Re: Crest CPX1500
what a wonderfully detailed explanation, thanks! Now I do understand resistance of pins 1-2.
Now, I just checked voltage on R114/115/117 CR102 in defeat (DDT led off), all carry around -15v, then I switched to enabled whitch should turn on the led but it didn't. While probing the different components the led would light up and turn off when the probe was lifted. Voltage was also -15v on all four when the led lit.
I made the same tests on channel B and voltages were similar, but with CGL enabled DDT led wouldn't light when probing, so in...
5inc
Senior Member
Last Activity: 09-30-2017, 06:24 AM
Joined: 12-30-2016
Location: Barcelona
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Re: Crest CPX1500
This is the tracer I built. Blocking cap included.
[url]http://musicfromouterspace.com/analogsynth_new/HOT_TIPS/ampsignaltracer.html[/url]
Pin5 has voltage, something around -15v both on U101/201(it is where the -25v was), also with CGL enabled and in defeat.
So as you said it could be limiting the input signal even though there is no reason to. Do you have any suggestions?
I just measured again the resistivity between pins of U101/201 and they are still the same
U101
1-2: 141ohm
2-3: 97ohm
3-6:...Leave a comment:
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Re: Crest CPX1500
I picked up clean signal on pins 2,3 of U201, and a nasty one on pin 7. but no short through inputs or output.
I tried to see what happened if I took out U201 and what happened was Q203 blew up.
I am now stuck in the debate of wether using or not the last pair of CA3080 i have. Assuming U201 died with that -25v, U101 could still remain unharmed. what do you think?Leave a comment:
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Re: Crest CPX1500
I first changed U200 in case the -25v killed it, but no luck. I haven't changed U101/201 because I'm down to the last pair, will need to order more if not, but they don't read short.
I found something funny, while I probe r203/204 with the signal tracer the amp jumps into short..
I tried on the other channel but the layout is different, there aint no r103/104.
Will keep on looking.Last edited by 5inc; 09-20-2017, 12:50 PM.Leave a comment:
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Re: Crest CPX1500
Why, yes. It is open circuit!
I replaced it, and that solved the first and third fault yay!
But the second fault still remains, something is still making U101 stop the signal through. The same happens with U201.
Signal tracing time?Leave a comment:
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Re: Crest CPX1500
Here you go, I made a quick coloured drawing over the schematic stating where voltage is most critical. If you want me to go further, just ask.
I DON'T get -25 on channel A thank god, and I can't read short on U401 in any direction......Leave a comment:
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Re: Crest CPX1500
So, bridges are ok then, thanks.
I don't know if I succesfully disconnected power only, but at some point I did take out R295, so that may have damaged U200, and also I did something similar on u202 so those are next on list.
I can't remember exactly where the probe slipped, but it made CR224 short out and blew the fuses.
I have done all voltage checks with negative lead on chassy, except for when I was checking bridge rectifier with channel B disconnected, I...Leave a comment:
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Re: Crest CPX1500
After a while going nuts about what was going on, yesterday, I gave the channel B board a good clean up with alcohol, and what do you think? it stopped blinking.
Channel B red DDT led still remains on, and checking voltages I found -25v between R234,CR214, and the point where it joins Q203, CR221 and C216. That includes the "-15IB" line that feeds U200, follows through "-15PB" and around R214, R215 it returns to -16v again.
I don't understand how the voltage is higher (or lower?) only in that area, if after all the...Leave a comment:
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Re: Crest CPX1500
After shorting the amp because of a probe-slip and restoring it to it's blinky restart loop point, I thougt I found something.
Disconnecting v+/0v/v- going to channel B makes the amp stay still, and from there i'm seeing there is no DC coming out of bridge rectifier D200 with black probe on chassy but since v+/0v/-v leads are disconnected this must be normal(AC is going in, allthough 53v on one side, 62v on the other). If I measure across the bridge rectifier itself for voltage I get +53V/0v/-53v DC.
D100 carries +82v/0v/-82v DC on it's...Leave a comment:
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Re: Crest CPX1500
ok that's a chunk of info I'll have to digest.
What has changed from the point I had signal at output A and a red ddt light?
I had tried replacing U301 which hadn't been changed yet, and believed it made no difference.
At that point is when I started checking every voltage I could compare and ended up seeing there was no -80v rail. Re-connected the bridge rectifier and begun getting these peaks.
All lights are off, and every 3 seconds channelA green+channelB's red/yellow/green lights blink. At the time those go off both red...Leave a comment:
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Re: Crest CPX1500
i've been comparing voltages, but don't comprehend some things, maybe you can help me understand, or at least see something I can't
THERMAL_A is 3.75v, THERMAL_B is -12.11v
pin6 of U202 carries -9.8v
Q104/105 carry 80.4v on their collectors, 1.4v on their emitters.
Q205 had nothing on collector, and followed all the way up to -leg of bridge rectifier, whitch was apparently disconnected, reconnected it, and now when I start it it starts fine for two seconds, then blinks(along with the lightbulb) every second and...Leave a comment:
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Re: Crest CPX1500
The IC is a NJM4560.
What you saw is stain a of permanent marker i made when replacing them. The track is ok, and there aren't any other obvious bumbps, flaps or cracks on the board.
Voltages at U102 pin5 has 1.6v and pin6 has 1.6v. This is ok
R118/119 have 1.6v on both ends.
U202 has 0.8v on pin5 and -9,9 on pin6. This is weird.
R218 has -9,9v and R219 has 0,8v on both ends.Leave a comment:
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Re: Crest CPX1500
Yes, I have audio all the way to the speaker. It seems to be at an ok volume on my testing speaker, havn't tried feeding it to a sub yet so I can't assure it is responding at 100% yet. It does sound pretty neat though.
I took voltages at pins 2,3,7 on U202 to compare with U102
pin-----2----------3---------7
U202 -14,3v_____10,9v_____14,6v
U102 14,4v_____14,5v____-14,2v
Here are pictures of the back and front of the zone, DDTS2A is pointed and written DDTS2B is only pointed out. U102/202 also appear. Ask if you want more...Last edited by 5inc; 08-09-2017, 10:49 AM.Leave a comment:
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Re: Crest CPX1500
Just plugged TX15/16/17 in to start troubleshooting Channel B.
Turned it on and averything started fine, but channel B DDT red led stayed on.
I then tried replacing U200, U202 thinking that would do the trick but nothing, still have red DDT led staying on.
I haven't replaced U201 again because I don't think I damaged it(and even so, on channel A U101 is blocking the signal anyway). What I may try is replacing CR200/201, those are still the originals, even though they read ok..
I tried to follow the steps you gave me to troubleshoot...Leave a comment:
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Re: Crest CPX1500
you see, channel B has been dissconnected at TX15/16/17 from almost the beggining.
Perhaps that has something to do with the fact the signal won't arrive to the output? I wanted to get channel A running before jumping on to B, for the sake of simplicity and a better learning experience.
And since everything looks stable now (no shorts) it could be the time to start laying hands on channel B...
But on the meantime, I started signal tracing, and could only hear up to R101/R102. Nothing around U100/101/102.
and about...Leave a comment:
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Re: Crest CPX1500
Sorry the short on U101 wasn't on pins 3-4 but on 7-8, that both go to 15V+IA.
That, and having a burned R194 seems to point that U100 was bad again instead. Replaced both, and now everything looks stable:
I fire it up and first both DDT leds turn on, then they go off for a glimpse to turn back on together with green power leds for a few seconds. Finally, after another second or two, DDT leds go off and only power leds remain on.
After seeing all this I plugged in my testing speaker, saw it made no difference in fan speed,...Leave a comment:
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Re: Crest CPX1500
I just replaced U102. I must have done something really wrong in the process because now it blinks again(both DDT leds and Channel A yellow led).
Found a short between pins 3-4 of U101.
R194 has raised to 76ohms
Gonna replace them both tomorrow evening unless you think there might be something that caused this to short again (obviously appart from me)Leave a comment:
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Re: Crest CPX1500
Yay, DELAYA seems ok!
I think I'm not overdriving anything, there's no load on the outputs, but I have pulled the volume knob all the way up to get the signal through the amp for tracing.
I just toggled GCL enable switch while the amp was on, it made no difference.
About U102, no, I still havn't changed it. I have tested it on diode mode on the DMM but didn't find any shorts. I could give it a shot, after checking resistors around.Leave a comment:
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Re: Crest CPX1500
I just replaced U100 and of course, it wasn't shorted. It still shows the same symptoms, so I have to go one step back.
-"Yes, U101 could be getting some incorrect signal or no signal from another part of the circuit. It could also be faulty."
I don't fully understand the feedback thing, so I followed BDFED (hoping it would stand for feedback) on P101 and ended up at the bridge/stereo switch. I saw it was set to bridged so switched it back to stereo, and fired the amp but everything is the same. I may be on the wrong foot but that's...Leave a comment:
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Re: Crest CPX1500
Thanks for the note on the JFET's
DDT led on that channel IS constantly on. I didn't find any low resistance between pin 3 and 4,6 or 8 (something like 200-400K).
I connected Q100 and Q101 one by one and still have signal on R102/CR101.
Will now proceed to replace U100.Leave a comment:
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