@@FluxCondenser Hello Flux, is there any posibilty you can give me advise on a hifi component I'm currently trying to fix? I'm ok if you can't, but I'd really appreaciate your help!
@@FluxCondenser I bought a Denon DR-M44HX deck last year in ebay. The deck was listed as for parts, so I thought I could give a chance and try to fix it. when I opened it it didn't sound the tape. Transport was ok, so the tape moved. However, there were 2 Zener diodes and a capacitor blowned up in the power board. I changed them, but them I realized that where the play heads connect if I put my finger closer a huge hum starts to sound. I thought the culprint was a M5220L dual opamp, however problem remains. I've also found the Amp board PCB has a dense flux layer, so I could think capacitors are the problem. But to be honest I'm approaching to the deck with my empirical knowledge, since I've had no degree on electronics. It's weird because when you inject sound to the line input and you select the source switch (it's a 3 head deck) music sounds but the VU meter doesn't move, and the tape does not record as well. However, when you play it, and if you raise the output volume to the max, the music sounds very quietly, like a whisper. Sorry for the long message. But I tried to condense as much as possible the issue. Thank you for your time!
Irwin J. Céspedes Hi, Irwin. Inducing hum from the play head or from any points connected to the play head seems like normal behavior to me. The amount of voltage created by the play head from the moving magnetic tape is tiny, so a preamp in the machine is necessary to boost voltage. So, again, getting hum from touching the input to the preamp is normal, just as I was able to induce hum in this video from touching the inputs of the preamp. Because you’re getting hum, I would think you’d get sound from a prerecorded tape playing. Are you? Reading your comment it seems that you do, but playback level is very low. If your induced hum is loud, but playback is low, that suggests that the amps are working after the head, but the head itself is not. Perhaps it’s out of alignment or is malfunctioning. Additionally, it could have a bad connection. Additionally, to diagnose the playback, record and VU problems, your first step should be to find the schematic for the unit and find the listed voltages at different test points. Any points that test bad will give a clue to where the circuit is malfunctioning. Additionally, you can try to pin down the play/record problems through signal tracing. Inject a signal at the inputs and probe with a signal tracer or oscilloscope to see where you lose the signal. I’m not sure what caused the zeners and cap to blow, but it may have been a power surge. If not, then something shorted after the board and of course that should be looked into as a possibility. The capacitor you replaced may have itself shorted, causing the diodes to go. Once you find the areas of the circuits that are problematic, the likely failure points are capacitors and transistors (although there could be other issues as well, of course). Test the electrolytic caps with an ESR meter and replace any that are out of spec. Additionally, test and replace any bad transistors. If you don’t have a transistor tester, you can sometimes get away with testing them with a good voltage meter. X-ray Tony just did a recent video explaining some methods. Sorry I can’t give you any specific help. If you narrow down the problems further, let me know what you find and I’ll see if I can provide some insight. Good luck!
I think the swapping of the meter leads on the negative power supply was intentional. Back when this was produced, almost all voltmeters were analog. You had to swap the leads to read negative voltages and mentally apply the minus sign (if you didn't swap, then the meter needle would peg hard to the left). But these days, your digital meter can show you a minus sign. I don't really consider it a "mistake" by Heathkit, they were just following the normal conventions of the day.
Not quite, but close. By this point digital meters that showed negative voltages were available. The reason for the issue was that Heathkit wanted the test done and didn’t want it skipped by people who didn’t have a volt meter, digital or otherwise. So instead, they instructed the builder to use one of the as-yet uninstalled LEDs from the kit to create a rudimentary test probe by attaching the LED to a provided resistor. This relates to your point. As with analog meters which can’t show negative voltages, LEDs can’t illuminate with a negative voltage applied to the positive terminal. Unfortunately, Heathkit used the same instructions for both those using a meter and those using an LED which led to some confusion. It is less of a “goof” on Heathkit’s part when you put it into historical context. Thanks for the great comment.
@@FluxCondenser You are right, you could get a digital meter in 1983. I just had a browse in a 1983 Radio Shack catalog. $79 for digital (about $200 in today's $) and about $39 analog for mid-range models. Don't think I could afford one until the 90's.
Paul Rose Yup, that would be a big difference in price. I was in middle school when this preamp was introduced so all this was just unobtanium in a catalog to me back then!
@@FluxCondenserIt seems to me that the authors of the instructions would have written them for the most basic meter a customer might have, which in this case would be an analog meter. The fact that expensive digital meters existed at the time doesn’t mean the instructions should be written for them.
Sometimes I wonder how my AA1800/AP1800 sounds compared to some of the Emotiva XPA2 Gen1 amplifiers combos, bought this stuff used a few years back locally after a long time looking and waiting. The Pre amp is alright, but I think it needs a recap since my NAD 1600 is far more transparent. The amp probably needs to be refreshed with new caps also. Hard to believe they are kits, nice and thick metal not the flimsy sheet metal used today. I wish they still made audio like this today without the esoteric prices and looks. I read somewhere that Heathkit company hired Harman Kardon engineers to help them design these products, I wouldn't be surprised, since Harman Kardon has some of the best vintage receivers and amps I ever heard. Looks kind of Harman Kardon also. Nice Job, I wish I had the time and the skills you have!
Thanks Sound Man. There were a number of components that tested bad on my kit which needed to be replaced, so it’s likely that your kits could benefit from a tune up. Interestingly, though, the electrolytics tested OK for the most part even though I didn’t use them. In the next video, I’ll be bench testing the preamp as well as doing some listening tests. Without letting the cat too far out of the bag, I can tell you that to my ears “transparency” is stellar. The preamp is dead quiet and the phono stages sound superb. Stay tuned. As far as Harmon Kardon, that company did provide the later stereo kits for Heathkit in the final years that they offered them. I’ve heard that these particular models (Pro Series) were Harmon influenced, but I’ve also heard that’s not the case and they’re pure Heathkit and that’s what I’ve come to accept. I’ve not read anything conclusive that confirms otherwise and there are no Harmon markings of any kind in the kit or its literature. For the later kits, Heathkit was very clear about the Harmon involvement.
Wool bits driven by a Dremel and Nutrol control cleaner. The bits are gentle and provide just the right amount of abrasion. The Nutrol lubricates and leaves a protective coating. Works really well. Here’s a link to the bits I use: www.amazon.com/Multifunctional-Grinding-Polishing-Accessories-Attachment/dp/B00XJINV42/ref=sr_1_3?dchild=1&keywords=Drexel+wool&qid=1602053831&sr=8-3
@@FluxCondenser Bookmarked! Anyway, I often use inter-dental cleaning brushes for this. They're better for cleaning nine-pin tube socket contacts, however, as the brushes have such a small diameter. They're available at your local Wal*Mart.
I hope you didn't paint over areas where the chassis is needed as a ground. Any place on the chassis that is used as a ground needs to have the pain carefully removed and the naked chassis exposed.
@alaingingras7224 This preamp has functionality to connect amplifiers and speakers for selection control. There is no amplifier in this unit. It’s explained in more detail if you watch all the videos in this series. Hope that clears it up.
Thanks for sharing! Also like the tip on testing components before installing -- even new ones.
The wait worth it! Excellent job. Indeed it looks that the preamplifer was meant to be built like a tank for years and years of service.
Thanks, Irwin.
@@FluxCondenser Hello Flux, is there any posibilty you can give me advise on a hifi component I'm currently trying to fix? I'm ok if you can't, but I'd really appreaciate your help!
Irwin J. Céspedes I can certainly try, what’s up?
@@FluxCondenser I bought a Denon DR-M44HX deck last year in ebay. The deck was listed as for parts, so I thought I could give a chance and try to fix it. when I opened it it didn't sound the tape. Transport was ok, so the tape moved. However, there were 2 Zener diodes and a capacitor blowned up in the power board. I changed them, but them I realized that where the play heads connect if I put my finger closer a huge hum starts to sound. I thought the culprint was a M5220L dual opamp, however problem remains. I've also found the Amp board PCB has a dense flux layer, so I could think capacitors are the problem. But to be honest I'm approaching to the deck with my empirical knowledge, since I've had no degree on electronics.
It's weird because when you inject sound to the line input and you select the source switch (it's a 3 head deck) music sounds but the VU meter doesn't move, and the tape does not record as well. However, when you play it, and if you raise the output volume to the max, the music sounds very quietly, like a whisper.
Sorry for the long message. But I tried to condense as much as possible the issue. Thank you for your time!
Irwin J. Céspedes Hi, Irwin. Inducing hum from the play head or from any points connected to the play head seems like normal behavior to me. The amount of voltage created by the play head from the moving magnetic tape is tiny, so a preamp in the machine is necessary to boost voltage. So, again, getting hum from touching the input to the preamp is normal, just as I was able to induce hum in this video from touching the inputs of the preamp. Because you’re getting hum, I would think you’d get sound from a prerecorded tape playing. Are you? Reading your comment it seems that you do, but playback level is very low. If your induced hum is loud, but playback is low, that suggests that the amps are working after the head, but the head itself is not. Perhaps it’s out of alignment or is malfunctioning. Additionally, it could have a bad connection.
Additionally, to diagnose the playback, record and VU problems, your first step should be to find the schematic for the unit and find the listed voltages at different test points. Any points that test bad will give a clue to where the circuit is malfunctioning. Additionally, you can try to pin down the play/record problems through signal tracing. Inject a signal at the inputs and probe with a signal tracer or oscilloscope to see where you lose the signal. I’m not sure what caused the zeners and cap to blow, but it may have been a power surge. If not, then something shorted after the board and of course that should be looked into as a possibility. The capacitor you replaced may have itself shorted, causing the diodes to go.
Once you find the areas of the circuits that are problematic, the likely failure points are capacitors and transistors (although there could be other issues as well, of course). Test the electrolytic caps with an ESR meter and replace any that are out of spec. Additionally, test and replace any bad transistors. If you don’t have a transistor tester, you can sometimes get away with testing them with a good voltage meter. X-ray Tony just did a recent video explaining some methods. Sorry I can’t give you any specific help. If you narrow down the problems further, let me know what you find and I’ll see if I can provide some insight. Good luck!
Very good job sr
Thank you, Karim.
I think the swapping of the meter leads on the negative power supply was intentional. Back when this was produced, almost all voltmeters were analog. You had to swap the leads to read negative voltages and mentally apply the minus sign (if you didn't swap, then the meter needle would peg hard to the left). But these days, your digital meter can show you a minus sign. I don't really consider it a "mistake" by Heathkit, they were just following the normal conventions of the day.
Not quite, but close. By this point digital meters that showed negative voltages were available. The reason for the issue was that Heathkit wanted the test done and didn’t want it skipped by people who didn’t have a volt meter, digital or otherwise. So instead, they instructed the builder to use one of the as-yet uninstalled LEDs from the kit to create a rudimentary test probe by attaching the LED to a provided resistor. This relates to your point. As with analog meters which can’t show negative voltages, LEDs can’t illuminate with a negative voltage applied to the positive terminal. Unfortunately, Heathkit used the same instructions for both those using a meter and those using an LED which led to some confusion. It is less of a “goof” on Heathkit’s part when you put it into historical context. Thanks for the great comment.
@@FluxCondenser You are right, you could get a digital meter in 1983. I just had a browse in a 1983 Radio Shack catalog. $79 for digital (about $200 in today's $) and about $39 analog for mid-range models. Don't think I could afford one until the 90's.
Paul Rose Yup, that would be a big difference in price. I was in middle school when this preamp was introduced so all this was just unobtanium in a catalog to me back then!
@@FluxCondenserIt seems to me that the authors of the instructions would have written them for the most basic meter a customer might have, which in this case would be an analog meter. The fact that expensive digital meters existed at the time doesn’t mean the instructions should be written for them.
Sometimes I wonder how my AA1800/AP1800 sounds compared to some of the Emotiva XPA2 Gen1 amplifiers combos, bought this stuff used a few years back locally after a long time looking and waiting. The Pre amp is alright, but I think it needs a recap since my NAD 1600 is far more transparent. The amp probably needs to be refreshed with new caps also. Hard to believe they are kits, nice and thick metal not the flimsy sheet metal used today. I wish they still made audio like this today without the esoteric prices and looks. I read somewhere that Heathkit company hired Harman Kardon engineers to help them design these products, I wouldn't be surprised, since Harman Kardon has some of the best vintage receivers and amps I ever heard. Looks kind of Harman Kardon also. Nice Job, I wish I had the time and the skills you have!
Thanks Sound Man. There were a number of components that tested bad on my kit which needed to be replaced, so it’s likely that your kits could benefit from a tune up. Interestingly, though, the electrolytics tested OK for the most part even though I didn’t use them. In the next video, I’ll be bench testing the preamp as well as doing some listening tests. Without letting the cat too far out of the bag, I can tell you that to my ears “transparency” is stellar. The preamp is dead quiet and the phono stages sound superb. Stay tuned.
As far as Harmon Kardon, that company did provide the later stereo kits for Heathkit in the final years that they offered them. I’ve heard that these particular models (Pro Series) were Harmon influenced, but I’ve also heard that’s not the case and they’re pure Heathkit and that’s what I’ve come to accept. I’ve not read anything conclusive that confirms otherwise and there are no Harmon markings of any kind in the kit or its literature. For the later kits, Heathkit was very clear about the Harmon involvement.
(1) Use a hair dryer. Much better than that goofy dust buster.
(2) Save the nut driver. THE BEST tool Heathkit provided. Unobtaniim now!
1. No, that “goofy” blower is one of the best tools you can have on your bench. A hair dryer? That’d be pure stupidity. 2. Yes. I’ve got dozens now.
Pre amplifier with speaker terminals. ?
Yes. This is explained in the video series.
What did you use to clean the contacts on the inside of the RCA jacks?
Wool bits driven by a Dremel and Nutrol control cleaner. The bits are gentle and provide just the right amount of abrasion. The Nutrol lubricates and leaves a protective coating. Works really well. Here’s a link to the bits I use: www.amazon.com/Multifunctional-Grinding-Polishing-Accessories-Attachment/dp/B00XJINV42/ref=sr_1_3?dchild=1&keywords=Drexel+wool&qid=1602053831&sr=8-3
@@FluxCondenser Bookmarked! Anyway, I often use inter-dental cleaning brushes for this. They're better for cleaning nine-pin tube socket contacts, however, as the brushes have such a small diameter. They're available at your local Wal*Mart.
*WHY ARE THERE SPEAKER OUTS if it is a preamp*
I hope you didn't paint over areas where the chassis is needed as a ground. Any place on the chassis that is used as a ground needs to have the pain carefully removed and the naked chassis exposed.
No, of course. I believe I mentioned this in the video.
Preamp ? Integrated amp ...
It’s a preamp.
O.K.then why ,on your pre. there are speaker connectors A and B 8 terminals ,so what do these terminals do?@@FluxCondenser
@alaingingras7224 This preamp has functionality to connect amplifiers and speakers for selection control. There is no amplifier in this unit. It’s explained in more detail if you watch all the videos in this series. Hope that clears it up.
Makes sense .Thank You for responding !@@FluxCondenser