[EdHolland]

...But only minor.

Over the holiday weekend, I made some use of my Yaesu FRG8800 https://www.eham.net/reviews/view-product?id=807

When we travel up to Northern Cal, I like to take a different set form the collection each time, as I can spend a bit of time listening while up there, and spend some quality time with the radios in turn.

Anyway, on AM, I noticed that the tuning band pass is a little shifted, meaning that one has to go a kc or so lower than the channel frequency to get the best audio. Now I know the set 's oscillators are aligned, as tuning in on SSB gives zero beat when the dial reads the station frequency. It looks like one of the crystal filters has drifted off center frequency with age - a bit like not having the IF transformers properly peaked, but the crystals are not adjustable... Since it is really noticeable in the wide bandwidth setting, this points the finger at a specific filter. Interestingly enough, I had a very similar but more severe issue with another radio, and the filter appears to be from the same series. Finding exact replacements is hard, but on the other set, I was able to make a small piece of perf-board to mount an electrically equivalent filter, and connect this to the main board with very short wire legs. The harder work will be to extract the main board from the radio - I already have a filter that will work. Before starting, I'll "jump" the filter with a small cap, which should confirm that it is the culprit.

The FRG8800 is a nice set, and I got this one as a pretty good deal a few years ago. In particular, it has good audio from a front facing speaker. Last weekend it was receiving Radio New Zealand (13,840 kHz) very happily on a small loop of wire strung around the living room window frame.

I tend to think of this 80's-90's era of radios as modern, but they are rapidly becoming classics. Restoration comes with some new challenges compared to our "tube" favourites, but they can be kept in service to good purpose. Nothing like them is made nowadays.

Cheers

Ed

[Simon Wa3uay]

Similar to yours Ed, I have a Kenwood R2000 that I have on my nightstand and listen to each night; but it has a ‘digital phosphor’ display, as opposed to your ‘digital LCD’ display. Mine needs to tune about 100 to 150 cycles up to sound correct on SSB: also, the ‘RF gain’ is not continuously variable, but other than that, It’s a very good receiver. I has however, developed a weird sort of feedback oscillating sound on certain frequencies that can be tuned out but makes me wonder if capacitors are getting old (or something) -Simon

[EdHolland]

Hi Simon,

I have thought about getting an R2000 for my collection as well - they have a great reputation.

Your radio could probably respond well to alignment, which would almost certainly correct the small frequency offset. Weird feedback could be an oxidised connector or something similar. One of my radios had a feedback issue that I traced to oxidation under a PCB shielding can - there was an intermittent contact that responded to audio vibration from the speaker. The R2000 service manual is available on-line https://www.manualslib.com/manual/982832...-2000.html

Cheers

Ed

[EdHolland]

With the covers off, it was immediately clear that there was quite a bit of preparation needed before accessing the main board. The first order of business was to label the wire harness elements with the corresponding connector numbers - quite a few must be detached to remove and turn over the PCB. That is now completed, and I can see the solder side of the board. That lets me note the pin-out configuration of the filters. One test I could do is to bypass a filter with a 2k resistor, which will help ID the culprit. That approach worked very nicely on the other radio which had a similar problem.

Cheers

Ed

[EdHolland]

I made another interesting discovery while taking notes on this radio yesterday. Last weekend, it was noted that the high impedance antenna connection was not providing very good sensitivity on the short wire I was using. It ought to have been the best option. The antenna terminals - spring clips and an SO-239 socket are attached to a small PCB. This assembly should also have a 9:1 impedance transformer, but mine doesn't. It is clear that the component was never soldered in to place, as the traces are still bare copper!

So, another task will be to attempt to make and fit a suitable transformer.

[EdHolland]

I tinkered at the weekend. With the board out of the radio, I was set to bypass some filters, to help identify troubles. On the underside of the board area where the 2.7 and 6 kHz filters are located, there was a block of foam rubber, adhered to the board using double sided tape. This took quite a bit of effort to remove, carefully picking the tape off with tweezers and then cleaning the residue. That made me consider if the residue was causing troubles, and pressing the meter probes on the foam rubber showed some current leakage (Ohms mode) and also nanofarads indication on the capacitance setting (leakages will sometimes appear as high capacitance). So, before doing anything further, the radio was returned to operation and the band-pass characteristics were checked. At first, everything seemed perfectly aligned, so I left the set running for an hour or two since it does warm up and drift a few hundred Hz when checked against WWV. Assessing it again after this, it seemed as if the slight downwards shift in pass-band had returned. Next up is to work out if this is systematic i.e. related to the frequency drift, or if there is a real change in the 455 kHz IF passband.

Who says modern can't be fun

[EdHolland]

More investigations over the weekend. The symptoms look like a passband shift. However, I got sidelined trying to complete an alignment. My cheap frequency counter module is not that reliable on some of the PLL circuits, so I have ordered a better instrument from the selections available on Ebay. It is something I wanted anyway, and should make life easier. After that, it will be back to diagnosing the IF

[EdHolland]

Hi Folks,

It has been a while since posting here on the Phorum, but I am still a radio tinkerer. Work on this Yaeusu side-tracked into doing a fresh alignment, and that side tracked into buying a frequency counter to add to the instrument shelf. I found a nice used LG counter, 9 digit precision and high stability reference for a good price on the auction site. So it is back to setting up the radio, then re-evaluating where the mis-alignment lies, if indeed it is still present. Further to that, since it is just a small "squint" in the passband, apparent only in the AM mode, it may not be worth going to the trouble of addressing it. at all. SSB and narrow AM are unaffected.

Cheers

Ed

[EdHolland]

With the smoke and horrible air quality here, I spent some time on alignment of the radio this morning. Another odd question has been answered. I worked on alignment of this set when I received it a couple of years ago. All seemed to go well, and I put down to drift, the fact that it needed the "Fine" tuning control to be adjusted to get the set to be spot on frequency e.g. zero beat on WWV.

This always puzzled me, because there were other reasons this didn't seem quite right. What was more strange, the USB and LSB modes seemed to be off by the same amount, so the problem couldn't be an error in the BFO frequencies, could it?

Yes - it could!! You see, I had been using one of the inexpensive frequency counter modules - discussed in a thread on test equipment a little while ago. Today, it's bad habits were exposed by my "new" counter. Both BFO adjustments were off by a good 300 Hz. Aligning with the new counter, the radio is spot on frequency

[EdHolland]

The auction site turned up the goods I found a replacement antenna input board which has the 9:1 impedance transformer fitted

[EdHolland]

Antenna input board arrived last week. We're travelling for the holiday weekend, do no radio work, but I did inspect the new part and it has all the components.

Ed

[EdHolland]

I managed time to work on this radio yesterday. The main board for the PLL oscillator section had to be moved to extract the old antenna connection assembly and replace it with the new part. With the two connector units side-by-side, it was evident that not only was the Hi-Z antenna transformer missing, but also the static protection diode. Somehow, this board missed part of the assembly line!

With the substitute board in place, all the antenna connections worked as advertised, presumably for the first time since this radio left the factory ~ 30 years ago. After this check, I went back to focus on the off-center filtering in the 455 kHz IF. Another pass through the alignment of this section seems to have improved the response, but it is a subtle effect, so will require more testing. I did find that my stock of parts has a possible replacement for the wide (6 kHz) ceramic filter if needed. I hope this won't be the case, as removing the circuit board is quite involved.

Ed

[EdHolland]

Here we go. Spot the difference?

   

[EdHolland]

I spent a little time with this radio yesterday, trying to track down the initial problem which seemed to be a misalignment in the 455 kHz IF. It is quite reproduceable, and at first, seemed to be apparent only with the radio in AM mode, and using the wide audio filter. It sounds slightly more "tuned in" and indicates slightly higher signal strength with the dial set ~ 1-1.5 kHz below the true carrier frequency. With eyes closed, if one rocks the dial and listens for best tone, the result is the same.

The general scheme of the IF is as follows. Just like a tube radio, there are several filter/amp stages:
1st IF is mixed down to 455 kHz>Transformer>20 kHz crystal Filter>Noise blanker>Transformer>6kHz or 3 kHz filter>2 Stages of amplification>Detector. The output from the last IF amp is also buffered and detected seperately to generate the AGC line.

I went through the alignment stage another time yesterday, and may have made an improvement, but I still think something is not quite right. OCD is the enemy of good enough and I like the detective work. Investigation shows that the effect occurs with either the wide (6 kHz) or narrow (3kHz) filter, not just the 6 kHz as first suspected. I tried injecting a 455 kHz signal at various points along the IF chain, thinking this might expose the culprit. One suspect could be the 20 kHz crystal filter - I have seen one other case where a part of this vintage and manufacture had gone bad. However, injecting downstream of this filter, and tuning the 455 kHz signal +/- 2 kHz also seems to show the offset.

I am now back to a close study of the circuit, to see if there is anything else amiss! This is one situation where an IF sweep tool would be very useful.

[EdHolland]

Backwards and forwards yesterday. In my kit of spares, I found one IF filter that would fit the first 455 kHz stage as a direct replacement. This was tried and made no difference whatsoever. In touching up the alignment, it was possible to get the S meter to be peaked at the exact carrier frequency, which had previously been slightly off. However the "tuned for best sound" point is still askew when using the AM wide filter. So I'm back to the opinion that the wider of the two filters in the 2nd IF stage is off centre. The narrow filter, also used for SSB, is in fine condition.

A determined search has found the required part - even these 80's & '90s parts are becoming quite scarce. I have 12 kHz bandwidth filters that could work, but they are not the correct pin-out.

/Ed