Crown CE 1000 Worth trying to fix?

[tonecat]

Hello Everyone,
I have a CE 1000 that channel 1 works fine on and channel 2's fault light stays blinking after power up with no sound. I have done some research and these amps sound like a real PITA to work on with the smt boards and micro components unless its just the power section. Anyone have any thoughts on this? Maybe its just not worth fixing due to the fact that they have a reputation of being unreliable and can fail again after being fixed. I don't really want to put a huge amount of time into this since they aren't worth that much anyway. Please let me know your thoughts, and as always, Thanks!!

[km6xz]

The worthiness of the amp for repair depends on the application and resources available. My personal opinion is that almost anything is worth repairing and would not hesitate to rebuild it. But I have the resources(test instruments and parts) to fix most things with electrons flowing through them. Most people don't so that is the grey area. Same with SMD parts, my preference is working with SMD pc boards, they tend to be reliable, rugged and easy to replace parts on if one has the equipment.
Do you have at least a metered Variac, DMM, signal generator and scope? If you do, the feasibility of repairing it becomes a lot better odds situation.
If not, do you known someone who will allow you to use their gear or help you?
Most shops would charge a lot, if a lot of power devices are damaged, in the $150-250 range. A minor problem, like one of those tiny surface mount devices, than you might be able to get a shop that is really competent to do in an hour or less, for $60-100. A bad tech or a decent tech who does not have a lot of experience with power amps will cost much more in blown up parts or shot-gunning, which a lot of amateurs do....replace parts until it works.
That is the upper range. If you are able and willing to repair it yourself, it could be a fun project or it could be a nightmare. The odds of repairing it is higher for those asking for and following advice from this forum.
What is it worth to you, repaired, and what is it worth to you when repaired?

[MarkusBass]

I have done some research and these amps sound like a real PITA to work on with the smt boards and micro components unless its just the power section.

With SMD components you need to have specialized tools or at least some manual skills. In my opinion these are stories usually repeated by people that do not have required tools nor skills. On your place I would try to fix it because fault light quite often is caused by failure of the output stage (which can be easily fixed). So I would at least check the ouptut stage. If this is not the output stage, you have to find the service manual (which is recomended in any case) and make some measurements. And then decide whether you can do it or not.

Maybe its just not worth fixing due to the fact that they have a reputation of being unreliable and can fail again after being fixed.

I wouldn't believe in this. Even Toyota can fail after being fixed but this doesn't mean that it is unreliable.

I don't really want to put a huge amount of time into this since they aren't worth that much anyway.

The time you spend of this amp depends of your experience and skills. I suggest to check at least the output stage and then decide what to do next.

EDIT: with this help: http://answers.yahoo.com/question/in...5215604AA3Esex ?

Mark

[tonecat]

Hello and Thanks for the replies!!
I decided to go agead and give it a go. I have not worked on a lot of solid state amps. Maybe ten or so. Here is what I have done so far. I am including a schematic if someone wants to help me look into this. http://www.crownaudio.com/pdf/legacy/137556-3_B_sch.pdf
I checked for DC on the output at L202 Inductor coil before the speaker relay K200 (page 7 of the schematic) and there was none. I compared driver emitter voltages Q212 and Q221 with CH1 Q112 and Q121 and they were the same. +82 and -82. Spec is +85 and -85. All rail voltages were in spec. It is my understanding that if something is wrong with the ouput section, I should either see DC at the output or wacky voltages at the drivers? Should I still check all the output transistors (MJ21194) out of circuit to be safe, or if one or more is bad should that be evident in some measurement? I also checked the flyback diodes D214 and D215 for shorts. All OK.
When powering the amp on, there is a 4-6 second delay before the speaker protection relays (K100 & K200) kick on. CH1 works as it should (makes a clicking sound) CH2 makes no sound and the amp goes into fault mode. (a red Fault indicator for each channel which will blink under 5 conditions: 1) When the amplifier is first turned powered up, until the unit is ready for operation. 2) If the heatsinks reach a temperature above normal working limits. 3) If the transformer thermal protection circuit is activated. 4) If the amplifier wires develop a short circuit, and 5) should the amplifier output stage become non-operational.)
I observed that U204 A,B,C, and D (LM339D) has a lot to do with the protection circuitry and the relay (K200) I compared readings to U104 on CH1 and thats where things were way different. No voltages were the same. Thats as far as I got tonight. I mean this morning. Time to quit. If anyone has any suggestions or if I have overlooked something or need to post more info, please let me know. I greatly appreciate your help!!!!! Thank You!!

[MarkusBass]

Should I still check all the output transistors (MJ21194) out of circuit to be safe, or if one or more is bad should that be evident in some measurement?

I would just check the voltages on emitter resistors for each transistors but it seems that they are OK.

A red Fault indicator for each channel which will blink under 5 conditions: 1) When the amplifier is first turned powered up, until the unit is ready for operation. 2) If the heatsinks reach a temperature above normal working limits. 3) If the transformer thermal protection circuit is activated. 4) If the amplifier wires develop a short circuit, and 5) should the amplifier output stage become non-operational.)

So it looks like in your amp one of the conditions is met.

I observed that U204 A,B,C, and D (LM339D) has a lot to do with the protection circuitry and the relay (K200) I compared readings to U104 on CH1 and thats where things were way different. No voltages were the same.

You have to understand ow the protection circuitry and the relay works.
The relay is switched by Q229 transistor under the condition that it has positive voltage on its base. The voltage is provided by U204 A,B, C, which compare a reference voltage with voltages on their inputs (SHORT - pin 4, TEMP2 - pin 6 and XFMR - pin 8). So I suggest to compare the voltages on these pins with voltages in the first channel.

Mark

[tonecat]

Thanks Mark!!
All the emitter resistors are underneath the circuit board and impossible to get to without complete disassembly of the amp. There are about 8 of these per transistor. Do you think I am ok without checking these? It would be much easier to check the transistors. Was I correct with assuming all is well with the output with the readings I found?

Q229 is also underneath the board so I will start with checking the differences between U104 and U204. I can't make out any notchs on these chips so I know which pins are which. 14 pins total. Does the # stamped on the chip help tell its orientation? http://focus.ti.com/lit/ds/symlink/lm339.pdfThanks!!

[MarkusBass]

Pin #1 is always marked somehow. Look at page 25 of the datasheet (look for: "Index area"). Did I tell you that this will be easy? I assume that all "logic" signals are underneath the board and sooner or later you will have to disassemble the amp.
If you can't check the resistors, why not check base-emitter voltages? For example, isn't emitter the same as the output inductor? And the base isn't the same as the emitter of the driving transistor (TP38)?

Mark

[tonecat]

OK. Did some more testing. I checked base-emitter voltages by using TP38 and the output inductor on CH1 and it was .33vdc. I then did the same thing using TP39 and output inductor on CH2 and it was also .33vdc. The spec is .31 +/- .05vdc so reading is in spec. This is outlined as checking the bias in chapter 2.5 of the service manual. Seems all is well with the output section.

I determined pin 1 on U104/U204 and compared voltages. Here are my readings:
U104_______________U204
Pin 1,2,10,14 = 7.8v__Pin 1,2,10,14 = -14.9v
Pin 3 = 14.9v________Pin 3 = 14.9v
Pin 4 = -4.1v________Pin 4 = 11.3v
Pin 5 = .75v________ Pin 5 = -5.0v
Pin 6 = 2.7v_________Pin 6 = 2.7v
Pin 7 = 5.1v_________Pin 7 = 4.5v
Pin 8 = -1.2v________Pin 8 = -1.2v
Pin 9,11 = 0v_______ Pin 9,11 = 0v
Pin 12 = -15.0v______Pin 12 = -15.0v
Pin 13 = -14.9v______Pin 13 = -0.1v

As you can see, a lot of differences here. The schematic shows Pins 1,2,10,14 all tied to the +15v supply through a resistor which probably drops it to the 7.8v I'm getting on CH1? CH2 should not have -14.9v on these pins. Pin 4 (Short) is way different between the two channels. Could this be the culprit? To me it still doesn't explain the -14.9v at the pins on U204. I'm kinda stumped here. I don't want to give up now, Got to much time into this. Any ideas would be appreciated. Thanks!!

[MarkusBass]

I think that you know that there are thousands voltages in this amp and if you try to list them all, nobody is going to read this thread. You need to list only the voltages that are important here. And for this you need to understand comparator. It has power supply rails, two inputs and output. If the IC is OK, the voltage on the output depends on the difference of voltages on inputs. So, in general, it gets some voltages from "outer world", possibly compares it with some reference voltage (e.g. from voltage divider) and generates output voltage. It means that if you get incorrect voltages on the output, they are most probably caused by incorrect voltages on the inputs. In your case, the U204 gets TEMP2 and SHORT signals. If you compare TEMP voltages, you can see that the input signal is the same in both channels. But if you look at SHORT signal (pin 4), you can see that this signal is different than in the other channel. As a result, the comparator mutes the amp and does not activate the relay. So you have to look at the preceeding stage, maybe at U202, U201. Or if you get information that the amp is shorted, and the amp's output is protected with a triac (Q231), maybe this triac is shorted? In this is not the case, you have to check why there is high voltage on pin 4 of U204.

Mark

[tonecat]

Thanks for all your help Mark!! Sorry about posting so many voltages. It makes sense to only post the ones that matter. This is so much more complicated than the tube amps I am use to working on. I checked the triacs (Q131,Q231) on both channels for shorts to ground. Both had none except for the pin that should be grounded. Should I check for anything else with the triacs? I need to continue to explore why I am getting a short reading at Pin 4 on U204. I appreciate you explaining how the voltage comparator works. It makes more sense to me now. I don't know how much time I will have to work on this over the weekend. but I will give her hell again next week. I really hope I can figure this out. Thank God for this forum and the great people who take the time to help novices like myself!! I wouldn't be able to do without you guys!! Thanks so much!!

[MarkusBass]

I would list the voltages in the following way:
U204 power supply: V+ (pin 3) +14.9V, V- (pin 12) -15V
U204-A:
IN- (pin 4) +11.3V, IN+ (pin 5) -5V, OUT (pin2) -14.9V
U204-B:
IN- (pin 6) +2.7V, IN+ (pin 7) +4.5V OUT (pin 1) -14.9V
an so on.
It is important to know that input signals are: SHORT, TEMP2, XFMR. The output of U204-A, B and C are tied together and this is also the input for U204-D which generates MUTE2 signal.
In this way voltages are more readable and (I hope) you can see that the problem is most probably related to the SHORT signal. Other signals seem to be OK.
If you are sure that the output transistors and the triacs are OK, I would look at the reason why the SHORT signal is different than in the other channel.
I would check voltages on U202-B (pin 1) and on U201-C (pin 8) and compare them with voltages in the other channel.
You may also notice that input pin 4 of U204 is connected both to +15V and -5V (through a diode and a resistor) so you may take a look a these components.

Mark

[oc disorder]

An old thread - possibly not that helpful at this stage but food for thought !

http://music-electronics-forum.com/t12646/

[jrfrond]

Repairing a CE or UT (Sam Ash-specific version; same thing) series amp is a labor of love for the owner, and only if they are a fairly competent tech with lots of time on their hands at that. Those amps tended to cook real good, and due to their physical architecture and SMD topology, were far from repair-friendly. We always did board swaps on these, which BTW became NLA a long time ago. When these come in nowadays, we pretty much turn them away, telling them to put the $$$ toward a new power amp.

Electronically, the CE1K/2K were similar to the old, reliable DC300A. In THAT respect, they were good, but the design did not translate well to SMD, in my opinion. This was Crown's first attempt at a budget amp using SMD technology, and superseded the much hardier Powerbase series.

The CE4K was a whole different story.

[tonecat]

Hello Again. I finally got back to work on this thing. Decided to give it one more try before aborting the mission. I took the circiut board out of the chassis so I could get a look at the bottom. No fried components anywhere. Double checked the output section and all is well. I compared the voltages on U202-B (pin 1) and on U201-C (pin 8) with CH1 and they were the same!!! This led me to look at the other components connected to U204 (pin 4). There is a diode (D228), a resistor (R274), and a capacitor (C221). These parts were covered with a green transparent epoxy? I scraped this away so I could test these parts in circuit. I checked them against CH1 and the values were similar. I powered the amp back on and CH2 worked for about a minute before the relay kicked off again. WTF? I decided to check the voltages at these parts on both channels to narrow it down.
CH1: D128 anode -14V, cathode -4.2V
CH2: D228 anode -14V, cathode +8.7V
CH1: C121 +15, -4.2
CH2: C221 +15, +8.7
CH1: R174 -6.2, -4.2
CH2: R274 -6.2, +8.7
It would seem to me from these readings that one of these parts is bad? I have never tried to remove a SMD component before. Can I just unsolder it and swap in a regular part temporarily to check? Can I get these parts from Mouser or Digikey? Is there anything else I may have overlooked? Thanks Again for all the help!!

[MarkusBass]

It was so long time ago that in the meantime I lost my schematic for this amp. This is one of the reasons I'm confused. It's because I remember that on my schematic the diode was labeled D216 (and not D228). If I look at the schematic you linked, I see that the R274 resistor and the C221 capacitor are marked as OPEN, which means that they are not assembled. So about which schematic are we talking?
I also wonder how did you test these parts and see that they are similar?
There is one more thing that is confusing; in the first channel you can see how the FAULT signal is converted to SHORT signal. But I cannot see how this is done in the second channel. I see FAULT output and SHORT input and nothing in between. It looks like the FAULT signal is not bad but the input that is incorrect is SHORT. I wouldn't assume that FAULT and SHORT are the same. Or, you have better schematic?
The voltages that you measured do not prove anything (especially that one of the parts is bad).
I think that there are three options:
either the SHORT signal is bad (and you don't know yet where it is coming from),
or one of the three parts is bad,
or the comparator is bad.
You could remove these components but I wouldn't do it if you don't have experience with SMD components. Usually you need specialized tools for this, or some experience with doing it with traditional tools.
I would clarify the problem with the schematic and find out where the SHORT signal comes from (if you can't see it on the schematic, you can look at the board). Knowing this I would decide what to do next.
Looking at the voltages I can see that the problem is with +8.7V on R274 (it should be rather -4.2V). Did you measure this resistor (if it is soldered in this channel)? Also if the C221 capacitor were shorted, you could get similar results. But first clarify the SHORT signal issue.

Mark