Marantz 4300 Update & question.

[(*steve*)]

Isn't the output a complementary pair? Or are there multiple pairs?

It looks like we've changes threads at some point and that information is lost in the other thread (more reasons for not starting new threads).

I'm working from memory. Post the circuit diagram again and tell me which transistor it is and what you have available to replace it with.

 

[mrmodify]

I don't know if they are complementary pairs or not. There are 4 sets of outputs. The NTE's are matched pairs.

I never thought about the issue with starting another thread. I was worried about thread getting to long. And it helps you.

The transistor that shows funny is H002 a NPN 2SC1403.

The originals from the factory are 4 2SA745's & 4 2SC1403's. When I received the unit it had 2 2SA745's & 2 2SC1403's & 2 2SD424's & 2 2SB600's which the later 2 are wrong and also were fried.

I found 2 sets of the suppose to be original transistors from a company in japan. I ordered them but was warned about these parts are possibly knock offs. I bought a couple of pairs of NTE 280 & NTE 281's since I have had good luck with NTE, ECG & SK's. The last set of NTE's I bought were matched pairs (NTE281MCP)

I have 3 nos ECG 280's from years ago.

This whole time I have had the 2SA745's and the 2SC1403's in the front left channel and the NTE's in the rear left channel.

Yesterday I removed the NTE's and installed the set of 2SA745 & the 2SC1403 to make all the outputs the same brand. The amp did the same thing but with a fm signal it was at a lower volume. No input it will let you go full volume.

 

[(*steve*)]

Yeah, there's only one pair of transistors for each output. As you have replaced these transistors, has the fault changed at all, i.e. moved from one channel to another?

Is it possible to remove or disconnect all but a known working channel and test that? with a signal, see if you can go from zero to full volume. See what it does with both the series bulb connected and not connected. Then try it (with the series bulb) with a channel that is presumed faulty and as you increase the volume level, note the first difference and stop there.

You want to measure power supply current and output offset voltage. Do the tests with a dummy load.

I am concerned that we're going in circles. Going and changing all the output transistors essentially resets everything meaning that we need to repeat all the tests we've done. It's better to change a minimum of things so we can see if there's improvement or not.

 

[mrmodify]

Evening Steve, I don't want to do the circle thing. Think I've been there.

Today I checked the right channel board and looked at the voltage measurements we took a while back. The volts on the base terminal on H711 was equal to the emitter and collector so I confirmed this and then removed it and checked it, It was open.

I checked H727 and it was good, I compared it to H728 and the readings were different. This varistor was bad when I first started and I replaced it with one I built it from information from a tec that use to be at work.

H727 was built from 2 1N4148 diodes epoxied to the original varistor.

Powered up receiver and bulb had a glow but not bright. I decided to try to adjust the bias. R739 would not adjust below 19mv. I needed 12mv.

I removed H727 and installed one from the left channel board that was very close to H728. Adjusted bias and all was fine. No smoke no oscilliation.

Changed selector knob to FM and feed signal through amp with dummy load. At about 1/2 volume the collector resistors, the 10ohm ones, smoked a little but unit did not start to oscillate.

H727 is called a Varistor - STV-3H(Y) They are no longer made as far as I can tell. NTE has no replacement. I did some research and found a blog on these diodes. They say you can use 3 1N4148 mounted to heatsink and this should work. I did find the specs on the STV 3H.

I also found out that a ECG605A is suppose to replace the STV-3H.

When you have time, Would you mind looking at the specs and see if you think the 3 1N4148 or the ECG605A diodes will work?

I still have to research the left board yet but one step at a time.

 

[(*steve*)]

I checked H727 and it was good, I compared it to H728 and the readings were different. This varistor was bad when I first started and I replaced it with one I built it from information from a tec that use to be at work.

The circuit diagram certainly seems to suggest that three diodes would be required for two of them and two diodes for the other two. I see no reason why that choice of diode would not be fine. My understanding is that these are there to provide a voltage reference that varies with temperature like n x a PN junction and is often used for temperature compensation or as part of a constant current source.

H727 was built from 2 1N4148 diodes epoxied to the original varistor.

Shouldn't H727 be three diodes? And what varistor was the original component mounted to? OK, I see, they call this diode thing a varistor. I presume they're mounted to a heatsink with the output transistors?

I removed H727 and installed one from the left channel board that was very close to H728. Adjusted bias and all was fine. No smoke no oscilliation.

OK, so it was fixed by grabbing the one from the other board. I would try a replacement with three 1N4148s to see if that also works (because I assume you need to replace the one on the other board...)

Lots of suggestions to replace them with 1N914's or 1N4148's (and these are pretty similar diodes). SO you're clearly on the right track there.

Good to see that you got the bias right

Changed selector knob to FM and feed signal through amp with dummy load. At about 1/2 volume the collector resistors, the 10ohm ones, smoked a little but unit did not start to oscillate.

Yep, smoke is expected. You might want to check the resistance of those resistors and just make sure they're not way different from 10R

I also found out that a ECG605A is suppose to replace the STV-3H.

I don't like them. Firstly because they don't appear to be easily mounted to a heatsink (and I think the originals may be). Secondly, the Vf seems too low. Sounds like 2 PN junctions, not 3.

When you have time, Would you mind looking at the specs and see if you think the 3 1N4148 or the ECG605A diodes will work?

I'd tend to go the three individual diodes.

The right board sounds like it is going much better now. If everything is stable, you might like to:

1) test the DC offset of the output at levels up to 1/2 volume
2) remove the 10R resistors and repeat (If the first test yields acceptable results)
3) continue up to full volume (briefly)
4) try connecting a speaker

Each step involves additional risk, try to be sure before you take each step that everything is stable and within spec. When you remove the 10R resistors, recheck the bias settings. I don't believe they should need tweaking, but best to be sure.

And as you say, then on to the other amplifier.

The advantage of having one channel that is known good is that you can then compare voltages between them. That should make fault finding a case of "spot the difference" (fingers crossed)

 

[mrmodify]

Yeah, there's only one pair of transistors for each output. As you have replaced these transistors, has the fault changed at all, i.e. moved from one channel to another?

No it has stayed the same. It would just burn parts. but mostly the front channels on both sides.

Shouldn't H727 be three diodes? And what varistor was the original component mounted to? OK, I see, they call this diode thing a varistor. I presume they're mounted to a heatsink with the output transistors?

I don't understand the difference for two or three diodes.The tec at work told me to use 2. The varistors are mounted on the driver transistors heatsinks H713,H714,H715,H716. The outputs are on mounted on a seperate heatsink.

Is it possible to remove or disconnect all but a known working channel and test that?

From what I have learned when amp is in 4 channel mode each amplifier becomes its own speaker driver. When in 2 channel mode the front channel drives the positive speaker terminal and the rear amp drives the negative speaker terminal by using a phase converter board to invert the signal.

The reciever will works fine when in 4 channel mode. In 2 channel mode it would burn both sides. I have only been working with one side at a time.


I have to purchase some more outputs. Do I need to purchase matched pairs or does it matter?

When you answer the above question can you clue me in on how you determined the answer?

Does it matter if the front channel is one brand and the rear channel is another brand?

Does it matter if the varistor in one channel is different than the other three?

 

[(*steve*)]

I don't understand the difference for two or three diodes.The tec at work told me to use 2. The varistors are mounted on the driver transistors heatsinks H713,H714,H715,H716. The outputs are on mounted on a seperate heatsink.

The ones with a symbol showing three diodes need three diodes, the ones with the symbols showing two diodes need two.

These are very important for the temperature stability of the amplifier. They are typically mounted on a heatsink with the transistor they're in the bias circuit of.

From what I have learned when amp is in 4 channel mode each amplifier becomes its own speaker driver. When in 2 channel mode the front channel drives the positive speaker terminal and the rear amp drives the negative speaker terminal by using a phase converter board to invert the signal.

OK, so in 2 channel mode, the amplifiers are bridged.

That means you really need to get them working first in 4 channel mode. When the amplifiers are bridges they can affect each other and that will make any faults harder to find and potentially more "messy"

The reciever will works fine when in 4 channel mode. In 2 channel mode it would burn both sides. I have only been working with one side at a time.

As above, need to get each individual amplifier working. There's also a small chance the problem is with the inverter board.

I have to purchase some more outputs. Do I need to purchase matched pairs or does it matter?

It's better to have matched pairs because that will result in the lowest distortion from your amplifier. However I'd tend not to until we're sure the amplifier is fixed. The matched pairs are likely to be rather more expensive and that just makes each one a more expensive failure.

When you answer the above question can you clue me in on how you determined the answer?

I think I may have...

Does it matter if the front channel is one brand and the rear channel is another brand?

If the amplifiers are being used individually, no. One amplifier may have a slightly higher output than the other, but it's unlikely to be significant. However if the front and rear amplifiers are bridged, it matters in pretty much the same way as I;ve described fir matched pairs above, since each amplifier essentially becomes half of a pair of matched amplifiers.

Does it matter if the varistor in one channel is different than the other three?

Not a great deal, as long as it has approximately the same voltage drop and temperature coefficient. The number of diode junctions effectively set both of these.

 

[mrmodify]

Hello Steve, I have tested DC offset in 4 channel and 2 channel modes.

4 channel mode front was 0% = 2.8mv and @ 100% = 3.0mv
4 channel mode rear was 0% = 4 to 6mv and @ 100% = 3 to 7mv
both results were not very steady and took a little time to settle. The rear was worse.

2 Channel mode was 0% = 2mv and @ 100% = 2mv. It was not a rock solid reading.It floated but not as bad as the 4 channel rear amp was.

4 channel mode
The quiescent current was at 15mv on pins 9 & 11 & 16.4mv on pins 33 & 35. The bias was at 1.1mv on pins 13 & 15 and .1mv to 2.6mv on pins 29 & 31.

2 channel mode quiescent current was 15.3mv on pins 9 & 11 and 17.2 mv on pins 29 & 31. The bias was at 1.8mv on pins 13 & 15, and 0mv on pins 29 & 31.

Probably dumb but I I was comfortable with connecting a 8" 8 ohm woofer to receiver and installed a 200watt bulb for my dim bulb.

On 4 channel mode it operated and sounded pretty good on both front and rear amps. On 2 channel mode it operated ok but was slightly distorted. When volume was turned up about a half of the way I could watch the diaphragm of the speaker start to push out then pull in in a very slow cycle and would stop when volume was decreased. It did not affect the already slightly distorted sound.

The 2 set of outputs that are in the receiver right no are the Japanese transistor that are not matched pairs and not sure of the quality. I only have one set of NTE matched pair transistor here.

Do you think this could be part of the problem because of the miss match of transistors on bridge mode?

On the other hand the rear channel voltage is not stable either. I would think the bias, quiescent, and DC offset should be a very solid steady voltage.

 

[mrmodify]

No questions just a thanks

Have not worked on receiver lately, Spring is here and have other projects. I wanted to finish receiver electronically but out of time.

I wanted to thank everyone who has help me with this project. Thanks to davenn, shrtrnd, poor mystic, Resqueline and to anyone else I have forgotten to mention.

I want to especially thank *Steve* for all the time help and patients you have spent on helping me. Thanks for putting up with me. I have learned a awful lot from you and you have gotten me a long way through this project.. I could not have gotten this far with out you. I thank you very much!!!!

If there is ever anything mechanically or electrically I can do to help please contact me.

I will periodically work on it, order parts, but will pick it up hard again around Nov. Dec.

 

[(*steve*)]

Unfortunately I don't feel that I've been too helpful. I'm glad if I have been able to provide some insight to this problem.

My suggestion for when you get back on to it is to try to get the 4 individual amplifiers working then look at the board that does the phase magic to allow them to be connected up as a pair of bridged amplifiers.

 

[mrmodify]

Believe me you have and are was very heplful. " I learned alot"

the board that does the phase magic to allow them to be connected up as a pair of bridged amplifiers.

A good while back I inputted a 100hz signal into the cd jacks and used my scope and followed the signal to the phase conversion board and seen the signal invert at the output of the coversion board, Thought that board was causing the problem in 2 channel. Thats part of how I found out how bridging worked. I also pulled the tranisitors and caps on that board and checked them. Unless the problem will only occur at a certain power levels.

try to get the 4 individual amplifiers working

They sort of do, I can run the volume up on my old set of bose 901's with no problems with a 300w bulb (It will barely glow) at 1/3 to 1/2 volume, but it does not sound crisp.

Thanks again
John.

 

[mrmodify]

Me again

Hello everyone, I am fixing to order some parts for my marantz winter time project. Can anyone tell me the difference between a complementary pair and a matched complementary pair of transistors.

When I ordered my last set of outputs I ordered matched complemetary pairs. But when I ordered my transistors that drive the outputs I did not specify and I bought each transistor individually (not matched or complementary).

Steve, I know you mentioned about waiting to order parts because of possibly frying expensive parts. I am going to use my old parts until I can get the reciever straight. But while I have some extra funds I would like to order another set of MCP's for the outputs and for the 4 sets for the drivers to help on distortion.

Thanks all.

 

[duke37]

A complementary pair will be one PNP (or P channel) and one NPN (or N channel).

A matched pair will have similar characteristics but since the PNP and NPN transistors are made differently it is not so easy to match them.