Foreplay III Upgrade Problems

[skins]

Fellow Bottleheads,

I have just installed the Foreplay III upgrade kit in my 2007 build Foreplay III.

Alas, the voltage and resistance checks do not look good. I have visually checked my connections and soldering with a 4 power loupe and cannot find an error.

The 3 boards light up as follows;

C4S A side, All four are bright red.

Shunt Reg, A end no lights, B end both are bright red.

C4S B side, A end left is bright red, A end right has no light. B end both are a dim red.

Terminal     Voltage      Resistance
H1               39.7            33.7k
H2               32.8
H4               39
H5               46

1                 97.7
2                 0
3                 0
4                 0
5                 0
6                 96.7
7                 233
8                 0
9                 229
10               225

11               0               470k
12               223           183k
13               0
14               0
15               88             infinity

16               0
17               0
18               0
19               0
20               0

21               223            260k    
22               40.4           38k
23               0                
24               0                0
25
              
26               0
27               0
28              
29               0
30               0

31               131            infinity
32               135.5         548k
33
34
35                0               470k

36                0
37                0
38
39                0
40                0  

Any and all suggestions will be followed to the letter. I want my music back!!

Thanks

Terry

[Paul Joppa]

I know they are hard to get at, but the tube pin voltages are the most useful for diagnosis. The ones I need are pin 1 of the A and B tubes (VA plate) and pin 3. All I really need to know about pin 3 is whether the bias LED on the tube socket is glowing - if I recall correctly, the LED goes from pin 3 to ground (the center lug of the socket). Pin 7 should be at the same voltage as pin 1, if it is easier to get at.

The shunt regulator tube cathode voltages would be helpful as well; they are pins 3 and 8.

I have some guesses, but I'd like to confirm them with the above measurements before I risk complicating the issue.

Your power supply voltages are as expected, so that part of the circuit is working fine.

[skins]

Paul,

Thanks for the help. I will work on those points this weekend and have the readings for you by Monday.

Terry

[skins]

Fellow Bottleheads,

I have the measurements that Paul requested.

  A tube
  pin 1, 85 vdc
  pin 3, 1.58 v and the led is glowing

  B tube
  pin 1, 134 vdc
  pin 3, 1.61 v and the led is glowing

  Shunt reg
  pin 3, 12.5 vdc
  pin 8, 17.0 vdc

Thanks for now,

Terry

[Paul Joppa]

Thanks, that helps a lot.

On the A tube, I think the board is OK; the LEDs are a bit bright because the applied voltage is high (223v instead of 150v). The 85v on pin 1 is on the high side, though well within an acceptable operating range. I wonder if the tube may be a bit worn or otherwise out of spec.

On the B tube side, I think the LEDs on the A end of the board are in backwards. This causes excess current in the VA triode, which pulls the supply voltage down (135v instead of 150v). The B end seems to be working, with dim light because of the reduced voltage.

On the regulator board, again I think the A side LEDs are in backwards. However, the 12.5v at the cathode (pin 3) is higher than I would expect, leaving me worried about some other problem that I have not guessed yet - possible a transistor or the 431 chip with incorrect orientation. The B side is probably OK.

If my guesses are correct, you should be able to correct the LED orientation if you are careful. That may or may not fix all the problems - only one way to find out!

If my guesses are incorrect, or correct but there are still problems, we'll proceed to simplify and isolate the problem step by step. You can cut the process short by just replacing the suspect boards, but we'll all learn more by doing it the slow and steady way. (And it's cheaper!)

[skins]

I noticed my H2 reading was not 32.8v as I indicated in my first post, but 46v, same as H5.

I built the boards in 2007. Looking at LEDs now, I cannot see any polarity determining features that I can use to assure myself that they are in the correct position. They do not have a silver side below the conductor as indicated in the photo on page 15 of my manual. Was there any other way to determine polarity? Was polarity indicated by the length of a lead?
Is there a test I can use to check the polarity?
I am using a Fluke 112.

Thanks

Terry

[Paul Joppa]

If you have tiny probes and are careful, you can measure the voltage across the LED. If it is about 1.6 volts, they are oriented correctly. Incorrect would give a larger voltage; I think the spec is at least 5 volts and average 12 volts, with no maximum specified.

I have data sheets from three different times; some of them show the stripe on the back side which is invisible if you have installed them face up. PB (Caucasian Blackplate) installs them face down so that the stripe is more easily seen; the light is dim but it seems a good idea - I intend to do it that way in future myself.

[2wo]

Look to see if you meter has a diode check,  diode symbol on my Fluke 87. If you have a large and small symbol, use the large. This will supply enough voltage to light the LED a little. when it lights the black lead corresponds to the stripe...John   

[skins]

LED voltages are as follows;

Looking at the underside of the chassis with the A tube socket on the left,

A side C4S board
A end
left, 1.52v
right, 1.52v
B end
left,1.53v
right, 1.53v
all four LEDs are bright.

Shunt Reg board
A end
left, 1.33v with just a trace of light
right, 1.37v very dim
B end
left, 1.52v bright
right, 1.52v bright

B side C4S board
A end
left, 1.61v very bright
right, 0.70v no light
B end
left, 1.51v less bright
right, 1.51v less bright

Thanks for the assistance,

Terry

[skins]

I tried moving tubes around and substituting other 12AU7 tubes as well, but the LEDs remained the same.

If we can isolate the problem to the boards, I will order new boards from Eileen straight away.

Thanks for the help,

Terry

[Doc B.]

I, too, think you have some LEDs in backwards. The only way to be sure is to pull them out which will wreck them. We can send some more to replace them, just contact Eileen at queen at bottlehead dot com.

[skins]

I have removed the A end LEDs from the shunt reg board and the B side board, 4 in total.
You are right, to remove them destroys them.
I have ordered 8 new LEDs from Eileen.

Awaiting the arrival of the new LEDs,

Thanks,

Terry

[skins]

When I replace the LEDs that I have removed, is it possible to mount them a little higher, say about 1/2" above the board?

Thanks

Terry

[Paul Joppa]

As long as they don't bump into anything else, that should be OK. What PB does is a good idea - mount them upside down, so the light shines down on the board, but the lead-identifying stripe is visible from above. Makes it easier to check the orientation.

[skins]

When I constructed the three boards I used a lead free Kester 275 solder with a 425 deg F melting point, (SN96.5, AG3.0, CU0.5).

I am now thinking that I may have overheated some of the more delicate components. We will see after I install the new LEDs.

I plan to use a much lower melting, 354 deg F, rosin core, 0.6mm solder for the repairs, (Sn62, Pb36, Ag2).

Regards

Terry