Fired up my Folded for the first time today! Everything lit up beautifully and measured well on the workbench. Once connected to my system I was only getting sound on one channel. First I thought it was an intermittent connection, loose RCA cable or such, but when I opened up the box I could see that there was an actual problem with one of the channels. The group of four LED's and the lone D1X won't light up anymore! I'm not getting any rail reading and the Q6X heatsink gets pretty hot after a while. No magic smoke anywhere though. Suggestions?
Assuming all semis are alright maybe you need unusually low a B+ to work right. Could be your input JFETs IDSS is low for the installed source resistors values and the bias has shifted down. Lower R3x with a parallel one to extend the bottom range with VR2x to see.
Technics SL-10 with a NOS Sonus SPM-4 line contact. With a T4P system you're options are quite limited unless you can spend a fortune on some of the Technics exotics of the era.
My dunce cap is fitting snugly
Well, now I see why my problem seemed unsolvable.
It was because I did not do what I thought I did.
Instead of adding resistance to R3x I added it R6x.
Thinking that this might have destroyed Q2x I replaced it with the 6ma IDSS fet.
This did not affect the TP1?TP2 reading. (still reading .7__)
IS it obvious what my clumsiness has done?
(mea culpa, mea mea culpa)
Well, now I see why my problem seemed unsolvable.
It was because I did not do what I thought I did.
Instead of adding resistance to R3x I added it R6x.
Thinking that this might have destroyed Q2x I replaced it with the 6ma IDSS fet.
This did not affect the TP1?TP2 reading. (still reading .7__)
IS it obvious what my clumsiness has done?
(mea culpa, mea mea culpa)
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That explains the LEDs dimming. It couldn't have destroyed Q2x but its no problem you exchanged it either. Now try a 47K//R3x to can push the B+ trimming range lower and see if going low can help toward proper TP readings. Are Q1, Q2 and R13 getting warm by the way?
That's one of the smartest looking TTs with a linear tracker. Certainly one of the most compact.
Let us know more on how it went along with FSP. Pics of the duet will be welcome too.
P.S. Can the Ortofon X1-MCP be any better cart than you already got BTW?
Will try tonight
Will do as you suggest.
Feel pretty certain something was destroyed.
Did not leave it on long enough yesterday to see if Qs 1&2 got warm.
THANKS,
Will do as you suggest.
Feel pretty certain something was destroyed.
Did not leave it on long enough yesterday to see if Qs 1&2 got warm.
THANKS,
Well, Qs 1&2 get pllnty warm
Yes, those devices are heating up. Can't tell you how much I hoped one of them remained cold. Those would be easy to replace!
What do you think would be the most likely device to have died and to replace?
My guess would be Q3. What do you think? Worth a try? I was using the 970 so I feel sure I have the original BC560C that I can substitute and if that works I can beg Mike for another 970!
Thanks and take care,
Yes, those devices are heating up. Can't tell you how much I hoped one of them remained cold. Those would be easy to replace!
What do you think would be the most likely device to have died and to replace?
My guess would be Q3. What do you think? Worth a try? I was using the 970 so I feel sure I have the original BC560C that I can substitute and if that works I can beg Mike for another 970!
Thanks and take care,
What would .73 signify?
If that is OK I think I need to replace Qs 1&2. Is there an easy test for those?
Thanks and take care,
I swear they are in the correct holes. Remember I was able to get the proper bias voltage initially. My rail/ground was low and that is when I placed the resistor in series with the WRONG resistor and created this BIG problem in an attempt to solve a little problem, damnit.
I did measure across the outer pins. I have those hook type measuring leads so they were firmly attached to the leads and no chance of them shorting. I attached the leads before turning on the amplifier. I let it fully warm up (20 minutes) to see if anything changed. It did start out higher - 0.76 and then settled down to 0.73.
Do you think I should replace this "970" with the BC560 and see what happens?
This one will be a simple swap (respecting the different holes for placement).
I am starting to wonder if the "369"'s are the problem. Any chance of that?
Thanks very much for your time and trouble,
Over 0.7V Vbe means too much current is channeled through the BJTs to R4 loads and that ties with the odd TP readings and their no response to VR2x. Having that condition points to either the 369s don't pull enough current or the 970s have a problem. You can check their current on R2 and R3 by mV across them divided by their value in Ohms. Normal is about 9mA each. Also check voltage across the 369s. Normal is about 8V. If those conditions are OK do the BC560C Q3Y instead of the 2SA970BL Q3Z thing and try the TP points goal with VR2x again. BC560C has CBE as we face it and its own D framed positions and orientations marked Q3Y on the boards.
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And I have made no progress.
Replaced Q3 - made no change with TP1/TP2 or anything else.
Measured the current across Rs 1&2 - comes out to just under 9mV - using 4R resistors.
I then replaced Q7.
I get the same TP1/TP2 and I am almost sure I have maintained the same polarity with the measurement leads and I now get a negative .755 V. But I am not sure about polarity of leads.
Gnd/TP1 - 8 V
Gnd/TP2 - 8.7 V
Rail/Gnd - 34.8 V
When the thing is first plugged in it seems like I am going to get a higher TP1/TP2 but then it drops down to .7_ and stays there.
I tend to think the reg is fine. Do you think this can be considered as working correctly?
This leaves only the output stage FETs in question (I presume since I have no real idea). Is it possible something could have gone wrong there?
One good thing is I am getting much more comfortable around semiconductors. Learning something, slowly, which is good. I can only pray I am not getting on your nerves!
Any suggestions?
Thanks and take care,
And I have made no progress.
Replaced Q3 - made no change with TP1/TP2 or anything else.
Measured the current across Rs 1&2 - comes out to just under 9mV - using 4R resistors.
I then replaced Q7.
I get the same TP1/TP2 and I am almost sure I have maintained the same polarity with the measurement leads and I now get a negative .755 V. But I am not sure about polarity of leads.
Gnd/TP1 - 8 V
Gnd/TP2 - 8.7 V
Rail/Gnd - 34.8 V
When the thing is first plugged in it seems like I am going to get a higher TP1/TP2 but then it drops down to .7_ and stays there.
I tend to think the reg is fine. Do you think this can be considered as working correctly?
This leaves only the output stage FETs in question (I presume since I have no real idea). Is it possible something could have gone wrong there?
One good thing is I am getting much more comfortable around semiconductors. Learning something, slowly, which is good. I can only pray I am not getting on your nerves!
Any suggestions?
Thanks and take care,
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Hi Rick:
My build also used 2SA970's and 2x369's (LOMC). I'm sure you have covered all this, but what was the measured Idss of the 369's, and what valu(s) did you use for R2/3?
When I built mine, when I used VR2x to get rail voltage ~35V my TP1/TP2 voltage was low. I had to use VR2x to drop the rail voltage quite a bit to get TP1/TP2 close (around 32V as I recall, can't remember now). Also, it takes some time to get TP1-TP2 into the right ballpark. It actually starts negative (maybe -0.7V or so) from cold and slooowly climbs. It is incredibly temperature sensitive. If I let it warm up with the box buttoned up until it was pretty stable, half an hour or more, as soon as I moved the case lid aside a bit to make an adjustment, the voltage would start to drop. I had to adjust it low then let it get back up to temperature. (I have concealed the power LED from my wife so I can leave it on all the time.
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I hope this helps a bit at least in terms of expectations. Were I you I would try to get back to "spec", don't worry about the absolute rail voltage. Try to get the TP1/TP2 voltage moving via VR2x with VR1 centered. Make sure you have about 9mA through the 369's (that is, across R2/R3). I feel like I'm not telling you anything new, but you need to be slow and patient with these measurements, especially in the LOMC configuration. If you want to take the output stage out of the equation, lift one end of R10/11.
Good luck, keep trying and posting, you will get it right very soon. I also predict that when it all comes right you will have a "D'Oh!" moment, at least I always do
My build also used 2SA970's and 2x369's (LOMC). I'm sure you have covered all this, but what was the measured Idss of the 369's, and what valu(s) did you use for R2/3?
When I built mine, when I used VR2x to get rail voltage ~35V my TP1/TP2 voltage was low. I had to use VR2x to drop the rail voltage quite a bit to get TP1/TP2 close (around 32V as I recall, can't remember now). Also, it takes some time to get TP1-TP2 into the right ballpark. It actually starts negative (maybe -0.7V or so) from cold and slooowly climbs. It is incredibly temperature sensitive. If I let it warm up with the box buttoned up until it was pretty stable, half an hour or more, as soon as I moved the case lid aside a bit to make an adjustment, the voltage would start to drop. I had to adjust it low then let it get back up to temperature. (I have concealed the power LED from my wife so I can leave it on all the time.
)I hope this helps a bit at least in terms of expectations. Were I you I would try to get back to "spec", don't worry about the absolute rail voltage. Try to get the TP1/TP2 voltage moving via VR2x with VR1 centered. Make sure you have about 9mA through the 369's (that is, across R2/R3). I feel like I'm not telling you anything new, but you need to be slow and patient with these measurements, especially in the LOMC configuration. If you want to take the output stage out of the equation, lift one end of R10/11.
Good luck, keep trying and posting, you will get it right very soon. I also predict that when it all comes right you will have a "D'Oh!" moment, at least I always do