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Old 17th Apr 2015, 4:58 pm   #1
davidgem1406
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Default Sanyo 17H-815 Problem

I have a Sanyo radio model 17H-815 on my bench that a friend asked me to look at for him as it has a problem.

On AM (LW & MW), I did not check the SW bands, it is unstable when tuning to a station as it reaches the station it starts to squeal and peaks as the station comes to it's tuning point.
It squeals between stations but at a much lower level.

FM is working so all that is out of the equation, I hope.

The chassis has been removed from the case and the first thing I did was to clean the band switches as they were sticky, particularly the FM switch.

When I powered it up I was met with total silence from all but the LW band that continued to howl, MW and SW bands were silent.

I have the service data (I have included it here) so started to check it out and it looks to be quite a complex radio all in all. Maybe it just looks more complex than it is in reality.
First I decided that I would check the operation of the IF strip, meaning I had to remove the scale pointers and back plate, then the auxiliary input/output and switches plate at the rear to gain access.

455KHz was injected into the base of Tr 7 (AM Mixer) but I had no output, the same applied to Tr 9.
I removed the termination pad and connected the generator directly. And again injected 455KHz with the full output of the generator (100mV or so) I had an output although it was quite a low level, especially as the volume was at full output.
The output from the generator was reduced and the volume output started to rise. I assume that AGC action was holding it back.
As the generator output continued to reduce it hit a point where the radio just went totally unstable and remained that way until the generator output was just to low.

I thought originally that the problem was probably within the radio front end (Tr8 Oscillator or Tr7 Mixer) but now im rather unsure about what is the cause of this instability.

As a foot note this radio is not a pick-nick to work on either. I have included pictures of the chassis.

Any help would be much appreciated.

Thanks Dave.
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Old 18th Apr 2015, 6:23 pm   #2
Herald1360
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Default Re: Sanyo 17H-815 Problem

FM does look to be out of the problem since there seem to be completely separate AM and FM RF/IF sections in the set.

The tuning drive arrangements wouldn't disgrace Philips either

At a guess, the problem may have something to do with decoupling or rather lack of in the AM IF strip. Possibly exacerbated by the odd grounding arrangements- positive earth for the PNP audio amp and complicated decoupling arrangements for the NPN RF/IF stages. Take a close look at all the caps approximately across the middle of the circuit diagram decoupling the emitters and collector feeds. Also any dry joints.
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Old 18th Apr 2015, 9:59 pm   #3
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Default Re: Sanyo 17H-815 Problem

Hello herald1360,
Thanks for the reply.

I had considered the IF decoupling capacitors and bridged each one by a replacement. I did not remove the existing ones. C120, C125, C128, C132, C133, C135.
I also replaced Tr7 (Mixer) as this is a Germanium device, the only one in the set.
All resulted in no change whatsoever.
I found no dry joints to date.

I shall now be replacing Tr8 (Oscillator) as I can see no where else to look at for now.

Regards Dave.
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Old 18th Apr 2015, 11:24 pm   #4
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Default Re: Sanyo 17H-815 Problem

I agree with 'Herald' and in addition, although he's hinted at it with the 'dry joints' just check those low value inductors on the power lines - I've known these not only to be dry jointed in the boards but to go high resistance themselves ( I suspect the wiring tarnishes where it meets the compont's leg ). In any case they're worth a look.
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Old 19th Apr 2015, 9:42 am   #5
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Default Re: Sanyo 17H-815 Problem

Have to agree with you David, these are 'fun' to work on. I have a couple of the '18' version, one with no FM and it's always been a case of taking the back off, peering inside and pondering if I can be bothered to undo all the connections. Good sound though and well built. Please let us know how you get on.

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Old 20th Apr 2015, 4:40 pm   #6
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Default Re: Sanyo 17H-815 Problem

Hello All.

Nick,
I did check the inductor in the AM supply rail (L17) it was OK at 6R.

Not really gaining any progress this is what I did to try and gain at least some ground with this thing.

First I removed Tr7 and Tr8 and was greeted with total silence, as expected. Then proceeded as follows:

Note: Ignore the FM band as this is working. Bear in mind that switch positions are shown in the FM position.

1/. Checked the IF strip again but this time injected the signal at the top of T13. Although the volume was down to what I expected it was quite stable without oscillation.
2/. I noticed that operating the LW switch an audible click was heard from the speaker, all other AM bands produced nothing.
3/. Refitted Tr7 the oscillations return LW only other bands silent
4/. Lift the wire from Tr7/b to S5/e silence on all bands. Refit the wire.
5/. Lift wire from S4/c to R30 (LW selected) still oscillating
6/. Lift wire from S5/f to R31 ( “ “ ) Silence.
Reconnecting either wire results in the return of the oscillation.

Now I decided that there was a feedback path causing this oscillation to occur. Looking at the wiring diagram we find that the base of Tr7 goes to S5/e and on to S4/b. If LW is selected it then goes to R30 and on to T13 completing the loop
It is actually from Tr7/c through the loop back to Tr7/b.
Why this does not oscillate when MW is selected as the same circuit applies except via R31 must be down to the value of the coils/capacitor combined values in the input tuning circuits.

I was now looking for something quite obscure, to me anyway.
All I kept coming back to was the connections to the tuning meter between T13 (AM IF) and T5 (FM IF) that was o/c as the meter was still in the cabinet (not removable)
.
7/. I measured the meter resistance, even though I thought it was completely daft, and fitted a resistor (330R) across PJ5 and PJ6 in place of the meter.
On switch on I was greeted with tunable noise on all AM bands but no oscillation.
8/. Refit Tr8 this brought back the original fault that was present before the chassis was removed from the cabinet. Instability/oscillations on all AM bands with stations that can be heard in the background.

I now have to try to find the reason for this and any help would be appreciated.

There are errors in the drawings both the circuit diagram and the layout.
The oscillator tuning does not look correct to me as VC5 and VC6 are connected to +Ve, in this set that is ground so how does this enable tuning of the AM bands.
Is the drawing correct or not?

Regards Dave.
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Old 20th Apr 2015, 7:21 pm   #7
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Default Re: Sanyo 17H-815 Problem

Dave

There's a lot of push buttons there, presumably for band selection. I would take another look there before delving any further.

The FM is still working probably because the owner used had it on that band only for years?

However, I have known ageing leaky electrolytics creating a s/c which then takes out the osc/mixer tranny...........

Have fun.

73
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Old 20th Apr 2015, 9:06 pm   #8
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Default Re: Sanyo 17H-815 Problem

Hi Richard,

Yes a lot of switches for band selection, they have all been cleaned twice.
I did try to make checks on the operation of each set of contact but basically a waste of time as it was proving nothing.
There are just to many coils connected to them that make readings across the contacts meaningless. The only way would be to disconnect all the coils and that is a real major strip down job.

The oscillator and mixer transistors have been checked electrically and by replacement.
Decoupling electrolytic's that could have been a problem have been checked.

All mentioned in earlier posts.

Thanks Dave.
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Old 21st Apr 2015, 4:52 pm   #9
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Default Re: Sanyo 17H-815 Problem

Well after my fiasco with the tuning meter needing to be in circuit for the LW oscillations to be resolved and the remaining AM bands to come back to life I have continued to try and resolve the original problem as mentioned in my previous post #6.

Before I continue with the current problem I would like to mention a bit more about requiring the tuning meter (Equivalent resistor in this case) to be in place for the set to work.
As I see it the meter somehow completes the path that produces the base bias for Tr7 (Mixer) and this seems a very strange way to do things.
Maybe I am a mile of target with that and somebody may be able to correct me if I am.
It also seemed to increase the sensitivity of the FM band.

Back to the task of resolving the original problem, I have solved it.
It turns out to be one of the electrolytic's C135.
I had bridged this out previously in my attempt to stop the oscillations on the MW band but it had no effect.
My belief is that as these oscillations were actually being generated by a feedback loop, and in effect were real, so the capacitor was having no effect anyway.

Now I think it would be prudent to replace all the electrolytic capacitors in this set as it could save future problems. Out with the order pad then!!

Still quite a lot of work to do then, before it can go back in the cabinet and be wrapped up.
When it is all done I will come back and add the final comments.

Meanwhile I will keep a lookout for any posts that might be added.

Regards Dave.

Last edited by davidgem1406; 21st Apr 2015 at 4:53 pm. Reason: Add # number of previouse post
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Old 28th Apr 2015, 7:27 pm   #10
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Default Re: Sanyo 17H-815 Problem

Nice radio, and well done on tracking down the fault!
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Old 1st May 2015, 4:20 pm   #11
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Default Re: Sanyo 17H-815 Problem

Hello all,

I am now in the process of replacing all the electrolytic capacitors, those I can get to without a total chassis strip down.
So far I have removed those that are in the AM and FM circuits and started replacing them.

I have come across a problem that I could do with some help on in as much as I believe the circuit diagram is incorrect for the FM circuits, it appears to have no +Ve rail.
That has given me a problem with C35 as the layout diagram does not show the polarity for this capacitor, nor does the circuit diagram indicate the + or - polarity for electrolytics.

The problem with the circuit diagram is that everything for the FM circuit, except Tr2, seems to go back to the battery -Ve. I will explain.

If we look at the FM front end and to R1 this is connected to 2 rails, the lower going to L4.
If we follow this rail from L4 to L6 and on to L7 it then goes to switch contacts 14 d/e/f. from contact e it connects to a point on the audio preamp.
Then going via R75 and R89 to the Adaptor/Battery changeover switch, to battery -Ve via the On/Off switch.

So both rails are at -Ve because they show as being joined below R1.

Having said that I see no way that the +Ve arrives at Tr1, Tr3 to Tr6. But does arrive at Tr2.

I could just assume that C35 is the same way round as C29 and C33, apart from it being connected across -Ve to -Ve

As the +Ve is in effect the common rail I would have expected to see the common points of the external auto antenna and the MPX jack socket going to the +Ve rail.

Thanks Dave.
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Old 1st May 2015, 4:34 pm   #12
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Default Re: Sanyo 17H-815 Problem

Hi Dave,

Looks like there is an extra dot on the line where the wire from R1 going to L4 crosses the ground line. If you take that dot (junction) out, the supply is fine.

Peter
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Old 1st May 2015, 8:35 pm   #13
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Default Re: Sanyo 17H-815 Problem

Hello Peter,

Thanks for the reply.

Yes I had considered that the dot joining R1 to the upper rail was not supposed to be there. That would separate the 2 rails making the lower rail the -Ve, seems sensible.

However the upper rail would have no supply at all as I cant find a supply connection.
As the FM is working maybe the supply connection has been omitted from the drawing.

Regards Dave.
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Old 2nd May 2015, 11:55 am   #14
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Default Re: Sanyo 17H-815 Problem

Hi Dave,

Yes, that schematics sure looks funny! The whole way it is presented!

It looks like that there is a dot (junction) missing, giving ground to that line there. It is the line going down from the "half" pot R12, below T4. There should be a dot there to the same line they had that extra dot on. That would give ground to the circuits there.

Regards, Peter
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Old 2nd May 2015, 12:48 pm   #15
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Default Re: Sanyo 17H-815 Problem

Hi Peter,

Yes the diagram is confusing the way it is laid out and using 4 point junctions is not good practice. One is never really sure if it is a junction or a crossover.
Maybe it is the standard way for Japan to draw circuit diagrams??

As you say the crossover below R12 if made a join would solve the problem.

I will try to verify things and then correct the original service info, if possible, and post the result.

Thanks very much
Dave.
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Old 14th May 2015, 10:02 pm   #16
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Default Re: Sanyo 17H-815 Problem

I have now completed this receiver with all the electrolytic capacitors being replaced.

The capacitors in the RF/IF section were the first to be replaced and that took care of the largest PCB. After replacement I checked the working state and all was working.

A word of caution here. This board is quite difficult to work on. Not only are there a lot of wires crossing the printed track but also the AM/FM tuning drive cords are in the way.
The tuning drive cords are the biggest danger as I sadly found out when I touched the AM cord with the soldering iron.
There is no second chance here the damage is instantaneous.

Next I tackled the audio output board, not to bad but a lot of wires in the way.
After replacing these again I checked the functionality, all working fine.

Then came the audio preamp board. This had to be down wired and removed completely to gain access to the track side of the board. There is no other way.
The electrolytic capacitors were dully replaced and the board refitted and wired up. On checking everything worked well on all channels with good reception and volume, for a short while. Then there was a loud crackling and the volume dropped significantly with a constant crackling.

Obviously my first thoughts were that I had done something whilst changing the caps on the preamp board.
First I made a thorough check that all the wiring had gone back correctly. This took some time checking against the circuit diagram (this was not correct anyway), the drawing I made before stripping out and the photo I took.
I concluded after some time that all was correctly assembled.

Now it was going to be difficult to pin down this problem as there is absolutely no information given on the circuit regarding voltages.
Anyway I gave it up for the evening. Later lying in bed I was thinking about this and suddenly thought I needed a signal tracer but I don't have one.
Gave over and went off to sleep.

In the morning I looked into what I could use as a signal tracer and came up with a powered speaker unit, the type used for a PC, made up a jack socket with connecting leads, 1 with crock clip and the other a prod, to plug the speaker into.

I then started at the input to the preamp and tuned in a usable station. Working my way through the preamp staged right up to the output and all was fine. Plenty of signal being supplied to the output stage.

Checking through the output stage to the base of Tr-15 there was plenty of signal but at the collector very little, I removed the transistor for checking.
It turned out to be absolutely fine, however I did notice that the solder on the ends of the wire looked rather grey and dull, then thought no more off it and put it back in place.
On switch on it was all back to normal and remained so no matter what I tried to do to it. It went back home last weekend and still works fine.

I can only put it down to the solder having degraded over time although it did not look that way whilst removing it, ah well!!

During the time I spent working on this radio several errors were found on the circuit and the layout/wiring diagrams
These I have corrected on the original pdf so have added a replacement and corrected copy here if anybody has use for it.

Regards Dave.
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