Marantz model 26 receiver: Almost done - Page 1
Forum section: electronics / repair

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 20, 2022, 10:15:36 pm
content: Hello AllI just picked up a nice specimen of a Marantz model 26 stereo receiver for a good price since it needed work. I have already fixed what was wrong with it but I thought I would ask this question to some of the more experienced techs out there.What I would like to know is if there are any capacitors that should be replaced due to their age, as this amplifier is bearing down on 50 years old. I will list the brands and types of caps in case anybody wants to know that.-Nippon Chemi-con, Nichicon, and Elna : Aluminum Electrolytic (I have always worked under the assumption that these are good brands).-Mallory: Aluminum Electrolytic-Matsushita (the triangle logo?): Aluminum electrolytic as well as some plastic purple ones labeled as electrolytic.-Unknown brand : polyester type-Unknown brand : Ceramic (I generally assume that these don't go bad)-unknown brand : mylar type (the flat green ones)I would love to hear you peoples opinions on cap brands and types, as well as my assumptions stated in parentheses. I know capacitors is a common topic so I hope I am not beating dead horse here, but hopefully I will learn something new!The below pictures are of the various boards and should show all the different types of caps.

author: bob91343
author_rank: Super Contributor
timestamp: May 21, 2022, 04:10:06 am
content: If you insist on fixing what isn't broken, I would limit the shotgun replacement to the power supply filter capacitors.If you get more ambitious than that, you risk making errors.

author: David_AVD
author_rank: Super Contributor
timestamp: May 21, 2022, 06:32:51 am
content: I agree. I've seen too many perfectly working vintage amplifiers mangled by bulk cap replacement.Some had traces torn off while others had created dry joints all over the place.Also, sometimes totally inappropriate replacements were used (low ESR or normal instead of low leakage).All of this makes getting the unit working so much harder and time consuming than repairing any original faults.Better to check for visible signs (corrosion / leakage) and maybe remove a couple of example types for testing first.

author: floobydust
author_rank: Super Contributor
timestamp: May 21, 2022, 07:05:13 am
content: I would replace all the small electrolytics. Why? I find the grey Elna electrolytic capacitors are pretty much end of life, they must be 45+ years old. They dry out and go low value, usually the small guys under ~220uF. Just test some to confirm.What I do is make a spreadsheet with a list of the caps, for each board. Or, go to eBay and see the cap kits for the 26. Small 1uF and 2.2uF it's common to use Wima film caps instead. Pic related, that guy gives new small transistors as well. The loudspeaker protect relay usually has badly oxidized contacts and need cleaning without breaking it.If you haven't done this before, or don't have a decent desoldering tool, patience and tenacity, then I would not do it.Touch the dial cord with a soldering iron and it's destroyed. Forget a cap location or polarity, and screw up the board (hint: take lots of pictures). Clumsy soldering and you'll ruin the PC board.I have a Marantz 2252b to recap, just haven't had the time and the dial lights are extra work.

author: beatman
author_rank: Regular Contributor
timestamp: May 21, 2022, 08:37:00 am
content: just replace all caps with good quality brand same capacitance and when not found the same voltage you can do with bigger.16v can be on his position 25v.i do a lot old complicated devices 25-35 years with succsess.just be very carefully when desolder don t made anny damage on traces and take care for the right polarity of the new caps.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 21, 2022, 04:05:20 pm
content: Thanks for the feedback so far.I understand the risks or firing the parts cannon, I have been guilty of that myself as I am sure everybody has. I was curious what experiences other people have had regarding recapping.One of the inspirations for this topic is another Marantz AMP that I repaired a while back where two caps shorted in the preamp causing low volume. At the end of the day I replaced all of the same brand/type of cap, thinking that the others were not far behind. With this topic I was interested to see if anybody had any input on similar problems.My ultimate intention is to sell the model 26, but I don't want to do that is there are caps that have a high chance of failure in the near future. I think I will sample some of the coupling caps for capacity and ESR, as well as check all the large filters, I will post an update on that hopefully later today.

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 21, 2022, 04:37:07 pm
content: I no longer find it easy to entertain a "recap", or "bulletproofing" of anything post vacuum tube unless it's showing trouble, revenue critical, or a known cascading failure point. I've done everything right one too many times only to have the thing quickly fail on me in some uneconomical to repair manner anyway, just with a bunch of time and money sunk in it instead of as found.In this case I would think it comes down to the market. If these things sell higher recapped, high enough to cover your parts and labor costs of doing it right with good parts, I guess go ahead. If not, ship it.

author: floobydust
author_rank: Super Contributor
timestamp: May 21, 2022, 09:06:40 pm
content: Vintage Marantz receivers and amplifiers etc. are commanding high price, so restoring them should be done with care and integrity. If it sells for $600+ who would leave in antique parts and assume age is the reason the bass isn't there. I recall they are "designed in USA" and Japanese manufactured, so some great metal work and looks, yet fairly straightforward designs.It would be interesting to see the real cost of a re-cap/re-lamp. I'm usually on the phone with friends while doing it to save labour costs. Then I forget which cap I've just pulled lol.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 22, 2022, 12:38:20 am
content: I bought this amp for 100$, and did a 2$ repair on it to get it to where it is now, which is not too bad, and given that many model 26s are being listed by people in the US for at least $400 I feel that is is worth replacing at least some of the electrolytic caps.With that being said, replacing all the electrolytics would cost only about 25$ shipped on Mouser. But here is where I may go down the rabbit hole a little, first question is are there any brand recommendations? $25 is probably the lower end on the cost of a cap set, but I chose a brand that was available(I have not bought these yet mind you). BTW has anybody heard of the brand "Wurth Elektronik"? I have but I don't know anything about them except that they are German and mouser has plenty of stock.My next question is, and this may be dangerous, are there any other caps worth replacing for reliability and sound quality? I am not saying that I would replace them on this particular device, just curious to pick the brains of some people.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 22, 2022, 01:22:45 am
content: As others have said, if you plan to sell it AND did not see a bad capacitor there AND does not see a price difference in recapped/original, I would leave it alone for maximum profit.Obviously that, if you want to consider the fun factor in recapping AND have the experience and resources, go for it. All in all, you can never pay too much for improvement in repair experience.Good luck with your decision.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 22, 2022, 01:36:20 am
content: Thanks for your advice, I am at the stage where profit is not the end all be all. I am a hobbyist and an engineering student who likes to repair electronics while learning a few things, profit is just a nice bonus on top of the experience that I gain from working on something.That aside I don't think it will be worth going after any other caps besides the electrolytics, they should be high quality and (hopefully) long lasting. If I had to replace any I think it would be the ones labeled as "poly" (polyester? polystyrene?) in the parts list, on the board they look like exposed rolls of foil and clear plastic of some sort, which just seems like it is waiting for moisture ingress to cause trouble.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 22, 2022, 01:45:57 am
content: Ok, a quick google shows that polystyrene caps are quite good and long life in the right conditions, I trust that Marantz knew what they were doing and I will not touch them. Should have googled first.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 22, 2022, 02:57:48 am
content: Quote from: Alex_Baker on May 22, 2022, 01:45:57 amPrecisely. Unless you see somethingreally bad, leave them alone.

author: slbender
author_rank: Regular Contributor
timestamp: May 25, 2022, 01:53:53 pm
content: Quote from: Alex_Baker on May 22, 2022, 01:36:20 amEach of those “exposed rolls of foil and clear plastic” parts are polystyrene caps, which are among the most prized, and most stable caps ever produced, often of close tolerance, high voltage rated, and could not be bettered, shy of some truly mega-buck caps - often twenty times their size, each likely costing more than a working Marantz 26 is worth.Steven

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 01, 2022, 03:55:57 pm
content: OK, so all electrolytics have been replaced, no issues there, however there is quite a bit of idle hiss. I traced the source of the hiss by grounding the signal connections(on one channel) J406, J408, J412, and J414 until the hiss went away, which it did when I grounded J408. J408 goes to the tone control knobs, service manual attached below.Does anybody have any input on this? there is also some 120Hz(line) hum, but I need to trace that more.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 01, 2022, 05:53:43 pm
content: There is 14mV ripple on the 38V power rail, is that ok? I would like to see lower but I don't really know.

author: james_s
author_rank: Super Contributor
timestamp: June 01, 2022, 06:00:31 pm
content: 14mV is nothing, that wouldn't concern me at all. A properly designed amplifier is very tolerant of noise and variation on the supply rails. As for capacitors, aluminum electrolytic are the only kind I would consider replacing unless something is obviously wrong with one of the others. I have had to clean up too many devices where someone thought it was a good idea to replace all the capacitors wholesale and screwed it up. The most annoying was a case where someone asked me to re-cap an amplifier, I quoted him a price and then he decided to do it himself, screwed it up and then asked me to fix it for him. No thanks.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 01, 2022, 06:16:19 pm
content: OK, thanks for the confirmation on the ripple. So I still need to find where the 120Hz hum is coming from, though I don't care about that as much as the hiss. I have attached some pictures of an audio spectrum app on my phone. The top picture is the noise floor in my work space(amp off), and the bottom pic is the amp on with nothing connected. I held the phone up to the speaker for the test.Not sure if that provides any useful information, I though it might give an idea how loud the hiss is.

author: andy3055
author_rank: Super Contributor
timestamp: June 01, 2022, 08:10:03 pm
content: If there is 120 Hz hum, look for bad screened leads on the signal paths. Often if a screen that is grounded comes loose, you will get hum. It could be a dry solder joint-considering the age.Also take a good look at the power supply and make sure the ground/chassis connections are intact.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 01, 2022, 08:32:13 pm
content: Everything regarding grounding looks good.Curiously, if you look at the audio spectrum if when the amp was on, there is a peak at 180Hz according to the app, I wonder what that is...

author: james_s
author_rank: Super Contributor
timestamp: June 02, 2022, 12:32:45 am
content: Is the noise identical on both channels?

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 02, 2022, 03:10:05 pm
content: effectively it is, the left channel might have a tiny bit more hum that the other but it is barely noticeable.

author: floobydust
author_rank: Super Contributor
timestamp: June 02, 2022, 06:19:01 pm
content: Where's the schematic for it? It could be many things, but I'd be measuring some voltages to see if anything is way off. It can "work" and pass audio even when a stage is starved for voltage, as well as cause PSU hum to get exaggerated. Or maybe it's just noisy due to design and grounding etc.I thought the volume control was ahead of the tone-controls, leading into the power amps? That gives a poor S/N ratio. Placing the volume control ahead of the power amp section is for best S/N.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 04, 2022, 08:59:23 pm
content: Sorry for the delay, I typed up a whole response for this and I don't know what happened to it. Service manual is attached below.Currently I am doing some more testing to try and determine where the hum and hiss is coming from, I will post if I find anything useful.Just for peace of mind, it is not likely for a recap to cause these two problems is it? provided everything was done correctly.

author: james_s
author_rank: Super Contributor
timestamp: June 04, 2022, 10:50:35 pm
content: I think you forgot to attach the service manual.

author: David_AVD
author_rank: Super Contributor
timestamp: June 04, 2022, 11:07:33 pm
content: You need to divide and conquer when troubleshooting. An example:Is the his affected by the volume control? YES: issue is in whatever is before that. NO: issue is in the tone or power amp stages.If not affected by the volume control, do the tone controls alter the hiss sound? YES: issue is in tone control stage. NO: see other tests.If there are pre-main links on the back panel remove them. Is the hiss gone? YES: issue is before them. NO: issue is in power amp stages.Is the hiss only when phono is selected? YES: issue is in phono preamp. NO: issue is in something common to all inputs.This is a simplified example, but hopefully you get the idea.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 12:28:09 am
content: OMG, yes I did forget to attach the manual, I apologizeI have narrowed the hiss and hum issue down to after the volume control (mostly) and before the tone control switches and knobs, The volume largely does not affect the noise, I can disconnect the wire from J404(which is the left channel) and it does not change, whereas the treble tone controls do affect the noise.Also of note, the hum mostly goes away if I touch the chassis with my hand, is that a ground problem?

author: andy3055
author_rank: Super Contributor
timestamp: June 05, 2022, 03:12:18 am
content: You should hit your head harder than that!

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 03:50:01 am
content: OK, I just realized what is going on. Not with the amp, don't get your hopes up, its way more stupid than thatI have been trying to attach a PDF that is 11MB, and as you know that is way too large. Earlier I couldn't figure out why I would get booted to a "create new topic" page whenever I tried to post a response with the service manual for the model 26.In my defense there really needs to be an error message for that thing.Anyway, now that I look like an idiot, I attached just two PNGs of the schematic, and the information in my last post is still valid, obviously.

author: David_AVD
author_rank: Super Contributor
timestamp: June 05, 2022, 04:43:05 am
content: From a quick look at the diagrams transistors H404, H402 are the potential source of the hiss.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 04:48:41 am
content: Is there any way to test that other than replacement? I don't have any replacements at the moment and it would take me a couple of days to get any.

author: andy3055
author_rank: Super Contributor
timestamp: June 05, 2022, 05:00:58 am
content: Does the hum and hiss present on both channels? If not you can interchange the transistors one at a time and see if the problem moves with it.What input have you selected?

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 05:04:16 am
content: Noise is the same in both channels and input selected does not matter.I disconnected J404 on the left channel and it makes hardly any difference, however when I disconnected J412 on the L ch it is almost silent.

author: andy3055
author_rank: Super Contributor
timestamp: June 05, 2022, 05:42:25 am
content: I can't find the jumper you are referring to. It is hard looking at the diagram on the phone!However check the circuitry before that jumper.Edit: Found one end of the J412 but not the other end. It seems like some sort of a feedback loop. Check that C414-3,3uF cap. It may be noisy.

author: strawberry
author_rank: Super Contributor
timestamp: June 05, 2022, 06:34:08 am
content: volume pot not making good contactor is it just set to Tuner or Phono

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 01:24:18 pm
content: I know a jumper can't cause noise I was just disconnecting signal wires to isolate different parts of the circuit.The volume control has no effect on the hiss, and it works normally for actually playing audio. All electrolytics have been replaced and I have the input selector on "aux".

author: strawberry
author_rank: Super Contributor
timestamp: June 05, 2022, 02:15:11 pm
content: could disconnect J408 to rule out gain stagefeedback resistors R412,R414 (gain ~36)R402,R404,.. possible noise source (replaced with metal film resistors)they use same transistors in phono stage so not much noise expected from thempower amp: R430,R438 (gain ~32)

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 04:24:16 pm
content: Disconnecting J408 makes the hiss (and hum) much louder.The hum is still affected by touching the chassis or ground connections.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 06:10:35 pm
content: With what I know, I believe that the majority of the hiss is coming from the second preamp stage(for example H404 and H406 on therightchannel, I misspoke earlier and said left).I think this because grounding H414 and H412 with a jumper wire reduces the hiss to nothing, however grounding J406, J408, and J410 does not change the hiss at all. Now the question is what can I do about it, I have seen that replacing carbon film resistors with metal film ones it supposed to reduce induced hiss.I have ordered a kit of MF resistors as well as an assortment of small transistors just to have on hand, but those will not arrive until Tuesday the 7th.

author: james_s
author_rank: Super Contributor
timestamp: June 05, 2022, 06:14:30 pm
content: I once fixed a loud intermittent hiss in a Montgomery Ward receiver by replacing a mosfet, but that was only affecting one channel. Semiconductors can become noisy, I know resistors can produce noise but I don't think I've ever seen a failure mode where the noise got worse.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 06:25:57 pm
content: Does anybody know the meaning of the letters stamped on top of some of the transistors? There are 4 different ones, GR, Y, O and R. I read somewhere that it was a code for a gain range, but I was unable to confirm this.

author: strawberry
author_rank: Super Contributor
timestamp: June 05, 2022, 08:49:19 pm
content: grounding J408 will reduce humit is possible that it is how this device is madehigher current gain is better (GR) datasheet

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 05, 2022, 09:09:20 pm
content: I tried grounding J408 a different way and it does reduce the hiss by a bit as well as eliminate the hum, so that is good to know.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 07, 2022, 05:13:57 pm
content: The metal film resistors that I ordered came in today, replacing R402 and R404 made no difference unfortunately.

author: strawberry
author_rank: Super Contributor
timestamp: June 07, 2022, 05:40:42 pm
content: amplifier gain could be problem (design) picking up static noisestage sensitivity ~60mVpower stage ~1V

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 07, 2022, 05:45:07 pm
content: So you are saying that there is nothing wrong with it? That is what I was about to ask.The spec for noise floor was -60dB, is there any way to measure that to see if the amp is still within spec or not?

author: David_AVD
author_rank: Super Contributor
timestamp: June 07, 2022, 10:03:27 pm
content: Why are you replacing resistors when transistors H402 and H404 are way more likely culprits. The number of noisy resistors I find is minuscule compared to noisy transistors.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 07, 2022, 10:44:11 pm
content: Do you think all the transistors in the preamp could be noisy? Because the hiss is equal in both channels. I tried putting some transistors from a cheap amazon transistor kit in, they are S9014s which crosses to a decent Fairchild part, but I doubt these are them. Anyways my point is it made no difference with these particular transistors.I just wanted to try putting some metal film resistors in the preamp because I had them and I was curious. Now I know that it does not improve anything.

author: andy3055
author_rank: Super Contributor
timestamp: June 08, 2022, 12:30:00 am
content: You said that there was a marked difference when you were poking around the tone or volume control. Spend your time in that area.Take a .1 uF (may be around 50 volts or so) cap and start grounding thesignalpathto find which stage is generating the noise.

author: strawberry
author_rank: Super Contributor
timestamp: June 08, 2022, 06:17:59 am
content: low noise preamplifier and oscilloscope. App Note 124 - 775 Nanovolt Noise MeasurementSNR = 10 log (Signal ÷ Noise)

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 08, 2022, 05:10:51 pm
content: Here I will try to compile a list of things I know, and from there we can try to narrow down the options for the noise source.-The background hiss is independent of volume setting(with inputs grounded, there is extra noise otherwise)-The balance control will cut out the hiss by turning it all one way or the other.-Both the treble tone knob and the high filter switch has an effect on the hiss, though the tone knob not as much.-Grounding J414 with a 0.1uF ceramic cap removes 90% of the hiss(what I would consider to be normal with vol control at min)-Grounding J412, J410, J406 or J404 has no effect(again with the 0.1uF cap)-Grounding J408 cuts the hiss down by about half(with the 0.1uF cap)I am not sure what to make of this, how would grounding J408 have an effect on the hiss but not J412, which should be further down the line?The other annoying noise besides the hiss is a 120Hz hum, which mostly goes away if I touch the chassis, could it be related to the 2.2M resistor R011 on the mains side of the transformer?

author: strawberry
author_rank: Super Contributor
timestamp: June 08, 2022, 08:53:07 pm
content: noise is amplified

author: El Rubio
author_rank: Regular Contributor
timestamp: June 09, 2022, 05:12:21 pm
content: I don’t want to point out the obvious, but have you inspected the solder side of the boards? Specifically for lifted traces? I would look closely at all of your solder joints as well as confirm polarity on electrolytics ( not trusting the silk screened labels) . I had recapped a receiver several years ago. It was completed and I was finishing up the alignment process. At the time, I had a shelf above my workspace made from that vinyl coated wire shelf that you can get at home depot. I would hang small wire cutters and pliers on the front edge. I had a particularly long needle nose that was top heavy. I bumped it, it fell into the receiver. Sparks flew and it was dead. It blew out a fused resistor and a zener in the PS. Got the power restored, but had low output and a hum. I stumbled upon a switch housing that was not grounded ( but should have been). Tracing that, I found the ground for the entire input board with the RCA jacks was broken. It was a trace on the board that was very thin and not easily noticed that it was broken. Jumpered that and all was well.So, never store things that can fall above your workspace, and closely inspect your previous work. If you get frustrated, walk away for a few days. Don’t get discouraged and keep at it. Good luck.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 09, 2022, 05:25:20 pm
content: Thanks for the tips.Every thing is fine on the other side of the board, and I double checked the caps after I replaced them. Funnily enough thee was a mistake on the silkscreen from the factory, three 407uF caps on the power supply board were labeled wrong and I did not check them, two minutes later I got a face full of capacitor steam. Needless to say I did not pay attention to the silkscreen after that.Honestly though, as a whole I am not impressed with the circuit design and fit and finish of this Marantz, I though they were supposed to be top of the line but the more I work on it the more it feels like a Marantz badged Panasonic, they both came from japan after all.

author: strawberry
author_rank: Super Contributor
timestamp: June 09, 2022, 05:54:27 pm
content: schematic C407

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 09, 2022, 11:08:55 pm
content: I just realized today that I had some signal wires crossed that go to the amplifier board, so I fixed that. Grounding the different pins with a cap still nets the same result though.

author: El Rubio
author_rank: Regular Contributor
timestamp: June 10, 2022, 11:20:11 am
content: I always take photos before I work on something just to be sure. Some guys will take a sharpie and put a dot on the board near either the pos or neg side of each cap. There are lots of silk screen errors. If I’m not sure, I find it on the schematic and trace out the position on the board. Do it enough and you will not forget to take the pics, lol.

author: rsjsouza
author_rank: Super Contributor
timestamp: June 10, 2022, 02:01:29 pm
content: Quote from: El Rubio on June 09, 2022, 05:12:21 pmThese are indeed excellent tips for repair, in particular the last one. Frustration and tiredness are the biggest enemies of any meticulous work.For capacitor polarity, I usually scribble on paper a map of the board and the polarity of capacitors as I was also burned by bad silk screens - things blew up on my face due to that.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 10, 2022, 02:57:44 pm
content: Does anybody have any idea as to why grounding J408 with the 0.1uF cap would reduce the hiss but not J412?If I ground J412 without the cap in series all the noise goes away, likewise grounding J408 also without the cap still cuts the hiss in half. Does this suggest that both the tone control pots and the second preamp stage is the source of most of the hiss?