Servicing a Marantz 1150 console stereo amplifier

In this post I revisit the steps I’ve been through while servicing my Marantz model 1150 integrated amplifier. This amp changed the way I listen to music. But it was not at the first moment I turned it on. I’ll explain why.

Last updated on June 11th, 2024

The links below allows for a quick access to a subsection of this post:

• P800 Power Supply Board
• PE01 Tone Amplifier Board
• P400 EQ Amplifier Board
• P700 Power Amplifier Boards
• PH01 Filter Amp&Switch Board
• PN01 Relay Board

Warning: Please be aware of the risks when servicing any electrical equipment. You must make sure the electrical equipment and installations are maintained to prevent danger. You can get seriously injured. Repairs should only be carried out by someone who has the necessary skills, knowledge and experience to work safely. Always double check everything before plugging the power cord on and before putting your hands on, EVEN when they are not being powered.

How I got into this

I was looking for a real equipment to start a decent sound system for my own. I don’t mean a piece of plastic from the 90s, when the industry was lowering their budget with cheap material chassis, design and other general parts. I’m talking about those big beautiful consoles from the 70s. There are some marvelous models from several brands from that period. I focused on Marantz for a personal reason: my grandfather. He used to have a few modules and I might say he’s the one who inspired me to get into this. I remember how pretty the sound was coming from the bookshelves in his living room. If I needed a place to start from, that’s what I had in mind.

On day one

Of course I bought my Model 1150 Integrated Amplifier second handed from a guy in the Internet. Definitely a difficult thing to do since he was in a different brazilian state than me and I didn’t have the chance to personally check it out. Both sound and serigraphy matters when buying an old equipment. It’s also very important to chat with the seller and try to pull out of him any relevant information about previous repairing attempts (remember he’s trying to sell it).

Long story short: he didn’t want to ship it to me but I happened to have a friend in that town for that particular weekend. Luck, I guess. But a great deal of uncertainty about the deal there was either.

The first thing I did, after having a couple of beers to thank my friend for the whole inconvenience I made him pass, was turn that on! And… not very impressed. It sounded better than what I was using at home though. Time to open it and take a look closer.

First tip: Before changing things around, take pictures of everything in advance. In fact, many! And from different angles. Sometimes a wire breaks and gets loose, or you need to verify which transistor is there in that circuit board, or you’re simply investigating an issue… Pictures are your best friend and they are much more reliable than your memory!

The P800 Power Supply Board

The audio amplifier console itself is composed by two, ideally identical, parallel circuits which stands for the left and right channels. It’s really two amplifiers in the same equipment. But they share one thing in common: the power supply. The DC voltages generated in this board supplies power to all other circuit boards in the equipment. Any instability in this block may cause spikes in the output signals, so we’ve got to check its health.

One great thing about this unit is the that it is mounted in modular boards. Each board can be removed, repaired or even replaced. We have to be very careful about cutting the wires and reconnecting them later. As we may need to do several steps while repairing them, I wouldn’t recommend soldering them each time you put the board back in. I managed to lengthen the wires and add a female crimp circular connector at them so its easier to take the board out for further inspections.

While giving the visual inspections on all boards, look for burnt places on the board due to excessive high currents, stewed capacitors, melted wires, or just something in suspicious condition. Anything that appears to me it was repaired or replaced is worth careful attention. Note, for example, a series resistors association right next to the big capacitor in the pictures above. The transistors H809 and H810 also didn’t match with their references in the parts list. For sure something went wrong, but luckily the unit was in a working state. Otherwise, we would have to identify the causes of failure first and try to fix them.

A very important thing came to light after searching over the web. Even if everything appears to be fine to your eyes, some components may get way off their specifications or stop working completely. Those components are the non-solid electrolytic capacitors (or wet capacitors). An amplifier, or any equipment in general, should need servicing for replacing the electrolytic capacitors (also known as Recap) after a few decades or so. In a 40 years power amplifier it is a must-do task. Fortunately in those days the equipments were sold along with its service manual guide with schematics, parts list, components reference and disassembling steps. Also they were built with big discrete components, instead of tiny surface-mounted devices like nowadays. But the thing is: some parts may be hard-to-find, discontinued, obscure, obsolete components. Most of them have an equivalent replacement but some time-consuming researching process is required. But that’s part of the job! Needless to say, they are not being made anymore. They belong to another era, so to speak. As time goes by, some of those units goes to the garbage, some get lost in someone’s basement, some are disassembled for other purposes. The ones the survives are getting rather rare today. So having any of these amplifiers from the 60s and 70s in your arms is already for few. Do not miss the chance of getting the real sound out of them. Buy audio grade components for it. Now, that leads to another issue worth of commenting: how much is it gonna cost me? After a quick search, you’ll find out a single capacitor can cost from half to tens US dollars. Of course you should go as deep as you can without getting drowned.

From the Parts List session of the Service Manual, I made a list of all the electrolytic capacitors and ordered them from PartsConnexion. I decided to go with the Elna RFS Silmic II (pretty much all of them) and the Elna ROA Cerafine in the power supply rectifier’s filter (C803 and C804) and on the relay board (CN05).

P800 – Replacing the electrolytic capacitors (13 caps)

While replacing the caps, pay attention to the values found in each position and to the polarity orientations as well. Some misleadings between the schematics and drawings on boards may occur and they are not that rare. Remember someone else probably worked on it before you, then double check everything!

Schematics Board	Board Reference	Replacement	Quantity	Notes
470uF, 63V 220uF, 200V	C803, C804	470uF, 63V Elna Cerafine	2	Replaced
10uF, 50V 10uF, 63V	C808, C809	10uF, 50V Elna Silmic II	2	Replaced
100uF, 50V 100uF, 63V	C810, C811	100uF, 50V Elna Silmic II	2	Replaced
100uF, 35V 100uF, 35/35/50/63V	C812, C813, C814, C815	100uF, 35V Elna Silmic II	4	Replaced
100uF, 16V 100uF, 16/16/63V	C807, C816, C817	100uF, 25V Elna Silmic II	3	Replaced

Clearly this board was previously serviced without much care and with cheap general purpose capacitors. Let me handle this for now on.

Much better now… but we’re just warming up. Now it’s time to check the voltages, adjust the trimpots and, if everything is as should, put the power supply back in and try the amplifier. While servicing, I rather taking steps slowly. Never make too much changes without hearing the overall results. You and your equipment are getting to know each other. Be nice and easy.

P800 – Checking the transistors (8 units)

Not only the capacitors in this board needed attention but the transistors health must be checked. Some transistors differs from the listed and I have the intention of replacing them back to the original reference parts as much as possible. That job may take some time. Differently from the capacitors, which I ordered them all from the same supplier, very unlikely the transistors can be found in one single supplier. So it’s a task of searching each of them every local shop I go.

When you’re working with the board off the power, check if the BJT terminals are not in short and verify if their PN junctions are alright. With the power on, carefully check the voltages. If the base-emitter bias voltage is correct, you can trust it for now.

It toke me some time to solve some sporadic pops I was hearing. I found out the transistor H804 was faulty and replaced it with a TIP42C that I had at home. It’s doing fine now. I also happened to find transistors H809 and H810 as the original listed parts and replaced them. H805, H807 and H806, H808 could not be found yet but they are doing their jobs.

Schematics Board	Board Reference	Replacement	Quantity	Notes
2SD313 D, E	H803	Original	1	Good
2SB507 D, E	H804	TIP42C	1	Damaged, replaced
2SC1318 Q, R BC337	H805, H807	–	2	Good, not replaced
2SA720 Q, R BC640C	H806, H808	–	2	Good, not replaced
2SC1384 Q, R 2SD1944 K	H809	2SC1384 R	1	Good, but replaced by original
2SA684 Q, R 2SB1185 E	H810	2SA684 R	1	Good, but replaced by original

This board has two trimmer potentiometers for adjusting the positive and negative voltage sources. They should provide +44V and -44V respectively. From that voltages the circuit generates secondary voltage sources of 22.6V and -22.6V by dividing the voltages and buffering them by means of transistors H809 and H810. In order to adjust those secondary sources we can change the values of R819 and R820. In my case, I had to change the resistor R819 from 15k to 20k for adjusting a symmetrical voltage source around 22.6V.

Replacing the Main Reservoir Capacitors

After every day of servicing, I always spend a few days listening to a some records to perform an ear-test. It was doing fine until one day I woke up with a 60Hz humming coming out of it. Time to investigate. So I unplugged the input source cable and made sure it wasn’t coming from a poor electrical contact in the input. Then I reconnected it and played some sound and checked the channels. Both were there but they couldn’t handle the lower frequency range and, by turning the volume up, it was getting more pronounced. At that moment I knew it should be power supply related. It could be in the P800 board itself, which I was working on the day before, so I checked the board output voltages and they were fine. Or it could be the Main Reservoir Capacitors which are responsible for storaging DC voltage to supply the output power stage of the amplifier. Those caps are generally large and must handle the high electrical current surge while feeding the output speakers. By checking the voltages It confirmed the positive terminal was way below from expected 45.8V. As predicted for a wet electrolytic capacitor, its dielectric insulator had been drying out for the last four decades and it was finally saying goodbye from its duty. This did not affected the power supply board voltages because it comes from different transformer wirings.

In this model, those capacitors come together in one single cylindrical three pin package and I couldn’t find a brand new replacement in my searches. What I found to be a good choice was to buy two capacitors and connect one’s positive terminal to the other’s negative terminal. This junction should be the ground terminal and the two others being the respective positive and negative terminals. The major concern then is where it would fit. It should not be left loose inside the console and it should avoid any electrical contact to its terminals by any chance.

I ended up buying a pair of Nichicon Gold Tune caps as they appeared to be a great option for that purpose and managed to find a place somehow once they arrived. It happened to fit very well alongside the transformer, between the power supply board and the right output channel as shown below. There are two concerns around this. First, the transformer normally gets quite warm and heats its surroundings. And second, it’s hard to find a way to attach them to the chassis. As a workaround, I’ve used EVA foam sheets for improving thermal insulation and filling the spaces around to prevent them from being displaced. Though it’s far from ideal, I’ve been running it like this for some time and didn’t have any issues.

How did it sound afterwards? I can tell It just marks the starting point for this whole servicing journey. Do not under estimate the role of these reservoir capacitors. Just think about it. By the end of the signal path throughout the whole equipment, it gets to a pair of bipolar transistors which act as a current source which pulls energy storaged in those capacitors to feed the speaker coils. It’s sort of saying the sound that actually is being reproduced by the loudspeaker system comes from energy in those caps! Hence, why don’t we say they are signal path capacitors?

Schematics	Board Reference	Replacement	Quantity	Notes
13000uF x2, 55V	C010	13000uF, 63V Nichicon Gold Tune	2	Replaced

The PE01 Tone Amplifier

The Tone Control in the front panel is implemented by two boards. The PE01 Tone Amplifier, which is a flat frequency response amplifier circuit, and PF01 Tone Control Volume, which is a feedback loop and contains the potentiometers for altering the amplifier’s frequency response. The Tone switch in the front panel allows to switch between the adjustable filters feedback or a fixed resistive feedback (for a flat frequency response). The Tone Control is very useful to correct some room interference such as sound absorption and reverberation. It’s highly desirable to have hi-fi loudspeakers and to choose an appropriate room for the audio system. Now remember: Its goal is to be as transparent as possible. Hearing music on a hi-fi audio equipment is sort of a travel in time. You can feel how albums were recorded and mixed around the decades. I always set the tone controls at flat. When no further improvement in the sound quality can be made by modifying the room acoustics, the effect of the tone controls can then be tried. If it’s still at flat, switching it off is preferable (and even flatter).

The amplifier board holds 18 electrolytic capacitors, some of them in the signal path and, as I was getting more and more excited about the recapping results, I felt its time has come.

PE01 – Replacing the electrolytic capacitors (18 caps)

All electrolytic capacitors were replaced. Most of them were tantalum caps. While replacing CE19 and CE20, there were 47uF caps instead of 33uF as listed in the Service Manual (both schematics and parts list). A larger capacitance is allowed where they are located and they were Elna capacitors, so I kept them 47uF for having the evidence of them being from factory.

Schematics Board	Board Reference	Replacement	Quantity	Notes
1uF, 25V (Ta)	CE01, CE02	1uF, 50V, Bipolar Nichicon	2	Replaced
33uF, 10V (Ta)	CE07, CE08	33uF, 25V Elna Silmic II	2	Replaced
4.7uF, 25V (Ta)	CE09, CE10, CE27, CE28	4.7uF, 25V Elna Silmic II	4	Replaced
100uF, 10V 100uF, 35V	CE11, CE12	100uF, 25V Elna Silmic II	2	Replaced
2.2uF, 25V (Ta)	CE13, CE14	2.2uF, 50V Elna Silmic II	2	Replaced
33uF, 10V 47uF, 10V	CE19, CE20	47uF, 16V Elna Silmic II	2	Replaced for 47uF as found
1uF, 35V (Ta)	CE21, CE22	1uF, 50V Elna Silmic II	2	Replaced
100uF, 25V 100uF, 35V	CE23, CE24	100uF, 35V Elna Silmic II	2	Replaced

PE01 – Checking the transistors (12 units)

No issues found in the transistors.

Schematics	Board Reference	Replacement	Quantity	Notes
2SA836 E, F	HE01, HE02, HE03, HE04, HE07, HE08, HE09, HE10	Original	8	Good
2SC1345 D, E	HE05, HE06, HE11, HE12	Original	4	Good

The P400 EQ Amp

This board is responsible for performing the RIAA equalization. In other words, it boosts the lower and attenuates the higher frequencies according to a specific standard curve. It’s also known as the phono preamplifier and either the phono and the microphones input signals can go through it. Only if your turntable does not have a built-in preamplifier stage you’re supposed to use the phono input. If it does have one, you might plug it to the aux input. Here is an interesting discussion about RIAA curve.

No issues where found in this board. Just replaced the tantalum electrolytic for the Elna aluminum electrolytic capacitors.

P400 – Replacing the electrolytic capacitors (6 caps)

Schematics	Board Reference	Replacement	Quantity	Notes
4.7uF, 25V (Ta)	C401, C402	4.7uF, 25V Elna Silmic II	2	Replaced
33uF, 10V (Ta)	C407, C408	33uF, 25V Elna Silmic II	2	Replaced
1uF, 35V (Ta)	C417, C418	1uF, 50V Elna Silmic II	2	Replaced

P400 – Checking the transistors (8 units)

Original Schematics	Board Reference	Replacement	Quantity	Notes
2SA872A D, E	H401, H402, H403, H404	Original	4	Good
2SC1885 S, T	H405, H406	Original	2	Good
2SA912 S, T	H407, H408	Original	2	Good

The P700 Power Amplifier Boards

The P700 boards are two separated boards, one for each channel, with the same component labels. There are two trimpots R741 and R742 for adjustment of the DC Offset Voltage and the Idling Current adjustment, respectively. After verifying the Power Supply Board, it’s a good practice to perform the Power Amplifier adjustments on both channels.

Tip 1: Use Alligator Clip type leads for proper measurement

Tip 2: Adjust these two parameters on one channel first then move to the other channel. Perform several interleaved measurements of both parameters until they seem stable.

Tip 3: JN04, JN05 and JN10 (Ground) are actually reachable at the Relay Board

DC Offset Adjustment

Connect the voltmeter to JN04 (left channel) and JN10 (or choose a good Ground potential) and adjust R741 until the meter indication reaches 0mV (or between -5mV and 5mV). Do the same for the right channel on JN05 test point.

Adjusting the Idling Current

Connect the voltmeter to J701 and J702 on the left channel and adjust R742 until the meter reads 10mV. Do the same on the right channel.

Continuing with the visual inspections, as can be clearly observed in the pictures below, some components were replaced like R740 (on the right) and transistors H705, H706, H707 and H708 were removed without being replaced (on both channels). There are some burnt places indicating over current. Capacitors C717 and C718 are missing but were not listed in the service manual either (so let it still).

The R740 is a block with two thermally coupled 0.2 ohm resistors. It had been replaced for two 0.33 ohm resistors. I didn’t spend to much time looking for the original part but surely replaced them by two 0.22 ohm resistors. For the future, I’m considering replacing it on the other board as well for sake of channels symmetry.

P700 – Replacing the electrolytic capacitors (3 caps per board)

The orange electrolytics in the pictures above are Elna 47uF capacitors. Seems like they survived the previous servicing! Let them rest in peace now. All of them have been properly replaced.

Schematics Board	Board Reference	Replacement	Quantity	Notes
47uF, 16V	C702	47uF, 16V Elna Silmic II	1	Replaced
10uF, 16V 10uF, 16/16V (right) 10uF, 63/63V (left)	C703, C704	10uF, 50V Elna Silmic II	2	Replaced

P700 – Checking the transistors (15 per board)

After replacing the capacitors and performing the necessary adjustments on both boards, I’ve checked if every transistor was fine and whether any of them was previously replaced. All four output power transistors had been replaced by MJ15003(G) and MJ15004(G) but were in bad visual condition. Also both power driver stage transistors H713 and H714 didn’t match with the parts list. At first, I didn’t replace anything. A few months later, while I was doing some tests, I accidentally touched an input cable hot connection and one of the channels went silent. Fortunately, replacing all four H002-H005 output power transistors fixed the issue.

Currently, I am studying and looking for replacing the transistors from the driver stage H713 and H714. I also bought H705-H708 transistors but I’m still being precautious about them. This section must have some updates soon!

Schematics Board	Board Reference	Replacement	Quantity	Notes
2SC1327 T, U	H701, H702	Original	2	Good
2SA721 S, T	H703	Original	1	Good
2SC1327 S, T	H704	Original	1	Good
2SC945 Q, R	H705, H707	Pending	2	Missing
2SA733 P, Q	H706, H708	Pending	2	Missing
2SC496 O	H709	Original	1	Good
2SA794 Q, R	H711	Original	1	Good
2SC1567 Q, R	H712	Original	1	Good
2SC1625 O, Y 2SC2073	H713	–	1	Good, not replaced
2SA815 O, Y 2SA940	H714	–	1	Good, not replaced
S40442 MJ15004 G	H002 (H004)	MJ15004 G	1	Replaced
S40443 MJ15003 G	H003 (H005)	MJ15003 G	1	Replaced

The PH01 Filter Amplifier and Switch Board

On this board I noticed the capacitors CH21 and CH22 were listed as film capacitors and appears as being electrolytic capacitors in the schematics and in the PCB below. For that reason I didn’t order any 4.7uF rating 35V or higher. Interestingly there were a tantalum and a cylindrical bipolar (which are both electrolytic) capacitors on the board. We can trust the tantalum to be original, as seen in many other places around the equipment, but very unlikely the other one has been replaced due to an issue (though early failures can happen).

There is a great discussion about capacitor types in audio signal path here. I admit I came across this topic after replacing both for bipolar caps. Although I believe the tantalum cap to be the original one, I have no doubt replacing both by bipolar caps was a great choice. But I’ll consider replacing them for film caps, or Elna Silmic II like the others, if I have nothing else to worry about.

PH01 – Replacing all the electrolytic capacitors (2 units)

Schematics Board	Board Reference	Replacement	Quantity	Notes
4.7uF, 35V (Ta) 4.7uF, 35V (Ta) 4.7uF, 100V	CH21, CH22	4.7uF, 100V BP	2	Good, but both replaced

PH01 – Checking the transistors (4 units)

Original Schematics	Board Reference	Replacement	Quantity	Notes
2SA836 D, E	HH01, HH02	Original	2	Good
2SC1345 D, E	HH03, HH04	Original	2	Good

The PN01 Relay Board

The Relay Board, commonly referred to as the Speaker Protection Circuit, is a mechanism mainly intended to prevent the loudspeakers, or the power stage itself, from being damaged due to an abnormal event. This circuit block also ensures a few seconds delay before releasing the signal to the output speakers during the power up transient period.

The output relay is a DPDT (Double Pole Double Throw) switch which releases the signal to the output while its coil is being energized and disconnects the output otherwise. For that reason, it may be responsible for some output signal loss. It’s important to remove any oxidation from its electrical contacts. Some people use a fine grain sandpaper. I rather use isopropyl alcohol for cleaning any kind of electrical contacts.

PN01 – Replacing the electrolytic capacitors (3 units)

Schematics Board	Board Reference	Replacement	Quantity	Notes
10uF, 50V 10uF, 100V	CN03	10uF, 50V Elna Silmic II	1	Replaced
47uF, 16V	CN04	47uF, 16V Elna Silmic II	1	Replaced
220uF, 10V	CN05	220uF, 10V Elna Cerafine	1	Replaced

PN01 – Checking the transistors (3 units)

Schematics	Board Reference	Replacement	Quantity	Notes
2SC945 Q, R	HN02	Original	1	Good
2SC1318 P, Q, R	HN03, HN04	Original	2	Good

Quick Guide

Alternative Replacement Parts for transistors

The table below is a compilation of alternatives parts for the transistors in Model 1150 found during my researches. I haven’t checked the datasheets of every item on this list, so I can not assure you this replacements are correct. I suggest you to double check every information you find over the Internet before replacing in your unit. If you have any suggestion or correction about these parts, please comment below. Thank you!

Schematics	Board Reference	Alternatives	Quantity
2SD313 D, E	H803	BD587 2N5298 NTE152 BD241A	1
2SB507 D, E	H804	BD590 2N6126 NTE153 BD178	1
2SC1318 Q, R	H805, H807, HN03, HN04	BCW36 2N4410 NTE128	4
2SA720 Q, R	H806, H808	BCW37 2N2904 NTE290A BC327	2
2SC1384 Q, R	H809	BD135 2SD1944	1
2SA684 Q, R	H810	BD136 2SB1185	1
2SC1327 T, U	H701, H702	BC547 NTE199 BC182L 2N5210	4
2SA721 T	H703	BC212L BC559 2N4061	2
2SC1327 S	H704	BC547 NTE199 BC182L 2N5210	2
2SC945 Q, R	H705, H707, HN02	2SC1815 BC407B BC182L 2N3710 BC167B	5
2SA733 P, Q	H706, H708	BC257 NTE290 BC212L 2N4061 BC557	4
2SC496 O	H709	BD135 NTE295 BD169 2N4923	2
2SA794 Q, R	H711	BD140 NTE211 2N5415S	2
2SC1567 Q, R	H712	BF457 NTE373 2N5100	2
2SC1625 O, Y	H713	BD239C 2N5241 2SC2073	2
2SA815 O, Y	H714	BD940 2N6180 2SA940	2
S40442	H002 (H004)	MJ15004 G	2
S40443	H003 (H005)	MJ15003 G	2
2SA836 E, F	HE01, HE02, HE03, HE04, HE07, HE08, HE09, HE10	NTE234 BSW24 2N3494	8
2SA836 D, E	HH01, HH02	NTE234 BSW24 2N3494	2
2SC1345 D, E	HE05, HE06, HE11, HE12, HH03, HH04	NTE199 BC414	6
2SA872A D	H401, H402, H403, H404	2SA893 NTE288 BF435-2N3930	4
2SC1885 S	H405, H406	2SC589 NTE399 KSC2310	2
2SA912 S	H407, H408	2SA712 2N5415 BF423	2

Thanks for reading!