Yamaha A-1000 Repair and Info Thread

Now that I look at your board more closely, I do see that the white silkscreen is gone. I did even know that you could sand them, neat!
I didn't think to use 1-watt resistors, will have to remember this if I have to do it again :thumbsup:.

Also, I didn't know that the tracks were for heat dissipation. I will have to beef mine up tonight.
 
Hey @tmsears did you measure the Class-A semi-variable resistor?

Mine appears to measure 50K rather than 100K the parts list claims. Mildly annoying since if so, I've ordered the wrong part.
I did find it a bit strange that they used 100K there when the A-700 uses a 20K but didn't think anything of it until I measured the A-1000 one.
 
Hey @tmsears did you measure the Class-A semi-variable resistor?

Mine appears to measure 50K rather than 100K the parts list claims. Mildly annoying since if so, I've ordered the wrong part.
I did find it a bit strange that they used 100K there when the A-700 uses a 20K but didn't think anything of it until I measured the A-1000 one.
SM says 100k for the class A, which is the value i bought for in a Bourne trimpot, so I hope it is 100k. I have not measured it yet but I will tonight. Keep you posted.
 
Well then.

I pulled the pot for the class A at VR103 and in measures as a 50k Ohm, not a 100k. And I have no idea why. A little concerning since I ordered a 100k to replace it. Should I not use that? Ir does it mater?

In other news I have finished up everything except the re-greasing the main power transformers, and I have hit a snag.

I pulled one of the transistors, and they do indeed need re-greasing - there are voids in between the heatsink and the mica insulators. Not super bad but not good either.

So, I went to lift the mica insulator, very carefully mind you, and....it separated into two pieces....unevenly... :oops: Guess what type of transformer package doesn't have mica insulators readily available...:(

So I bought some Kapton Polyimide as @avionic suggested in this thread many a year ago: http://audiokarma.org/forums/index.php?threads/sanken-transistor-insulators-mt200.181686/
in the form of 1mil, 1 inch tape. Thing is, I have no idea how to use it in this application. Do you grease both sides, or just the non adhesive side? Do you stick the adhesive side to the heatsink or to the transformers?
http://audiokarma.org/forums/index.php?threads/sanken-transistor-insulators-mt200.181686/
I was also able to buy some MT-200 mica insulators from B+D and am waiting on them, but it would be nice to know how the Kapton stuff works.:idea:
 
Guess the next person who does an A-1000 can learn from our mistake haha. Yamaha misprints win again.
I ordered a 50K to be safe and called it a $2 mistake (my national RS-components does free post which is kinda handy).
I don't have the knowledge to say if it would be OK or not (I suspect it'd be fine but I didn't want to risk it), I'd just use the stock pot until it's convenient to get another.

Not sure about the kapton but there's some info about the adhesive in post #9 here:
http://www.diyaudio.com/forums/car-...k-transistor-insulating-tape.html#post3451953

From memory kapton has a lower thermal conductivity than mica, probably why avionic usually recommends mica first, and I bet the adhesive has a lower thermal conductivity than thermal transfer compound too.

I'm a fan of the mica, it's good you found some more. I've managed to re-use the stock ones each time so far, I feel my luck might run out on this set. From memory the trick was to minimise bending, pushing down and sliding the transistor off the pad, and trying to do the same with the pad from the heatsink. I think a bit of paper or a razor blade to break it free with minimal bending helped.
 
That's probably how I broke them, I lifted the edges up 5 degrees to get under them.

Here is a pic of the cleaned up amp board:
IMG_20170607_172358861.jpg

Will update again when the insulators get in.
 
Just checked where the pot mounts, shouldn't matter at all using the 100K over the 50K apart from giving coarser adjustment.
My stock value was 31.2K in case it's useful to anyone, I did get a 50K just to maintain the factory range and granularity.
pot.jpg

I really wanted this to be a long term project but tmsears has inspired me to get into a bit faster than I planned.
This giant mess is probably familiar:
mess.jpg mess2.jpg
 
Good to know that the pot I have is usable, in a pinch, as I am low on money at the moment. I think I will stick to the old pot and if it goes starts trying to go haywire during adjustments, I will pull it and use the 100k.
It makes me wonder about the nature of the error in the service manual. If they misprinted or if they found out later that the lower value pots were better/easier to use?:idea: Yes the mess is very familiar :yikes:.

In other news, the mica insulators came in today so tonight will be the moments of truth... I will be using the dim bulb tester for initial startup. If there are any tips/tricks/etc. to doing this I will be checking this thread prior to firing it up.
Wish me luck!
 
Most of this old audio gear is notorious for errors unfortunately. Everything from SMs to schematics to the board screenprinting, the Sansui forum has a running thread of all the errors so it's not just Yamaha.
eg. on the A-1000, D148 is right below D136, but the screenprinting shows "D148" as a resistor. Might be useful to someone in 10 years doing a channel rebuild ha.
Similar mistake on the A-700 ("D153" screenprinted in error from memory) which caught me out.

The general rule is to stick to the parts in the amp, from what I've seen these changes are usually made immediately pre-production but post-printing (board, schematic, SM), so all the amps are usually built the same. Sometimes there's running changes too but from what I've seen they're often documented.

Those pots are fine in my experience, a burst of deoxit, a few cycles and then drying it works alright. I've heard one bad story but mine have all been OK.

I think it's quite safe on the DBT, you'll be fine. You probably already know, can't set bias until it's on full mains power so make sure any new pots are set to the old values.
Fingers crossed it comes right out protection and the problem was just a cracked solder joint - it's likely. If the relay doesn't click in the normal (for DBT) time do turn it off quickly, as small parts can still overheat/fry while on tester.

A smart person would wrap meter leads and screwdrivers before poking around in there but I'm stupid and lazy. Doesn't hurt to mention anyway.
 
Last edited:
It Lives (With a few minor issues)!

The Yamaha is up and running with a few issues I have questions on and may need help in solving:

1) I first tried turning the unit on with a 60 watt bulb - no relay click. Then a 75 watt - no click. Then I jumped to the 150 watt I used to test with when the unit went haywire - relay clicked....why did I have to go so high for the relay to be able to activate? Is this bad?

2) it takes the unit about 6 seconds before the relay clicks on, is this normal?

3) the right channel heatsink gets hotter than the left channel - 116F vs 105F - specifically the 2nd black power transistor in. The two little transistors on that heat sink seem to get a little hotter than the other side as well. Any reason for that? I thought that maybe I didn't put enough thermal grease on that one but if I hadn't the heat wouldn't be going to the heatsink, and it is most certainly doing that.

4) I am having some sort of grounding issue? I hooked up a pair of headphones to check for hums/static and when I select DAD I get a bad him when I fidget with the volume knob and the hum stats when I crank the volume nearly all the way up...BUT, the hum disappears if I place my hand on the chassis. It doesn't seem to do this on the other inputs and if it put my terminators for the phono inputs from my older preamp the hum disappears. Also the hum will get way more prominent if I put my fingers near the audio leads going in and out of the volume control or mute switch. The hum will even "follow" my fingers from one channel to the other depending on where I put gone on the audio lead.

Observations: the amp sounds wonderful even with the above issues I need to resolve.
The idle current was but low and I was able to adjust them out pretty close to spec but my God this pots have got to go! Nearly had a heart attack when the voltage went from 9mv to 28 to 33 to 14 just from turning the pot just a hair.. haven't even touched the class a adjustment pot yet.

Decided to keep the meters on when I activated the class A mode, and nearly freaked when I saw the voltage go from 11 to 153 and 134mV, right and left channel s respectively. But I guess this is normal as an went from sounding solid state to sounding a little bit like a tube amp... Not that I will be using that mode because..

That hear! The heat is alright in normal mode but as others have said before, you put this amp into class A model and you might as well throw a few steaks on it.

Any advice for my mentioned issues are welcome and would be greatly appreciated.
 
A smart person would wrap meter leads and screwdrivers before poking around in there but I'm stupid and lazy. Doesn't hurt to mention anyway.

You mean like this :biggrin::

IMG_20170609_153323331.jpg

I would be doing it exactly as you do, but the horror stories I have read here on AK have me scared (that and I can't afford to mess anything up)
 
Last edited:
No shame in playing it safe!

1) Yes that's normal on the A-1000 - mine wouldn't click with a 77W bulb but did with 100W. I was going to mention this earlier but figured you already knew since you said you'd being playing music on it with the DBT. So if you want the minimum safe bulb, 100W is the answer there.
2) Is normal in my experience, does vary a little from amp to amp. I'm guessing you already replaced C177, C178 (22uF, 220uF)?
3) Let the amp idle for 15-20mins on mains power and check the idle current, sounds like an adjustment mismatch to me. Before you do that, put your multiturn trimpots in for the L/R idle adjustments - I just assumed you put those in since they were on your purchase list, definitely important - the stock single turns are way too touchy for idle adjustment.
4) Is the hum present on the Tuner or Aux inputs or only DAD? Because if so it will likely just be an issue in the DAD wiring path - I'd check solder joints on that RCA and the plug that comes out of the phono board immediately after the RCA connects to the board... you could unplug and plug the DAD wire's other end from the input selector board too and check that socket's solder joints onto the selector board too. Before all that hassle tho, I'd spray some isopropyl into the front of the DAD selector switch, I have found that excess *whatever* in there not drying up can cause a buzz too. If it's *only* that input it will be a minor problem.

Regarding the bias voltages, get those Bourns multiturns in for the idle pots, then re-check.

My A-700s live in Class-A mode, no dramas. These amps are built to handle it, though I feel it takes a good set of speakers to really appreciate the difference. The bias transistors mounted to the heatsink will regulate the values to a more constant (and lower) value after about 30-40mins in my experience. The A values won't stabilise in 2mins. With that said, I do think the amp needs to be built strong to take the heat (hence redoing all the solder joints, recapping, etc).

The switching point adjuster won't have any impact on those bias voltages either, it only affects what happens when the amp would clip in Class-A mode (~10-12W of output power, will actually be well above comfortable listening levels on most speakers). You do need some 8Ω 100W load resistors to make that adjustment. It's not critical to do as long as you kept it at the factory value, in my experience.
 
Last edited:
Well, I went ahead and put my scope on the test points for the class A switch, and I have problem where the "notches" do this kind of rolling wave thing here is a photo of both the + and - of one side:

IMG_20170611_020549573.jpg

Full disclosure: I am very, very new to scopes, and I realize that I don't have the audio signal displayed; I did have it up on the scope as well before putting the probe on the other side of the resistor used as a test point, but I could never get the two scope shots to "line up" so I thought I would show it this wait to demonstrate the issue, if it is indeed an issue at all, I don't know enough to say..but I don't think it is supposed to do this:

200w.gif



For the set point for the class A, on my meter, when adjusting the pit, it goes from +16v to -14, sometime soon lower. Changing the pot out with the 100k didn't help, but adjusting was easier, even though value is higher as was discussed.

Any ideas? I am trying to learn as much as I can but just not there yet on this kind of thing..
 
To set the Class-A switch point all you need to do is feed a 1kHz sine wave to the input, you don't need a scope (unless it's just used as a sig gen).

Did you connect an 8Ω load to L/R speaker terminals and turn the volume up until meter (AC volts) reads 15.5V across each of the loads?
There is only one test point for this (TP101), the other is chassis ground. For the switching point adjustment there will be a + and - value. It should be 16.xx in both directions, you need to turn the pot (slowly) as described in the manual and stop the moment the polarity changes. Worth reading both A-700 and A-1000 manuals for this step.

"Step 3" is the only thing that requires a scope and it's not mandatory as it's not an adjustment - just a confirmation that the APS system is working (they call it X-AMP but it's different to what Yamaha used the X for in previous years, and is basically the same system as the APS in the M-60 and M-80, using an extra set of output transistors to perform power supply switching). This has nothing to do with the Class A adjustment / switching point. It doesn't use TP101, only R275/R276 and ground. I have no experience with this one so maybe check with avionic, though I suspect if you've followed the manual (30VAC output, no load, 1kHz sine input) and correct test points, I'd guess your display issues might just be an issue with the scope's trigger settings. I'm new to this part too.

I think you might be overcomplicating things here. Set the idle and switch point, plug in some speakers, and see if she sings.
If it drove 30W into the 8Ω loads, it'll be safe to test with speakers and see.
 
Last edited:
I think you might be overcomplicating things here. Set the idle and switch point, plug in some speakers, and see if she sings.
If it drove 30W into the 8Ω loads, it'll be safe to test with speakers and see.

You are probably right that am overcomplicating it.

I completely forgot to mention that, yes, I used an 8ohm dummy load running at 30 watts (15.5vac) per the manual. I I did adjust the pot to the switchover spot using the test point and a multimeter. What had me confused was the meter going from 16+ to 14- instead of 16-. So, I decided to use the scope confirmation method in the manual -probing the resistors specified and that is when the "wavy" output of those resistors started to cause me a little alarm as I believe they are supposed to be flat like in the service manual, not like a wave machine at a water park:D. I am indeed new at the scope thing - I tried adjusting the trigger seeing as you say, but that just made it "fuzzy".

I just figured I would ask while I was busy trying to track down my hum/noise issue.;)
 
Last edited:
Yeah the 2V difference seems a little strange but to be honest I can't really comment on how normal it is as mine is in a million pieces, just put my mouser order through yesterday actually. From my understanding the Class A adjustment and APS aren't directly related, but if you're concerned about your output maybe shoot avionic a message, suspect he'd be familiar with that test since it's common to the M-60 and M-80 (albeit those are tested under load interestingly). I'm certainly no expert. All I know is that those are two separate measurements/adjustments entirely so the problem with one may not have anything to do with the other, but with that said, I know when something goes wrong in these, the voltages go haywire everywhere so it's not entirely crazy either.

Does the amp play fine with speakers, and did the idle match better after the new trimmers went in and readjusting?

I meant to say regarding the hum thing, you should swap the DAD plug going into the input board sockets (orange or red one from memory) with a different input like AUX/Tuner which would help isolate whether the problem is before or after that board. The plugs/sockets make it really easy to narrow things down.
 
The bias adjustments are easier to make with the new trimmers, but the idle current seems to drift from 10mV to 12.8 no matter how much I try to tweak it. Granted, this is within tolerance, so I am guessing it is ok.

Keep in mind, my educational and professional background is in IT, so I am used to more precision in regards to parameters (i.e. I'ma perfectionist), but I will get used to it.

Yamaha likes to change their names up for their features during this era: X-AMP, ADS,ZDR.. small wonder I didn't get more confused than I already am!:confused:

I got the x-amp and the auto class A setups jumbled together from another thread here that had said the x-amp was just a visual scope confirmation of the class a adjustment, which is how I got confused; if I can find it again I will post a link to it.
 
Update:

I've got the hum somewhat under control by bridging the ground wires that connect the equalizer/phono board to the main amp board with solder on the equalizer board side just like it is done on the main board side, that seemed to reduce the hum in the DAD circuit so that now there is just mild hum on all non-phono inputs. This happens when you crank the volume knob to about 7/8 of it's entire range. The hum goes away the second you connect an input source to any of the non-phono inputs. I don't know if this is normal or not, as I don't recall having about hum under any of these circumstances on my older M4 and C6.

I had a faint ticking sound in the phono section in addition to the expected him that normally occurs when there is no table connected, but I got rid of that by readjusting the input cables.

I going to do a distortion test tonight and report back with the results.
 
Going back through the adjustment steps just to done check everything:

Step 1 in SM:
Re-checked the Bias and I think I finally got it to stabilize on 11.6mV on both sides.

Step 2 in SM:
Still low by 2 volts on the negative side:

IMG_20170614_040741896.jpg IMG_20170614_040800577.jpg IMG_20170614_040926770.jpg

Gonna PM Avionic and see if he can peruse this thread and tell me what step 3 in the SM is for and why it looks the way it does in the gif i posted earlier in the thread.
 
Back
Top Bottom