Sunfire Cinema Grand Signature repair woes

[tutor turtle 7]

I have a Sunfire Cinema Grand Signature, five channel (Serial 99051200081) that has a missing capacitor on the Left Rear Channel amplifier. (board # 731-026-?)

C41. One Leg goes to a 5W resistor R76, the other to 1/2 watt zener diode Z2. I have a few loose pages of schematics I'm not sure that they are for this particular model. This one has the big iron core power transformer, not the toroidal. I am hopping this little missing cap is causing my noise issue

There is a little buzzing on start-up (goes away) The main issue is this unit seems to be particularly prone to picking up any stray EMI. My shop is electrically quite, but if I run anything that makes sparks, like a wire wrap gun, it picks it up and comes loudly through the speakers. Clearly a shielding issue. The big power supply caps and bridge rectifiers have been replaced. As well as the 11 supply caps (1,000 uf @16V) each of the three power amp boards. (a suggestion I read on this website's forum) What I could use are the correct schematics and service manual that shows how to set bias and offset.

T-T, Vintage HiFi Restoration,

[itchitch 3,243]

I am really hoping @wrf sees this thread... he's been working on a lot of Sunfire amps...

[Nahash5150 9,369]

C41 is not installed.

 

Your noise issue is likely a bad grounding connection somewhere, or the Mains EMI filter is blown/worn out.

[tutor turtle 7]

I will check on the EMI filter. Any idea on what value the missing C41 might be?

It's on the single channel Left Rear card. 

[tutor turtle 7]

Sorry, I just read the part where C41 was not installed. Duh.

Funny because there are leads going through the PCB... 

But again, there are lots of vacate part locations

[4krow 3,868]

Once in rare while, I see a component installed on the other side of the board. Only one way to find out. And you might be able to measure it in circuit, but I wouldn't bet on that.

[tutor turtle 7]

I have 11 pages of schematics I have down loaded from this site, but nothing that shows the power transformer/bridge rectifiers/EMI circuitry or the big filter caps.

Did I miss a page somewhere?

653-060-00 Rev G (Right Rear)

653-061-00 Rev H (Dual Channel Amp THX) -2 pages

653-062-00 Rev F1 (Power Source)

653-063-00 Rev A3 (CGSA 17" Amp Daughter Board)

653-064-00 Rev G (Power Source Daughter Board)

653-065-00 Rev E (Cinema/Sunfire II Auto-On)

653-068-00 Rev C1 (CGSA 17" Amp Daughter THX)

653-079-00 Rev E1 (Stereo 17IN Amplifier)

 

653-131-00 Rev A3 (7 Channel Amp Downconverter) -2 pages This likely does not apply, as I have a 5 channel amp

 

[BobTFM35 521]

@tutor turtle Take a look at this video. Its not the most steady but if you can get to the 7min 33 sec mark you will start to see that the resemblance of that board to your board. It also doesn't have a C41 installed.

 

Did not finish watching it as the camera movement was terrible for me. I hope it sheds some light on your problem.

[tutor turtle 7]

At one point I rebuilt the power supply with new bridge rectifiers and replaced the main caps with the same physical size and voltage rating of the originals. With those dimensions and 160vdc rating, the microfarad rating at least doubled, possibly more, as modern caps usually are larger values for the same size. (I forgot how big I used, the label is face down) On startup, there is a slight buzzing that goes away as the caps charge. After about 30 seconds or so it is dead silent. If I keep it plugged in, restarting the amp, it remains dead silent. I am fairly certain the customer switches off the amp with a power strip after use, and the caps discharge fully. It sounds beautiful, but It has way too much power for my needs. My Altec Lansing Voice of the Theater speakers are ~100 watt rated and at 102db/watt/meter efficiency, you are getting blown away before the amp even breaks a sweat. My other speakers are Klipsch Cornwal IV's, similarly rated in power and efficiency.  

I got this amp in for repair some years back for this very complaint. The original owner never came back for it even after repeated attempts to contact him. After two years of waiting, I simply kept it and placed on a stereo consignment shop. Every customer who brought it home registered the same complaint. A buzzing noise on startup. So the big guy is destined to be an orphan.

[tutor turtle 7]

1 hour ago, BobTFM35 said:

@tutor turtle Take a look at this video. Its not the most steady but if you can get to the 7min 33 sec mark you will start to see that the resemblance of that board to your board. It also doesn't have a C41 installed.

 

Did not finish watching it as the camera movement was terrible for me. I hope it sheds some light on your problem.

Where did you post the video?

[BobTFM35 521]

@tutor turtle Here is the link. I just forgot to paste it in.

 

 

 

[Nahash5150 9,369]

On 3/19/2023 at 6:44 PM, tutor turtle said:

At one point I rebuilt the power supply with new bridge rectifiers and replaced the main caps with the same physical size and voltage rating of the originals. With those dimensions and 160vdc rating, the microfarad rating at least doubled, possibly more, as modern caps usually are larger values for the same size. (I forgot how big I used, the label is face down) On startup, there is a slight buzzing that goes away as the caps charge. After about 30 seconds or so it is dead silent. If I keep it plugged in, restarting the amp, it remains dead silent. I am fairly certain the customer switches off the amp with a power strip after use, and the caps discharge fully. It sounds beautiful, but It has way too much power for my needs. My Altec Lansing Voice of the Theater speakers are ~100 watt rated and at 102db/watt/meter efficiency, you are getting blown away before the amp even breaks a sweat. My other speakers are Klipsch Cornwal IV's, similarly rated in power and efficiency.  

I got this amp in for repair some years back for this very complaint. The original owner never came back for it even after repeated attempts to contact him. After two years of waiting, I simply kept it and placed on a stereo consignment shop. Every customer who brought it home registered the same complaint. A buzzing noise on startup. So the big guy is destined to be an orphan.

 

If you doubled the capacitance, then you increased the in-rush current. This is probably okay, but I imagine that would cause some transformer groaning.

 

So am I to understand that the buzzing is heard from the speakers for 30 seconds then it goes away? If that is the case, it's probably the DTC malfunctioning.

 

Put your DC meter on an output transistor collector and tell me what the voltage is when it starts up, then after 30 seconds. There will be a PNP (MJL1302) and a NPN (MJL3281). Measure both.

[timmyjim 43]

On 3/19/2023 at 6:44 PM, tutor turtle said:

If I keep it plugged in, restarting the amp, it remains dead silent. I am fairly certain the customer switches off the amp with a power strip after use,

Ya - if you keep these things plugged in, they are not really "off", at least the one I own isn't. If I turn mine off with a switched outlet, I find it yanks hard on the inputs as it powers down. This causes all kinds of disturbance in my system, eventually resulting in huge pops through the speakers. I have to either leave it on standby, or make damn sure I turn off the preamp first.

 

 

Certain configurations of these amps will inevitably cook the 12V caps on the main power supply board. You didn't mention replacing those? It's unlikely to be your problem as the buzzing would likely persist. It would not go away after 30 seconds. Might be worth looking at what the +/-12V supplies are doing when the amp is in buzz mode. If those are not stable, you will hear it in the outputs.

[tutor turtle 7]

The +12 volts supply is down to 8.5Volts with 10% ripple. The filtering caps for this circuit are running really hot, like you can't keep your finger on them hot. While the regulator is cool. The +12 adjustment pot functions correctly up to half way, then won't go above 8.5v. I don't believe it is a short of any kind. I'm going to just pull and replace all the parts ~a dozen or so fairly cheap components. The minus 12 is clean and at the correct level.

[timmyjim 43]

6 hours ago, tutor turtle said:

The filtering caps for this circuit are running really hot, like you can't keep your finger on them hot. While the regulator is cool.

So if the caps are hot, they have to have some internal low impedance DC current path. DC current has to go through the regulator circuitry.

The regulator must be dissipating a decent enough amount of power? I don't understand how it is not hot or at least pretty warm?

 

Sorry - but I don't have a schematic to reference. I know there was an effort to secure as many Sunfire schematics as possible. Way better than nothing. I've never had things map out 1-1, but close enough. The double sided boards and tight spaces make these very challenging to work on.

[tutor turtle 7]

The regular is cold to the touch. I am looking a a perfectly formed half wave (60hz) signal on the caps going to the collector of Q1. 

[timmyjim 43]

 

OK - If this is the schematic you are referring to then the hot cap is C5? In that case this is before the regulator and it would appear that C5 is no good. If C5 is acting like a 2200uF capacitor, I don't see how it's possible to have a "perfectly formed half wave signal across a 2200uF capacitor.

[Nahash5150 9,369]

Nice 12V regulator design from 1980 M1.5

 

If the 2200uF cap is hot, then it's more like a resistor than a capacitor, so I imagine you'd be seeing more of a rectified waveform than a DC approximation.

[tutor turtle 7]

At this juncture, (time-wise) I'm simply going remove and replace every component in the circuit. I don't need to know which part has failed, I just need it out of my shop and back to it's owner.

[timmyjim 43]

I'm only replying to this thread one more time because I found this post from EXACTLY one year ago today:

 

 

Is this the same amp? If so - According to this thread, you replaced the 12V caps back then. One year later and there is still an issue with the 12V circuit, even after the caps were already replaced?

Ignore me if this is a different amp, but if it's the same one shouldn't there be more questions as to why, or was it not repaired properly a year ago?

 

2 hours ago, tutor turtle said:

At this juncture, (time-wise) I'm simply going remove and replace every component in the circuit. I don't need to know which part has failed, I just need it out of my shop and back to it's owner.

Here's the part where I type something that will get me into trouble with the admins: I'm just a hobbyist. Mostly I like to fix broken stuff. The first thing I do when I have a rectangular black box filled with electronics thats not acting as it should .... take off the cover and check the supplies.  Go from there. This can be challenging with a triac switched supply, which many Carver amps have, but usually simple to check basic supplies in preamps and amps with more traditional supplies.

I'm confused at how a  self-proclaimed repair shop with 35 years experience took almost a week (year?) to find a 12V supply sitting at 8V (with excessive ripple), then, despite the fact that a filter cap was "can't keep your finger on them hot" and there was a "perfectly formed half wave (60hz) signal on the caps" decided the correct approach was to shotgun the entire circuit?

Maybe I'm crazy, but how about removing the hot cap and putting an ohmmeter across it?

I'm just a FNG hobbyist who enjoys audio electronics. Hope to learn a thing of two on this site. In one week I've seen multiple help requests from "repair shops" that are truly unimpressive in their content. It seems backwards. Shouldn't "repair shops" be giving repair advice to hobbyists?

 

Admins and other members: I apologize for my aggressive post. I'll take whatever punishment is deemed appropriate. I certainly won't reply to this thread again.

[Nahash5150 9,369]

3 hours ago, timmyjim said:

Here's the part where I type something that will get me into trouble with the admins: I'm just a hobbyist. Mostly I like to fix broken stuff. The first thing I do when I have a rectangular black box filled with electronics thats not acting as it should .... take off the cover and check the supplies.  Go from there. This can be challenging with a triac switched supply, which many Carver amps have, but usually simple to check basic supplies in preamps and amps with more traditional supplies.

I'm confused at how a  self-proclaimed repair shop with 35 years experience took almost a week (year?) to find a 12V supply sitting at 8V (with excessive ripple), then, despite the fact that a filter cap was "can't keep your finger on them hot" and there was a "perfectly formed half wave (60hz) signal on the caps" decided the correct approach was to shotgun the entire circuit?

Maybe I'm crazy, but how about removing the hot cap and putting an ohmmeter across it?

I'm just a FNG hobbyist who enjoys audio electronics. Hope to learn a thing of two on this site. In one week I've seen multiple help requests from "repair shops" that are truly unimpressive in their content. It seems backwards. Shouldn't "repair shops" be giving repair advice to hobbyists?

 

Admins and other members: I apologize for my aggressive post. I'll take whatever punishment is deemed appropriate. I certainly won't reply to this thread again.

 

Actually you are correct.

 

[tutor turtle 7]

5 hours ago, timmyjim said:

I'm only replying to this thread one more time because I found this post from EXACTLY one year ago today:

 

 

Is this the same amp? If so - According to this thread, you replaced the 12V caps back then. One year later and there is still an issue with the 12V circuit, even after the caps were already replaced?

Ignore me if this is a different amp, but if it's the same one shouldn't there be more questions as to why, or was it not repaired properly a year ago?

 

Here's the part where I type something that will get me into trouble with the admins: I'm just a hobbyist. Mostly I like to fix broken stuff. The first thing I do when I have a rectangular black box filled with electronics thats not acting as it should .... take off the cover and check the supplies.  Go from there. This can be challenging with a triac switched supply, which many Carver amps have, but usually simple to check basic supplies in preamps and amps with more traditional supplies.

I'm confused at how a  self-proclaimed repair shop with 35 years experience took almost a week (year?) to find a 12V supply sitting at 8V (with excessive ripple), then, despite the fact that a filter cap was "can't keep your finger on them hot" and there was a "perfectly formed half wave (60hz) signal on the caps" decided the correct approach was to shotgun the entire circuit?

Maybe I'm crazy, but how about removing the hot cap and putting an ohmmeter across it?

I'm just a FNG hobbyist who enjoys audio electronics. Hope to learn a thing of two on this site. In one week I've seen multiple help requests from "repair shops" that are truly unimpressive in their content. It seems backwards. Shouldn't "repair shops" be giving repair advice to hobbyists?

 

Admins and other members: I apologize for my aggressive post. I'll take whatever punishment is deemed appropriate. I certainly won't reply to this thread again.

I do repairs part time. It is a hobby. I don't run a professional shop. I do this now in my retirement, I help out friends. I changed the caps as noted in BobTFM35 post. DIFFERENT CAPS! There is only about 200 caps in this unit. This particular amp was working and being used over the last two years, when a different problem cropped up. Maybe I was mistaken thinking I could talk to fellow audio enthusiasts about an amp that has almost no documentation on. I was not expecting judgment to be past on me in my effort to help out others. Yes nash your pre judgement of me and my motives was overly aggressive and uncalled for. Stay classy.

[Nahash5150 9,369]

11 hours ago, tutor turtle said:

I do repairs part time. It is a hobby. I don't run a professional shop. I do this now in my retirement, I help out friends. I changed the caps as noted in BobTFM35 post. DIFFERENT CAPS! There is only about 200 caps in this unit. This particular amp was working and being used over the last two years, when a different problem cropped up. Maybe I was mistaken thinking I could talk to fellow audio enthusiasts about an amp that has almost no documentation on. I was not expecting judgment to be past on me in my effort to help out others. Yes nash your pre judgement of me and my motives was overly aggressive and uncalled for. Stay classy.

 

What are you talking about? I have been giving advice and helping out however I can. I haven't said anything about you or your motives.

 

Timmyjim is entitled to his opinion in an open forum so if you don't think he's worth listening to then just block him and carry on.

 

Sheesh.