Extended FP Help for a Newbie needed

[Sh7eleven]

Hi,

A few months ago I finished installing the extended upgrade. Upon first power up, I blew a fuse, and saw a tiny puff of smoke, oops! Well it turns out in my haste, i had installed the UF4007 rectifier with the silver end in the wrong direction between terminal 1 and 7 on the power supply on the right side. After correcting my mistake, and doing a more thorough check i powered her up again, everything seemed smooth upon start up, but the pair of LED's on the B side of both C4S boards did not light up. On the A side the LED's light up dimly. The LED's underneath the Tube sockets and the LED's on the Shunt Board all light up brightly. The Tubes get hot, but do not seem to glow very brightly.

I took the resistance measurements provided by the Extended manual - they all checked (although when i went to measure 15 and 31 they read 0 on my multimeter and not infinity, I'm new, does 0 on the meter equal infinity?? The others all measured properly.)

The Voltage readings on the other hand were significantly off:
15 (11.6 V), should be 150
31 (12.6 V), should be 150

Instead of reading 0 V:
20  .4 V
26  .5 V
29  .6 V
30  .54 V
(Is being off by this margin when it should read zero a problem?)

The rest of the voltages matched as indicated by the manual.

Interestingly after incorrectly installing the rectifier, the readings on both sides of the power supply were identical, I figured i'd have a problem there, although they were a bit low:
5: 0 - 0
7: 221 - 222 Should be 230
9: 217 - 217 should be 225
10: 210 - 210 should be 220

So I noticed that, of all the measurements, terminal 15 and 31 were significantly off, these are also were the red leads from both the auricaps are attached, and a black wire leading from 15 U and 31 U also connects to the B sides of the board. The third connection at this point is a red wire 15L and 31L from A and B 8 respectively. My wiring seems correct after having gone over it again, and i have a feeling that, while i'm no soldering expert, something other than a poor solder job is blocking the voltage from reaching both B sides. I'm going to fire up the iron again touch up those areas, but might my problem be related to the initial blow up i had? Other than going back and resoldering I don't really have any ideas of what else i can do. I have also checked my PC boards making sure they are properly populated. Does anyone have any suggestions of where and how to look? As a newbie, I would be gracious if anyone could point me in the right direction!

[Grainger49]

Sean,

I can't help you much with the extended package since I don't have the schematic or the manual.  But I thought some reinforcement would be nice early in the morning.

If the tube gets warm then the heater voltage is fine.  The loss of the LEDs on the C4S board means the high voltage, B+, is missing or low. 

"Infinity" can sometimes read 800,000 ohms or higher.  Zero means that point is shorted to the common terminal.  So something is odd there.  The voltage readings are as you know off.  But they indicate something other than a "dead short" to common.  If 15 and 13 were shorted they would be zero volts.

The readings that should be zero are close enough.  That is a good "zero" reading for all of them.  But the readings would say that your meter is a good one.

The puff of smoke means something should be replaced.  Most often it is the capacitors on the channel where the diode was reversed.  Even if it works now it will fail later, and could spew the electrolyte out.  That gets messy, I know!  The B side, where the LEDs do not light, is this the channel that had the diode reversed?

I hope this helps till someone who knows the circuit chimes in.

[Sh7eleven]

Thanks for the reinforcement i definitely need the help!! By your description I'm starting to learn more about how the pieces fit together, which is gold for me because part of the fun is understanding how these things tick.

The B sides on both C4S boards do not light at all, and it was the B side power supply where i had put the rectifier in backwards. The A sides light dimly. So i will try replacing the capacitors on the B side power supply. I just checked my left over original power supply for the FP III, and it includes two 220 uF 250 V capacitors. I suppose i could play the capacitor guessing game, and try to guess which of the three is blown, if not all of them, but I'd rather just replace all three and move on, could i pick up another 220 250 V at radio shack? or is this something i should order from Bottlehead? (because its a special part or something)

[Doc B.]

Hi Sean,
I need a little more info to start the triage:

Did you replace the backward rectifier with a new one, or just reinstall it correctly?

Also I'm a little confused when you say "Interestingly after incorrectly installing the rectifier, the readings on both sides of the power supply were identical, " Do you mean after you reinstalled the rectifier correctly that you got these numbers?

If you can clarify these for me we can start to work through the circuit to find the fault.

[Grainger49]

Sean,

Triple check the orientation of all diodes and capacitors before the next "smoke test."  I searched RS web site and nothing in that range showed up.  Interestingly enough, to me, all the resistors and some car speakers came up in a search for "Capacitors."

As much as I have knocked around with this stuff I don't have anything to check capacitors.  My only hint is that bad ones often have the ends "bulged."  A close inspection might show the ends are no longer flat.  I would suspect the one closest to the diodes got molested worst.  After all that one gets the first surge of current.  But I would also replace all three.  

Depending on where you are there might be an electronics supply store.  If you can't exactly match the value (220uF) and voltage (250V) then you can size up.  Use the original caps closest to the diodes and the different one closest to the tube circuit.

[Sh7eleven]

Hey Doc,
        I did not replace the backward rectifier with a new one. I simply re-oriented the backward rectifier to the correct position. After doing this i took resistance and Voltage checks. The voltage measurements on the 1-10 terminals on both power supplies were identical. I suppose after the blow up i would have expected the measurements on the B side power supply terminals 1-10 to be different than the A terminal 1-10 (which had no blow up).

Grainger,

thanks for the research, but unfortunately the radio does not work in my car right now so the car parts probably won't help! Would it be possible to use the 47 uF 450 V that is in the original power supply?

Sorry don't mean to split the thread into two discussions!

[Grainger49]

RS=Radio Shack.  Only they think that car speakers go under capacitors.

The original 47uF capacitor is fine. 

[Sh7eleven]

Ha RS, i know, this article sums up my impression of the shack:

http://www.theonion.com/content/news/even_ceo_cant_figure_out_how

anyway, i've taken out the capacitors, and in a little while i'll be installing the salvaged capacitors from my original FP III. So are there consequences from using the uF 47 450 v capacitor as opposed to the 220 - 250 capacitor? should i just use it as temporary solutions until i can get a 220 - 250?

[Grainger49]

Sean,

You were not specific as to where you were going to use the 47uF@450V cap.  I can only look at the stock PS schematic, see my first response.  Are you saying that the extended uses 3 - 220@250V caps?  If so, the 47 will work till you get a replacement.  I'm guessing that you don't have any electronics store.

[Sh7eleven]

I can't really find an electronic supplier that is not a wholesaler, but i could certainly get a couple online which is not a problem, but if i have parts to at least temporarily solve it, i'll do so today as I'm on vacation this week and have the time.

The extended has in the same pattern two 250's upright, like the original, and in place of where the 450 is at the end of the formation, there is a third uF 220 250 V, and i thought if the 47uF 450v was an adequate substitute i would simply place it at the end of the line like in the original FP III. That would place the 250 caps nearest the diodes, and the 450 closer to the tubes. If you think this is too risky that i will fry some other part, then i will wait and get a third 250.

[Paul Joppa]

Power supplies are quite different. The stock FP-III uses a single voltage doubler with a two-stage CCRC filter. The upgrade uses two independent fullwave bridge power supplies with three-stage CRCRC filters.

[Doc B.]

OK, it sounds like the power supplies are working alright if you are seeing more or less right voltages at around 220VDC.You shouldn't see 150V at 15 and 31, it should be about 75VDC. Do you measure 150VDC at 12 and 32?

[Sh7eleven]

At terminal 12 I reading 150 V ,
At terminal 32 I 116 V
but at terminal 15 i read 11.6 V
At terminal 31 i read 12.6 V.

so I'm guessing i shouldn't replace the 250 v with the 47uF 450?

Terminal 12 and 32 are fine and read similar, but 15 and 31 are well below 75 V, but seem pretty close in their read outs, and both connect to the B sides of the C4S boards, might i have blown something else out that is preventing the voltage from reaching that point when i originally started her up? or do the PS readings near 220 indicate that I probably screwed up somewhere else?

[Doc B.]

I'm guessing there might be a couple of things going on. There could be a problem in the power supply or shunt regulator on the side where T32 reads 116 instead of 150. Or it is possible that something is shorted on the C4S board on that side of the circuit and it is pulling that voltage down to 116.

The very low voltages on 15 and 31 might possibly be due to transistors being accidentally swapped, i.e. MJE340 where MJE350 should be, 2N2222A swapped for 2N2907, etc. Or there is a slight possibility that some resistor on the C4S board is the wrong value. It might be useful to inspect all of those things.