japanese versions which run 56.5 volts rail voltage, but again there are too many Japanese versions to be accurate for each version they put out.

The line voltage at my residence is 121.5 VAC (a little high). The Transformer secondary measures 88.2/43.9/4.9 VAC (I did not see a spec for this).

Those voltages are fine, although for the 4.9Volts for the lamps I get 5.8volts to 6.1 volts.

The C1 & C2 caps are 20,000/100 as opposed to the original 22,000/60. Is that a factor?

No. this is fine, I use 22,000.00/80Volts.

The bleeder resistors R601/R602 were changed out to 3 watt components. They seem to run hot. I this normal? Along with the R517/R518... They get rather warm also... My heat gun puts them in 150-170 deg range. Just wondering if this is correct behavior?

Yes, they run hot, and this is normal.

So is this close enough or is there some adjustment that I can make?

No need for further adjustments, have you done the power output clipping adjustment in the manual.

Also, when a single channel is powered up, it will draw ~41.3 watts. Does that sound about right?

I've also attached a new transistor substitution list. The one I attached in the previous post had some mistakes...

With both channels connected and zero input (input shorted with a 600 ohms resistor plug) Power drawn is generally between 45 watts to 80 watts, depending on the bias. I run my own units with the bias set around 17.5 mv. Unit runs a bit warm, but S/N figure are the best at this setting and so is the sound.

Cheers,

Wade

One advise, whatever you do, do not power on the unit with bias transistor disconnected.

 

[GRonald]

I have replaced all of the resistors on the right channel board with the exception of R513 & R519 both of which are precision resistors that I don't have replacements for yet.

You can use Vishay CPF2 resistors in there.

Replaced the electrolytic cap C507, still deciding on the tants but I have electrolytic replacements for them if I need them (I do plan to change these out). I did not change any of the yellow Philips caps they were all good and the way I understand it, they very rarely go bad.

I disagree on those yellow caps. those caps are in crucial position, they are the first to go in my units, I replace them with Panasonic higher voltage rating MPR capacitors (667-ECW-H6104HC). Including that .22uf capacitors (ECW-F4224HL). 10 years back I did not replace them but now I do.

I'm wondering is anyone has used the 2N3904/2N3906 as replacements for 2N4123/2N4125? The gain on my new components is so much higher than the old.

They will do the job fine. In my units that run all day in my workshop/man-cave I use ZTX651/751STZ

I've attached before and after pics...

Here is my semiconductor list:

Q507	TRANSISTOR, PNP, 2N3931	2N5415
Q508	TRANSISTOR, NPN, S40447	2N3440
Q510	TRANSISTOR, NPN, S40445	2SC783
Q511	TRANSISTOR, PNP, S40446	2SA483
Q501	TRANSISTOR, NPN, 2N5961	Still Available
Q502	TRANSISTOR, NPN, 2N5961	Still Available
Q503	TRANSISTOR, PNP, MPSA65	Still Available
Q504	TRANSISTOR, NPN, SPS1951	BC547B
Q505	TRANSISTOR, PNP, 2N4125	2N3906
Q506	TRANSISTOR, NPN, 2N4123	2N3904
Q516	TRANSISTOR, NPN, MPSA43	NTE287
Q517	TRANSISTOR, PNP, MPSA93	Still Available
Q518	TRANSISTOR, PNP, MPS6519	BC557
Q519	TRANSISTOR, NPN, SPS1928	BC550C
Q520	TRANSISTOR, NPN, 2N4123	2N3904
Q521	TRANSISTOR, PNP, MPS6519	BC557
Q801	TRANSISTOR, NPN, MJE180	Still Available
Q803	TRANSISTOR, NPN, SJ2519	MJ21194G
Q805	TRANSISTOR, NPN, SJ2519	MJ21194G
Q802	TRANSISTOR, PNP, SJ2520	MJ21193G
Q804	TRANSISTOR, PNP, SJ2520	MJ21193G

Q516/Q517 I use ZTX series as well. (ZTX757STZ) and (ZTX657STZ)
for the Q503 the MSA65 will work ok (I don't trust those available from central semiconductors), there is a better On-semi-Darlington (BC516-D27Z) that has worked well for me over the last decade.

 

[hedroom]

Man, you are really working me.... So, I'm doing the yellow caps... So, what about the mica caps? do you change all of those out also?

I'm trying to put my last Mouser order together for this project... I know, wishful thinking...

I am really indebted for the help you've give me...