Need help with Foreplay III extended

[Anton]

Hello,
I have my extended Foreplay for more than a year now.
Recently I changed the set of resistors on my Foreplay - the ones going from central switch to terminals 20, 26, 27, 29, 30, 36. I needed to decrease loudness and I installed 1/2 watt 470K-Ohm resistors (are these specs OK?), I bought in local RadioShack. When later I connected Foreplay and turned on music, I noticed my right channel gone. I checked wiring and found that the wire to RO1 central pin was broken. I re-soldered it, but right channel did not come back.
I made resistance and voltage check - results are below.
I personally think that the problem may be in some internal failure of the central switch - when I was switch it between the inputs - it does not into position right away.  And as you see below resistance check on terminals 20, 26, 27 doesn't look right - I have infinity resistance reading for all switch positions. My guess - I need to replace central switch.
I also measured resistance across each new resistor individually - they are fine.
I would appreciate your feedback guys, may be somebody had this problem before.

RESISTANCE CHECK

Terminal                Nominal               Actual

Power Trans 1   infinity                infinity
Power Trans 2   infinity                infinity
Power Trans 3      
Power Trans 4   * 10K to 100K   30,200
Power Trans 5   * 10K to 100K   30,200
Power Trans 6   infinity                1.37 Mohm and climbing
Power Trans 7   infinity                1.37 Mohm and climbing
Power Trans 8      
Power Trans 9   infinity                1.37 Mohm and climbing
Power Trans 10   infinity                1.37 Mohm and climbing

LO1   470,000                             471,600
LO2   470,000                             472,100
RO1   470,000                             472,100
RO2   470,000                             472,600
LI1   33-48K / infinity                465800 / infinity
LI2   33-48K / infinity                465600 / infinity
LI3   33-48K / infinity                466.8K / infinity

H1   30,000                             29,700
H2      
H3      
H4      


Terminal strips      
1   *                             1.37 Mohm and climbing
2   *                             0.6
4   *                             0.6
5   0                             0.6
6   *                             1.37 Mohm and climbing
7   *                             14 Mohm and dropping
9   0                             9 Mohm and dropping
10   *                             6 Mohm and dropping
11   470,000                             471,200
12   83,000                             60,000
15   infinity                             infinity
16   0                             0.5
17   15,000                             15,010
19   0                              0
20   33K / infinity                infinity/infinity/infinity
21   83,000                             60,000
22   30,000                             29,700
24   0                             0.6
25   *                             infinity
26   33K / infinity                infinity/infinity/infinity
27   33K / infinity                infinity/infinity/infinity
28   0                             0.4
29   33K / infinity                466K / infinity/466K
30   33K / infinity                infinity/465K/infinity
31   infinity                             40Mohm and climbing
32   150,000                            150,600
35   470,000                            472,000
36   33K / infinity               infinity/infinity/466K
37   15,000                            15,000
39   0                             0
40   0                             0

VOLTAGE CHECK

      
Terminal   Nominal  Actual   


H1   26.5   27.03
H2   32.8   33.43
H3    -   
H4    -   


Terminal strips      
1   -    94.00
2   -    0.00
3    -   
4   0.0    0.00
5   0.0    0.00
6    -    95.20
7   230.0    226.80
8    -   
9   225.0    221.50
10   220.0    216.00
11   0.0    0.00
12   150.0    151.00
13    -   
14    -   
15   75.0    74.70
16   0.0    0.00
17   0.0    0.00
18    -   
19   0.0    0.00
20   0.0    0.00
21   150.0    151.00
22   26.5    27.03
23    -   
24   0.0    0.00
25    -   
26   0.0    0.00
27   0.0    0.00
28    -   
29   0.0    0.00
30   0.0    0.00
31   75.0    73.00
32   150.0    150.40
33    -   
34    -   
35   0.0    0.00
36   0.0    0.00
37   0.0    0.00
38    -   
39   0.0    0.00
40   0.0    0.00

[Grainger49]

First, swap the tubes.  Always easy and it might work, might not.

If it is the right channel you are missing I will give you some troubleshooting clues to find where in the signal path it is open.  This is tracing the signal path to the first tube.

When you lose the signal path it should measure infinity.  There is a break between whatever points you get continuity with and the one you don't get continuity with.

Clip one meter lead to the incoming "hot" of the right channel RCA Jack that is selected.  Measure ohms.  If you meter beeps for continuity try that so you don't have to look at the meter so often.  

Place the other lead to the center conductor, right where the other lead is clipped, you should get a beep.  

Then move to terminal 20-36 and find where it is attached, you should get a beep when you find the incoming lead.

Then once you have located that terminal where it appears at the front of the chassis put the lead on the selector switch (SS) terminal that it leads to.  You will measure across the resistor so you might not get a beep.  You should read the resistance of the resistor that you have between the terminal and the SS lug (270k ohms).  

Then put the lead on the SS output lug.  If it is selected it will still give you that resistance.  

Now place the lead on the volume control (SW) input lug, you can see the STP that runs between the SS and SW.  You should read the same resistance.

As the SW is rotated the resistance decreases so place your lead on the output of the SW (terminal 17) and run the SW from full on to fully off.  You should see the resistance rise and fall. 

From Terminal 14 there is one resistor to the first tube pin 2. 

[Anton]

Grainger,
Thanks a lot for your advise. I was busy at work for last several days - so didn't have time to try it out.
But regarding swapping the tubes - that was the first think I tried and that didn't help.

I will follow will troubleshooting process you described and once finished - will let you know. Hopefully - will find some time tonight.

[Anton]

Hi Grainger,
I followed the procedure recommended by you:
I was followed the signal path until input terminal on SS (selector switch) - I have 470 kOhm as I replaced resistors. But on the selector switch output I read infinity for 2 of 3 SS positions.
So I tend to make a conclusion that since signal is lost somewhere in SS itself, it should be some problems with SS internals - I probably applied too high temperature during soldering and melted something inside...

What do you think?

I think I have to replace SS (not happy doing that though - a lot of wiring on it, have to be careful to resolder everything in right order.

Looking forward for advise. Thank you

[Laudanum]

Even though that selector switch is only a 3 position switch, it still rotates to 11 (I think) positions just like the attenuators. Only 3 of those postions are active, the rest are "dead".   So just make double sure that you are actually rotating the switch to those active positions and not the "dead" ones.  I know this is simple and obvious and it would seem to be a "dumb" thing to overlook.  But it's not that hard to do and I do stuff like that a lot.  Worth double checking before getting another switch.

[Anton]

Even though that selector switch is only a 3 position switch, it still rotates to 11 (I think) positions just like the attenuators. Only 3 of those postions are active, the rest are "dead".   So just make double sure that you are actually rotating the switch to those active positions and not the "dead" ones.  I know this is simple and obvious and it would seem to be a "dumb" thing to overlook.  But it's not that hard to do and I do stuff like that a lot.  Worth double checking before getting another switch.

Selector switch I have, has only 3 positions, not 11.

[Grainger49]

Anton,

The SS is the hard one to describe.  There is an input for all three inputs and one output.  With the SS in the first position you should be able to trace from the RCA center conductor to the switch input with a resistance reading of the dropping resistor.  The output will only show a resistance reading for the input that is selected.  The other two input lugs will read infinity.  

Once you get the dropping resistor reading at the output of the selector switch you can read to the volume control, run it wide open, and to the grid of the tube.  

This just traces the audio path to the first tube.

[Paul Joppa]

It certainly does sound like this is a switch problem. Contact Eileen; she can get you a new one. Higher quality switches are available but costly; goldpoint for example offers a suitable one at $67 (model 4P1D-3).

[Laudanum]

Anton, the selector switch you have only TURNS 3 clicks?  If so, nevermind.  If if turns 11 clicks, reference my post ... if you so desire.

Good luck.

[Anton]

Anton, the selector switch you have only TURNS 3 clicks?  If so, nevermind.  If if turns 11 clicks, reference my post ... if you so desire.

Good luck.

Yes - selector has only 3 clicks.

[Laudanum]

Ok.  Sorry, didnt mean to cause any confusion.  They must have put stops in some of them and not in others, either on accident or purpose.  Or, Bottlehead has used 2 or more different switches.  Or I just got a one off ... mine has no stops so it has, I believe, 11 "clicks", same as the attenuators.  Not a problem once I realized this during the build.

Again, good luck tracking your problem.

[Anton]

It certainly does sound like this is a switch problem. Contact Eileen; she can get you a new one. Higher quality switches are available but costly; goldpoint for example offers a suitable one at $67 (model 4P1D-3).

Paul, thanks a lot for recommendation. I am thinking about upgrading to goldpoint selector. It is a bit pricy, but considering all upgrades I did to my Foreplay - it looks like logical way to go. I also saw they have attenuators - which model can I use as a replacement for stock ones?

Thank you

[Paul Joppa]

The Whispers is 15K, so either the 10K or the 20K will work well. The 10K will have less gain, the 20K more gain - but it's only +/-3dB difference. Notice the reversed connection of the Foreplay pot - there's a nearby thread where it is mentioned.

[Laudanum]

Hey Paul.  Check my post 2 or 3 replies up.  My selector switch has 10 or 11 steps like the attenuators.  Obviously, only 3 of the steps work to select the 3 inputs.   It looks exactly as it should otherwise and seems to work fine.  I figure that they just didnt install the stops when they built it.    Any thoughts?

Thanks

[Anton]

Just an update.
I ordered Selector switch (4P-3T-1D) and two Mini-V mono attenuator (20K value) from Goldpoint (www.goldpt.com). It is a bit pricy, but considering all the updrades I already made on my Foreplay III (mundorf silver/oil caps, new tubes etc.) I decided to go for it. Should get order delivered sometime later this week - as soon as installed it, I will let you guys know about results. Thanks to Paul for recommendation and to Grainger and Laudanum for the advise. This community is really great.