Discussion in 'Yamaha' started by tmsears, Apr 13, 2017.
Yeah, a little on the pricey side, but not terribly so. Good find!
I went ahead and ordered a pack of the above-mentioned resistors, as it seems to be nearly impossible to find them in that value and form factor anymore. At least this way I won't have to worry about folding the resistors over accidentally when I work on our near the phono/eq board, as they do stand off a good ways above the board. I still don't know what I am going to do about the bridge rectifiers though. Maybe I could buy four diodes and whittle my own?
Well, for bridge rectifiers, the only one I saw on mouser that fit the bill was the 905-BR62
I think it should work as a replacement for both bridge rectifiers.
Since I will have to go back into the power supply board, I thought about replacing the 4 rectifier diodes as well. I am stuck between these two:
The only issue is the first one is 1.3 max forward voltage instead of 1.0 With the second one I get to the original forward voltage, but it would drop my surge current from 200 to 150 A.
I don't know which value is more important...
If there is anyway if cleaning it up to make it less "family circus" I would be happy to hear them for sure.
Well, the new power resistors for the eq board arrived yesterday. A slight modification was required:
In addition to the leads being double pronged instead of single, the legs are a lot longer than the originals. They still clear alright, and hopefully the added length will help dissipate heat more efficiently in that area:
When the new rectifiers come in I will re-post the voltages and maybe I can get some help with further troubleshooting at that time.
Kudos go out to @zaibatsu , @avionic , and @Hamish119 for there expertise and guidance. I would not have gotten this far without their help.
Well, the rectifiers arrived yesterday. I must live close to the warehouse; it's like Wiley Coyote and the Acme Co. On ship times here, on ground UPS.
Anyway, got those installed and the caps resoldered on.
No pic but I had to trim the ground leads as most of the ends had corroded, some more than others. I have no idea how they could corrode underneath solder but they did.
It was late when I finished so I will look over my work and take some voltage readings later tonight and provide an update.
Well, somehow the AC coming out of the DC outputs of the (new) rectifiers is now DOUBLE what it was before I replaced them. This doesn't make any sense...
That's strange, they look like they're in the right way.
I wonder if any of C179, C180, C181 metallized mylar caps might be shorted.
Can you remove and check those on your component tester?
D167 1SS82 -> BAV21 by the way. If there's any suspicion of that.
I'm thinking your AC issue is a wild goose chase..
Maybe a recap of where you are now and what symptoms you're going after would help everyone catch up. Since this is a general thread there have been a bunch of posts in between so it's a bit hard to follow.
I'm working on an A-700 right now that had all sorts of weird problems that turned out to be dry solder joints pretty much all over the place. It would randomly go into and out of protection with differing amounts of DC on the relay terminals, sometimes the dim bulb would be dim, other times it would pulse, sometimes it would just be bright.
Not sure if you've gone over the boards but this particular amp was the most solder cracked piece I've ever worked on. If yours is anything like this it could very well be some of your problems.
Yes, I have gone over every solder joint with new solder added...sometimes the joints were so bad they collapsed like a ruined souffle when I would try to reflow them.
That is an excellent idea Cat!. I will printout the thread and highlight the main points and then post a recap to get everyone up to speed. Very good idea indeed! It may take a little time, but it should be worthwhile.
I have put the repairs on hold for the moment so that I can take the time to work on restoring my C-6 and M-4, and get some tunes running again.
Been busy for the holidays but I will be updating soon with a summary.
Looks like when I posted in #23 I thought you were finished. 18 pages later, guess I was mistaken. Following along, but not sure I can be of much help.
Got the rough draft of the summary in Microsoft word; down to 1,00 words - Avionic was right, it is hard to follow. First thread so that is my excuse.
I will get it up here this week hopefully. I'm gonna try to link all the posts in so people can refer to them if desired.
It certainly has been a learning experience .
In an effort to get back into reviving both this amp and the thread; here is a summary of what has happened so far:
I bought this amp for use as a backup as my main setup needed some TLC. It turned out that this A-1000 was in worse shape that the combo that it was supposed to fill in for, and was suffering from the usual issues:
The dreaded conductive glue had corroded jumpers and resistors.
The “BBQ board” aka eq board 14 was cooked and its resistors had cracked casings.
The speaker protection relay had stopped working.
Trimmer pots were erratic.
Most of the solder joints had cracked joints/poor joints.
Many of the electrolytic capacitors were out of spec.
With @zaibatsu ‘s help I put together a parts list for the resistors, trimmers, and capacitors needed to get this unit back up to snuff.
All corroded and glue-contaminated parts were removed and the boards were cleaned of any remaining residues. Restoration of the main, eq, flat amps, and eq14 boards were all done in sections and power on tests were performed in between ‘boards. The mica insulators on the outputs were replaced and both the drivers and the outputs were re-greased with the appropriate thermal grease. All solder joints were re-flowed and touched up with fresh solder.
Afterwards the amp was in a working state with a few glitches that were worked through:
- When setting the “AUTO CLASS A” adjustment, the voltage goes from +16 to -14 Vdc instead of -16 Vdc for the “L” level. The problem may be IC 102- See posts #72,88,96,&98. I ordered two of each ICs but never installed them.
- Idle voltage would wander from 10mV to 12.8 I got it to finally stabilize at 11.6 for both channels with some 25-turn trimpots and some persistence (see post #62).
- Some mild to moderate background hum, (see post #81). In hindsight I think the hum is due to outside interference, but at least that should be easy to remedy, if I am right.
Where It All Went Horribly Wrong:
Aside from the above mentioned issues, the amp was doing good, that is, until this (post #119):
It was later discovered that during my attempts to find and clear up the source of hum that my little ham- hands fatigued the leads of the bias compensation transistors. This caused one of them to fail, causing a thermal runaway which then in turn, trashed the outputs, drivers, predrivers, and several resistors in the right channel. The other compensator did not have a chance to fail, so the left channel was spared. The known damage was as follows:
*=iffy. replaced them anyway.
Here is a pic of the checked area:
View attachment 1085360
The Repair Attempt:
All of the above were replaced with the correct substitutes, or uprated equivalents. I can go back into the amp and provide part numbers if necessary, but I did not think to make a replacement parts list at the time.
Also at this time I corrected a factory diode error for the 22 volt supplies on the eq board as indicated in post #206.
I got all the parts in, hooked the amp back up to the DBT, and…no click. There was a parts mismatch (see post#228). I contacted B&D and they sent me the correct parts free of charge. Swapping the correct parts in unfortunately did not remedy the problem. I then started comparing readings between both channels to see if I could find a discrepancy, but I was unsuccessful. After receiving some guidance The rail voltages were checked, with the following results:
D164 was suggested as a possible cause for the difference between RP+ and RP-.
Upon further instruction, AC presence was checked for at the output collectors, and this was the result:
RP+ 107.9 <------The 49.2 Vdc one
Upon additional instruction, I checked D168,D162,D163,D164,D165,and D166, out of circuit, and they all tested good (see post#296).
Then it was suggested to test the components inside the triangle in the schematic in post #285:
View attachment 1085361
I measured these components against their counterparts in the working channel and they were identical, so I think those can be ruled out. I then checked for AC voltages as suggested in the same post (#285) and the following was the result:
AC coming out of the secondaries:
BL= 0v (reference)
DC Rail Voltages (with ac present as noted):
HB+ 57.9Vdc and 128.2Vac
LB+ 34.3Vdc and 75Vac
LX/LP+ 33.8Vdc and 74.3Vac
RX/RP+ 49.7Vdc and 109.6Vac
22+ 21.5Vdc and 47.1Vac
With those issues noted, I was instructed to check into the +- 22v further, by making sure there was -9V at the junction of D606 & D604, and -15V at the junction of D602 & D604. The results were:
At the junction of D606 & D604 = -4.6Vdc
At the junction of D604 & D602 = -9.2Vdc
I then verified that the diodes were correct, and correctly installed (to my knowledge) . Then I was told to measure the resistance of R759, and it was determined that it was failing (post#316). On my own volition, I replaced R759 and both bridge rectifiers. The rectifiers were both replaced with two BR62’s..which Only served to DOUBLE the AC coming out of the outputs! WUT?!
As It Stands Today:
After the repair attempt failed I put the unit away so I could get ready for the holidays and work on my main system. Having recapped and tuned up those units, I am now turning my gaze back onto the A-1000. This summary should get the thread back up to speed. Hopefully with some help, I can get this baby up and running, because my main system still had some issues that need attention.
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