At low volume (and by that I mean phone set to low volume, not the preamp - certainly don't want to overdrive the phono stage) I don't see the harm. I've done this many times to test potential Craigslist purchases; I know it'll sound bad because of applying a RIAA EQ to a "flat" signal but it's a lot easier to carry a headphone plug to 2xRCA cable in my jacket pocket than to bring a turntable into someone's house, and really I'm just testing for functionality and lack of bad noises, no sense getting all worked up about perfection when you're looking at cheap used gear that you're going to probably end up doing minor repairs on anyway
Yamaha CR1040 no click (relay) : Worth repairing?
- Thread starter Jpkwd
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- yamaha cr1040
At low volume (and by that I mean phone set to low volume, not the preamp - certainly don't want to overdrive the phono stage) I don't see the harm. I've done this many times to test potential Craigslist purchases; I know it'll sound bad because of applying a RIAA EQ to a "flat" signal but it's a lot easier to carry a headphone plug to 2xRCA cable in my jacket pocket than to bring a turntable into someone's house, and really I'm just testing for functionality and lack of bad noises, no sense getting all worked up about perfection when you're looking at cheap used gear that you're going to probably end up doing minor repairs on anyway
Latest voltage readings reinforce that the left power pack is bad. I still don't have any compelling reason to think there's anything wrong with either pre-driver. On the other hand, I also still don't have an idea about why the offset can't be zeroed on the channel that seems to have a good power pack.
At this point I think it would make sense to remove the left power pack and see if the receiver will come out of protection.
I can't think of any plausible way for that to happen.
Cheers,
chazix
At this point I think it would make sense to remove the left power pack and see if the receiver will come out of protection.
I can't think of any plausible way for that to happen.
Cheers,
chazix
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That's my concern, but I can believe that the iphone volume can be turned down enough that it's not a problem.
Cheers,
chazix
Ok, Power Pack removed. Clean job for a first timer.
Amp not back from the dead yet : still in protection mode.
Reading at test point is now 0.350v. Still high voltage on the second test point (Right channel) -4.6v can't bring it down to zero.
i've got a sudden urge to go ahead and remove Ppack 2 but i,ll wait for input before i do that.
I'm reading the large CR1040 : i understood removing the powerpack and soldering resistors could allow me to check predrivers and confirm they are working. That could be a second step.
Should i go ahead and remove Ppack 2 to see if the relay clicks ? then perhaps test the predrivers.
im wondering if the second ppack might be the reason of the high reading on the test point at 4 volts.
Amp not back from the dead yet : still in protection mode.
Reading at test point is now 0.350v. Still high voltage on the second test point (Right channel) -4.6v can't bring it down to zero.
i've got a sudden urge to go ahead and remove Ppack 2 but i,ll wait for input before i do that.
I'm reading the large CR1040 : i understood removing the powerpack and soldering resistors could allow me to check predrivers and confirm they are working. That could be a second step.
Should i go ahead and remove Ppack 2 to see if the relay clicks ? then perhaps test the predrivers.
im wondering if the second ppack might be the reason of the high reading on the test point at 4 volts.
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Glad the power-pack-ectomy went well.
If you also remove the other power pack, I expect the receiver would come out of protection, because there should be no way for any appreciable DC to reach the output points. This finding would not necessarily mean that the second pack is bad, though. (In fact, I guess I would bet that the second pack is OK. I'm assuming it is the one that had 0.047V between its 3 & 8 pins, which is a strong indicator of good health.)
Pre-driver testing, with both power packs removed, and the feedback-loop-closing resistors added, is probably what I would do at this point. If you're up for that, my hat's off to your enthusiasm!
Cheers,
chazix
If you also remove the other power pack, I expect the receiver would come out of protection, because there should be no way for any appreciable DC to reach the output points. This finding would not necessarily mean that the second pack is bad, though. (In fact, I guess I would bet that the second pack is OK. I'm assuming it is the one that had 0.047V between its 3 & 8 pins, which is a strong indicator of good health.)
Pre-driver testing, with both power packs removed, and the feedback-loop-closing resistors added, is probably what I would do at this point. If you're up for that, my hat's off to your enthusiasm!
Cheers,
chazix
removing the Ppack went very well in fact.
I'm trying to understand why the dc voltage would be so high (4V) on the channel where the good Ppack is still in (which keeps the relay from clicking i'm assuming).
Bad predriver could cause that you think Chazix?
as for the test, i think i recall 200ohms resistors would suffice, right ?
So say we are right :
the first Ppack is bad -> i replace it with an STK module
the second Ppack is good -> i can keep this guy in place (or replace it with another brand new stk module but i read this is not necessary).
and Both predrivers turn out to be good.
COuld the dc voltage still high on the good ppack (right) channel ? What could cause that you think ?
Really wondering what could cause that.
This is proving out to be very fun so even if the amp stays dead, it'll have been well worth the fight !
I'm trying to understand why the dc voltage would be so high (4V) on the channel where the good Ppack is still in (which keeps the relay from clicking i'm assuming).
Bad predriver could cause that you think Chazix?
as for the test, i think i recall 200ohms resistors would suffice, right ?
So say we are right :
the first Ppack is bad -> i replace it with an STK module
the second Ppack is good -> i can keep this guy in place (or replace it with another brand new stk module but i read this is not necessary).
and Both predrivers turn out to be good.
COuld the dc voltage still high on the good ppack (right) channel ? What could cause that you think ?
Really wondering what could cause that.
This is proving out to be very fun so even if the amp stays dead, it'll have been well worth the fight !
Definitely could.
200 ohm parts would be OK, if you have some on hand. If you're going to need to pick up some resistors for the purpose, I would suggest 330 ohms, a very common value.
One of the signs of pre-driver health is to push about 6 milliamps of current through the resistors, leading to a voltage drop of about 1.2V across each resistor if you use 200 ohms, or about 2V for 330 ohms.
Another sign of health, which is more in question in this case, is whether the pre-driver can regulate the voltage at the center point of the resistors (which is the output point of the power amp circuit) to zero volts.
Yep.
If the output stage of the pre-driver is working correctly, the resistors will dissipate a miniscule amount of power (2V squared divided by 330 ohms = about a dozen milliwatts), so you could go with even lower-power parts if that was convenient.
If the pre-driver has a fault that's severe enough to overheat the resistors (which I believe is pretty unlikely), that's a finding that's well worth the cost of a couple of "popcorn parts". (Though now that I think of it, it wouldn't hurt to use flameproof resistors if you can find some easily, just in case they do make the ultimate sacrifice for knowledge.)
ok, Powerpack ectomy 2 went perfect
Amp relay clicked in without the two ppack
Thinking about it, I should have taken mesures on the predrivers pins when the resistors weren't tacked. I'll do it after i remove them if needed
Tacked 330 Ohms 1/4 watt resistors across the power pack pins 1 to emittor resistor 1 and power pack pin 10 to Emittor resistor, left and right side.
On power up, no relay click (that was a little disappointing but hey, we're working this slowly)
No smoke and no loud bang, that was less disappointing, to me at least it was !
Left 1 emittor 1 2.89 V
Left 10 to emittor 2 -2.24V
Right 1 to emittor 3 -3.19V
RIght 10 to emittor 4 2.27V
Voltage at emittor solder point (where i tacked the resistor) is also the same as the TP values below
TP1 -5.13V
TP2 -6.37
predriver pins
left 8 -5.0V
Left 10 - 5.0V
left 13 -7.96V
left 14 -2.96V
left 15 50.4V
Right 8 -6.3V
Right 10 -6.3V
right 13 -9.45V
Right 14 -4.18V
Right 15 50.4V
Amp relay clicked in without the two ppack
Thinking about it, I should have taken mesures on the predrivers pins when the resistors weren't tacked. I'll do it after i remove them if needed
Tacked 330 Ohms 1/4 watt resistors across the power pack pins 1 to emittor resistor 1 and power pack pin 10 to Emittor resistor, left and right side.
On power up, no relay click (that was a little disappointing but hey, we're working this slowly)
No smoke and no loud bang, that was less disappointing, to me at least it was !
Left 1 emittor 1 2.89 V
Left 10 to emittor 2 -2.24V
Right 1 to emittor 3 -3.19V
RIght 10 to emittor 4 2.27V
Voltage at emittor solder point (where i tacked the resistor) is also the same as the TP values below
TP1 -5.13V
TP2 -6.37
predriver pins
left 8 -5.0V
Left 10 - 5.0V
left 13 -7.96V
left 14 -2.96V
left 15 50.4V
Right 8 -6.3V
Right 10 -6.3V
right 13 -9.45V
Right 14 -4.18V
Right 15 50.4V
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Have you tried adjusting the offset pots to see if the test points can be zeroed? If they can't, it points strongly to bad pre-drivers.
On the other hand, it would be so unusual (in my experience) for both pre-drivers to fail that I can't help wondering if there's something else (also unusual) in the works. The only suggestion I have along those lines, though, is to make a very careful examination for hairline cracks in the circuit board. I'm thinking that there might be a ground integrity issue, but the only way I can think of that that could happen within the power amp circuit of a CR-1040 is a broken circuit board trace.
On the other hand, it would be so unusual (in my experience) for both pre-drivers to fail that I can't help wondering if there's something else (also unusual) in the works. The only suggestion I have along those lines, though, is to make a very careful examination for hairline cracks in the circuit board. I'm thinking that there might be a ground integrity issue, but the only way I can think of that that could happen within the power amp circuit of a CR-1040 is a broken circuit board trace.
Days later, I just thought of one simple test that could be made to check on my notion that there might be a ground integrity problem. That is to make an ohmmeter check (with the receiver having been powered off for a while) between pins 2 and 9 of the pre-drivers. Both those pins are connected to ground traces on the circuit board, and those traces should be connected together somewhere (though I confess I haven't tracked down where, exactly). So, there should be very low resistance - less than 1 ohm - between the pins.
Yours slowly,
chazix
Oho, sharp eye for trouble! I must admit I never thought of that. There is a series network comprising 0.05uF and 10 ohms between the amplifier output point and ground.
I'm not facile enough with stability criteria to evaluate the risk. I can say that I've rigged up such loop closures on a number of CR-x40s and never observed oscillation, but I have no clue how close or far away it may have been. Maybe I'll try fiddling with the RC network next time I have the chance, to see if I can deliberately provoke oscillation.
When you say "I would remove it to do this test", I assume that you mean to remove the output RC network. In case Jpkwd wants to take that precaution, it could be done by disconnecting:
At least one terminal from any of C647, C649, or R641 (left channel)
Ditto for C648, C650, or R642 (right channel)
Thanks for the tip, amr2!
chazix
amr2
Well-Known Member
Yes, I mean remove any output RC network. I'm sorry, my English isn't very good...
HI Chazix, amr2, my turn to apologize for the slow response. I've been away from the amp so couldn't continue testing
0,4 and 0.5 readings at both Preamp chips : i should've probably taken amr2 advice and further details provided but read the answers from amr2 too late.
There must be something else going on
which we should find at one point or another
0,4 and 0.5 readings at both Preamp chips : i should've probably taken amr2 advice and further details provided but read the answers from amr2 too late.
There must be something else going on
which we should find at one point or another
I take it those are the ohmmeter readings between pre-driver pins 2 & 9 - they look good.
To be honest, I can't think of further tests that I feel very comfortable about suggesting in the present context. Having said that, if you feel like carrying on with what might turn out to be tilting at windmills, you could try:
1. Measuring the DC on pins 1 and 3 of each pre-driver. These are the input pins - very sensitive, so a probe slip will almost surely result in the pre-driver being overdriven, though it should be awfully difficult to cause any damage. To make these measurements, it would be best to ground the meter's negative lead at a point that's close to the pre-drivers. You can probably spot the sort of Y-shaped circuit board trace that connects to both pre-drivers' pin 2 - that would be a good ground point for these measurements. The voltages on pins 1 & 3 should be quite small. (Tens of millivolts, maybe? I can't remember.) For each pre-driver, after measuring the pin 1 & 3 voltages, it would make sense to also measure pin 10 at the same time. That pin connects to the power amplifier output point - same as the TPs - and will have a much larger voltage, according to your previous work.
2. Force the protection relay to engage, and check the receiver's output meters to see if there's any indication that the power amp circuits are oscillating. You would do this with the receiver powered up (under a DBT rig, if at all possible), volume set to minimum, and the METER switch set to LEVEL. Now for the hard part. The least risky way I can think of to force the relay to engage is to identify transistor TR809, and make its collector terminal conduct to ground. The collector terminal is the middle one of the three terminals. You could use a small metal-bladed screwdriver or something similar to temporarily make a short circuit between TR809's collector and another of its terminals. (As it happens, shorting the collector to either of the other terminals will work for this experiment.) You should hear the protection relay click on when you make the short-circuit, and then you can check the receiver's meters. The meters should show zero output. They might twitch a bit when the relay switches on or off, but they should quickly settle down to zero and stay there. If the meters detect any output when the protection relay is engaged, then there is an oscillation issue, and amr2's precaution is probably the next step. (Especially because I can't think of any other steps in this case...)
Long-windedly,
chazix
Chazix,
I ended replies to this thread quite abruptly since your last post, i see i've been idled for almost 6 months !
Will try you suggestions before the end of the summer
Judt need to target one of those rainy
Days and, i'll get Busy on this
I didnt give up, just took a looooong pause
Appreciate the help
