Hi Harry,
So, your first fault. A cracked trace near a pad?
Now, looking at a cleaner copy of the schematic, I see that Q205 base is not connected to Q206 C. I think this must be an error.
At any rate, Q205 B is connected to:
D201 C
R204, then Q202 C and Q203 E
C202 A
R218 (check for an incorrect value here (22K)
Q206 C
The action of the circuit is to charge C202 up slowly allowing the amplifier circuits to settle down before connecting them to the outside world. So Q207 B is normally positive 0.65 VDC ish. That means that D201 A and Q205 E are at some positive voltage, less than 16 VDC since C202 is rated for only 16 VDC. The base of Q205 is at the potential of C202 A.
What I would do is disconnect C202 and try it again, then pull Q202 and Q203 and try it. Let me know.
-Chris
So, your first fault. A cracked trace near a pad?
Now, looking at a cleaner copy of the schematic, I see that Q205 base is not connected to Q206 C. I think this must be an error.
At any rate, Q205 B is connected to:
D201 C
R204, then Q202 C and Q203 E
C202 A
R218 (check for an incorrect value here (22K)
Q206 C
The action of the circuit is to charge C202 up slowly allowing the amplifier circuits to settle down before connecting them to the outside world. So Q207 B is normally positive 0.65 VDC ish. That means that D201 A and Q205 E are at some positive voltage, less than 16 VDC since C202 is rated for only 16 VDC. The base of Q205 is at the potential of C202 A.
What I would do is disconnect C202 and try it again, then pull Q202 and Q203 and try it. Let me know.
-Chris
Chris,
Yes first fault was a cracked trace close to a pad. Changed R218 22K no difference. Removed C202 relay began to buzz building in intensity and then closed or activated. Harry
Yes first fault was a cracked trace close to a pad. Changed R218 22K no difference. Removed C202 relay began to buzz building in intensity and then closed or activated. Harry
Clue!!!
Hi Harry,
-Chris
Hi Harry,
What does that tell you? Inspect and check C510 and 511 (6,800 uF 50 V) for excessive ripple. Check with a 'scope if you have one. They may be going open. If you don't have a 'scope, what are the DC and AC voltages on your 40 VDC rails?
-Chris
Chris,
I dont have a scope. DC and AC voltages with respect to ground are as follows -44 volts + 43.6 volts .024 volts AC and .033 volts AC. Harry
I dont have a scope. DC and AC voltages with respect to ground are as follows -44 volts + 43.6 volts .024 volts AC and .033 volts AC. Harry
Chris,
Here is a little info for you. I removed both the 50 volt 6800 uf caps in order to test them when I reinstalled them I can only assume that I reversed them meaning the cap that was on the negative rail was reinstalled on the positive rail and vice versa. Powered it up and the relay moaned the transformer groaned and the fuse blew. One of the two caps in question was hotter than a firecracker. Needless to say they have already been ordered. Harry
Here is a little info for you. I removed both the 50 volt 6800 uf caps in order to test them when I reinstalled them I can only assume that I reversed them meaning the cap that was on the negative rail was reinstalled on the positive rail and vice versa. Powered it up and the relay moaned the transformer groaned and the fuse blew. One of the two caps in question was hotter than a firecracker. Needless to say they have already been ordered. Harry
Hi Harry,
Sorry to hear about your "incident". Using a 'scope is far easier. Your caps probably needed replacing anyway though, given their age. Let's have you install those and give it another try.
-Chris
Sorry to hear about your "incident". Using a 'scope is far easier. Your caps probably needed replacing anyway though, given their age. Let's have you install those and give it another try.
-Chris
was looking at the title of this thread.....
thought you'd like to know, Centerpointe used to sell the Japanese Transistor Substitution Handbook published by Toshiba
thought you'd like to know, Centerpointe used to sell the Japanese Transistor Substitution Handbook published by Toshiba
Hi unclejed613,
What you want is book #1 in the series, the transistor spec book. "Japanese Transistor Substitution Handbook" is number 3 in the series and is not completely accurate. You need the spec book mostly so you can confirm the information in book #3.
My last set is from 1999 and I have some from 2002. I wish it came in English and on CD with a search function.
-Chris
What you want is book #1 in the series, the transistor spec book. "Japanese Transistor Substitution Handbook" is number 3 in the series and is not completely accurate. You need the spec book mostly so you can confirm the information in book #3.
My last set is from 1999 and I have some from 2002. I wish it came in English and on CD with a search function.
-Chris
Chris ,
I wont have my caps till next monday 8/20. In the mean time are there any things I should check with regard to the power supply and the fact that it is producing higher voltage than it should 81.6 V on the 74 V rail. Thanks Harry
I wont have my caps till next monday 8/20. In the mean time are there any things I should check with regard to the power supply and the fact that it is producing higher voltage than it should 81.6 V on the 74 V rail. Thanks Harry
Hi Harry,
Yes. Check the values of the sensing resistors in the area of Q501 ~ Q504. Also clean or replace SVR503 (voltage adjust control). C526 and C527 should be replaced as well.
The circuit is regulating, the range is incorrect. If you can't find any problems there, make sure Q503 and Q504 are matched as they form your error amplifier.
Let me know how you make out. I have not seen this problem before, but the amp is so old that we are at a stage were components may fail for no external reason. I'm not saying your amp is unreliable, I'm just saying we are now into the odd problem phase.
-Chris
Yes. Check the values of the sensing resistors in the area of Q501 ~ Q504. Also clean or replace SVR503 (voltage adjust control). C526 and C527 should be replaced as well.
The circuit is regulating, the range is incorrect. If you can't find any problems there, make sure Q503 and Q504 are matched as they form your error amplifier.
Let me know how you make out. I have not seen this problem before, but the amp is so old that we are at a stage were components may fail for no external reason. I'm not saying your amp is unreliable, I'm just saying we are now into the odd problem phase.
-Chris
Chris,
Have installed the new 6800 ufd caps and checked out GC-377. GC-377 is a soldered in module covered with a black plastic lid which contains Q501- Q504 anyway I changed every resistor and all the caps on this module as 3 of them were no good C526, C527, C528. Reinstalled C202 and fired it up. The relay pulls the contacts closed and then snaps. It acts kind of sluggish if you know what I mean. At this point B+ is down to 76.9 volts from 81.6 Harry
Have installed the new 6800 ufd caps and checked out GC-377. GC-377 is a soldered in module covered with a black plastic lid which contains Q501- Q504 anyway I changed every resistor and all the caps on this module as 3 of them were no good C526, C527, C528. Reinstalled C202 and fired it up. The relay pulls the contacts closed and then snaps. It acts kind of sluggish if you know what I mean. At this point B+ is down to 76.9 volts from 81.6 Harry
Hi Harry,
Punctuation, please my friend. Caps would be nice at the start of a sentence too.
There may still be some issues, but you are solving them one by one. That's the way it is with older amps sometimes. They are restorations, not repairs.
-Chris
Punctuation, please my friend. Caps would be nice at the start of a sentence too.
Yes, it's covered so that probes don't cause giant issues. This is the power control circuit.
There may still be some issues, but you are solving them one by one. That's the way it is with older amps sometimes. They are restorations, not repairs.
So, can you set to 74 VDC at the test point? The trimmer should not be completely over to one side.
Still looking for issues then. The good news is that these amps will run for a long time when fixed and they are one of the better looking Carver amps.
-Chris
Hi Harry,
Did you say you replaced R509 ~ R515? Look for other reasons why PC501 might be on too hard. R506 may have drifted in value as well. Yes, it could be that simple.
-Chris
Yuk. I don't like that. Let me look things over again. Have you checked Q502,503 and 504 for gain? Q503 and Q504 should be matched. Also give Q505 ~ Q508 a check. This makes up an improved diac for symmetrical triggering. Also check D515 and D516 and associated resistors. Be aware that you are now working on the primary side of the AC line.
Did you say you replaced R509 ~ R515? Look for other reasons why PC501 might be on too hard. R506 may have drifted in value as well. Yes, it could be that simple.
-Chris
Chris,
The first thing I noticed is R 506 had a 56K in there per Todd. I changed this prior to having the proper schematic. M500T uses 56K and M500 uses 47K so I replaced that. Next SVR 503 had increased to 300K so I replaced that. B+ now is 73.5 volts when first plugged in and about 20 minutes later it reads 74.3 volts. It also seems to fluctuate between these two points periodically. It would appear that increased resistance in the collector base circuit of Q 502 causes an increase in power supply voltage. Thanks, Harry
The first thing I noticed is R 506 had a 56K in there per Todd. I changed this prior to having the proper schematic. M500T uses 56K and M500 uses 47K so I replaced that. Next SVR 503 had increased to 300K so I replaced that. B+ now is 73.5 volts when first plugged in and about 20 minutes later it reads 74.3 volts. It also seems to fluctuate between these two points periodically. It would appear that increased resistance in the collector base circuit of Q 502 causes an increase in power supply voltage. Thanks, Harry
Hi Harry,
Try to get it so the voltage is around 74 VDC midpoint on the trimmer. Don't forget to check those other things too. I am glad you remembered that part change.
-Chris
Edit: Harry, try to set the bias on both channels. It may want some current draw.
Try to get it so the voltage is around 74 VDC midpoint on the trimmer. Don't forget to check those other things too. I am glad you remembered that part change.
-Chris
Edit: Harry, try to set the bias on both channels. It may want some current draw.
Chris,
Bias should be 6mV +/- 1mV. I have both channels set at 5mV. Remember I stated that the protection relay seemed sluggish? It takes about 6 seconds for it to snap or click and I stated that the contacts are touching before the click. I am beginning to wonder if someone bent the relay contacts and that is why they are touching prior to the click. I am also thinking about a power switch for the amp, I dont like the fact that it does not have one. Possibly a switch with a silver button similar to Marantz. Which would energize a 120 volt coil on a ten amp relay.What do you think? Harry
Bias should be 6mV +/- 1mV. I have both channels set at 5mV. Remember I stated that the protection relay seemed sluggish? It takes about 6 seconds for it to snap or click and I stated that the contacts are touching before the click. I am beginning to wonder if someone bent the relay contacts and that is why they are touching prior to the click. I am also thinking about a power switch for the amp, I dont like the fact that it does not have one. Possibly a switch with a silver button similar to Marantz. Which would energize a 120 volt coil on a ten amp relay.What do you think? Harry
Hi Harry,
-Chris
Excellent.
I hadn't considered that. Struck by technician. Buy a new relay if you can. The contacts were probably burnt, so assume the relay is toast. Sorry.
-Chris
Chris,
I inspected the relay and the contacts are not burned. Actually they are in very good condition. I am going to see if I can bend the contacts back a little to alleviate the condition of them touching prior to the click. Harry
P.S. What allerted me to this was someone had the cover on the relay opposite the way it was represented in the pictures posted by Todd. So someone has been poking around in there.
I inspected the relay and the contacts are not burned. Actually they are in very good condition. I am going to see if I can bend the contacts back a little to alleviate the condition of them touching prior to the click. Harry
P.S. What allerted me to this was someone had the cover on the relay opposite the way it was represented in the pictures posted by Todd. So someone has been poking around in there.
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