Fault Tracing a Carver M-500t

[Enzo]

For 6v lamps running on 8v, then why not just put a couple diodes in series with the bulbs. The natural junction drop across the diode will lose the volt and a half for you. 2 or 3 diodes, and if you need AC instead of half wave DC, then add a parallel string of diodes facing the opposite direction. Cheap, simple, dissipates next to nothing. Parallel to the other diodes, not parallel to the lamps.

Have you tried the old U601? So it got hot, but does it worEven just grabbing a lead in your needle nosers.

[Enzo]

Damn, why does it do that? It chopped out a few paragraphs. HAs done that before.

Does the old 601 work, was one.

Mentioned that your current is appraently not out of line, but that it was under the 200ma of the one meter and certainly within the 10A of the other. And even if it WAS 10A, you'd have the 30 seconds to turn the amp off. Plenty of time. But don't bother now.

Then discussed freeze spray. In the absence of freezit, a squirt of contact cleaner - or most any aerosol - will chill a component. ALso pliers will make a better heat sink than your fingers, even just grabbing a lead wire.

Agreed that R212 and relay are the problem. I'd compare the other amp to this one in terms of voltages and currents and relay coil resistance.

[bob p]

Enzo, I've also had problems with the board software choking and losing data. To try to avoid being bitten by that, I do a couple of things:

1. Break up a long post in to several smaller ones; commit your comments to a post so they don't get lost.

2. I routinely use the Preview Post button, so your browser keeps committing the data from its buffer to the software at the Ampage end. I'm not sure if the problem is at your end or at their end, but this seems to happen to you more than other people. Maybe its your PC or your dialup connetion. Maybe more frequent submissions would help. I try to do a commit of some type after EVERY paragraph.

At any rate, I know its really frustrating for you to lose your posts -- but its even more frustrating for me!!!

[bob p]

Does the old 601 work, was one.

Enzo, your message apparently got truncated again, and I have absolutely NO CLUE what you are talking about with respect to U601. I have no idea if it works or not, and I have no idea how to safely test it.

Yesterday I looked at the data sheet and I have no idea how to test it to see if it is good. I am afraid that if I plug a shorted U601 back into the amp, that it might short the supply rails together or that it might blow-up something else, and I'll have to start replacing the same parts that I replaced yesterday. I'm reluctant to put an "iffy" part back into the amp, because I'm afraid that it may damage the new parts I've just put in, and force me to go through another round of troubleshooting.

Is that reasonable? I have to admit, it was easier (and cheap) to just to a blanket replacement of all of the 20-year old 'lytic caps instead of trying to figure out which ones were good and which ones were bad.

Is there any way to test U601 to see if its good or bad?

[Enzo]

I think the 601 sentence was just me getting distracted, not the boards fault. It was going to say something like the one you took out got hot but might still be good.

If it were me, I'd just plug the thing back in and see what happened. If it did short the rails together, you would I hope turn it off after a couple seconds and the rails should remain just fine. At worst, R601, 602 would heat up. Those resistors hook right to the rails, so they won't affect anything else. Dragging rails down does no harm to other things on the rails. That is why when one of a row of parallel output xstrs shorts E-C, the rest are not harmed. All the current flowed through the shorted one, leaving no current for the others, and dragging the voltage across them down as well. In fact the easiest life an output could ever have is a shorted next door neighbor.

It would be very hard for the 601 to harm anything outside its own circuit. It burnt up at the same time as the other stuff burnt up for the same reason that stuff went. They didn't burn because of anythiing 601 did. It is isolated from the rails by the two 1.8k resistors. It does have a ground connetion at pin 1, so internally it could short the rail pins together or either - or both - to ground. But there would always be that 1.8k of resistance in the path. And that is 22ma draw from the rail if it happens. And the resistor would then dissipate 0.9 watt. That gets hot, but is within the 2w rating of the part.

Another failure mode would be a short from rail to input pin. That sends 40v towards the amp chanel output at the speaker terminals. But there is 82k in series with that, and also from the output a 10k to ground, whuch would do an 8/1 divide on the voltage making it 5v. THat ought to be no stress for the output bus.

COnceivably the meters could be harmed. They are referenced to -40, so if the meter drive pins shorted to +40, the meters would have 80v across them. OK, disconnect the meters and look to see if +40 is on the drive. To be scientific I guess I'd throw a resistor in place of the meters of roughly whatever the meters' resistance is.

SO I don't think there is a lot of risk with trying the old one. But if you are not comfortable with it, then don't.

AS to how to test it other than plug her in, on the bench I could breadboard it, feed it +/- rails from a bench supply, and some signals in, and whatever else the data sheet says it needs to wake up. But I didn't think you had bench supplies, so...

And I am used to haveing a pretty extensive parts collection on hand already. SO most times I hve something to install, but not this chip. This chip would be a very unlikely failur in most cases. Your possible lightning scenario makes it a more likely failure.

The 7317 IC I mentioned earlier is what Samson (and Hartke) uses in most of their amps as the relay driver. It is a chip designed to monitor amp outputs and drive the speaker relay. Takes the place of all that Q200 series circuitry.

Hey! You could duplicate the LED meter circuit from the PM1.5, replace the U601 stuff with that. Then take the movement out of the meters but save the scales. Then drill a curved line of small holes in each meter dial. Now mount a row of LEDs along those holes. Voila! New LED meters. What you think?

Ah... maybe not...

[Enzo]

As to the posting. Yes I know the tricks. WHen I feel unlucky, I just copy the text with a right click, and it is on my clipboard. But I get into typing my thoughts and am not viewing myself from afar to remember to do all the things I should.

That last time was not really a very long post, it was about the size of your post #45. I post a ton, as you know, and it doesn't happen all that often, but it irks me when it does.

I know guys who write in Notepad and then copy to the post box.

This only happens to me on this board, not on any of the other places I go.

SOmetimes I do it to myself. On the old AMpage, I learned to scroll the post box down so the post and clear buttons at the bottom were off screen. I am a clumsy mouser, and every now and then, and always when doing a long post, of course, I would move the mouse down to set the cursor somewhere, and overshoot and hit the CANCEL button. And of course there is no retrieval from that.

SOmetimes my little finger misses the shift key and hits the control key instead. So if I meant to type a capital "I", which is shift-i, I would instead get CTL-i. Well that sets italics. SO after typing my sentence, I look up and see that instead of a capital I at the start of my sentence I see the I missing and the rest of the sentence is in italics.

That I can fix with the mouse. But sometimes I hit CTL-??? instead of the shift and whatever letter it is launches like the Misrosoft calendar, and connects me to favorite radio stations or something. Of course that leaves the post box I was working on behind, and when I close the other crap and back up, it is now empty. I don't know what letters I hot to do that, but I scream at the machine when I do it. I am tempted to pull the caps off the CTL buttons. Well the left one, my right hand doesn't do it.

I only use the little quick reply box at the bottom, I never use the full size box. I don't think that matters as 99% of the time I can type as long a post as I want that way.

[bob p]

i think i had more problems like yours when i was using internet explorer. since i switched to firefox, it hasn't been a problem for me. for example, if you're working on a post in firefox and you hit the wrong link on the page, and you move forward to a new browser page, you can use the "back" button to go back to where you were before the mistake. the text that you had been typing will still be there with firefox. its never there with internet explorer. with firefox i will even intentionally surf in and out of a page like the post editing window. i know it sounds crazy, but you can do it.

i found that mousing got a lot easier when i went to an optical mouse rather than a wheel-based mouse. i don't know if that applies to you or not, but the optical stuff doesn't seem to become as jumpy because of fouling with debris. i also like trackballs better than mice. they seem more precise to me.

when i used IE/Windows I sometimes ran into the nasty problem of the browser locking up in the middle of a really long post, and then losing everything. it didn't happen often, but when it happened it was really devastating. i really hated that. i moved to linux for my web surfing box because of that and its never happened since.

[Enzo]

It's not my mouse, just my motor skills are not so great. I also moved the mouse over to the left next to me screen a couple years ago, so I do it left handed, one more challenge. But it used to happen on the right as well. Oh yes, I have been playing guitar for over 40 years and I still suck. I can practice and practice, and I will still miss notes and screw up left and right. Manual dexterity does not come easy to the worlds clumsiest human here.

I know there are alternative browsers and OS out there, but I have no idea what they do and do not make different, and frankly I hate computers - zero interest - and the last thing I want to do for an evening is muck around with the software. ANy time I have to pull the cover off the damn thing to change a CPU fan or power supply or whatever malady befalls a computer, I grit my teeth and curse softly. And I am used to my software more or less working all the time, and if I ran into ANY sort of compatability issue, I'd want to throw the thing against a wall. I mean things like when folks report, "Gee, I cannot open your image link on my browser."

MY computer should be like a telephone - plug it in and communicate through it, never have to think about what is going on inside it.

[bob p]

The TA7318 seems to be in stock for $3 at B&D.

www.bdent.com

Is the TA7318 at all different from the TA7318P?

I see that BD does have the TA7318 in stock for $3.00 or so. The only problem is that they won't accept any order below $15, and they have an $8 flat fee shipping charge. $23 is a lot to pay for the $3 part that weights as much as two aspirin. Its too bad that their inventory is so narrow -- they carry nothing but semiconductors I don't need, and caps that are way overpriced.

Do you know of any other sources for the 7318? If not, my only option is to buy stuff I really don't have any use for, just so that I can come up with a minimum order.

[Enzo]

I rarely use BD, but they are a source of Sanken xstrs I use. I can usually pad an order with some 2SC3264 or something that I use. But I hear you on minimums. I need a dollar DC power jack for a wall wart thing, and the only place I found the size I need is MCM and they have their $25 minimum, so there it sits waiting for other things I might need from them.

No, I just found that source by looking in my usual suspects file. Google the part number and see where it leads. Try Carver Pro to see if they have any.

I think the P on the end means plastic. The letters after the number generally refer to the package. See fi yu can link to a data sheet. You con't want a DIP or a SOIC if you need a SIP.

[bob p]

oh, i've been googling the chip for months. you won't find anything that way other than data sheets and middlemen companies who have no inventory, yet offer to locate/broker parts for you if you plan to buy a boatload of them.

i understand that minimum orders are sort of a necessary evil. at least with MCM they have a wide enough selection of inventory that you could find enough dumb stuff to complete an order. with BD though, its another story altogether: the only thing that they have are semis and obscenely overpriced caps. i don't need their semis (i bought more than i needed last time to get to a minimum order) and i just can't bring myself to pay $18 for a $7 snap in cap.

i was hoping that you knew of another source that wasn't coming up on google searches. BD was a good recommendation that other time. since the meter chip is such an odditiy, i guess i could get a couple of them for a rainy day, but its hard to imagine ever needing another one.

[Enzo]

SO did we already try the Carver Pro route and get nowhere? If they don't have them, oh well, but if they do...

No. Other than BD and potentially Carver, I can't think of anyone. If I do I'll let you know.

Looking through comsumer electronic part suppliers:

Tritronics, Inc www.wehaveparts.com shows 8 different listings, all out of stock. I used to use them sometimes.

www.partstore.com seems to have them. I know nothing of these folks.

www.hbfelectronics.com lists them for $1.95. I have no idea if they are in stock. Never used them.

[bob p]

i was on the phone with CarverPro earlier this week. the parts manager knows me, as i've been calling him about all sorts of obsolete parts that they don't stock any more. AFAIK the Pro division never used the TA7318P.

thanks for the leads on other suppliers.

[Enzo]

Could have been a legacy part from before the split. What is the other half - Sunfire? - maybe they have them.

[bob p]

As it turns out, Carver Pro has never had any of the Consumer line parts, and I think I've mentioned before that they get really pissed off when I keep asking them these questions; asking them the same questions over and over again makes the parts manager upset because he thinks I'm just stupid. I don't want to aggravate him, out of the fear that doing so would make him less likely to help me find rare parts for the amps that they actually do carry parts for. So I listened to what they've told me and I've stopped asking about parts for amps that they've never had in inventory. If the amp was not made by Carver Pro, they don't have parts. Period. If the amp was made by Carver Pro, they might have parts. But just about all of the parts for the Bob Carver era amps are long gone. They only stock parts for the new stuff that Phoenix Audio has been making under the Carver Pro name.

After the split, Carver (consumer) went bankrupt. In the bankruptcy liquidation *ALL* of the Carver consumer parts inventory was bought by a fellow named Rolland at High-Tech electronics in Washington state. He performs flat-fee repairs on Carver amps for $300. He won't look at an amp for less, and he doesn't sell his parts inventory to other people. He is hoarding all of the original Carver parts and won't let them go. The only way to get the original Carver parts is to send your amp to him for a $300 repair. That's not something that I would do for an amp that needed $2 in caps and a $3 IC.

Sunfire was a totally different corporation. They have never had Carver parts. They refer you to High-Tech Audio.

These are the facts as I have gotten them first-hand from CarverPro, High-Tech Audio, and Sunfire. I exhausted those options months ago.

The only options left are finding parts in the open market.