Greetings, all:
I have with me now an EV-7300 stereo power amplifier. It was being used as a PA amplifier for a band of musicians. The band has three of these amplifiers, and the last time they got together, each of the three amps lost power in one channel. I do some tube amp repair for the guitar players in the band, and they had me over to check it out.
Well, the place where they were playing at had a guy running a variac to turn his neon lights down to the point where they flickered on and off. It was neglected to ensure that the amps were not on the same power bar (d'oh).
Although I do have tube amp experience, I'm not very familiar with solid state. I was wondering if anybody had some suggestions as to where I might start my inspection.
Again, the problem is one channel is not working. Fuses check OK, and the XLR inputs are on the circuit board without any physical damage. . . The big blue caps test ok. . . I'm wondering if this is one of those "crowbar" protection systems I keep hearing about. Seemed to me that "crowbars" were intended to avoid power spikes, not power sags (I went to the location afterwards and the guy had his neon lamps and variac down to 90VAC). Anyhow, what do I know!
I have a link to the owner's manual, in PDF format. This contains the only schematic I was able to find for this amp, as well as performance specifications. The skeemos are on pages 9-10-11, or therabouts, right near the end of the PDF:
http://archives.telex.com/archives/EV/Amplifiers/Owners Manual/7300 Owners Manual.pdf
I imported the PDF into photoshop in an attempt to sharpen/contrast and make the schematic clearer, but it was futile, and nothing I did made the original PDF look any better
I also have an album of 19 pictures of this amp (one of three, each with the same, one channel only problem) uploaded to Photobucket:
http://s2.photobucket.com/albums/y21/the_boy_of_a_thousand_shirts/EV 7300/
Any help would be much appreciated!
Will
I have with me now an EV-7300 stereo power amplifier. It was being used as a PA amplifier for a band of musicians. The band has three of these amplifiers, and the last time they got together, each of the three amps lost power in one channel. I do some tube amp repair for the guitar players in the band, and they had me over to check it out.
Well, the place where they were playing at had a guy running a variac to turn his neon lights down to the point where they flickered on and off. It was neglected to ensure that the amps were not on the same power bar (d'oh).
Although I do have tube amp experience, I'm not very familiar with solid state. I was wondering if anybody had some suggestions as to where I might start my inspection.
Again, the problem is one channel is not working. Fuses check OK, and the XLR inputs are on the circuit board without any physical damage. . . The big blue caps test ok. . . I'm wondering if this is one of those "crowbar" protection systems I keep hearing about. Seemed to me that "crowbars" were intended to avoid power spikes, not power sags (I went to the location afterwards and the guy had his neon lamps and variac down to 90VAC). Anyhow, what do I know!
I have a link to the owner's manual, in PDF format. This contains the only schematic I was able to find for this amp, as well as performance specifications. The skeemos are on pages 9-10-11, or therabouts, right near the end of the PDF:
http://archives.telex.com/archives/EV/Amplifiers/Owners Manual/7300 Owners Manual.pdf
I imported the PDF into photoshop in an attempt to sharpen/contrast and make the schematic clearer, but it was futile, and nothing I did made the original PDF look any better
I also have an album of 19 pictures of this amp (one of three, each with the same, one channel only problem) uploaded to Photobucket:
http://s2.photobucket.com/albums/y21/the_boy_of_a_thousand_shirts/EV 7300/
Any help would be much appreciated!
Will
does the protection relay for the dead channel click on and connect the amp to the speaker terminals?
If it does, Is there signal at the + term of J7? and after the op-amp.
If the relay does not click on. is there DC offset at the amp output before the relay? If there is heavy DC offset there. IE rail voltage. then there are blow output transistors. check drivers too.
If there is only half wave signal there. check drivers.
If it does, Is there signal at the + term of J7? and after the op-amp.
If the relay does not click on. is there DC offset at the amp output before the relay? If there is heavy DC offset there. IE rail voltage. then there are blow output transistors. check drivers too.
If there is only half wave signal there. check drivers.
burnedfingers said:
Hi Burnedfingers,
Yes, nothing out of one channel.
There are two correctly positioned jumpers in each of the octal sockets, the bridge/mono switch is set to stereo, and both gain controls were tested in unision up to 12 noon (half gain).
Zero Cool said:
Hi Zero Cool
The protection LED for both channels (the dead one as well) clicks on at startup, and then the protection LED at the front goes off. The band members say that when it was working properly, this is what the lights would do--protection on briefly at startup, and then off again fairly fast. Beyond what the LED is showing, I'm not sure.
I intended to start getting some testing done this weekend.
As far as testing the amp is concerned, I have a question.
Because I work on tube amps, I always keep a big brute of a speaker connected when I do my testing. Do I need to do this with this transistor based unit? If so, just one channel, or both?
Burnedfingers and Zero Cool - - thanks a bundle to both of you for your replies. Much appreciated.
Will
Will,
The protection leds should both come on for roughly 4 seconds or so and then go out. This is the same basic circuit as the EV2600 which is a later model amplifier. Unfortunately I cannot read the schematic at all.
I would re-check the amplifier by putting a sine wave into it and looking at the output with a scope. I usually look at the output without a load and then attach a load and see how it behaves. If the sine wave is good check the cap in the input and the feedback cap to ground. Just replace them as they are cheap. See where you are at this point and post again.
Joe
The protection leds should both come on for roughly 4 seconds or so and then go out. This is the same basic circuit as the EV2600 which is a later model amplifier. Unfortunately I cannot read the schematic at all.
I would re-check the amplifier by putting a sine wave into it and looking at the output with a scope. I usually look at the output without a load and then attach a load and see how it behaves. If the sine wave is good check the cap in the input and the feedback cap to ground. Just replace them as they are cheap. See where you are at this point and post again.
Joe
burnedfingers said:
Hi Joe
Indeed, it is a 4 second period of light from the protection LEDs at power-up, and then out.
The schematic in the PDF is really terrible. I probably shouldn't even have linked it, but I wanted to share all that I could provide.
However, I've gone ahead and ordered a large schematic for the 7300. It should be here in the following week. I have a great flatbed scanner. When it arrives I will add the scans to my Photobucket account with a new link.
I will go ahead and check the amp as indicated. The caps you mentioned will be investigated.
Again, I am grateful for your help. It is much appreciated.
I've spoken with the Neon sign/variac owner, and the variac has been boxed up!
Will,
You are dealing with an amplifier that is around 20 years old. I sincerely doubt that the variac had anything to do with the problem in one channel of the amplifier. I have run a number of amplifiers on the bench hooked to a variac running at lower voltage than normal in order to track down problems. Basically if the amplifier will turn on and the protection circuit latch up it will run at lower voltage without any damage to the amplifier.
You are dealing with an amplifier that is around 20 years old. I sincerely doubt that the variac had anything to do with the problem in one channel of the amplifier. I have run a number of amplifiers on the bench hooked to a variac running at lower voltage than normal in order to track down problems. Basically if the amplifier will turn on and the protection circuit latch up it will run at lower voltage without any damage to the amplifier.
burnedfingers said:
Right!
The amp is dated "Recieved 2-11-88"
Just about 20 years to the day when the store (or whomever) first got this thing. The power came from the variac, then went to a short white extension cord with only two prong outlets (with the little plastic nub cut off so a three prong power bar could be plugged into the end of it), which had a chain of neon signs plugged into it, as well as a large 10-outlet power bar made from wall outlets (looked like a construction site item that had been seriously battered and as a result, retired). The 10 outlet power bar was plugged into the last of the three two prong outlets on the short white extension cord attached to the variac. Although the 10 outlet power bar had a ground prong, this ground prong was taking the spot of the removed little white nub on the short extension cord. . . So, no ground either. I'm not sure what the deal is with this setup, but it is changing, or never being used again. From what I hear a Furman power conditioner was just purchased today, and is to be added to the rack setup, along with a tester to check for wall voltage levels and grounds.
Anyhow, I'm posting again because I've scanned in some better schematics that I went hunting for today.
http://i2.photobucket.com/albums/y21/the_boy_of_a_thousand_shirts/EV 7300/ev_7300_pt1of2.jpg
http://i2.photobucket.com/albums/y21/the_boy_of_a_thousand_shirts/EV 7300/ev_7300_pt2of2.jpg
These are limited by the photobucket size; the scans are quite good, high res, and around 4.5 MB each (part 1 and 2).
It's a bit of a mess to pull apart. I did check over the input board,
and everything seems to be running properly there.
Going to investigate the Potter-Brumsfield T90S5D12-24 relays.
Edit: Also added two pictures of the back side of the input board:
http://i2.photobucket.com/albums/y21/the_boy_of_a_thousand_shirts/EV 7300/IMG_2798.jpg
http://i2.photobucket.com/albums/y21/the_boy_of_a_thousand_shirts/EV 7300/IMG_2792.jpg
Find out if it's the power amp thats faulty first. Inject a signal directly at J7/J107 and see if it comes out in any way BEFORE the relay.
On a hunch, as this amp was used for PA and might have been driven hard - check the VI limiter transistors Q8/Q9 (or Q108/109 for right channel). If they have failed short, then it will have shut the outputs off totally, and possibly damaged the drivers or preceding stage.
I concur - being run on a Variac at low voltage won't have damaged the amp.
On a hunch, as this amp was used for PA and might have been driven hard - check the VI limiter transistors Q8/Q9 (or Q108/109 for right channel). If they have failed short, then it will have shut the outputs off totally, and possibly damaged the drivers or preceding stage.
I concur - being run on a Variac at low voltage won't have damaged the amp.
If the relays latched up upon startup there is nothing wrong with them so why bother. Do as suggested and inject a signal a J7/107
and see what it looks like before diving into it and causing anymore problems.
Forget about your high hopes with any power conditioner. That is money now gone that could have been used in your system elsewhere to better it.
Forget about the ground as it didn't cause any problems either. I will mention here for the sake of the moderators that a ground should always be connected. There I said it!!!!!!!
The lack of it however didn't cause a problem with the amplifier.
I have a 9444 Altec sitting in my garage. Its the same thing as a EV2600 and only slightly different than this model as I believe it came out roughly in 1991 or so. I can run it so low on the variac that it would scare you. The end result it that the power output is lower that the specifications and no damage resulted in doing it.
Pictures of the boards don't help but a GOOD copy of the schematic would surely help.
In summary here..... inject a signal and look at your scope and see what it looks like before going further and tearing more stuff apart. I'm sure the problem is roughly a 5 min fix. So, lets put a signal into it and go from there. Now, a picture of the sine wave would be helpfull.....................................
and see what it looks like before diving into it and causing anymore problems.
Forget about your high hopes with any power conditioner. That is money now gone that could have been used in your system elsewhere to better it.
Forget about the ground as it didn't cause any problems either. I will mention here for the sake of the moderators that a ground should always be connected. There I said it!!!!!!!
The lack of it however didn't cause a problem with the amplifier.
I have a 9444 Altec sitting in my garage. Its the same thing as a EV2600 and only slightly different than this model as I believe it came out roughly in 1991 or so. I can run it so low on the variac that it would scare you. The end result it that the power output is lower that the specifications and no damage resulted in doing it.
Pictures of the boards don't help but a GOOD copy of the schematic would surely help.
In summary here..... inject a signal and look at your scope and see what it looks like before going further and tearing more stuff apart. I'm sure the problem is roughly a 5 min fix. So, lets put a signal into it and go from there. Now, a picture of the sine wave would be helpfull.....................................
jaycee said:
Right! We will have to get to the bottom of the situation and then if possible determine what caused the problem, with no more idle and unsupported speculation on my part as to what it may or may not have been!
Thank you, Jaycee! I will be sure to check the limiter transistors as well. J07/J107 is located, and definitely on the list.
burnedfingers said:If the relays latched up upon startup there is nothing wrong with them so why bother. Do as suggested and inject a signal a J7/107
and see what it looks like before diving into it and causing anymore problems.
Forget about your high hopes with any power conditioner. That is money now gone that could have been used in your system elsewhere to better it.
Forget about the ground as it didn't cause any problems either. I will mention here for the sake of the moderators that a ground should always be connected. There I said it!!!!!!!
The lack of it however didn't cause a problem with the amplifier.
I have a 9444 Altec sitting in my garage. Its the same thing as a EV2600 and only slightly different than this model as I believe it came out roughly in 1991 or so. I can run it so low on the variac that it would scare you. The end result it that the power output is lower that the specifications and no damage resulted in doing it.
Pictures of the boards don't help but a GOOD copy of the schematic would surely help.
In summary here..... inject a signal and look at your scope and see what it looks like before going further and tearing more stuff apart. I'm sure the problem is roughly a 5 min fix. So, lets put a signal into it and go from there. Now, a picture of the sine wave would be helpfull.....................................
Right-o!
I am going to pick up a Tektronix 475a tomorrow morning. With any luck at all I'll have some sine wave pictures soon!
I checked the pictures of the new schematics that I uploaded to the photobucket album, and they looked quite a bit more legible than the PDF one. Not sure if they are entirely clear, though.
Thanks so much for your help!
EV 7300 amplifier
I have read the post concerning this amp not working on both channels-you mentioned you were going to scan schematic and post on Photobucket. The link for the image does not work. I have an exact EV 7300 amp that had suffered a fall-breaking circuit board and frying some components. I had taken this amp to a repair shop but they were unable to repair because of lack of schematic. I am wondering if you still have scanned images of schematic still available? Would greatly appreciate your reply...
Respectfully,
Brad
I have read the post concerning this amp not working on both channels-you mentioned you were going to scan schematic and post on Photobucket. The link for the image does not work. I have an exact EV 7300 amp that had suffered a fall-breaking circuit board and frying some components. I had taken this amp to a repair shop but they were unable to repair because of lack of schematic. I am wondering if you still have scanned images of schematic still available? Would greatly appreciate your reply...
Respectfully,
Brad
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