Asking for help on a blown channel on Pioneer SA-510 - Page 1
Forum section: electronics / repair

author: Dan75
author_rank: Contributor
timestamp: October 25, 2021, 09:29:36 pm
content: Hi, guys,There is a Pioneer SA-510 (Blue Line series) here that I sold to someone and I got it back because he insisted on thatThe reason was that he says it suddenly got a blown channel. The right channel is out.When powered up, it clearly shows that it is blown. The VU meter does not show output either.I checked inside for visual damage but couldn't find anything so far.The thing that I did find is that fuse 3 is done for.So before I go any further, I wanted to ask for your expertise on repairing this and ask for the next step.My guess is that the next step could be checking the output transistors.Can this be done with a MM meter, set in Ohm mode, black probe on the heat sink and the red one on the collector of the transistors?And perhaps other components like diodes, but which onesHave added the schematic to this message.(Note: it is a EU model.)Thanks,Dan

author: bob91343
author_rank: Super Contributor
timestamp: October 26, 2021, 04:25:31 am
content: I didn't bother looking at the schematic but if a fuse is blown, an output transistor failure is likely. A simple ohmmeter test on the transistors will show which one or ones are blown.Having said that, replacing blown output transistors is a mistake unless you verify the driver circuitry and bias network. There may be thermistors as well. Otherwise the new transistors may fail.

author: Dan75
author_rank: Contributor
timestamp: October 26, 2021, 07:11:37 am
content: I measured the transistors but couldn't find a fault. I took out another multi-meter with a lower Ohm mode than the one I used earlier. Maybe the other (a cheap one) isn't that great, because it did not show any readings in the lowest mode.So, I used the other one and that one shows readings on all collectors of all 4 output transistors.This result, combined with the fact that I did not trust the buyers remark because he told two different stories about what happened to the amp to me I decided to just replace the blownfuse and see what happens. Maybe not the best action but because the fuse protects the unit I thought that it was worth the shot and.... it works just fine!?So, what may have happened to it and how it was handled about, stays a guess...Is it a good move to recap the unit just for the sake of faulty or degraded electrolytics?If so, are there area's in the amp that need more specific rated caps (ESR, etc) ?

author: sean0118
author_rank: Frequent Contributor
timestamp: October 26, 2021, 07:34:04 am
content: Quote from: Dan75 on October 26, 2021, 07:11:37 amThey probably had a short in the wiring between it and the speakers, or they tried to hook it up while the amp was on.I had a similar experience, I bought a broken Rotel amp for $5, replaced both output fuses and it worked fine.Just to be safe, with the speakers disconnected, check for DC on the outputs, should only be a few 10mV or so. I assume it's okay if it sounds okay, a large DC offset will blowup your speakers.edit: With regards to capacitors it's really up to you. If they are a good brand I'd probably leave them. If you want to do a recap I think any moderately low ESR, long life capacitors from Nichicon, United Chemicon, Rubycon, Kemet etc would be okay. I've been sourcing them from LCSC, seems pretty well priced for small quantities.

author: Dan75
author_rank: Contributor
timestamp: October 26, 2021, 09:41:05 am
content: Hi Sean,That is my guess too.He didn't know how to connect the speakers to it, I tried to explain to him about the speakers connections on the back as this amp has two connections, A + B.Being not a novice on electronics, I just checked for the first time a DC offset.I took my MM, set it to 2V= (DC) and on the left channel I got: .009 / .010and on the right channel I got: .006 / .007So I guess that is ok. Measured after powered on for about 5 to 10 minutes.Do you have experience with the quality of MM's? I have one that seems to go all over the place, when put in the 2V mode it shows all different numbers on the display when not in use.Is it just sensitive in picking up frequencies in its surroundings?

author: sean0118
author_rank: Frequent Contributor
timestamp: October 26, 2021, 10:16:26 am
content: Quote from: Dan75 on October 26, 2021, 09:41:05 amI don't know as much about multimeters as others on here, you could checkout Dave's multimeter shootout videos though. But seems yours is working correctly, those measurements look good, probably just jumps around from stray fields when unconnected as you mention.

author: Dan75
author_rank: Contributor
timestamp: October 26, 2021, 12:26:55 pm
content: Thanks!I will use the amp for a while to test how he holds up for time being. Other than that I don't know what else I can do about it and resell it once more to a more careful user this time.

author: andy3055
author_rank: Super Contributor
timestamp: October 26, 2021, 05:04:42 pm
content: Quote from: Dan75 on October 26, 2021, 12:26:55 pmYes, don't sell it to the same person. Obviously he doesn't know how to do some basic things.When I was much younger, there was a guy who worked on a ship who brought an Amp home. These guys had parties and would blow the thing regularly. I found that he was connecting speakers to both channels all the time thereby, lowering the impedance. At one point I had to rewind his speakers. The voice coil formers were looking like charcoal! In the end, I disabled the B channel. That did not help as he twisted two speaker wires and showed them on the remaining channels! After that, I refused to repair his amp.

author: Dan75
author_rank: Contributor
timestamp: October 26, 2021, 07:53:51 pm
content: Hi @andy3055Yes, you're right, some are really not knowing what the heck they're doing.One giveaway is the glazed look in their eyes when you explain something, you can almost hear the crickets chirpYou mention that you rewound speakers, well that is somewhat interesting, I wonder if it is possible to rewind the damaged coil of the motor from a Dual 1019 turntable.It got damaged whilst taking it apart for servicing. The prying tool got away and ruptured 2 windings. Yes I can help things to bits tooIt is lying around so long now that I recently thought of parting out the unit as a donor, but if it could be salvaged that would be great.Only thing is wondering to determine how many windings it has now and match that.Dan

author: andy3055
author_rank: Super Contributor
timestamp: October 26, 2021, 08:24:17 pm
content: Winding those motors should not be that hard. If it has just 2 coils, it is a piece of cake. If it has more than that, it is still not a problem. Just needs a little more time. Post a picture of the interior of the stator if you can.

author: Dan75
author_rank: Contributor
timestamp: October 26, 2021, 08:39:05 pm
content: the damage is on the top half, it is dented and a couple of wires / windings snapped

author: andy3055
author_rank: Super Contributor
timestamp: October 26, 2021, 09:41:56 pm
content: That one is an easy fix but you have to wind a new coil, since it is more than just 1 or 2 turns. Just see if you can get the same Guage of magnet wire and cut the thing across that coil. You can then straighten the two sides and pull it out. Not sure if they have put any varnish. If so, it might be a bit hard but if you are patient, you can pull it out. Count the number of turns and just make a wooden former to wind a new coil. Just note down the way the coils are connected to make the right polarity. I think it is a 4 pole configuration. If so, the connection will be such that one will be cw and the next ccw. Cw, ccw,cw and ccw.I can't see the real damage though. If you are sure, only a couple of turns are damaged, you can carefully separate them and patch them. Just make sure to patch each end on the right to the corresponding end on the left. Make sure to insulate them from one another and the rest. You can use a smooth plastic piece to lift them up. Slip some sleeving or heat shrink on either side and pull them over the joints afterwards.

author: bob91343
author_rank: Super Contributor
timestamp: October 27, 2021, 12:17:19 am
content: Back on topic, replacing electrolytic capacitors on old gear is a controversial subject. If the current ones don't run warm and the ripple is low, leave it alone.If we are wandering off topic, I have a vintage Pioneer dual cassette deck, top of the line, that needs motor work. I don't want to fix it but if someone would want to trade me something for it I could be interested.

author: andy3055
author_rank: Super Contributor
timestamp: October 27, 2021, 01:07:32 am
content: Interesting! I have Pioneer single deck and can't remember when I used it last. It could very well be the belts and/or clutches. I wish I was into it.You are correct about the caps in these audio stuff. If it is working OK, I would leave it alone. If at all, I would replace only the power supply caps. But if you are selling it, why bother?

author: bob91343
author_rank: Super Contributor
timestamp: October 27, 2021, 03:36:59 am
content: I had a similar situation. A friend had a Fisher integrated amplifier and its power supply filter capacitors were running almost hot. I told him that was a time bomb about to explode. He ended up selling it to someone who probably could take care of it.

author: andy3055
author_rank: Super Contributor
timestamp: October 27, 2021, 04:02:19 am
content: Those amps were easy repairs. My first amp was one that I built myself after a Pioneer FMB100 tube amp. It had ECL82 push-pull output stage. I still have the schematic. Mounted the tubes horizontal to make the height 3 inches!Fun days

author: Dan75
author_rank: Contributor
timestamp: October 27, 2021, 12:27:52 pm
content: Hi, Andy and BobThanks for your elaboration on the coil windings. As I live in Holland, resources are more scarce to find these kind of things like copper wire. I did a search some time ago but that didn't give much results.If it will become a thing of sourcing overseas, then it will probably not worth it due to the total costs.Maybe better indeed for this to start a separate thread to stay on topic.As far as the recap goes, I do want to flip it, it sounds great as far as I can tell now. So what ever happens after selling it, is out of my hands. If a cap goes then it could be the next day, the next week or perhaps after some years. Who knows.But I always do a visual check to see if I can find something odd like a leaking or bulging caps. There are maybe 2 that have a minor rising, but I wonder if that really is a faulty going cap or that it is how it left the factory. I am not sure if the electrolytic capacitors are always flat on their tops. Sometimes you'll get fooled by some just by how they were manufactured. For example, the larger coupling caps in this Pioneer have that plastic on top instead of aluminum(?) and that plastic usually is not entirely flat.But indeed it works, so I'll leave it as is. Have enough other things on the shelf to wrap my head aroundI am liking of the idea I will have my own build amp some day. Nice that you did that, do you still have it Andy?

author: andy3055
author_rank: Super Contributor
timestamp: October 27, 2021, 03:30:34 pm
content: Oh no! Long beore I left Colombo, I sold it off. He was a friend of a friend! He wanted to buy my hand built speakers also but I hung on to them and sold them with an Akai amp I bought later. This was in the early '90s.Yes, open a new topic on the motor and post some close up pictures and we can go from there.

author: TimFox
author_rank: Super Contributor
timestamp: October 27, 2021, 04:03:47 pm
content: Quote from: Dan75 on October 26, 2021, 09:41:05 amSome DVMs have very high input impedance on lower-voltage full-scale settings, and use a roughly 10 megohm voltage divider to get the higher-voltage settings.Also, with nothing connected to the input, an auto-ranging voltmeter will set itself to a low-voltage input range.With the very high input resistance, and an open circuit connected to the input, the input will drift as the inevitable bias current flows through the high resistance. Shorting the input (either directly or through a reasonable resistance) should give you a very low voltage reading, sometimes limited by thermal emfs (depending on the metals in the circuit).

author: Dan75
author_rank: Contributor
timestamp: October 28, 2021, 08:14:23 pm
content: Andy, I will make a separate thread but not right away as I have few other projects going in front of this one.For example a Dual 505-3 where there is no service manual of to source for info. It has only a very small PCB, but a fairly large resistor starts smoking as soon as I let the motor run.Guess that either the caps (2 old plastic RIFA) are toast or that the motor is pulling too much current or something.And as far as the wire gauge for the new thread goes, I do not have a micrometer to measure such thin wires but maybe a caliper will do.But that's something for later on.

author: andy3055
author_rank: Super Contributor
timestamp: October 28, 2021, 10:48:13 pm
content: Those motors are very solid. Unless the bearings are ceased and/or there is some mechanical lockup, they will run forever. If it is a direct drive, definitely the bearings may be the cause. Belt drives will not load the motor that much to smoke the motor even if the platter bush is dry. So, you must be correct about the caps which is an easy fix.Yes, you can use a caliper to check the wire gauge. Make sure to burn off the varnish and the coating on the wire before taking a reading. You have to use a very weak flame like a birthday candle so as not to melt the copper!

author: Dan75
author_rank: Contributor
timestamp: October 29, 2021, 04:13:47 pm
content: Hi Andy, I just opened a new thread about the coil

author: andy3055
author_rank: Super Contributor
timestamp: October 30, 2021, 12:36:41 am
content: Great, I will check.

author: Dan75
author_rank: Contributor
timestamp: October 30, 2021, 11:49:07 am
content: Well, I did not expect this to happen. This morning, I got around finishing a simple entry level turntable from the eighties, from cleaning and checking.I hooked it up to what I thought was a problem free Pioneer SA-510, and to my surprise the right channel was sounding a bit less, with some crackles.So initially I thought that it was the cartridge on the vintage turntable or something else for that matter. But no, when I switched to cd on the aux channel, the right channel still sounded less.Also on the meter it is visible that R channel has less output. Played different kinds of music, just to be sure.I guess I am back to the drawing board on this one. Kinda sucks.... At least now I know that I have to eat my words in saying that the buyer was incapable of hooking it up correctly.Opening up the thread once more I guess. Don't know where to go from here though, I have been searching for the output transistors, but they aren't available anymore. If they need replacing that is.

author: andy3055
author_rank: Super Contributor
timestamp: October 30, 2021, 05:48:13 pm
content: If you have a scope, you can feed a known signal and start probing identical points on the 2 channels to compare. You can always get some equivalents for the transistors if need be.Keep the speakers disconnected for time being.

author: Dan75
author_rank: Contributor
timestamp: October 30, 2021, 07:09:49 pm
content: Hi Andy, I do have a scope but never used it. As I am fairly new with electronics, that is road I haven't taken yet.Not sure if the things works, never tried it out. Found it on a flea-market a few years back.It is this this one:

author: andy3055
author_rank: Super Contributor
timestamp: October 30, 2021, 11:41:05 pm
content: Wow! That looks pretty old! You may want to power it up and see.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: October 31, 2021, 11:16:18 am
content: Unfortunately your scope has only one channel, Harder to compare with the other channel, you have to just move the probe and remember what the trace was. But it should be really nice for audio work..15 MHz is just fine for audio. This type of scope is probably better for audio purposes than the newer digitizing ones, I have both types.I would take the cover off first and just look for anything obviously bad first.You should probably get a cheap 10X probe though, if it fires up without smoke. I like to power old stuff up in the garage in case a big cap goes bang! If you have an auto transformer, you could "warm" the thing up slowly starting with half volts and increasing voltage every five min or so.If you get any trace on the screen then get a probe and attach it to the Probe Adjust Lug, you should get a square wave on the screen.Just my opinion, maybe I am wrong about this but:If the final transistors go in an amp, they usually go in a big way, usually they burn up. So no output at all. They are also hard to replace, since they need to be matched and the equivalent transistors might not be exactly like the originals and especially may require different bias. So maybe the fault is not in the final transistors. (Hopefully)Wally

author: Dan75
author_rank: Contributor
timestamp: October 31, 2021, 08:03:24 pm
content: Hi guys,It is old indeedThe specs I found on the internet say it is indeed a one channel scope and is produced in 1972.I haven't fired the scope up since I bought it, so I don't know if it still is operational but the seller told me it worked. But that could also mean 25 years back?It came with three probes. I'll try to make an image of them. Been busy today with another project that almost is giving me sleepless nights. A Dual turntable that has a hum in it.But that is for another topic and time.I sure hope it isn't a failing transistor but maybe bad caps. I can see that some in there seem a little out of spec, visually that is. Gradually bulging tops. I think I will solder out some of them and run them through my meter, I have a meter that is similar to the Peak ESR meter.I had noticed that after a while of using the Pioneer the right channel got faulty as I described, but also got back in spec again? It fluctuates, you might say.Maybe I can hook up a (working) turntable to the Pioneer and play a audio test record on it to see what it does along a period of time. And maybe make a video of it.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: October 31, 2021, 08:11:53 pm
content: Lots of times intermittent problems are just bad solder joints on the PCB.Simple but not necessarily easy to find.I would not think a blown or leaky cap would be intermittent.

author: Dan75
author_rank: Contributor
timestamp: October 31, 2021, 08:52:56 pm
content: Hi Wallace, thanks, I will look into that, maybe there are broken connections. Maybe due to vibrations or degrading material?I also heard of that some transistors have a thing going on called thin whiskers. Could that also be causing these symptoms?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: October 31, 2021, 11:16:05 pm
content: Probably not whiskers, I think this is not intermittent. My cat is nowhere near you. HAReally just look for bad (cold ) solder first. Push on different parts of the board with a plastic or wood stick, see if the channel comes up.

author: andy3055
author_rank: Super Contributor
timestamp: November 01, 2021, 12:02:47 am
content: Points above are correct. In an amp this old, dry/cold solder joints are quite common due to the age. Most often those will happen in the high currant carrying areas like the leads of power transistors, Emitter resistors that get heated up, power supply components etc., although it is also possible to see them in other areas of the boards also. Mostly due to heating and cooling over a number of years of use. Hot running Emitter resistor leads are mostly at fault.Going back on my memory, I used to find faulty transistors by merely tapping on them like in the above post. Not that they had poor solder on the leads but internally they had faults. Those old transistors had weird things going on in them! Mostly when you hear odd, crackling noise that are intermittent.Also check the small electrolytic caps C25/26/75 and 76. D5 and D7 are also culprits. Once I remember I had to replace a similar diode like the D7. After making sure there are no dry joints, if you do not have replacements in hand, try interchanging the transistors and diodes between the L and R channels and you should be able to find the culprit. Luckily, you have only a handful of transistors and diodes after the volume control.Try not to adjust the idle currant pots if at all possible-unless you replace a transistor and you have the adjustment information.

author: Dan75
author_rank: Contributor
timestamp: November 07, 2021, 07:05:50 pm
content: Hi Andy,I did not forget about this but I had other priorities that got first.The caps C25, C26, C75 and C76 were soldered out of the board and checked using my MTester (Peak ESR meter like device).The C75/C76 came up with an ESR of resp. 15 Ohms and 10 Ohms and a voltage loss of resp. 2,1 % and 1,9 %.The caps C25/C26 came up with an ESR reading of resp. 5,4 Ohms and 6,1 Ohm, with a voltage loss of 1,1 % and 1,9%.The C25 and C26 were changed out for new ones with the same specs but the other two were not changed out as I do not have them in stock.Don't know if it is of any use to you. But I wonder if the ESR on the C75/76 is normal that high?The transistors are swapped. I numbered them on the rail and on each of the transistors themselves. Then I made a swap as you suggested.Took the transistors off the board using solder wick and soldering them back with fresh new solderI regret that I did not first check the result after the recap and before the interchanged trans'.Also did a visual check for dry soldering but couldn't find any yet. So maybe, when things start to fall back again, maybe a recap is in order.I hooked the unit up now to some speakers and a CD player and will test it to see what happens.Greetings,Dan

author: andy3055
author_rank: Super Contributor
timestamp: November 07, 2021, 08:35:01 pm
content: Hi Dan,As for the ESR of a cap, I believe there are charts you can refer to. Personally, I have never used an ESR checking device. At the time I did audio repairs, I used an analog meter to check the "kick" of an electrolytic, reversing the probes a few times. If a cap is leaky, the needle will start creeping back after the "kick," so to speak. I still use this method as I still do not own an ESR meter! I may decide to make one with all the schematics available freely these days.Regards,Andy

author: Dan75
author_rank: Contributor
timestamp: November 07, 2021, 08:53:01 pm
content: Hi Andy,Well, I hooked the Pioneer up to my speakers and also connected a CD player and a turntable.It looks the problem switched between channels. But what I also discovered is that the problem does not seem to exist in the AUX input butdistortion is very evident in Phono mode. It crackles, squeeks etc.Maybe also in CD mode, but I have to test that some more to be sure.I have an test record for audio equipment but it plays like sh*t. And just to be on the safe side, I also hooked the Pioneer up with a differentturntable, just to be sure the problem isn't within the TT. But no, it definitely is the amp.But in Phono mode, it seems both channels are out of spec. In AUX mode (where my CD player is connected to) it seems fine now. Maybe I have to test it for a longer period of time.

author: andy3055
author_rank: Super Contributor
timestamp: November 07, 2021, 09:07:40 pm
content: The age of that amp is sort of a clue here. Those old amps had transistors that developed internal problems, if I remember correctly. Some people used a "freeze" can to find the culprits also. I think they are still available. On the other hand, you could probably apply heat. But how can you direct it to a narrow area? Bring the tip of the iron close to the transistor?Just looked at the diagram and I am wondering if the Function selector is dirty, which is another common problem. For whatever it is worth, re-solder the leads of those transistors before that switch also.

author: Dan75
author_rank: Contributor
timestamp: November 08, 2021, 11:05:54 am
content: I will check the selector switch.But that could not have caused a fuse to blow I guess.Do you remember what you used to replace the transistors with back then? I want to order some parts for some other appliances soon and it would be nice if can order these as well.

author: Dan75
author_rank: Contributor
timestamp: November 08, 2021, 12:40:40 pm
content: By cleaning, do you mean all parts of the switch, as from face plate to on both print boards?

author: andy3055
author_rank: Super Contributor
timestamp: November 08, 2021, 05:58:37 pm
content: Did you say a fuse blew? I am sorry I did not notice that and that is not caused by the selector switch! My apologies. I was only thinking of weird noise that is intermittent. If you have to clean the switch, you will need to take it apart and from the looks of it, that is a bit of a process as it needs to come out of the board. It could be possible to take the metal cover off without taking the thing out of the board though.Which transistors are you planning to replace? Before you buy them, interchange between the two channels to find out if one of them is really gone bonkers.This is a good site to find equivalents for transistors in case you cannot get the original:https://alltransistors.com/transistor.php?transistor=13424

author: Dan75
author_rank: Contributor
timestamp: November 08, 2021, 07:06:02 pm
content: Yep, it was written in my very first post in this threadTo rewind: I sold a what I thought was a good solid amp to someone that initially did not seem to have the understandings of how to use audio and hook it up with othercomponents for example the speakers. I could tell, because I had to explain more than once how the speakers should be connected but he kept a look in his eyes that showed that he did not get it.The Pioneer has 2 terminals on it, A and B.So when it came back I was surprised that it had a defect because it was performing good when it left here.Upon inspection I found that fuse 3 had blown and when I replaced it after visually checking the components and measuring the output, it fired right up.That being said, that was when the amp started showing distortion and dropping on the same channel as the buyer reported as failed.The channel has output but is distorted. But I think I have to make a longer test run in order to determine if it is only on the Phono stage and not the others like AUX, Tape etc.And the interchange was already done as wellThat was explained in my post yesterday. The output transistors I meanThere are no exact, same (or NOS) replacements for this amp anymore, only other transistors which come close but have other specs that will make your bias different and that is something beyond my understanding to adjust.

author: andy3055
author_rank: Super Contributor
timestamp: November 09, 2021, 12:05:57 am
content: Ah! I remember that. But then, after you replaced the fuses it started working but with this noise and the crackling, if I recollect. Am I correct? So, if that is the situation now, we can forget about the fuse issue and just look for the distortion and the noise. So, for that noise, it is quite possible the switch is dirty. But if there is distortion, that is something else like a bad transistor or a resistor for that matter.By the way, if you have a can of switch cleaner, you can inject it in to the switch while operating it so that the crud will come off of the contacts.

author: Dan75
author_rank: Contributor
timestamp: November 10, 2021, 02:36:46 pm
content: Hi Andy,I have cleaned switches and pots. I have a can of CRC cleaner that I use for this.The next thing I did today was replace some caps that I have on hand. Going over the unit I saw something that did not notice earlier.On a spot on the board that runs towards the selector switch.I will look the numbers up in the service manual to tell you which ones.It comprises of a transistor (D880 if I'm correct), a diode, and two resistors. This small section shows a blackened area that to me, seems to have been overheated at some point.From the emitter of that transistor, a red wire runs directly to the selector switch (the Tape/Phono/AUX switch)My best guess is, I haven't got around to check it yet, that one or more of these components are faulty.I took a picture of the spot but in the photo the blackening is less prominent then with the naked eye.Will post it next.

author: Dan75
author_rank: Contributor
timestamp: November 10, 2021, 02:42:55 pm
content: This is a close up of the spot:

author: Dan75
author_rank: Contributor
timestamp: November 10, 2021, 02:54:05 pm
content: It is transistor Q25, a 2SD880and a 3,3 K Ohm resistor from what I can tell from the service manual, and another oneAnd lastly a diode D17 which should be MZ-192 ?? Think that are Pioneer part numbers. that is not a Pioneer part number but seems to be the specific coding for a thermal fuseBecause something must have been causing that fuse number F3 to blow, that does not happen without a reason off course

author: andy3055
author_rank: Super Contributor
timestamp: November 10, 2021, 05:59:12 pm
content: That picture shows some sort of residue from a spill(?) like thing. There must be bad solder joints underneath. Clean and re-flow the solder in the vicinity and check the resistors for their correct values. MZ192 is a Zener diode with a voltage of 19.2 volts from what I can gather.If you need to replace the 2SD880, I believe I have some of those which I can put in the mail. PM me of necessary.

author: Dan75
author_rank: Contributor
timestamp: November 11, 2021, 09:37:45 am
content: I will go through them soon. I already took the trans out and that one seems ok. Measures .460 and .457 over Base - Collector and Base - Emitter.Other direction no reading.

author: Dan75
author_rank: Contributor
timestamp: November 17, 2021, 08:24:52 pm
content: Hi!It took some time but I have checked the parts in the area I mentioned in my former post. The resistor R79 in the service manual shows that it should be a 3,3K (if that is not a fault in the manual!?)but the one I took out measures 1577 Ohm on my meter.The measurement complies with the color code on the actual resistor: Gold, Red, Green, Brown and not with what is says in the service manual: 3,3K ??The diode (D17, which according to the SM is a MZ192) gave this measurement: Uf= 779mV C= 58pF

author: andy3055
author_rank: Super Contributor
timestamp: November 18, 2021, 01:41:41 am
content: R79: sometimes you do find discrepancies like that. As long as the resistor has the value according to the color bands, it should be ok unless someone before you had changed it.Check R80 and R76. Also check the voltages in that part of the circuit. Q25 emitter and base. If that Zener diode is good, you should see the 19.2 volts on the base.

author: Dan75
author_rank: Contributor
timestamp: November 18, 2021, 09:23:15 am
content: I read your post just now, but I soldered the parts back in and wanted to check if it works, especially since you also wrote about cleaning the switches etc.I did that, and after spraying them and turning the switches over for 50+ times, I also noticed they moved a whole lot smoother and easier.This morning (different time zone off course) I hooked it up to the cd player and TT and all sounds good.Don't know if those exist but I would like to have a test cd which one can use to test out audio equipment.I have a record but that is only suitable for the phono input naturally as you cannot hook the TT up on a tape input, well maybe with a pre-amp?The input selector switch runs from the face of the unit to one point on the PCB and to a second one via a sliding mechanism. I cleaned all three of these, as wellas all other switches and potentio meters on the unit.Anyway, I don't know if it is still necessary to check the ones you pointed out, but as for now, it's working. No distorted sound on the phono either

author: andy3055
author_rank: Super Contributor
timestamp: November 19, 2021, 12:06:07 am
content: That is good news. To be safe, check the voltages on that transistor. The values are in the diagram. I think you must have gone through a cold joint and fixed it. There could be other similar issues given the age.

author: Dan75
author_rank: Contributor
timestamp: November 19, 2021, 11:59:34 am
content: Not sure how to do that. Measuring voltage on the transistor in circuit. Which MM mode should it be and where do you place the leads? And with the unit powered up?Sorry, but that is where my know how ends

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: November 19, 2021, 12:28:04 pm
content: To have the voltages you will need to have the unit turned on: you can easily compare the voltages on the components, having as a reference the working channel, the components are mirrored

author: andy3055
author_rank: Super Contributor
timestamp: November 19, 2021, 06:24:21 pm
content: Quote from: Dan75 on November 19, 2021, 11:59:34 amThe voltages must be checked with power on. The older amps had a bottom plate that could be removed leaving everything open from the bottom. If not, you have to do it from the top. In either case, you must be careful not to slip the probe and short the legs of the transistor. The base voltage can be checked from the two ends of the Zener diode that connects to the transistor base. The emitter is easier as it goes out from the board - see point marked 1 inside the circle.Put the negative lead of the meter on the ground connection or the point marked 9 (or 51) inside a circle and check the two voltages per the diagram. Just be careful not to blow anything!

author: Dan75
author_rank: Contributor
timestamp: November 20, 2021, 01:40:43 pm
content: Up until now it has been working fine and realizing that I haven't had the best of luck recently I will leave as is now just because it seems to do its job.I did replace some of the caps you had mentioned earlier, not all of them as I did not have every type needed.Maybe indeed I jumped upon a cold solder somewhere or it's just a combination of the things that have been done.So far,

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 20, 2021, 02:02:23 pm
content: Years ago my SO's Kenwood receiver had a similar problem. I was looking at the board and the SO (who is to be obeyed) pushed on a screw and the unit came back to life.Tightened the screw 15 years ago and still works. Bad ground probably.

author: andy3055
author_rank: Super Contributor
timestamp: November 20, 2021, 06:08:06 pm
content: As long as it works without any issue, you can leave it and hope it will not come back!

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: December 01, 2021, 11:30:11 pm
content: I do not remember the circuitry in that unit but static and pops can be a diode or transistor breaking down intermittantly usually it will be a TO92 type transistor (not always). Heat/cold can be used to isolate the defective part. A scope at the amp input capacitor can tell you if its in the preamp or output section. Good luck.Jeff