Harman Kardon TD202 Tape Deck SLOW boot-up

[Dannyx]

Good day folks. Today I got something which I haven't worked on very often because they're falling out of fashion: a tape deck - sounds lame, but it's a challenge I'm willing to accept.

It's a rather basic one: no auto-reverse, though it's got Dolby on it, so I guess it's decent and worth saving.

There are 2 issues with it:
A) it takes its sweet time to finally output any sound after being powered on, despite the transport running and the LEDs coming on fine

B) the left channel is dead

A) I had a look at the schematic on page 49, towards the bottom-left of the page. It took me a while to understand how it works, but I THINK I got it: when you turn on the power switch at the front (S1), C52 slowly charges up via R53. Meanwhile, the emitter of Q1 gets 12v right away from the 20v rail off the bridge rectifier (stepped down to 12v by D52 and R55). Because Q51 is a PNP, at this point the emitter is still more positive than the base, because C52 has not charged enough, so the C-E path is "open" and 12v flows to point K which keeps the board in "mute" until C52 finally becomes more positive than the emitter of Q51, "releasing" mute. The way it does this is by turning on Q707, Q708 and the cascaded Q711-Q714 (don't know why they cascaded SO many of them there) which pulls to GND both the output jacks at the back and the signal paths from the head itself, if I'm not mistaken. THIS is the problem: it takes WAY too long for point K to drop low enough to release the "mute rail" and I can't quite place it. I obviously pulled C52 and C51 first, but they read fine on my meter, so I didn't replace them just yet, although I WILL just for good measure. I also did the same with C4 on the left there and the same thing happened - not out of spec in the slightest.

Taking some measurements indeed confirms the base of Q51 is slowly charging up after a cold start. At around 11v, point K "snaps" off, the LED vu-meters start dancing around and I get an output (though only the right channel - the left is dead), which brings me to:

B) No sound coming out of the left channel AT ALL -I even tried different tapes. The VU meter doesn't dance either There's something wrong either with the head-amp circuit which sucks because it's all discrete components, or with IC501 which sucks even harder because if the signal is not making it through it, finding a replacement for that whole chip is probably not be easy :| Since I do not have a scope, I'm thinking of using a small amplified speaker to "probe" after C513 and C514 (pins 3 and 39 respectively of IC501 in the middle there) to see if I get any sound output from the head amp part directly. It will probably be very weak because it's not amplified by IC501 there, but enough to figure out if the left channel is giving IC501 anything to work with....either that, or my idea is bad and I blow something up

[R_J]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

What is the voltage at D51 cathode? it could be that R51 or R52 have gone high in value, You should have 20vdc on C51 if the cap is good.
Do both channels work if you feed a signal to the left & right inputs?

[Dannyx]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

What is the voltage at D51 cathode? it could be that R51 or R52 have gone high in value, You should have 20vdc on C51 if the cap is good.

I'll measure again, though I remember the two resistors are OK. That is actually a single package with 2 diodes combined. The cap does read around 19v, but I don't recall if it slowly ramps up or if it's instant.

Do both channels work if you feed a signal to the left & right inputs?

I tried this today but I do not have a blank tape to check, since the level meters don't work when in stop mode as I was hoping - it has to be in REC mode for this to happen, which makes sense when you look at the schematic, because Q713 and all the others after it to the right of the page are "on" (thus muting the meters) when in stop mode. Point K can also be triggered (pulled high) by point C, which goes to pin 29 of IC801 MCU on page 52, which is what happens in stop mode: pin 29 goes high, so even if Q51 is off, that line is still high, killing the meters.

[redwire]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Who's afraid of a little transistor- a discrete tape head amp is a walk in the park- just compare readings between the good and bad channels.
One way to work on cassette decks is record a (stereo) 1kHz sinewave on a cassette using a good tape deck, and play that back. Then a multimeter on ACmV or a scope to check signal.

This unit does have a lot of muting transistors, complicated. Three just at the head input Q701, Q702, Q705, Q707.
RJ suggests looking at power on/off muting circuit.

I tend to follow the signal, start checking the signal out of the head pre-amp, at the level trimpots. Or at the CMOS switch IC301 CD4066B, compare DCV between channels if that IC is blown. It would not REC properly as well.

[Dannyx]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Three just at the head input Q701, Q702, Q705, Q707.

Right - didn't even noticed those...

Or at the CMOS switch IC301 CD4066B, compare DCV between channels if that IC is blown. It would not REC properly as well.

The 4066B is only for the 102 model and you managed to troll me a bit there, as I went on goose chase trying to find it

[redwire]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Ahh the TD202 has Dolby-C and a different mega IC501 HA12088 does the REC/PLAY switching.

You can also measure the RCA Line Outs, they have some DC coupling it's strange. If the output is shorted to GND (muted), the VU meter will not light. So also look at muting transistor Q711 or for DC present if there is a bad cap.

[petehall347]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

hope you wear safety goggles as this might go bang soon ..

[petehall347]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

besides that cap ....
i find with things like this its a corroded switch or board connector ..

[redwire]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

The Rifa cap is across the on-off switch so it can't explode, like an X-cap.

These single-sided PC boards with a million jumpers, I'd look for fractured solder joints. I alway do a gentle tap with a plastic pen to see if there's a bad connection.

[Dannyx]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Ok guys, here's what I did today: I think I've been looking in the wrong place trying to track down a nonexistent issue. See, at first I thought the deck takes too long to output ANY sound and the lack of sound in the left channel is a different problem altogether, but the truth lies somewhere in between: the left channel IS the one that's slow to turn on and is what the guy meant, so forget about the general turn-on time of the machine - that one is normal and takes around 5s to give me an output, even if just in the right channel. What I did today is as follows:

I soldered a stereo jack directly to C513 and C512 respectively (close to the left side of IC501 on page 49) and plugged some powered speakers into that. I got a signal out of both channels, albeit a pretty weak one. Still, it was enough to confirm the part on the left is working and there IS some signal going into IC501. The signal appears to get stuck AT IC501, though only for the left side. I began measuring each of the pins and comparing the two sides, since they're symmetrical, as well as compare the readings to the values given in the schematic - most commonly 6.1v for some reason.

This makes me believe there's something wrong with the chip itself. Take pins 8,9 on the "left" side and compare those to 35,34 on the "right" side as an example: on the right channel, the one that works, 34 and 35 read precisely 6.1v as the schematic indicates, however 8 and 9 on the other side only read 1v, which is not right.

Then this happened: while I was messing around measuring stuff, the left channel suddenly came on too, which is in line with what the guy told me about it taking ages to output ! OK, "suddenly" is too strong a word: what happened was the music started to get all distorted and got somewhat louder without me touching the volume, then the left speaker started playing too and the level meter started blinking too ! The volume then went back to normal, as if the volume tried to ramp up but then an "auto gain control" kicked in and stabilized to what it was before. I quickly measured those sets of pins again and now the voltage on 8 and 9 had increased to around 2v, which apparently is enough to get the internals of that chip to put out sound in the left channel too. Hit "stop" and that voltage remains on those pins, so the next time I hit play, I got sound in both channels again. However, kill the power and voltage goes back to 1v again on pins 8,9 and I get no sound on the left. The time it takes for the left channel to resume seems to depend on how long the power's been off, which is in line with what the owner told me. Ironically, if I leave it on long enough, it DOES eventually increase more and more until it reaches 6v also ! I replaced C517 and C518 mostly at random to see if it changes anything, but of course it didn't. I'm thinking it could be caused either by the chip internally, or by some component that's mirrored on both sides, since if it were a common components between both of them, it would affect the other one as well. Not that many stuff to check there though - I'm not quite ready to pull out all those caps one by one to check. They're mostly poly caps too (if I'm not mistaken) - very few electrolytics....

Could not find a clear enough schematic for a HA12088 to see what its pins each do and how the signal is routed internally. Here's a clearer picture of the board too.

[redwire]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

The IC has a bunch of variable-gain elements and it acts like one of them is up and down. Sort of a fuzzy HA12088 datasheet at https://www.datasheetarchive.com

Is Dolby on or off, B or C? Try switching different modes, matching the schematic's voltages at TP1 pin 6. If wrong, then look at C516. So the IC is not halfway on in some mode. That voltage must be accurate, compare to TP2 pin 37.

The output op-amp is pin 8 (playback in-) and 9 playback out. 1V is a problem for it, maybe check C519 to see if muting transistor Q711 is not leaky too or activated.

The other pins I would also compare voltages like pins 15,20 with 28, 23 etc.
Given the age of the small electrolytics, I do find them going bad and some of them likely control the noise reduction gain and envelope.

[Dannyx]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Today I measured and wrote down the voltages on every pin of IC501. I compiled a little table so I may follow along better. I don't have that file on me right now because it's on my work PC, but I distinctly remember TP1 only reading 1v, despite the other 3 TPs (TP2, TP7 and TP8) reading fine. Also definitely worth mentioning is pins 16 and 17 reading 10v, which is way too high ! As the left channel slowly starts to fade in and the pins which read too low slowly start to increase, pins 16 and 17 do the opposite and gradually drop down to around 8v, which is enough to give me an output somehow.

It doesn't matter if Dolby is on or off and the line which control its state measures fine too (so C516 too).

Out of sheer curiosity, I swapped C519 with C520, the thinking behind it being that if one was faulty it would shift the fault over to the functional channel, but nothing changed. I also tried gently heating the area with my hot air nozzle to see if the increase in temperature has any effect on any part, but it doesn't - in fact, it seems to make the values DROP even further, so I didn't do that very long.

Q711 doesn't appear to be bad - reads exactly the same as Q712 - plus I also get the indicated voltage on both bases.

If worse comes to worst, I'd start swapping caps around from one channel to the other, maybe even the LC filters - ANYTHING to see the fault replicated on the other channel, provided it's not the chip itself that's bad all along...

It's also not very clear to me how this IC gets power - VCC is pin 42 which DOES read 13v, but I can't tell for the life of me where it's coming from - either I'm not seeing it, or there's an error in the schematic...

[R_J]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Page 45, ic501 pin 42 connects to R530, jumper wire, jumper wire, follow trace which connects jumper wire to C4,R7 (13.5 volt supply) page 46
It's not marked on the schematic

Compare the voltages on LC501, pin 1 and pin 3 to LC503, maybe pin 1 is being taken to ground by c501 or Q501?

[Dannyx]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Page 45, ic501 pin 42 connects to R530, jumper wire, jumper wire, follow trace which connects jumper wire to C4,R7 (13.5 volt supply) page 46
It's not marked on the schematic

Ok, right - got that one out of the way.

Compare the voltages on LC501, pin 1 and pin 3 to LC503, maybe pin 1 is being taken to ground by c501 or Q501?

I measured around that area too, but can't remember any readings right now. I'll have to measure again and write those down too.

I'm trying to work out how that circuit operates: if Q501 turns on, it means pin 1 of LC501 is pulled to GND and if Q503 turns on, C505 is given a path to GND. Because I'm not familiar with radio circuits and the likes, I don't know how LC501/2 should work and what's inside them. I mean I know they're LC filters, so there's probably a coil ("slug-tuned" coil?) and a cap inside those those metal cans, but I have no clue how they're wired to the outside circuit. I see 4 connections, including GND, and looking at a simplified LC filter schematic, there's 3 connections: a common GND, an input and an output, so I don't know how this translates here. Q501 probably pulls something to GND to "defeat" it or "tune it" differently....not sure. I wonder if the LC itself could be faulty internally....

I found a schematic for an Onkyo deck which also uses this chip. I wanted to see if it shows the pinout more clearly and also to see if there are similarities between the two. On page 5, pins 6 and 7 (and 36 and 37 for the other channel), connect to a block called "MPX" inside the chip. On page 12 (you need to flip it 90 degrees to see it better), this one also uses an LC filter, marked as MPX-FILT (L151), placed between pins 6 and 7 and GND. There are no transistors around, hence why I believe the MPX feature on the Onkyo deck is "fixed" (or whatever the correct term for it is) and cannot be turned on/off, while on the Harmann it can, which is what those transistors probably do - they alter the connection between pins 6/7 in such way that it enables/disables the MPX filter. I assume it's not as easy as pulling the pin straight to GND, so the transistors probably alter something inside those LC cansl. The Onkyo is a bit easier for me to follow: one pin of L151 goes to the GND rail, one pin goes to pin 6 and the other to pin 7...standard LC filter. HOW it works, is still a mystery since I don't know what pins 6/7 actually DO !

[R_J]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Have you checked the resistance between pins 3 & 4 of LC501? I wonder if they are connected and the 19khz filter (cap/coil) are connect between 3/4 to pin 1
The only way I can see LC501 causing a problem is if it was internally shorting to ground. If q501 was always on or shorted, it would only insert the filter into the path not kill the signal or the 6v voltage.
Here is a mpx filter from a different cassette machine, you can see what could be in in the can.

[Dannyx]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Ok guys, believe it or not I managed to fix it ! TLDR: C513 was bad.

Detailed version: today I started off by YOLO-ing it and just swapped caps from the good channel over to the bad one, while also measuring them as I went. After going though most of them with absolutely no change, I reached C513/C514 which I completely overlooked at first because when I connected their "output" side (towards the chip) directly to a set of powered speakers, I got sound on both channels, so I thought - nope - those guys are probably fine. Pin 3 DID read slightly lower than pin 39, its equivalent - around 5.7v as opposed to 6.4v, so I thought what the heck - let's swap those too. I removed C513 and plunked it on my tester and it came up with the "unknown component" message....ok....took it out, jiggled it a bit thinking perhaps I didn't get a good contact on there, try it again, this time it DID recognize it as a cap at least, but it just hung there for a good 20 seconds before giving up and showing the same message. Well...I may be on to something here after all. I removed C514 too and threw that one on the tester as well. This guy had slightly high ESR, but at least gave me some clue as to where my problem lies. Without even hesitating, I replaced both of them and tried it out: success ! The voltages came up equally on both sets of pins and I got nice audio on both channels !

From an electronic standpoint, because I don't know how this chip operates, I can't tell for sure how this cap going bad resulted in those values going wacky, particularly pins 17-18 which shot up to 10v ! I'm thinking those caps are there to block DC, but because it failed, pin 3 was being sunk to GND via VR101 and R135, forcing the IC to try and compensate for that SOMEHOW - just a hunch...audio guys may fill me in on this one.

Thanks guys ! Cheers !

[redwire]

Re: Harman Kardon TD202 Tape Deck SLOW boot-up

Hey that's good news! It looks like a decent cassette deck and the big IC you couldn't even buy a replacement back in the day, due to Dolby's bullshit licensing agreements. As if you would buy one IC to take over the world lol.

The IC is composed of several VCA and VCF to do the Dolby encode/decode. Playback, it cuts back on treble at low volume to give you noise/hiss reduction, as well as expanding the signal. Recording, it compresses the signal so that the quiet parts of a song are louder and above the noise floor. There's lots to Dolby B/C- I would say it never worked that great though. Even today surround-sound movies the volume is too low at quiet parts, they are still monkeying around with dynamic range to keep the company relevant.
So most of the IC is DC-coupled and it uses this for the variable gain elements and variable filters to react to signal level. The filters are complex because they are based on the human ear's response.

I would expect those light blue Matushita electrolytics to be end of life, I find they are drying out or leaking, anything from the 80's they are dead. You could offer a recap service to the customer, if the rest of the deck (tape head, belts, capstan bearing) are not worn out.