Eros malfunction [resolved]

[Thermioniclife]

Man it sure looks like those large resistors are shorted to that smaller resistor passing under them. Are you sure they are not touching?

[Ascari]

Absolutely..    No question, just a bad photo.

[Paul Birkeland]

PJ may have some other ideas about what's going on, otherwise you may need to send it in for repairs.

[Ascari]

I appreciate that and would have already sent it in.   The web page indicates you are not doing that right now.     Either way, we did some further checks starting from the beginning.   So far everything has checked out.    Will wait to see PJ has any other ideas.

[Paul Joppa]

I agree with PB, the bias servos are not working.

The relevant resistors are on the B side of the board; R3 is the small 174-ohm resistor and R4 is the larger 27K. You have reported 137v at breg (which is connected to R4) - what is the voltage at the other end? It should be around 0.7 volts. You should see the same voltage at the end of R3 nearest R4. Can you check those voltages?

[Ascari]

I got a voltage reading of .9 volts from the distal side of both R3 and R4.


Thanks

[Ascari]

Just a bit of an update.   Since this was my only phon preamp, I invested in a cheap phone preamp that handles both MC and MM.   The only cartridge I currently have is a Hana SL.   When I connected it to my turntable and then to the Beepre via MM, I got the exact same response and I did on the Eros.   Nothing...   Keep in mind I have that connected to a external SUT.    Once I pulled the SUT out of the line, the MC portion of the cheap preamp worked and I had how shall I say descent sound but no where near what the Eros could produce.    Me Soundsmith cartridge is currently in for rebuild and is still weeks off, so I purchased a inexpensive MM to use as a spare.    That should arrive in a few days, and I will check that on the MM part of the preamp.   I think there is a chance that the problem my lie in the SUT, but it seems strange to  me that both sides would go out within minutes of each other.

Just a note: I checked every single resister on both sides and they have all of the same voltage within  a 10th of a volt.

With this info, any further ideas?

[Doc B.]

First thig to do is check to see of the Eros has DC on the input. Measure voltage across each RCA input jack center pin to jack outer shell with the Eros turned on. You should not see any significant DC voltage. Once you have verified this, check if the MC cart will also make sound directly connected through the Eros without the SUT in the circuit. Obviously it won't be as loud as you want, this is just to determine that the Eros is passing signal. If it works then check the continuity of each winding on the SUTs, and make sure the center pins of the RCAs on the SUTs haven't become grounded somehow.

[Ascari]

I checked for DC voltage at the inputs and it was zero on both left and right.    I put the EROS back into the system bypassing the SUT.    There IS sound coming through the system, but is is very very faint at full volume.    In the past when I had done this, I could get almost listenable music with the volume at 75%.  Your correct that is not optimal.   After checking the continuity of the SUT's I only had continuity on three pins out of 8.   

[Doc B.]

OK, so as is often the case you seem to have two separate issues. You need to get the voltages right on the Eros, and also determine what is going on with the SUTs. An analysis of what connections might have been crossed when the tubes were swapped may help. I am headed out of town and have to run, but perhaps someone else can have a look at the pinouts and see if that could have created a problem.

[Ascari]

I'm not surprised and was coming to the same conclusion.   The SUT's I have are Beyer dynamic  TR/BV 370 215 006

[Paul Joppa]

I got a voltage reading of .9 volts from the distal side of both R3 and R4.


Thanks

OK, that's too high. Assuming you still get 4v at Kreg, the 2N2222 is not doing its job. Could be solder joints on the PC board.

----------- Added 2021 Jan 26 6:20PM -----------

Looking over the whole thread again, I see some problems on the 6922 socket (C) resistance measurements.  You might re-check - it's tricky to get the right pin on those smaller sockets!

* Pins 4 and 5 are the heater, so one should be zero and the other less than 10 ohms; you said one zero and the other infinite

* pin 7 should be 75K, you said 0.

* pin 8 should be 27K, you said infinite.

[Ascari]

I rechecked again this morning.    First off the kregs were reading 3.9 volts and 4.2 volts.   Haven't gone into the 2n2222's to check the solder connections yet.   Either way the transistors are easy to replace.    When I checked the 6922 socket this morning I was being super careful and did it from the component side came up with the following.    I think we may be getting somewhere.

C1  46.8K
C2  75.4K
C3  27.8K
C4   0
C5   0
C6  46.8K
C7  75.4K
C8  27.5K
C9   0

I'm going to go in and reheat the solder joints to see if that changes things and let you know.    If indeed the C4 socket is the culprit after so many years could it have caused a failure on the 2n2222's?

[Paul Birkeland]

With the tubes in the sockets, C4 will show as 0 ohms.  If the tubes are glowing, C4 is fine.

[Ascari]

C4 is showing zero with or without the tube in place.   They all glow when turned on albeit the EF86's are very dim in comparison.