Yamaha A-1000 Repair and Info Thread

Well, here are hte measurement for all the voltages. I have them paired up as they are in the schmatic, but I tested each line anyway since I was at it:

AC coming out of the secondaries:

RE= 47.6V
BL= 0v (reference)
BE= 28.2

DC Rail Voltages (with ac present as noted):

HB+ 57.9Vdc and 128.2Vac
HB- 57.9Vdc
LB+ 34.3Vdc and 75Vac
LB- 34.5Vdc

DSC -30.2Vdc

LX/LP+ 33.8Vdc and 74.3Vac
LX/LP- 33.8Vdc
RX/RP+ 49.7Vdc and 109.6Vac
RX/RP- 33.9Vdc

Now, I am not an expert by any means, but I don't think that is normal. I found it odd that D162 was spewing 128Vac straight out of the positive dc terminal..
 
Last edited:
Maybe @avionic or @Hamish119 can weigh in. I assume that both of the bridge rectifiers are shot? if so, can anyone suggest suitable replacements? Would I need to go ahead and replace those big diodes as well?
Are the big caps fried now?

I am on a limited budget as usual but shipping kills me more than anything else so a single mouser order would be the best option if possible.
 
AC coming out of the secondaries:

RE= 47.6V (x 2)
BL= 0v (reference)
BE= 28.2 (x 2)

DC Rail Voltages (with ac present as noted):

HB+ 57.9Vdc and 128.2Vac
HB- 57.9Vdc
LB+ 34.3Vdc and 75Vac
LB- 34.5Vdc

DSC -30.2Vdc

LX/LP+ 33.8Vdc and 74.3Vac
LX/LP- 33.8Vdc
RX/RP+ 49.7Vdc and 109.6Vac
RX/RP- 33.9Vdc

Now, I am not an expert by any means, but I don't think that is normal. I found it odd that D162 was spewing 128Vac straight out of the positive dc terminal..
Thanks for the 'interesting' (and confusing) voltage measurements. :confused:
Here's why they're confusing;

The maximum AC voltage from the secondary winding on the transformer is <100V (RE - RE). That suggests the 128V AC must be coming from an external source (nothing but the bulb limiter should be connected to the amplifier).
Or it's a 'ghost' reading. :eek:


Furthermore, if it is from an internal source, it should be seen equally on both channels as there is only 1 x transformer, 1 x lower voltage/higher current bridge rectifier (D168 - for Class A operation), 1 x higher voltage/lower current bridge rectifier (D162 - for Class AB operation) & 1 x set of smoothing/reservoir capacitors shared between both channels. :idea:

Can you measure the AC voltage at the smoothing/reservoir capacitors?

However, there is a further anomaly with the plus & minus ?X/?P DC voltages. I'm assuming (dangerous) that the 'Auto Class A' switch was OFF: i.e. the amplifier was in Class AB mode. Therefore, I would expect these voltage measurements to be closer to the plus & minus HB voltages. :idea:

Whilst on the bulb limiter/tester, measure the plus & minus ?X/?P DC voltages with the 'Auto Class A' switch ON. The measured DC voltages should be within 1 volt of the voltages measured on the 33000µF capacitors.

Also, don't forget to measure the plus & minus 22 volt rails - they're critical to the correct operation of the amplifier.

Good Luck!
 
Thanks for the 'interesting' (and confusing) voltage measurements. :confused:

Oh, trust me, if there is incompetence to be had, I will fully accept responsibility. I agree the reading is odd, which is why I tested it three times in a row...I had the amp plugged into the DBT, with a 100watt bulb. The bulb stayed dimly lit, and never wavered from that brightness the entire time. The only exception to note is that I am using a cheapy $30 multimeter from Home Depot (home improvement chain). I actually have two of them. Also, the electricity here runs a little high, at around 122V.

I did measurements again, This time with the other multimeter and the results are the same. Tried the DBT on a different power outlet - again, the same. Checked the DBT, and it is working fine. I checked the voltages on the power outlets that are built into the amplifier and they read at about 102 volts or so, I am assuming, due to the DBT.

The maximum AC voltage from the secondary winding on the transformer is <100V (RE - RE). That suggests the 128V AC must be coming from an external source (nothing but the bulb limiter should be connected to the amplifier).
Or it's a 'ghost' reading. :eek:

Didn't know a ghost reading was a thing, but that wouldn't surprise me.

Can you measure the AC voltage at the smoothing/reservoir capacitors?

Using the reference point, on the smaller of the smoothing caps that is closest to the main amp board one leg measure the 128Vac and the other leg measures the 75Vac. On the larger cap closest to the main amp board one leg measures the 75Vac and the other leg, which has all the ground wires connected to it, measures nothing.The others measure nothing on AC.

I'm assuming (dangerous) that the 'Auto Class A' switch was OFF: i.e. the amplifier was in Class AB mode.

Yes, the Auto class A switch was off.

Whilst on the bulb limiter/tester, measure the plus & minus ?X/?P DC voltages with the 'Auto Class A' switch ON. The measured DC voltages should be within 1 volt of the voltages measured on the 33000µF capacitors.

I just finished testing them. All the ?X/?P voltages drop about 1 volt when Auto A is turned on, and they are all still within 1 volt of the 33000 caps.

Also, don't forget to measure the plus & minus 22 volt rails - they're critical to the correct operation of the amplifier.

Sorry about that, I took the measurements with the others before and wrote them down, but I forgot to post them. 22+ is 21.5Vdc, 47.1Vac. 22- is 14.5Vdc, with no AC present.
 
I just finished testing them. All the ?X/?P voltages drop about 1 volt when Auto A is turned on, and they are all still within 1 volt of the 33000 caps.



22+ is 21.5Vdc, 47.1Vac.
22- is 14.5Vdc, with no AC present.
Excellent work!

Ignoring the other issues, the low -22V issue needs to be resolved first. Any voltage anomaly at the power amp input stage will be propagated to the output stage with GAIN!

As the plus & minus HB supplies are good, check the voltage (with reference to 0V) at both ends of D604.
You should measure -9V at the junction of D606 & D604.
You should measure -15V at the junction of D602 & D604.

Yamaha_A-1000_-22V.jpg

Good Luck!
 
Last edited:
At the junction of D606 & D604 = -4.6Vdc
At the junction of D604 & D602 = -9.2Vdc
That's NOT good! :no:

Check that the Zener diodes are the correct values: i.e. 1 x 9V1 + 2 x 6V2. The measured voltages suggest the the installed Zener diodes are 4V7. :eek: :no:
Or it may be that resistors R759 (on Equaliser 1) & R760 (on Equaliser 14) have substantially increased in value!

Measure the 'in circuit' resistance of R759. If it's >675R, disconnect Equaliser 14 and measure it again. It should be less than or equal to1k8.

With Equaliser 14 disconnected, measure the 'in circuit' resistance of R760. If it's >1080R (10 x 27k in parallel = 2k7... 2k7+1k8 in parallel = 1080R). Good hunting! :whip:

Good Luck!
 
That's NOT good! :no:

Check that the Zener diodes are the correct values: i.e. 1 x 9V1 + 2 x 6V2. The measured voltages suggest the the installed Zener diodes are 4V7. :eek: :no:
Or it may be that resistors R759 (on Equaliser 1) & R760 (on Equaliser 14) have substantially increased in value!

Measure the 'in circuit' resistance of R759. If it's >675R, disconnect Equaliser 14 and measure it again. It should be less than or equal to1k8.

With Equaliser 14 disconnected, measure the 'in circuit' resistance of R760. If it's >1080R (10 x 27k in parallel = 2k7... 2k7+1k8 in parallel = 1080R). Good hunting! :whip:

Good Luck!
Will when I get some free time, hopefully today or tomorrow.
 
Here is what I removed from the equalizer 1 board, per previously mentioned post:

IMG_20171031_020303104.jpg
The one on the right is different from the others. I do not recall the order of where it originated from.
 
OK, I have not had the chance to take any more measurements, but I looked and I can confirm that I did install the (4) 6V NZX6V2B zener diodes in D601-D604, and the (2) 9V NZX9V1E zener diodes in D605-D606. Made sure I had not put any of them in backwards, etc. Mouser hasn't messed an order up yet so I will assume they are the correct type? Hamish's Whipping List is next up on the to-do list :biggrin:.
 
That's NOT good! :no:

Check that the Zener diodes are the correct values: i.e. 1 x 9V1 + 2 x 6V2. The measured voltages suggest the the installed Zener diodes are 4V7. :eek: :no:
Or it may be that resistors R759 (on Equaliser 1) & R760 (on Equaliser 14) have substantially increased in value!

Measure the 'in circuit' resistance of R759. If it's >675R, disconnect Equaliser 14 and measure it again. It should be less than or equal to1k8.


I measured R759 with the equalizer 14 at 518 Ohms. So, I disconnected it and re-measured.The resistance "climbs", slowly but surely, until it reaches 1380-14000 Ohms.
 
Yes those diodes sound correct to me, and it sounds like R759 is toast. Should be a stable value.
Replace it and proceed with the Hamish list.
 
Yes those diodes sound correct to me, and it sounds like R759 is toast. Should be a stable value.
Replace it and proceed with the Hamish list.

Probably will replace all of the power resistors, the three on the equalizer 1 board and the one on the #14 board. That was the end of @Hamish119 's list so far - I had only skimmed through it before I started, and I thought it would be more work than it was, when it really wasn't.
 
Last edited:
So, pardon my ignorance, but doesn't the issue of the bridge rectifiers spewing out AC on the DC outputs still need to be addressed? Or is that normal?

I hate to try to count my eggs before they hatch, but I have limited funds so I need to make my shipping from mouser count. Any troubleshooting help to identify parts needing definite replacement would be most appreciated. I will be charged the same in shipping wither I buy 1 component or 50.
 
What's the current build state of the main cap / PSU board assembly?

I've never seen an output failure on this amp family go back that far (especially since you caught the fault and turned it off quickly), so I actually wonder if this AC issue was pre-existing and perhaps the cause of the hum you were struggling to track down earlier.

If the issue was created by the melt-down, your main caps should still be fine. If it was pre-existing then the caps may have seen a beating, but maybe the amp wouldn't have clicked / worked at all if the rectifiers weren't working properly.

- Rectifiers aren't expensive and it won't be hard to find a match for both of those if needed.
- I doubt you'll need to replace the caps to get the amp going in any case (you can measure them with your basic tester if you like just to see if the numbers seem normal, even though it's not a proper working-voltage test), and wouldn't bother doing that until / unless you get it working.

Maybe avionic and hamish can confirm / deny / elaborate.
 
What's the current build state of the main cap / PSU board assembly?

I've never seen an output failure on this amp family go back that far (especially since you caught the fault and turned it off quickly), so I actually wonder if this AC issue was pre-existing and perhaps the cause of the hum you were struggling to track down earlier.

Makes plausible sense, and it would explain the hum, but I didn't have the foresight to check the voltages at the start, so probably no way of knowing for sure. This has been educational to say the least! As for condition, I think the caps are still good (I hope) but based on my limited knowledge, I think the rectifiers are shot. I don't know about the diodes, but I would replace them out of an abundance of caution if I can get confirmation that the rectifiers are shot. I re-flowed all the solder joints on the board when I had it out. I had to disconnect a few wires and put heat shrink on the sections of them that I had burned during my desoldering fiasco. :rolleyes:

If the issue was created by the melt-down, your main caps should still be fine. If it was pre-existing then the caps may have seen a beating, but maybe the amp wouldn't have clicked / worked at all if the rectifiers weren't working properly.

Good question. maybe @avionic or @Hamish119 or any member for that matter.

- Rectifiers aren't expensive and it won't be hard to find a match for both of those if needed.

No they are not to bad on price I don't think but I had no luck with replacements because I don't know what specs to look for/what is a tolerable range in the specs. That's why I mentioned them earlier in the thread. I am pretty good with caps, and resistors now, but semiconductors, no.

- I doubt you'll need to replace the caps to get the amp going in any case (you can measure them with your basic tester if you like just to see if the numbers seem normal, even though it's not a proper working-voltage test), and wouldn't bother doing that until / unless you get it working.

I tested the caps when I pulled them with the china capacitance tester and they still show to be within range, so hopefully they are okay. They would be expensive to replace I would imagine.

Maybe avionic and hamish can confirm / deny / elaborate.

Hopefully they will chime in soon. But I may have scared them away! :rflmao: I have sunk so much money into this beast that I will never get back - but if I can fix it at least it will have been an education.
 
Last edited:
I'm watching with interest what you find out. Sounds like you might be fighting with two issues between the hum and then the bias transistor shorting.
The one I picked up was Chernobyl'd in the normal way thankfully so no huge troubleshooting was needed on my part.
 
Back
Top Bottom