H/K Citation 17S and 19 project.

Greetings all! A new project for me. First set of separates. They are a little scruffy but I think they will be a cool first project. First thing was to pop the covers off, blow the dust and stuff out and have a look. A fair amount of rust here and there but not too bad.

Next step, power up on the dim bulb tester. The 17S preamp powers up with nary a glimmer from the dim bulb tester. Power indicator comes on. Nice! The 19 makes the bulb glow pretty bright and no indicator lights come on. So I shut it back off and think about it for a bit. I remember reading that sometimes it takes a bit for the big filter caps to charge so after sniffing around and feeling for any heat and not finding anything I turn it back on again. Soon the bulb begins to dim and the right power indicator comes on. It continues to dim and the left power indicator starts to flicker and then comes on solid. After a while the bulb on the dbt is barely glowing.

I didn't want to try the power meter test on the dim bulb tester so I plugged it into the wall and tried it out. Shockingly all the LEDs worked! I let it warm up for a while and then checked DC offset. Had 25.8mv on the right channel and 23.8mv on the left. After running for a while the right heatsink peaks out at 106f and the left at 89f hmmmm! I wonder if the delay in the left power indicator coming on and the lower temp on the left heatsink is related. Will need to check idling current at some point. More soon.

Cheers..........................Todd

After a quick Deoxit bath on pots, switches, connections and terminals I hook it all up. Hmmm, speaker terminals are a minor pain as others have mentioned, and the inputs/outputs are a little close together for your average interconnects. I think I've read this elsewhere as well.

Anyway all hooked up and......Nothing, not a peep. Was trying it with the turntable and the cassette deck. Tried connecting the tape-out back to the cassette deck line-in to see if I had a signal anywhere but nothing. Since the cassette deck has variable output I connected it directly to the amp and it works! Actually sounds pretty good. It thumps a bit on power on but that's not surprising. It also gives a small pop on power off after 10 seconds in the left speaker and 20 seconds in the right speaker. Interesting. On to the pre-amp.

Cheers..........................Todd

Don't worry about the thud/pop. That's the way they work.
Get yourself some banana clips for the speakers and enjoy a nice amplifier.

Careful with the power until you check the DC offset.

On the preamp, there's a muting relay for the output jacks. It is one relay so controls both channels.

You'll need to check the power supply that all of the voltages it produces are ok. The easiest way to do this is to remove the bottom cover and see that all of the socket pins are labeled.

With the negative side of a volt meter grounded, you can step through them very quickly. If they're ok, this is a good sign.

Then, reseat each board. Pull it out and plug it in a few times to be sure the contacts are making. Clean 'em with DeOxit while you're at it just to be sure.

No output at this point? Focus on the line stage only first. That's where the output relay is. Insert an audio signal to the AUX input and then measure the input side of the relay to confirm there's a signal on both channels. If you're using an AC volt meter, they should be the same level.

Service Manual is at hifiengine. You'll need it if you've gotten to this point.

Cheers,

David

Thanks Westy! Already did. Per my first post +25.8mv on the right channel and 23.8mv on the left.

David, thank you, Yes I have the service manual. I'll post my findings on the pre-amp shortly. Been working on the post off and on all afternoon between work . And yeah, rail voltages, not so good .

Cheers.............................Todd

Ok so checked the rail voltages first +24v and +15v had 24.8v & 15.2v respectively. I say had. Because embarrassingly I didn't listen when folks around here keep repeating that you need to use a hook type probe and connect your probes and then power on. I thought 'I can do this, my hands are steady'! Well, I can't. Pow! blinding white flash! Now I have +19v and +12V respectively. But I'll deal with that later. Hopefully....

Now on to the -24V and -15 volt rails. On the -24v I had +1v and On the -15v I had +2.2v. (this was all pre-BWF by the way .) It didn't make sense to me that positive voltage could be coming from the voltage regulator so I began removing the other boards and then checking again. It remained the same until I got the hi/low cut filter board out. I then had
-0.6v and -1.7v on the -24v and -15v rails. I find it a bit baffling how I can have a higher negative voltage on the -15v rail than I have on the -24v rail. Where's it coming from?

I see a lot of evidence of prior work on that filter board. At least one of the op-amps has been replaced. Along with damaged and lifted traces and pads. I have a number of questions about this stuff That I'll try to post later. Thanks for looking in!

Cheers.................Todd

Hello again all.

My plan at this point is to lift one leg of wire 1 and 2 and check current flow through the circuit from there. My thinking is either the voltage regulator outputs are just low. Or something else in the circuit is pulling the voltage low. I'm thinking if something is pulling them low then the current flow through the -24v wire should be higher(since the voltage is lower). And if the voltage regulator outputs are just low then the opposite would be true. Does this thinking sound reasonable? Or am I all wet here?

Also on the -24v rail what are the chances that 1 or 2 volts reverse polarity has fried everything else in the circuit? Thanks for the help!

Edit; Messed up one of the pics.

Cheers.....................Todd

HI all.

So on the voltage regulators, a search on Digikey and Mouser for uA79M24UC and uA78M24UC turns up nothing. But a google search turns up a NTE971 and NTE972 From Vetco Electronics. Do these sound like suitable replacements? Or is there something else available from mouser or Digikey that would be better that I'm just not finding. My track record for finding stuff at Mouser is very poor. I find maybe 1 in 10 things I look for. How do you guys do it?

Cheers................Todd

just type 78m24 or 79m24 this works better.
uA is a prefix originating at Fairchild so you might get only made-by-Fairchild components....

be aware the filter board uses an op-amp, which could be destroyed (and shorting power), now. The other boards are probably not harmed if voltage is too high. First replace both voltage regulators, whether they are still okay or not, also the pass transistors for 24 to 15 volts you can replace by almost any standard lowpower transistor to make sure, or you can test them for shortage first.

90% sure strange voltages come from one or both opamps at the filter board when it is in, so buy them also, it will cost a few dollars only. They seem the only user of the +/- 15V so if something happens with +/- 15V with board in or out they are the culprit.
CA3100 opamp is very obsolete and does not exist anymore, an OPA604 is what I used in my 17 (which is a little different from the 17S as it has a filter board without the switches on it).

myself, I used (good) ic sockets when replacing opamps in my 17 , here is a link with some pictures http://members.quicknet.nl/gerard.slikker/hkcitation17.htm

Gerard, thank you very much. And thank you for the link to your pages. A lot of very helpful information there. I feel like I'm getting somewhere !

The idea of using IC sockets for the op-amps appeals to me very much. but unfortunately my track record at Mouser still stands. When I look in the IC socket section I see a bewildering array of options. None of which get me any closer to anything that resembles what I need. You don't happen to have a part number for those do you?

Cheers...................Todd

Hi Todd, no, I pulled them from some scrap board of electronics. I like the ones with round pins/holes. I used them since I had them...

example of these:
http://www.mouser.com/ds/2/418/NG_CD_1571552_E4-652389.pdf
TE part number 2-1571552-2, mouser p/n 571-1571552-2 it seems.
(no affiliation and they are very expensive also for an ic socket, there are cheaper alternatives)

Mouser's searching and filtering system can be quite daunting until you spend some time there _and_ know pretty much what you're looking for. It took a while for me for those reasons.

For the 7824 voltage regulator, it looks like they have 7 options for a 1.5 amp version with TO220 case and through hole legs.

Same thing for the 7924 regulators here.

You should be able to pull all the boards in the Cit 17 except the power supply board and read the regulated outputs for the 78/7924 devices just fine. This will tell you if you have a problem elsewhere. Then, add one board back at a time and watch the voltages. Since the +/-15 volts are derived from them, you'll have a good starting place.

I've redone a Cit 17 and can confirm they're excellent when redone. Do use a vacuum desoldering tool if you have one. The runs on the boards will come up with even a little excess heat needed if you're using a solder sucker or solder braid.

Cheers,

David

dshoaf said:

Mouser's searching and filtering system can be quite daunting until you spend some time there _and_ know pretty much what you're looking for. It took a while for me for those reasons.

For the 7824 voltage regulator, it looks like they have 7 options for a 1.5 amp version with TO220 case and through hole legs.

Same thing for the 7924 regulators here.

You should be able to pull all the boards in the Cit 17 except the power supply board and read the regulated outputs for the 78/7924 devices just fine. This will tell you if you have a problem elsewhere. Then, add one board back at a time and watch the voltages. Since the +/-15 volts are derived from them, you'll have a good starting place.

I've redone a Cit 17 and can confirm they're excellent when redone. Do use a vacuum desoldering tool if you have one. The runs on the boards will come up with even a little excess heat needed if you're using a solder sucker or solder braid.

Cheers,

David

Click to expand...

Thanks David, Actually no, not only do I not have one but until this morning I wasn't even aware there was such a thing. Up until this point I always assumed that the solder sucker was the pinnacle of the desoldering art. So in my research I see that prices range anywhere from 30 bucks ish to Holy Crap!!! So what in your opinion and experience would be a good starting point?

On the subject of the voltage regulators, I was reading data sheets on some and a lot of them have an "absolute maximum" input voltage of 40v. My rectifier puts out 40 volts on one leg and 42 volts on the other. I don't remember now which on was pos. and which one was neg. Didn't think much of it at the time. But I wonder if that is going to be a problem.

Yeah, Mousers filtering system. Grrrrrr!

Gerard, Thanks for those links. Yeah maybe a little expensive in comparison but fortunately I only need two for this project.

Cheers......................Todd

On the desoldering tool, I have the earlier version of this model from Hakko. I see from a quick search of Amazon, there are knock-off models, too.

I only wish I had purchased one far earlier. There have been quite a few discussions about it at AK, too.

On the input voltage specs for the regulators, if there was a problem with it you would have seen it after 40 years. The fact is that integrated circuit technologies have come a long way in that time. I'm not sure how you're reading those input voltages, but my quick calculations tell me that the regulators, under normal operation, would likely be hot as fire but they don't give off that much heat. This indicates that the actual input voltage under load is, in fact, lower.

Cheers,

David

Thanks David. Noted. As a professional auto tech I appreciate the value of quality tools and use almost exclusively Snap-On. But I also know that for an occasional hobbyist it would be hard to justify the cost. I fear that may be the case here. I think I'll have to stick with the good old solder sucker and hope for the best!

Ok, Parts ordered! I got two ea. -24v 1a voltage regulator. two ea. +24v 1a voltage regulator. Two ea. NPN GP transistors. Two ea. PNP GP transistors for power supply, Some LF356N op-amps and a couple of the sockets suggested by Gerard. I got extras in case I f*** something up. I didn't order any caps or darlingtons or anything else yet. One step at a time.

Cheers............................Todd

dshoaf said:

Mouser's searching and filtering system can be quite daunting until you spend some time there _and_ know pretty much what you're looking for. It took a while for me for those reasons.

For the 7824 voltage regulator, it looks like they have 7 options for a 1.5 amp version with TO220 case and through hole legs.

Same thing for the 7924 regulators here.

You should be able to pull all the boards in the Cit 17 except the power supply board and read the regulated outputs for the 78/7924 devices just fine. This will tell you if you have a problem elsewhere. Then, add one board back at a time and watch the voltages. Since the +/-15 volts are derived from them, you'll have a good starting place.

I've redone a Cit 17 and can confirm they're excellent when redone. Do use a vacuum desoldering tool if you have one. The runs on the boards will come up with even a little excess heat needed if you're using a solder sucker or solder braid.

Cheers,

David

Click to expand...

Thanks for the suggestions on the 1.5 amp regulators. But the link you have there for the 7924s goes back to the 7824 +24v regulators. If I enter the quagmire that is their filter system I can't find any -24v regulators in 1.5a. Only -25v. Weird! I can only find matching + and -24v regulators in 1a. So that's what I ordered.

Cheers...........................Todd

P.S. I know that everyone loves Mouser and I'm sure I'll learn to love them too but I swear to god their website was developed by a bunch of chimps!

TConnelly said:

...P.S. I know that everyone loves Mouser and I'm sure I'll learn to love them too but I swear to god their website was developed by a bunch of chimps!

Click to expand...

Actually, the main site is, I believe, built for engineers and buyers of quantity parts. They can sort on all the specs that would interest those 2 buyer and specifier groups.

Us hobbyists aren't their target market but at least they allow us to purchase in small quantities.

Cheers,

David

They do, and for that I am thankful. I was just venting.

I could have made my order a little bigger too. I forgot about the electrolytic caps I need to get for a B&O RX2 turntable project I have going. Dangit!

Cheers....................Todd

Greetings everyone. Well I finally got all the parts and supplies together and got started on the work this morning. I've replaced the + and -24v voltage regulators. And the + and -15v transistors Q3 and Q4.

So now I have +24.2v and -23.5v. and +16.2v and -15.7v. Much better than before. I'd like to see them closer but I suppose 0.7 volts isn't too bad. I have another -24v regulator on hand, I wonder if I should try it and see if I can get closer or do you folks think it'll be ok? Next is to put the output amplifier board and phono amp boards back in one at a time and see how my voltages hold. And see if I get any activity from the relay. Wish me luck!

Oh, before I tackle the opamps in the high/low cut filter board do you suppose I could just jumper around it? Jumper pins 1 to 12 and pins 3 to 5 and see if I get sound? Or should I jumper the input grounds as well? 2 to 11 and 4 to 6?

(Schematics are in post #7)

Cheers......................Todd

It works! That's worth two happy dance bannanas !

So after each board was reinstalled the gap between the rail voltages narrowed until with all the boards back in it was down to less than 0.2v difference on the 15v rails and less than 0.5v on the 24v rails.

Installed the op amps on the high/low cut filter boards using the sockets recomended by gslikker. They worked great! The subsonic filter works perfectly. I've never had any rumble problems from my turntables but using a tone generator app on my iphone I can see it's working. The high cut filter is working also but it's a bit noisy. A bit of hiss and a little hum. It looks like some one has replaced the transistors in the high cut circuit. At least they don't match the silk screen printed on the pcb. And they don't match the numbers in the parts list. Parts list says; npn, low noise (GE D38S7). With a real quick look I'm having no luck finding substitutes so far. But I don't think they're anything super special other than low noise. Anyone have a go-to for this application?

It has a couple other minor issues yet but work is continuing. And it's sounding fine!

Cheers.....................Todd