Can you post a photo of the top and underside of the PCB?
Eros voltage reading problem
- Thread starter Steve Reese
- Start date
Steve Reese
New member
Are these good enough to see?
Steve Reese
New member
If anyone would read this, http://www.bottlehead.com/smf/index.php/topic,3671.0.html, could another big resistor may be compromised?
Its hard to tell from the photo, but some of those solder connections especially in the middle of the PCB look like they might bridge two traces. I just think it might be a good thing to check with a magnifying glass while waiting on PB and others who are more knowledgeable than me respond.
Ken
Ken
Paul Joppa
Moderator
I reviewed the whole thread this evening, since it's gotten rather long. I notice that the regulator 12BH7 was working initially, so the lack of heater voltage now is probably something simple - hopefully, just s single bad connection. Until we get the heater power restored, there is no point in looking for other problems, in fact it's quite likely there aren't any.
I can't tell from the picture whether all four 1N5820 diodes are pointing in the same direction. I'm looking at that because you read 7vAC between power transformer terminals T4 and T5 (or perhaps where they connect to the PSU board, with the same labels). There should be more than 9vAC between those two points. I do not actually think this is the problem, but it's best to be certain. If you still get 7 volts, I'll have to ask if your meter is accurate - test a fresh 9v battery (on DC) to confirm.
There should also be around 9vDC at the forward ends of each of the two diodes that lie nearest the output terminals on the board. I specify both of them in case one is not soldered well - like the large chips, these diodes can absorb enough heat to slow the soldering process.
The terminals on the board labelled 6.3vDC should have 0 volts on the negative terminal and +6.3v on the positive terminal. If the positive voltage is zero, then it may be worth the trouble to attempt to measure the middle leg of the '1085 regulator - be careful there, since it is probably only accessible with a probe, and you don't want to slip and short the pins! Pin 3, which is the one closest to T4/T5, should have 9vDC on it.
I'm afraid those are all the test points that seem to me to be accessible within reason. Make those measurements, in that order, and we should be able to make a good guess as to where the problem is.
I can't tell from the picture whether all four 1N5820 diodes are pointing in the same direction. I'm looking at that because you read 7vAC between power transformer terminals T4 and T5 (or perhaps where they connect to the PSU board, with the same labels). There should be more than 9vAC between those two points. I do not actually think this is the problem, but it's best to be certain. If you still get 7 volts, I'll have to ask if your meter is accurate - test a fresh 9v battery (on DC) to confirm.
There should also be around 9vDC at the forward ends of each of the two diodes that lie nearest the output terminals on the board. I specify both of them in case one is not soldered well - like the large chips, these diodes can absorb enough heat to slow the soldering process.
The terminals on the board labelled 6.3vDC should have 0 volts on the negative terminal and +6.3v on the positive terminal. If the positive voltage is zero, then it may be worth the trouble to attempt to measure the middle leg of the '1085 regulator - be careful there, since it is probably only accessible with a probe, and you don't want to slip and short the pins! Pin 3, which is the one closest to T4/T5, should have 9vDC on it.
I'm afraid those are all the test points that seem to me to be accessible within reason. Make those measurements, in that order, and we should be able to make a good guess as to where the problem is.
Steve Reese
New member
Okay, again sorry it took me a while... I retouched the diodes, and yes, they're all pointing the same direction. After attaching the wires, I measured T5, and it measured just over 9VAC. I measured the outer most diodes, and they measure just over 10VDC. I measured the +6.3 post, and it didn't even read a volt. It has what I think is a solid connection. I then measured what I thought was pin 3 on the 1085 regulator closest to T4,5, and it read just a hair over 9vDC. I just don't get why I'm not getting 6.3vDC......
My best guess at this point is a cold solder joint on the 1085.
Steve Reese
New member
Okay, I reattached the wires once more and before hand retouched the 1085. And I got the same thing. I wonder when that 100uF 450V cap blew that is also ruined the 1085....?
Paul Joppa
Moderator
The high voltage supply is extremely unlikely to have an effect on the low voltage supply.
Before going to the trouble of removing and replacing the 1085 (it will be neither easy nor fun!), check the voltage at its middle pin as suggested. In fact, check the voltage at each of the three pins - you've already got the right input voltage at pin 3; let's be sure about the others.
The reason I suggest making these measurements is that it worked before, so the 1085 was not "dead on arrival" and it's not that easy to damage it. That makes me think that merely replacing the chip won't address whatever the real problem is. But if measurements can't resolve this, that would probably have to be the next step.
Before going to the trouble of removing and replacing the 1085 (it will be neither easy nor fun!), check the voltage at its middle pin as suggested. In fact, check the voltage at each of the three pins - you've already got the right input voltage at pin 3; let's be sure about the others.
The reason I suggest making these measurements is that it worked before, so the 1085 was not "dead on arrival" and it's not that easy to damage it. That makes me think that merely replacing the chip won't address whatever the real problem is. But if measurements can't resolve this, that would probably have to be the next step.
Steve Reese
New member
Sorry.... I didn't read it correctly. Pin 1 reads .4vDC; Pin 2 reads .78vDC; and Pin 3 reads 10.83vDC
Paul Joppa
Moderator
OK, looks like the 1085 is dead all right. Contact Eileen on Monday and she'll send a new one; there's at least a good chance that will fix whatever was wrong.
Meanwhile you can try to remove the old one. Once it's out, read the resistance to ground from pins 1 and 2; they should be 499 and 623 ohms respectively - you'll have to pull the tubes in order to make these measurements (the heaters will short these resistors, which are the voltage divider that sets the 6.3 volts). This check will help assure that this portion of the PC board is working correctly, giving I hope increased confidence that the new 1085 chip will work when installed.
I still have no good theory what happened to the chip, but if a new one works then you don't have to care!
Meanwhile you can try to remove the old one. Once it's out, read the resistance to ground from pins 1 and 2; they should be 499 and 623 ohms respectively - you'll have to pull the tubes in order to make these measurements (the heaters will short these resistors, which are the voltage divider that sets the 6.3 volts). This check will help assure that this portion of the PC board is working correctly, giving I hope increased confidence that the new 1085 chip will work when installed.
I still have no good theory what happened to the chip, but if a new one works then you don't have to care!
Steve Reese
New member
Paul, let me see if I understand this correctly... Once I take out the 1085, you want me to do an ohm test on it, or once I have the new one in place, that's when I do an ohms test. Cause you're talking about making sure the tube is out cause the heater will short the resistors. Or am I to take the readings from the power supply Pins 1 and 2...?
You want to take readings on the PC board with the tube pulled out.
-PB (the other Paul)
-PB (the other Paul)
Steve Reese
New member
oh, where Pins 1 and 2 are respectively... and powered off correct?
You can find the pin assignment on page 2 for the TO-220 package:
http://cds.linear.com/docs/Datasheet/108345fg.pdf
The drawing assumes that the writing on the chip is facing up, so if you have the writing facing up and the hole in the metal tab facing left, the pins go 3, 2, 1, down the right edge of the chip.
-PB
http://cds.linear.com/docs/Datasheet/108345fg.pdf
The drawing assumes that the writing on the chip is facing up, so if you have the writing facing up and the hole in the metal tab facing left, the pins go 3, 2, 1, down the right edge of the chip.
-PB
Steve Reese
New member
Okay.... I have tried like crazy to get that huge heat sink out, but no luck. I've tried to remove the two small resistors near the edge of the board, but can't get them out cause for me it's hard try to heat two leads in order to remove them because my thought was to get those out then clip out the 3 pronged 1085 resistor. If anyone would have any experience in removing these parts, please share. I've been out of town for while but plan tackle this again when I get back. Thanks.
I'd leave the heatsink there, it doesn't need to come out.
Go buy a spring-loaded solder sucker and suck all the solder out around the pins on the 1085, then remove it (removing the hardware that holds it to the heatsink as well).
Same for those two resistors, you can suck the solder out around them, then pull them out.
-PB
Go buy a spring-loaded solder sucker and suck all the solder out around the pins on the 1085, then remove it (removing the hardware that holds it to the heatsink as well).
Same for those two resistors, you can suck the solder out around them, then pull them out.
-PB
Steve Reese
New member
Okay... I've gotten the 1085 resistor in place, along with the two 10uF capacitors which I had to have Eileen send me some after basically destroying them trying to get them out. Tried to get a reading, and once again I get the same high reading on D1. It hovers around 307 for a good 5 seconds, then stops between 325 and 332. It gets the same when I remove the tube. I'm at a loss.
Steve Reese
New member
Okay, I'm begging now... if anyone has an idea what I should check next, please tell me. I keep looking at the big can capacitors wondering if something may be compromised with them. I didn't do anymore checks other than D1 and D6 which were same, so I thought that any other readings I'd be asked previously would also be the same. Any thoughts are welcomed. Thanks.
Hi Eros fans --
I've built from scratch and modded more gear than I can remember. I'm now in the process of smoke-testing an Eros kit I built for a friend. I would think that following Bottlehead's extremely well-documented manual would result in a first-trial success story. Uh, not quite.
I'm at a point where I can't seem to see the forest for the trees. 
The left channel uses the led-biased input stage (to experiment) while the right channel follows the original Eros servo design. I have 1.8v at the L cathode; the R sits at 1.5. The plate voltage on the left is 97, the right is 94. A bit low in each case. BUT, the plate voltages on the EC88 are both 107! That's way off!!! B+ from the power supply card is 221 and filaments are at 6.2. Close enough.
My wiring appears to be spot on. So, what is my problem? ??? (Besides the likelihood of overlooking something all too obvious)
Atom
I've built from scratch and modded more gear than I can remember. I'm now in the process of smoke-testing an Eros kit I built for a friend. I would think that following Bottlehead's extremely well-documented manual would result in a first-trial success story. Uh, not quite.
I'm at a point where I can't seem to see the forest for the trees. The left channel uses the led-biased input stage (to experiment) while the right channel follows the original Eros servo design. I have 1.8v at the L cathode; the R sits at 1.5. The plate voltage on the left is 97, the right is 94. A bit low in each case. BUT, the plate voltages on the EC88 are both 107! That's way off!!! B+ from the power supply card is 221 and filaments are at 6.2. Close enough.
My wiring appears to be spot on. So, what is my problem? ??? (Besides the likelihood of overlooking something all too obvious)
Atom
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