Citation XX #2 also with issues......
- Thread starter wlhd1610
- Start date
Diodes D5~12 should be replaced with a EGP20DFSCT-ND (200V, 2A rectifier). Certainly all the electrolytics on this board should be replaced. And the regulators, of course.
Digikey does NOT have a good sub for the stock 2SB649. Mouser normally carries the KSA1220AYS, but they are out of stock.
Edit: I see that Digikey carries some 2SA1507 transistors that will do nicely as replacements for the original B649's. Digikey #2SA1507S-ND.
Digikey does NOT have a good sub for the stock 2SB649. Mouser normally carries the KSA1220AYS, but they are out of stock.
Edit: I see that Digikey carries some 2SA1507 transistors that will do nicely as replacements for the original B649's. Digikey #2SA1507S-ND.
Parts all arrived a week ago last Wednesday.
Between the 14 and 12 gauge wiring and virtually no slack I had to unsolder multiple wires to access the underneath of the power supply board.
I installed new IC1 and IC3 regulators with a 7805 and 7905 from Digikey.
Also renewed Q1 and Q3 with 2SA1507's also from Digikey.
Renewed R7 and R141 with the correct replacements.
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I purchased all new components with the intent of renewing all the left channel regulated ps parts but stopped after replacing D7.
Even though I use a Hakko 808 desolder gun(which does a very good job of removing solder) they apparently used a higher melting point solder on this amp which meant lingering a little longer than I'd have liked.
The component leg holes were(are) extremely tight tolerance and the foil traces are very fragile.
With that being said and the remaining components testing ok I made the decision to proceed and test the board having replaced the known faulty components.
After replacing all the wiring I had disconnected the ps board was reinstalled.
I purposely left the +HVL and -HVL wires to the main amp board disconnected to test the voltages thus far so as not to risk power supply board failure due to an amp board anomaly which might have caused the initial failure in the first place.
Here is the board with multiple meters to simultaneously watch various parameters.
I used my 300 watt Franken dbt to power it up for the initial test.
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After the bulbs glowing brightly as the four 10,000uf caps charged....
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It settled down to barely a glow!
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At this point the "Infrasonic Interference" and "Safety" lights are no longer lit and a relay can be heard picking up!
That meter next to the dbt is connected to the left amp speaker output showing dc offset.
It initially was 15.1 vdc !! when the amp first arrived so at this point 336 mv dc is looking better.
With the +HVL and -HVL voltages looking similar with no load....
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It's time to reconnect the regulated feeds to the left amp board BUT I wanted to monitor the current draw so I inserted a dc ma meter in series with each of the two legs.
The meter labels should read +HVL and -HVL( not +MVL and -MVL which is the main rail voltage).
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Seeing that no shorts or abnormally high current draw was evident it's time to up the dbt wattage.
With 500 watts in the dbt the dc offset has come down...
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At this point in time it was getting late in the evening but I just had to know..
The alternative would have been a sleepless night of tossing and turning so I hooked up a pair of "sacrificial" speakers and connected the XX to the pre out of my Marantz 2330.
Fired up the XX (still on the 500watt Franken dbt) and it works!!
I'm happy ,time to call it a day!
The next day I wanted to check the bias voltage before retiring the dbt and firing it up on full line voltage.
This unit has a user selectable choice of three bias voltages:
Low,Medium and High
The Low bias position reduces bias if you're using the amp continuously at high power levels. Also recommended for high ambient temps in the room location.
The Normal bias is just that- normal use - heat sinks run a little hotter though.
The High bias is used for "delicate reproduction of Baroque music".
Heat generation is higher and heat sinks may reach 50 degrees C.
I choose the "Normal" pushbutton....
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Bias is actually set with these three pots on each amp board.
The front panel pushbuttons select which bias setting shall be used via small board mounted relays.
For initial testing I found both amps at around 10 mv dc on Normal and left them at that setting for now.
[/URL][/IMG]
Things are looking up but we're not outa the woods yet.
Between the 14 and 12 gauge wiring and virtually no slack I had to unsolder multiple wires to access the underneath of the power supply board.
I installed new IC1 and IC3 regulators with a 7805 and 7905 from Digikey.
Also renewed Q1 and Q3 with 2SA1507's also from Digikey.
Renewed R7 and R141 with the correct replacements.
I purchased all new components with the intent of renewing all the left channel regulated ps parts but stopped after replacing D7.
Even though I use a Hakko 808 desolder gun(which does a very good job of removing solder) they apparently used a higher melting point solder on this amp which meant lingering a little longer than I'd have liked.
The component leg holes were(are) extremely tight tolerance and the foil traces are very fragile.
With that being said and the remaining components testing ok I made the decision to proceed and test the board having replaced the known faulty components.
After replacing all the wiring I had disconnected the ps board was reinstalled.
I purposely left the +HVL and -HVL wires to the main amp board disconnected to test the voltages thus far so as not to risk power supply board failure due to an amp board anomaly which might have caused the initial failure in the first place.
Here is the board with multiple meters to simultaneously watch various parameters.
I used my 300 watt Franken dbt to power it up for the initial test.
After the bulbs glowing brightly as the four 10,000uf caps charged....
It settled down to barely a glow!
At this point the "Infrasonic Interference" and "Safety" lights are no longer lit and a relay can be heard picking up!
That meter next to the dbt is connected to the left amp speaker output showing dc offset.
It initially was 15.1 vdc !! when the amp first arrived so at this point 336 mv dc is looking better.
With the +HVL and -HVL voltages looking similar with no load....
It's time to reconnect the regulated feeds to the left amp board BUT I wanted to monitor the current draw so I inserted a dc ma meter in series with each of the two legs.
The meter labels should read +HVL and -HVL( not +MVL and -MVL which is the main rail voltage).
Seeing that no shorts or abnormally high current draw was evident it's time to up the dbt wattage.
With 500 watts in the dbt the dc offset has come down...
At this point in time it was getting late in the evening but I just had to know..
The alternative would have been a sleepless night of tossing and turning so I hooked up a pair of "sacrificial" speakers and connected the XX to the pre out of my Marantz 2330.
Fired up the XX (still on the 500watt Franken dbt) and it works!!
I'm happy ,time to call it a day!
The next day I wanted to check the bias voltage before retiring the dbt and firing it up on full line voltage.
This unit has a user selectable choice of three bias voltages:
Low,Medium and High
The Low bias position reduces bias if you're using the amp continuously at high power levels. Also recommended for high ambient temps in the room location.
The Normal bias is just that- normal use - heat sinks run a little hotter though.
The High bias is used for "delicate reproduction of Baroque music".
Heat generation is higher and heat sinks may reach 50 degrees C.
I choose the "Normal" pushbutton....
Bias is actually set with these three pots on each amp board.
The front panel pushbuttons select which bias setting shall be used via small board mounted relays.
For initial testing I found both amps at around 10 mv dc on Normal and left them at that setting for now.
Things are looking up but we're not outa the woods yet.
fred soop
Super Member
The first 3 iterations of the Fisher 600-T had open bottom wirewound pots that were subject to many problems. Other locations had pots similar to those in the Citation XX.
Here is the replacement bias network (4 places). The fixed resistors "trap" the value between upper and lower limits.
1424
After taking my wife out for breakfast and hanging out with her all afternoon I got a little shop time in.
I fired up the XX on full line voltage and everything looked ok.
Ran the amp for 5 minutes or so at low volume and she sounded good.
The main rail voltages were steady at +80vdc and -80vdc on each amp board.
In checking the HV regulated power voltages I had +86vdc and -85.1vdc on the repaired left side and +93.5vdc and -94.6vdc on the stock right side.
The current draw on +HVL was 73.3dc ma and +HVR was 76.7dc ma.
I isolated +HVL and -HVL from the amp board and the voltages stayed the same as when they were under load.
The output voltage of R1 and R2 were both +98.1vdc with R3 and R4 at -98.2vdc indicating that both supplies were delivering the same/correct voltages to the inputs of IC1,2,3 & 4.
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I took some reference voltage tests from the untouched right side(even numbered) components and compared to the left side(odd numbered) components.
D10 anode to grnd. +81 vdc
D9 anode to grnd. +80.1vdc
Across R8 62vdc
Across R7 25.3vdc
The following are in reference to grnd.
Q2
E 94.2 vdc
C 62 vdc
B 94.1 vdc
Q1
E 80.1 vdc
C 25.1 vdc
B 80.1 vdc
+HVL 86 vdc
- HVL -85.1 vdc
+HVR 93.6vdc
- HVR -94.6vdc
IC1 and IC3 were replaced along with Q1 & 3.
I checked the data sheets on these and the pinouts are same as originals.
At this point I have not renewed any caps or diodes as I mentioned the reasons why earlier but did test them in circuit,which I realize is not foolproof.
I did order a complete set of replacement components.
I thought a fresh set of eyes on this would help as I only want to go under this board one more time.
Thanks , Bob
I fired up the XX on full line voltage and everything looked ok.
Ran the amp for 5 minutes or so at low volume and she sounded good.
The main rail voltages were steady at +80vdc and -80vdc on each amp board.
In checking the HV regulated power voltages I had +86vdc and -85.1vdc on the repaired left side and +93.5vdc and -94.6vdc on the stock right side.
The current draw on +HVL was 73.3dc ma and +HVR was 76.7dc ma.
I isolated +HVL and -HVL from the amp board and the voltages stayed the same as when they were under load.
The output voltage of R1 and R2 were both +98.1vdc with R3 and R4 at -98.2vdc indicating that both supplies were delivering the same/correct voltages to the inputs of IC1,2,3 & 4.
I took some reference voltage tests from the untouched right side(even numbered) components and compared to the left side(odd numbered) components.
D10 anode to grnd. +81 vdc
D9 anode to grnd. +80.1vdc
Across R8 62vdc
Across R7 25.3vdc
The following are in reference to grnd.
Q2
E 94.2 vdc
C 62 vdc
B 94.1 vdc
Q1
E 80.1 vdc
C 25.1 vdc
B 80.1 vdc
+HVL 86 vdc
- HVL -85.1 vdc
+HVR 93.6vdc
- HVR -94.6vdc
IC1 and IC3 were replaced along with Q1 & 3.
I checked the data sheets on these and the pinouts are same as originals.
At this point I have not renewed any caps or diodes as I mentioned the reasons why earlier but did test them in circuit,which I realize is not foolproof.
I did order a complete set of replacement components.
I thought a fresh set of eyes on this would help as I only want to go under this board one more time.
Thanks , Bob
To me - I think your repaired channel is right, and the other is a little off. Emitter of Q1 supplies the reference for the 5 volt regulator, and it should be about the same as +MVL (80 volts) which would mean its output should be around 85 volts. The negative regulator tracks the positive, so that seems okay. Based in the voltages on Q2, IC2 is gone and D6 and d2 are suspect. Maybe Q2 is "leaky"... My 2 cents.
Last edited:
fred soop
Super Member
The interesting thing about this circuit is that +/-HVL are forced to be at least 5 volts higher than +/-MVL, but there is nothing to prevent them from floating to a higher value. For example, starting with +MVL at 75V, D5 will ensure the base of Q1 is 75V (not counting Vbe or diode drops to keep it simple) So, Q1 emitter is 75V and output of IC1 will be 5V higher at 80V. D7 and D9 are reverse biased and out of the picture. If +HVL wants to float higher, say 85V, IC1 would raise Q1 emitter to 80V, base to 80V, and D5 is reverse biased. So, the voltage at Q1 base is actually indeterminate and Q1 collector current (along with everything else out to +HVL) depends on the beta of Q1.
Similarly, Q3 allegedly causes -HVL to track +HVL but the collector current of Q3 is also dependent on beta so -HVL is forced to at least -75V but can float higher and is indeterminate as well.
The 80 volt readings at the anode of D9 and D10, are those readings really at the cathode? The anode should be very close to +MVL/MVR at 75V.
I would not be concerned about the caps or diodes. There are only 3 caps that are probably ok and the diodes all end up reverse biased in normal operation anyway.
I'll chew on this a bit more, but at least it appears that the one channel is now ok. I'd probably replace Q2 and Q4 (IC2 and IC4 are probably ok), and hopefully the beta would be closer to that of Q1 and Q3, bringing that channel in line.
The fact that +/-HVL and HVR is more than 5 volts above MVL/MVR is probably not serious. The reason for having this slightly elevated supply is so the driver voltages will be high enough to drive the output transistors as close to the supply rail as possible. In smaller amplifiers, if the peak output is a couple of volts short, it isn't a big deal, but on a tank like this, every volt counts. If that elevated voltage is 10 greater rather than 5 greater, it won't hurt anything.
Similarly, Q3 allegedly causes -HVL to track +HVL but the collector current of Q3 is also dependent on beta so -HVL is forced to at least -75V but can float higher and is indeterminate as well.
The 80 volt readings at the anode of D9 and D10, are those readings really at the cathode? The anode should be very close to +MVL/MVR at 75V.
I would not be concerned about the caps or diodes. There are only 3 caps that are probably ok and the diodes all end up reverse biased in normal operation anyway.
I'll chew on this a bit more, but at least it appears that the one channel is now ok. I'd probably replace Q2 and Q4 (IC2 and IC4 are probably ok), and hopefully the beta would be closer to that of Q1 and Q3, bringing that channel in line.
The fact that +/-HVL and HVR is more than 5 volts above MVL/MVR is probably not serious. The reason for having this slightly elevated supply is so the driver voltages will be high enough to drive the output transistors as close to the supply rail as possible. In smaller amplifiers, if the peak output is a couple of volts short, it isn't a big deal, but on a tank like this, every volt counts. If that elevated voltage is 10 greater rather than 5 greater, it won't hurt anything.
Yes ,referenced to ground, D9 anode +81.4vdc,(cathode +86.6vdc) whereas D10 anode +80.8vdc , (cathode + 95.3vdc).
Keep in mind that D9 and D10 cathode voltage is + HVL and +HVR actual output voltage at this point in time.
fred soop
Super Member
The anode of D9 is connected to +MVL through a 4.7 ohm resistor and should be very close to the same 75 volts at +MVL. A higher voltage at the cathode of D9 (or D5) can't pull up the anode voltage because the diodes are reverse biased. Or is +MVL up to 81.4V?
Sorry for the confusion as some of the voltages noted in my earliest posts were taken with a 300 to 500 watt dbt in the early tests.
I was proceeding very cautiously , checking and double checking my work progress so as to prevent any further failure to this special piece of equipment.
Measurements taken during my last three posts were with full line voltage to the amp.
I rechecked just now and have the following voltages referenced to ground:
+MVR +81.2vdc
- MVR - 81.6vdc
+MVL +81.8vdc
- MVL - 81.5vdc
fred soop
Super Member
Got it. Didn't notice that the early readings were with a dbt. Everything on the rebuilt channel seems to be as expected.
For the other channel, IC2 has the same voltage on the output and the control pin and 94 volts at +HVR indicates that either IC2 is shorted, or it is being driven right up to its drop out voltage.
Since the big issue is labor to get the board out and work on it, and the parts are not expensive, I'd replace IC2, IC4, Q2, and Q4 because we really don't know which part or how many are bad.
For the other channel, IC2 has the same voltage on the output and the control pin and 94 volts at +HVR indicates that either IC2 is shorted, or it is being driven right up to its drop out voltage.
Since the big issue is labor to get the board out and work on it, and the parts are not expensive, I'd replace IC2, IC4, Q2, and Q4 because we really don't know which part or how many are bad.
duckster2000
New Member
Wow! After years of searching for info on such a rare piece of audio, to see this thread has me very excited.
I currently have a working Citation XX. I use it sparingly for fear of failure. It is good to see that these talented AK members are sharing there technical knowledge on this outstanding amplifier. By the way Wardsweb, I also live in San Antonio.
Wow! After years of searching for info on such a rare piece of audio, to see this thread has me very excited.
Five years after your last post: Did you get that Service Manual that EW suggested?
Schematics for this amp lack some important sections. Bob and I have both run into this. While contacting Harman International yielded some additional info, the information is still incomplete. This is where AK members have really stepped up with circuit forensics, reverse engineering and functional descriptions.
Probably could not find one...I certainly could not.
Bob, I'll answer here again. First, if you're having problems with the solder, could it be an issue with your soldering iron? I've never had problems such as you describe with my Weller WESD51 (other unrelated problems cause me to not recommend it, but when it works, it works fine). I dunno what you're using now, but if you're not using a good temp-controlled iron, sounds like it's time for an upgrade along with a good selection of chisel tips. The Hakko FX888D is tough to beat. 650°F and you're in bizness.
Here's a little blurb on desoldering I wrote a while back. Might be something there that helps.
I'm also big on doing to one channel whatever was done to the other. Qxx gets replaced on one channel, the corresponding part gets changed in the other channel. And with regulated supplies that usually are the hardest working section of any piece of electronic gear, I have no problem swapping out wholesale every semiconductor, electrolytic capacitor, and power resistor with the toughest and best parts I can find. Whether you follow this general dictum is your call, but if the solder side of that board is as tough to deal with as you describe, I'm gonna make sure that I have to deal with it once, rather than find out that something I skipped is going to force me to pull it all apart again.
I sympathize with the difficulty you're having, but all I can say is that there's a reason why people decline to tackle projects like this and hand them over to a pro. Small consolation, I'm sure, but patience and perseverance will pay off.
