HK 630 Receiver - FM Issues and Amp Adjustments

[Ylli]

5 and 5' are circled. Are you seeing audio on these points?


This would be the jumper I suggested. Yes, you would only get mono out of one channel.

 

[David_NC]

View attachment 2627194
5 and 5' are circled. Are you seeing audio on these points?

View attachment 2627195
This would be the jumper I suggested. Yes, you would only get mono out of one channel.

Yes, I do get audio with the jumper, though it seems to be at a lower level than from the Aux input, but that's something to investigate once it's working. I take it that this means the issue is likely the MC1307P IC. The pinout for that IC is in the manual; is there any reason to probe those pins to help isolate it further?
Thanks!

 

[Ylli]

Not surprised the audio level is lower. This is some gain in the de-mux. You can go ahead and measure the voltages at each of the 1307's pins, may or may not confirm anything. While you are at it, also measure the voltage's on the B, E,and C of TR304 and TR305.

 

[David_NC]

Not surprised the audio level is lower. This is some gain in the de-mux. You can go ahead and measure the voltages at each of the 1307's pins, may or may not confirm anything. While you are at it, also measure the voltages on the B, E,and C of TR304 and TR305.

I didn't find a Q305, but I did measure 301-304. Values are listed in volts as E - C - B:
301: 0 - 19.7 - 19.7
302: 20.4 - 32mV - 19.8
303: 1.4 - 6.42 - 1.8
304: 1.1 - 6.5 - 1.8

I also measured 1307's pins:
1: 18-20KHz (19KHz first filter)
2: too unstable to measure (19KHz second filter)
3: changes with tuning (audio input)
6: 0V (stereo lamp)
7: good (ground)
9: 13.94V (B+)
10: too unstable to measure (38KHz high)
11&12: changes with tuning (L & R audio output)
13: too unstable to measure (38KHz low)

 

[Mantolaman]

Any progress or updates on this unit?
Forget this, I see that the thread is still very current. Didn't check the dates before posting!

 

[Ylli]

I didn't find a Q305, but I did measure 301-304. Values are listed in volts as E - C - B:
301: 0 - 19.7 - 19.7
302: 20.4 - 32mV - 19.8
303: 1.4 - 6.42 - 1.8
304: 1.1 - 6.5 - 1.8

OK, the layout shown in the manual does not match the schematic shown in the manual. Q301-Q304 match the layout drawing. Typical... The voltages on Q303 and Q304 look OK. Q301 and Q302 are questionable. The board receives only +14 volts, how do we get the about 20 volts you listed for these? Please recheck.

I also measured 1307's pins:
1: 18-20KHz (19KHz first filter)
2: too unstable to measure (19KHz second filter)
3: changes with tuning (audio input)
6: 0V (stereo lamp)
7: good (ground)
9: 13.94V (B+)
10: too unstable to measure (38KHz high)
11&12: changes with tuning (L & R audio output)
13: too unstable to measure (38KHz low)

Are these 'scope measurements? Was actually just looking for DC voltages measured with your digital voltmeter. Do all the pins, even those that seem not to be used.

 

[Ylli]

Q301 and Q302 are questionable. The board receives only +14 volts, how do we get the about 20 volts you listed for these? Please recheck.

Never mind. This +20 is coming through the stereo indicator lamp. The voltages on Q301 still don't look right - per your measurements I see zero on the emitter and +19.7 on both the collector and base. That is not normal biasing and with +19.7 volts on the base feeding back to the MC1307P pin 14 might be disabling the 1307 - and may or may not have damaged it.

Remove Q301 from the board and see if you now get audio through the MPX board.

 

[David_NC]

Never mind. This +20 is coming through the stereo indicator lamp. The voltages on Q301 still don't look right - per your measurements I see zero on the emitter and +19.7 on both the collector and base. That is not normal biasing and with +19.7 volts on the base feeding back to the MC1307P pin 14 might be disabling the 1307 - and may or may not have damaged it.
Remove Q301 from the board and see if you now get audio through the MPX board.

Will do. Is it necessary to completely remove Q301, or can I just remove one leg? I'll check pin 14 again. Thanks!

 

[David_NC]

Are these 'scope measurements? Was actually just looking for DC voltages measured with your digital voltmeter. Do all the pins, even those that seem not to be used.

I listed voltages on most (from my meter), but I tested some with the scope, too, since that's what was listed for those pins. I checked every pin on the1307; the ones I didn't list have no signal and aren't labeled in the diagrams.

 

[Ylli]

You can just lift the transistor pin (base) that goes to the 470 ohm resistor R310, or lift one of the legs of R310.

 

[Ylli]

For reference - Rather than driving the stereo indicator lamp from pin 6 of IC301, it is driven from pin 14 via the attached circuitry.

 

[David_NC]

You can just lift the transistor pin (base) that goes to the 470 ohm resistor R310, or lift one of the legs of R310.
View attachment 2631028

I lifted the lead from Q301 and got audio, though it's really bad quality and only works when in FM Stereo mode on the selector, not on FM. I measured all the pins on 1307 again. Here they are:

1: 13.45V
2: 3.19V
3: 4.01V
4: 0V
5: 0V
6: 0V
7: 0V
8: 13.89V
9: 13.94
10: 4.93V
11: 11.58V
12: 11.6V
13: 4.94V
14: 0V​

 

[Ylli]

Does pin 14 stay at zero even if you tune through strong station?

 

[David_NC]

Does pin 14 stay at zero even if you tune through strong station?

It does.

 

[Ylli]

We're up to about 80% chance it is a defective MC1307P. All the other voltages on that chip look *reasonable*, except for that in 14. I'm throwing together a quick LTSpice sim to confirm those other voltages as good, but won't have that done until tomorrow.

 

[David_NC]

We're up to about 80% chance it is a defective MC1307P. All the other voltages on that chip look *reasonable*, except for that in 14. I'm throwing together a quick LTSpice sim to confirm those other voltages as good, but won't have that done until tomorrow.

Well, at least it's an available item, if it does need replacement. I just looked up LTspice... that's really cool!

 

[Ylli]

I'll need you to fully pull Q301 and test it with your Digital meters 'diode' range. If you don't know how to do this, here is one of many tutorials:

.
I suspect you will find a collector to base short and an open emitter. Let me know the results. I suspect that the collector to base short channeled excess voltage back into the MC1307P chip and damaged that also.

So you will need two parts.

MC1307P or equivalent. Two options here - ebay has some listing, but they would all be coming from overseas. Shipping could take a long time, and some of the products shipped from China are of dubious quality. The NTE722 is an equivalent. NTE parts can sometimes be problematic, but most of the reports I have seen indicate this one works well to replace the MC1307P. I found:

https://www.ntepartsdirect.com/ENG/PRODUCT/NTE722
https://vetco.net/products/nte722-ic-fm-stereo-demodulator
https://www.electronicsurplus.com/nte-electronics-nte722-ic-fm-stereo-multiplex-demodulator
I am sure there are other sources too.

Q301 is listed in the manual parts list as a 2SC828. I'm going to recommend an NTE199 mostly because it has the right pinout and should be available from some of the same sources as the NTE722. It is a pretty generic NPN, and almost anything with a voltage rating of 30 or better would probably work, but if you go with something else, use caution on the pinouts.

 

[David_NC]

I'll need you to fully pull Q301 and test it with your Digital meters 'diode' range. If you don't know how to do this, here is one of many tutorials:

.
I suspect you will find a collector to base short and an open emitter. Let me know the results. I suspect that the collector to base short channeled excess voltage back into the MC1307P chip and damaged that also.

So you will need two parts.

MC1307P or equivalent. Two options here - ebay has some listing, but they would all be coming from overseas. Shipping could take a long time, and some of the products shipped from China are of dubious quality. The NTE722 is an equivalent. NTE parts can sometimes be problematic, but most of the reports I have seen indicate this one works well to replace the MC1307P. I found:

https://www.ntepartsdirect.com/ENG/PRODUCT/NTE722
https://vetco.net/products/nte722-ic-fm-stereo-demodulator
https://www.electronicsurplus.com/nte-electronics-nte722-ic-fm-stereo-multiplex-demodulator
I am sure there are other sources too.

Q301 is listed in the manual parts list as a 2SC828. I'm going to recommend an NTE199 mostly because it has the right pinout and should be available from some of the same sources as the NTE722. It is a pretty generic NPN, and almost anything with a voltage rating of 30 or better would probably work, but if you go with something else, use caution on the pinouts.

I'll pull Q301 and test it, assuming one of my meters has a a diode setting. Amazon has both the NTE722 and the 199 with free Prime delivery, so that's handy. Thanks!

 

[David_NC]

@Ylli
I pulled and tested Q301.
B>C = .649V
B>E = .655V
I get no continuity between any pins.

 

[David_NC]

I'll need you to fully pull Q301 and test it with your Digital meters 'diode' range. If you don't know how to do this, here is one of many tutorials:

.
I suspect you will find a collector to base short and an open emitter. Let me know the results. I suspect that the collector to base short channeled excess voltage back into the MC1307P chip and damaged that also.

So you will need two parts.

MC1307P or equivalent. Two options here - ebay has some listing, but they would all be coming from overseas. Shipping could take a long time, and some of the products shipped from China are of dubious quality. The NTE722 is an equivalent. NTE parts can sometimes be problematic, but most of the reports I have seen indicate this one works well to replace the MC1307P. I found:

https://www.ntepartsdirect.com/ENG/PRODUCT/NTE722
https://vetco.net/products/nte722-ic-fm-stereo-demodulator
https://www.electronicsurplus.com/nte-electronics-nte722-ic-fm-stereo-multiplex-demodulator
I am sure there are other sources too.

Q301 is listed in the manual parts list as a 2SC828. I'm going to recommend an NTE199 mostly because it has the right pinout and should be available from some of the same sources as the NTE722. It is a pretty generic NPN, and almost anything with a voltage rating of 30 or better would probably work, but if you go with something else, use caution on the pinouts.

Is it safe to go ahead and replace MC1307P, even with Q301 testing OK, or should both be replaced anyway? I'm probably going to use a socket for the IC. Doing so will make it much easier to replace again if there are any compatibility issues with it, or if it is damaged from another component.