motorcityguy
Active Member
MTF, using that fuse as a knife switch, there was NO popping in speaker as power was cut on/off. Also, no popping when pre/out jumpers removed.
Correct Pin-Out on SX-850 Protection Relay
- Thread starter motorcityguy
- Start date
MTF, using that fuse as a knife switch, there was NO popping in speaker as power was cut on/off. Also, no popping when pre/out jumpers removed.
motorcityguy
Active Member
DC offset (unadjusted) is 9.8-10.8mV on LH channel, and 1.5-1.9mV on RH channel.
That tests suggests that the turn off (and on) does not have an overt fault - that it IS functioning - but not exactly.
(the overt fault does NOT sense the turn off ac voltage - but rather is influenced by other collapsing voltages that this circuit is supposed to BEAT!!)
BUT
That suggests that the relay opening IS being beaten by some other turn off transient.
The ONLY way I can see that happening is that the protect off signal is being slowed down by something.
Now, as far as the turn off:
D8 rectifies the 7.5v ac turn on / turn off signal from the lamp circuit.
R25 2.2k charges C5 4.7uf, but R24 15k forms a voltage divider with r25 - limiting the voltage (negative voltage!!) on C5.
Then THAT negative DC voltage (-5.1) modifies a bias on Q6 (R29 4.7k) that comes from the -13.5v supply.
EVENTUALLY Q6 is turned on (base goes 0.6v positive of the emitter (which is grounded)
The original q6 is 2sc945a. The kit Q6 is ksc2383, which is a transistor who's die has a greater Safe Operating Area (the ability to handle an instantaneous burst of heat) to handle the energy of discharging C6 100uF through R27 22 ohms. Eventually C6 is discharged enough that the base of q7 is no longer 0.6v above it's emitter (which is RAISED up from ground by about 8 volts by the current of the relay coil flowing through R28 220 ohms.
Complicated - with MANY time constants interacting in a chaotic looking (but elegant to me) dance.
EVERY value of component varies the time constants - and you / we are looking for a change (intentional or not) that SLOWS IT DOWN.
Too big of a cap?
First, try it with the original relay. look for the pop.
If it goes away, well, TELL US. Head scratching SQUARED time. wonder if it's a Omron DPDT LY2F-AC24 with a shading ring on the pole.
Try it with the original Q6, look for the pop.
then leave Q6 in, and put back in the Original Q7, look for the pop.
Gain on Q6 or Q7? hmmm....
Looking at mouser.com - backtrack to EXACTLY the part number of the relay that you paid for, then read the markings off the component.
(the overt fault does NOT sense the turn off ac voltage - but rather is influenced by other collapsing voltages that this circuit is supposed to BEAT!!)
BUT
That suggests that the relay opening IS being beaten by some other turn off transient.
The ONLY way I can see that happening is that the protect off signal is being slowed down by something.
Now, as far as the turn off:
D8 rectifies the 7.5v ac turn on / turn off signal from the lamp circuit.
R25 2.2k charges C5 4.7uf, but R24 15k forms a voltage divider with r25 - limiting the voltage (negative voltage!!) on C5.
Then THAT negative DC voltage (-5.1) modifies a bias on Q6 (R29 4.7k) that comes from the -13.5v supply.
EVENTUALLY Q6 is turned on (base goes 0.6v positive of the emitter (which is grounded)
The original q6 is 2sc945a. The kit Q6 is ksc2383, which is a transistor who's die has a greater Safe Operating Area (the ability to handle an instantaneous burst of heat) to handle the energy of discharging C6 100uF through R27 22 ohms. Eventually C6 is discharged enough that the base of q7 is no longer 0.6v above it's emitter (which is RAISED up from ground by about 8 volts by the current of the relay coil flowing through R28 220 ohms.
Complicated - with MANY time constants interacting in a chaotic looking (but elegant to me) dance.
EVERY value of component varies the time constants - and you / we are looking for a change (intentional or not) that SLOWS IT DOWN.
Too big of a cap?
First, try it with the original relay. look for the pop.
If it goes away, well, TELL US. Head scratching SQUARED time. wonder if it's a Omron DPDT LY2F-AC24 with a shading ring on the pole.
THAT would DEFINITELY slow the relay release. DC fed into an AC relay can pull in the relay coil, at the expense of a slower release.
Try it with the original Q6, look for the pop.
then leave Q6 in, and put back in the Original Q7, look for the pop.
Gain on Q6 or Q7? hmmm....
Looking at mouser.com - backtrack to EXACTLY the part number of the relay that you paid for, then read the markings off the component.
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motorcityguy
Active Member
Got tied up with life, and didn’t get back to the shop for over a week. Here’s the update….
Before running the tests that MTF specified, I pulled one leg of the resistors that were mentioned in his circuit explanation, so I could verify they were within spec:
- R25 (2.2K) verified at 2.17K
- R24 (15K) verified at 14.8K
- R27 (22) verified at 22.3
- R28 (220) verified at 221
- R29 (47K) verified at 46.5K [post had typo & referred to this as 4.7K]
Now for the actual tests and questions:
1. Old Q6 (2SC945) reinstalled—NO CHANGE (shut-off pop still audible)
2. Old Q7 (2SC1384) reinstalled AND still with old Q6 (2SC945)—NO CHANGE (shut-off pop still audible)
3a. Reinstall original relay: Much to my surprise, the shut-off pop was still audible—no better/no worse. I am puzzled by this, because I never noticed the pop prior to changing the relay. Previously I reported there was no pop with old relay. My lame excuse is that I barely used this unit before replacing the relay. It may also suggest the problem is intermittent and/or varies in intensity (and therefore sometimes not noticeable).
3b. Left the old relay in, and reinstalled the “new” Q6 and Q7. No change. Same results as 3a.
4. Finally, there was a question about the part number marked on the actual relay that was installed: It is “OMRON LY2F 24VDC”.
2. Old Q7 (2SC1384) reinstalled AND still with old Q6 (2SC945)—NO CHANGE (shut-off pop still audible)
3a. Reinstall original relay: Much to my surprise, the shut-off pop was still audible—no better/no worse. I am puzzled by this, because I never noticed the pop prior to changing the relay. Previously I reported there was no pop with old relay. My lame excuse is that I barely used this unit before replacing the relay. It may also suggest the problem is intermittent and/or varies in intensity (and therefore sometimes not noticeable).
3b. Left the old relay in, and reinstalled the “new” Q6 and Q7. No change. Same results as 3a.
4. Finally, there was a question about the part number marked on the actual relay that was installed: It is “OMRON LY2F 24VDC”.
These tests were enlightening because after reinstalling the original relay and still hearing the pop, it proves that the new relay is NOT the problem (although I had previously suspected it was). Is there anything else, perhaps outside of the protection board (dirty switches, etc) that COULD cause this low-level pop in speakers at shut-down?
motorcityguy
Active Member
Any further thoughts on this?
merlynski
Curmudgeon Electronicist
This makes me think it is not the protection circuit.
Try it with one Pre-out/Power-in jumper installed, and then the other, to see if it is one channel or both.
motorcityguy
Active Member
Thanks for the suggestion. I removed (only) the RH jumper, still heard pop. Reinstalled RH jumper and then removed (only) the LH jumper. Got same pop noise. No difference with either one jumper out or none out. (No pop with both removed.)
During the course of this, I noticed that touching the RH jumper with my fingers produces a massive hum in RH channel. Conversely, touching the LH jumper results in a super low level imperceptible hum. Something not grounding properly on RH channel? Guessing this is unrelated to the pop, but there is such a difference in hum between channels, I've got to believe something's not right. Any thoughts on THIS?
motorcityguy
Active Member
Sure! I measured between center pin of each respective jack, and the chassis. Here are the results (with jumpers removed):
RH: pre-out 0.8mV*, main-in 0.3mV**
LH: pre-out 1.2mV*, main-in 0.3mV**
*Both pre-outs started at a larger values initially, but dropped quickly to these values after a minute or so. Might have gone down even further if I waited longer.
**Making the measurements at the main-in produced audible hum in that channel's speaker when test lead was connected (equal magnitude on either channel). This hum was much less than the objectionable hum mentioned in post #27, from finger-touching the (installed) RH jumper.
FWIW, these measurements were made with the old relay re-installed, as part of prior MTF diagnosis. I intend to reinstall the new relay (which made no difference in speaker pop). I will re-measure the pre-out/main-in and report back if numbers are any different after relay change.
motorcityguy
Active Member
Got it! I won't. Will leave in the old relay for now.
Just to clarify: measure BETWEEN pin 1 and 3? Or, two measurements: 1) between pin 1 and chassis ground, and 2) between pin 3 and chassis ground? THANKS!
motorcityguy
Active Member
Ok, here's the results....
Jumpers OUT
1. POWER OFF: Both pin 1 & 3 at ~0.2mV
2. TURN ON: Both pin 1 & 3 spike to ~ +5V before relay clicks; both are < +2V at time of relay click
3. STEADY-STATE ON: Both pin 1 & 3 drop quickly to ~ +5mV, and continue to drop to under +1mv (~0.8mV)
4. TURN OFF: Both pin 1 & 3 jump to peak of ~ -5V, then decay to zero
Jumpers IN
1. POWER OFF: Both pin 1 & 3 at ~0.2mV
2. TURN ON: Both pin 1 & 3 spike to ~ +5.5V before relay clicks; both are < +0.5V at time of relay click
3. STEADY-STATE ON: Both pin 1 & 3 drop quickly to ~ +5mV, and continue to drop to under +1mv (~0.8mV)
4. TURN OFF: Both pin 1 & 3 jump to peak of ~ -3.6V, then decay to zero
1. POWER OFF: Both pin 1 & 3 at ~0.2mV
2. TURN ON: Both pin 1 & 3 spike to ~ +5V before relay clicks; both are < +2V at time of relay click
3. STEADY-STATE ON: Both pin 1 & 3 drop quickly to ~ +5mV, and continue to drop to under +1mv (~0.8mV)
4. TURN OFF: Both pin 1 & 3 jump to peak of ~ -5V, then decay to zero
Jumpers IN
1. POWER OFF: Both pin 1 & 3 at ~0.2mV
2. TURN ON: Both pin 1 & 3 spike to ~ +5.5V before relay clicks; both are < +0.5V at time of relay click
3. STEADY-STATE ON: Both pin 1 & 3 drop quickly to ~ +5mV, and continue to drop to under +1mv (~0.8mV)
4. TURN OFF: Both pin 1 & 3 jump to peak of ~ -3.6V, then decay to zero
Couple of comments... The voltage spikes at turn-off, are negative. All other measurements were positive voltages. Also, the turn-off pop occurs immediately, and is not coincident with the voltage spike on pins 1 & 3. Lastly, I carefully proof-read this before posting, so the units of mV and V should be accurate as stated above.
merlynski
Curmudgeon Electronicist
That is great info!
Flip around the AC plug in the wall and try it.
Do you have a 512-KSA992FBU on hand, if so replace Q5, 2SA733, on the protection pcb.
Jumpers in, check for pop.
Look at these points when powering off for a quick drop in dcv before the relay drops:
On AWR-101,
Pin 10:
Pin 14:
Pin 18:
Pin 17:
Flip around the AC plug in the wall and try it.
Do you have a 512-KSA992FBU on hand, if so replace Q5, 2SA733, on the protection pcb.
Jumpers in, check for pop.
Look at these points when powering off for a quick drop in dcv before the relay drops:
On AWR-101,
Pin 10:
Pin 14:
Pin 18:
Pin 17:
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motorcityguy
Active Member
Actually Q5 was already replaced with KSA992 during the protection board rebuild. Looking back at my earlier post detailing the parts I changed, I see that I forgot to include Q5. Oops! I went back and edited that post to add the Q5 description: 2SA733>>KSA992FBU
Switched AC plug and remeasured. Same results. With jumpers out, the "on" surge is maybe a bit higher (7V vs. 5V) but it's all before relay engages. All in all, I think it's same results, within measurement error.
Jumpers in, check for pop: It's still there.
Voltages as follows:
Pin 10: 35.8V; no surges on power-off (just quick smooth decay)
Pin 14: 49.8V; no surges on power-off (just quick smooth decay)
Pin 17: 44.9V; no surges on power-off (just quick smooth decay)
Pin 18: 44.9V; no surges on power-off (just quick smooth decay)
merlynski
Curmudgeon Electronicist
After rebuilding the entire Protection Board, I STILL have the speaker "pop" when shutting the unit off.
I went back and reread the whole post, if the volume control is affecting the pop then its origin is at or before the volume control. I am digging into this . . .
merlynski
Curmudgeon Electronicist
The pop maybe happening faster than your meter can respond. Do you have an oscilloscope?
Power on, on the Flat Amp, AWG-038:
Measure dc volts on the negative side of C5 and C8. Check their orientation.
Measure dcv on the wiper of volume control, VR2a and VR2b, and see if any is present, and if it changes as you adjust the volume control.
Check C27, (100µF, 50v) it is +51vdc power supply decoupling cap for both channels on the Flat Amp.
Check that pins 2, 5 and 8 are 0vdc with power on, and 0Ω to chassis with power off.
Power on, on the Flat Amp, AWG-038:
Measure dc volts on the negative side of C5 and C8. Check their orientation.
Measure dcv on the wiper of volume control, VR2a and VR2b, and see if any is present, and if it changes as you adjust the volume control.
Check C27, (100µF, 50v) it is +51vdc power supply decoupling cap for both channels on the Flat Amp.
Check that pins 2, 5 and 8 are 0vdc with power on, and 0Ω to chassis with power off.
motorcityguy
Active Member
Merlynski, First let me THANK YOU for your patience and continued trouble-shooting support. Second, here are the responses...
New, additional clue: While trying to perform step 3, and turning up volume control to about 1/3, I found that I sometimes got a hum in speakers, but if pot shaft was wiggled I could silence the hum. (This was conducted with selector on PHONO 1.) This suggests that my volume pot is not as clean as I thought it was. I will perform this next unless you advise otherwise.
1. Unfortunately, I do not have a scope or access to one.
2. The neg side C5 = +0.5mV; orientation on board matches schematic & board marking. On C8, I was unable to recognize which side is "neg". One side measured 0.1mV; Other side measured a couple of mV at turn-on, and quickly decayed to about 0.2mV
3. I was unclear where to make this measurement. Guessing it's on some of the legs of the volume pot, but not sure which ones. See pic attached---can you mark the spots? Also, see new clue at bottom of post....
4. Wasn't clear if you meant check its capacitance, or measure voltage. I am unable to measure capacitance, but voltage was measured to be +47.4V
5. Power ON: pins 2, 5, 8 are each at 0.3mV. Power OFF: each pin (2, 5, 8) show ~0.3ohm between pin and chassis
New, additional clue: While trying to perform step 3, and turning up volume control to about 1/3, I found that I sometimes got a hum in speakers, but if pot shaft was wiggled I could silence the hum. (This was conducted with selector on PHONO 1.) This suggests that my volume pot is not as clean as I thought it was. I will perform this next unless you advise otherwise.
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merlynski
Curmudgeon Electronicist
You are most welcome!Merlynski, First let me THANK YOU for your patience and continued trouble-shooting support. Second, here are the responses...
1. Unfortunately, I do not have a scope or access to one.
2. The neg side C5 = +0.5mV; orientation on board matches schematic & board marking. On C8, I was unable to recognize which side is "neg". One side measured 0.1mV; Other side measured a couple of mV at turn-on, and quickly decayed to about 0.2mV
3. I was unclear where to make this measurement. Guessing it's on some of the legs of the volume pot, but not sure which ones. See pic attached---can you mark the spots? Also, see new clue at bottom of post....
4. Wasn't clear if you meant check its capacitance, or measure voltage. I am unable to measure capacitance, but voltage was measured to be +47.4V
5. Power ON: pins 2, 5, 8 are each at 0.3mV. Power OFF: each pin (2, 5, 8) show ~0.3ohm between pin and chassis
New, additional clue: While trying to perform step 3, and turning up volume control to about 1/3, I found that I sometimes got a hum in speakers, but if pot shaft was wiggled I could silence the hum. (This was conducted with selector on PHONO 1.) This suggests that my volume pot is not as clean as I thought it was. I will perform this next unless you advise otherwise.
View attachment 1907348
RE 3: The middle leg of three is the wiper, it is a 2 gang pot (one for each channel), 1 gang is closer to the front panel, one toward the inside.
FWIW, the Phono input is likely to introduce noise when it is selected with no turntable connected, because it is such a high gain input. Do testing with AUX selected for troubleshooting.
Some Faderlube would be good for the volume control. You can use D5 first to clean it, but make sure to use Faderlube after, as D5 will clean the lube off the pot surface and cause excessive wear.
motorcityguy
Active Member
Thanks! I did test #3 (on AUX) and saw NO increase in DC voltage at those points (VR2a/VR2b) as I moved the volume knob up from 'zero'. Reading was a couple of mV, and remained unchanged with increasing volume.
Will do! This is what I used initially (D5 followed by F5), but apparently it needs further treatment.
I stand ready waiting to investigate further, based on your advice. Thanks!