Kenwood R5000 gone weird on LSB - UK Vintage Radio Repair and Restoration Discussion Forum

simonjp · 21st Mar 2017, 10:00 pm

Hi folks.

Just wondering if anyone has any pointers for my r5000 that has gone peculiar on LSB.

The other week I set about trying to improve the dim digits on the very bottom of each and every digit. I did manage to make some improvements.. The front display is a right bitch to get to and involves removal of the 2 inner pcbs behind the vacuum display module.

When I finished and rebuilt the receiver, it was working fine on USB, however on LSB it sounds awful, just as if the signals are going through an extremely narrow filter and of low amplitude.

The W position ( on LSB) is the only position where it is just possible to resolve a signal.. The same position should be selected when in Auto mode, but it isnt, it sounds narrow and unreadable.

The USB mode works normally.

I was so convinced that the filters were not being selected properly, that I decided to check the cathodes of each diode that switches in the filters, and they seem to be correct.
It also makes no sense, since the correct selection of filter is done in USB mode, and works fine as I said above.
The filters should be the same whether in lsb or usb, so I ruled out that fault.

Can anyone think what might have happened, during disassembly of the front panel and subsequent rebuild that would cause this problem.

Any help would be appreciated.

Best 73

Simon

Andrew2 · 21st Mar 2017, 10:54 pm

Could it be the carrier insertion osc which has moved off frequency in LSB? I'm not sure how the two freq's (USB and LSB) are generated in the 5000, but given its age I would guess it is either two separate ocs or one osc with two selectable xtals, each with a trimmer.
My first move would be to check the frequency of this oscillator in LSB mode.

Station X · 21st Mar 2017, 10:56 pm

The service manual can be found here:-

http://www.iw2nmx.it/Kenwood%20-%20T...e%20Manual.pdf

Andrew2 · 21st Mar 2017, 11:11 pm

Cor! Looking at that, the BFO cct is quite a thing in itself! And here's me thinking it was just a dicky trimmer...

g4aaw pete · 22nd Mar 2017, 1:44 am

Whilst removing & refitting the control PCB at the front panel area of the receiver, I noted how easily the wirelooms can be pinched between fixing posts. Wonder if this could have happened during reassembly of yours?

Regards
Pete.

simonjp · 22nd Mar 2017, 8:53 am

thanks all for help so far.

Pretty sure that there are no wires trapped.

Yes, the cct is more complex than average and the workshop manual is a help but I am finding that the cct spread over countless pages is tiresome.

I will take a more detailed look at how the ssb is generated, but I had a quick glance and thought it was derived from a "divide by" chain.

John KC0G · 22nd Mar 2017, 3:16 pm

There is a block diagram of the PLL unit in figure 2 of page 3 of the service manual. The BFO signal is generated by its own PLL, followed by a division of 200 and then a mixer.

Given that the radio works OK on USB, this might be a good way to start. Are you able to measure the frequency of the BFO signal, either on the PLL board or near the detector, for both USB and LSB?

HTH and good luck

73 John

simonjp · 22nd Mar 2017, 8:38 pm

Update.
Great suggestions all, John's guidance led me to the PLL.. It was 600khz out.
Seems as though the logic which tells the PLL what to divide by, is screwed.

Looks like the 4 bit source originates from one of the front panel pcb's.

Now hunting for damaged tracks etc.

thanks all

Station X · 22nd Mar 2017, 10:39 pm

I've found a Logic Probe to be useful when tracking down these type of faults.

John KC0G · 23rd Mar 2017, 5:59 am

Well done on finding that the fault is somehow related to VCO4.

I assume that the 600kHz error is at the output of the VCO before the divide by 200 divider. Which way was the error - was the output frequency too low, in which case it would have been close to the USB frequency, or was it too high ?

I think that there at least two possible problems:
i) as you surmised, the PLL is not being told to do the right thing
ii) the PLL is running out of control action, and the control voltage is at the minimum, or at the maximum of its range.
If it is easier, I would check the VCO control voltage first

73 John

simonjp · 23rd Mar 2017, 5:50 pm

Hi John

Back from the salt mine, so able to continue on the r5000.

the frequency was 34.9744 Mhz and I think it should be 34.3Mhz

73

simon

John KC0G · 23rd Mar 2017, 10:43 pm

Hello Simon

I also think that it should be 34.3MHz. I presume that PLL gives 33.7MHz on USB ? If so, the VCO can cover the range, and then what - bad data?

Good luck and 73

John

simonjp · 23rd Mar 2017, 11:33 pm

Hi John.

Yes, USB is fine... I've given up for tonight, I hate the service manual.. So many schematics cut in half and on different pages, makes it very difficult to follow the circuit.

I have identified that it all "kicks off" from A0 and A1 of the 7800 microprocessor.

I am trying to trace the cct from their, forwards to the pll.. Mainly cos I just cannot get my head around how the damn pll works with that "swallow" counter..

Bit out of my depth their, so I am hoping that I might find a broken wire whilst I am tracing the logic from the uP.. instead of banging my head against a wall with the PLL.

I'll give it a few more days, thenif I cant find it I'll move the radio into the sales section and get shot at a bargain price, or scrap it... It seems that even the case, knobs etc fetch good money.

21st Mar 2017, 10:00 pm	#1
simonjp Tetrode Join Date: Sep 2014 Location: Lewes, East Sussex, UK. Posts: 55	Kenwood R5000 gone weird on LSB Hi folks. Just wondering if anyone has any pointers for my r5000 that has gone peculiar on LSB. The other week I set about trying to improve the dim digits on the very bottom of each and every digit. I did manage to make some improvements.. The front display is a right bitch to get to and involves removal of the 2 inner pcbs behind the vacuum display module. When I finished and rebuilt the receiver, it was working fine on USB, however on LSB it sounds awful, just as if the signals are going through an extremely narrow filter and of low amplitude. The W position ( on LSB) is the only position where it is just possible to resolve a signal.. The same position should be selected when in Auto mode, but it isnt, it sounds narrow and unreadable. The USB mode works normally. I was so convinced that the filters were not being selected properly, that I decided to check the cathodes of each diode that switches in the filters, and they seem to be correct. It also makes no sense, since the correct selection of filter is done in USB mode, and works fine as I said above. The filters should be the same whether in lsb or usb, so I ruled out that fault. Can anyone think what might have happened, during disassembly of the front panel and subsequent rebuild that would cause this problem. Any help would be appreciated. Best 73 Simon

21st Mar 2017, 10:54 pm	#2
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,037	Re: Kenwood R5000 gone weird on LSB Could it be the carrier insertion osc which has moved off frequency in LSB? I'm not sure how the two freq's (USB and LSB) are generated in the 5000, but given its age I would guess it is either two separate ocs or one osc with two selectable xtals, each with a trimmer. My first move would be to check the frequency of this oscillator in LSB mode. __________________ Andy G1HBE.

21st Mar 2017, 10:56 pm	#3
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Kenwood R5000 gone weird on LSB The service manual can be found here:- http://www.iw2nmx.it/Kenwood%20-%20T...e%20Manual.pdf __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

21st Mar 2017, 11:11 pm	#4
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,037	Re: Kenwood R5000 gone weird on LSB Cor! Looking at that, the BFO cct is quite a thing in itself! And here's me thinking it was just a dicky trimmer... __________________ Andy G1HBE.

22nd Mar 2017, 1:44 am	#5
g4aaw pete Heptode Join Date: Jan 2008 Location: Birchington Kent, UK. Posts: 596	Re: Kenwood R5000 gone weird on LSB Whilst removing & refitting the control PCB at the front panel area of the receiver, I noted how easily the wirelooms can be pinched between fixing posts. Wonder if this could have happened during reassembly of yours? Regards Pete.

22nd Mar 2017, 8:53 am	#6
simonjp Tetrode Join Date: Sep 2014 Location: Lewes, East Sussex, UK. Posts: 55	Re: Kenwood R5000 gone weird on LSB thanks all for help so far. Pretty sure that there are no wires trapped. Yes, the cct is more complex than average and the workshop manual is a help but I am finding that the cct spread over countless pages is tiresome. I will take a more detailed look at how the ssb is generated, but I had a quick glance and thought it was derived from a "divide by" chain.

22nd Mar 2017, 3:16 pm	#7
John KC0G Hexode Join Date: Mar 2009 Location: Minneapolis, Minnesota, USA. Posts: 278	Re: Kenwood R5000 gone weird on LSB There is a block diagram of the PLL unit in figure 2 of page 3 of the service manual. The BFO signal is generated by its own PLL, followed by a division of 200 and then a mixer. Given that the radio works OK on USB, this might be a good way to start. Are you able to measure the frequency of the BFO signal, either on the PLL board or near the detector, for both USB and LSB? HTH and good luck 73 John

22nd Mar 2017, 8:38 pm	#8
simonjp Tetrode Join Date: Sep 2014 Location: Lewes, East Sussex, UK. Posts: 55	Re: Kenwood R5000 gone weird on LSB Update. Great suggestions all, John's guidance led me to the PLL.. It was 600khz out. Seems as though the logic which tells the PLL what to divide by, is screwed. Looks like the 4 bit source originates from one of the front panel pcb's. Now hunting for damaged tracks etc. thanks all

22nd Mar 2017, 10:39 pm	#9
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Kenwood R5000 gone weird on LSB I've found a Logic Probe to be useful when tracking down these type of faults. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

23rd Mar 2017, 5:59 am	#10
John KC0G Hexode Join Date: Mar 2009 Location: Minneapolis, Minnesota, USA. Posts: 278	Re: Kenwood R5000 gone weird on LSB Well done on finding that the fault is somehow related to VCO4. I assume that the 600kHz error is at the output of the VCO before the divide by 200 divider. Which way was the error - was the output frequency too low, in which case it would have been close to the USB frequency, or was it too high ? I think that there at least two possible problems: i) as you surmised, the PLL is not being told to do the right thing ii) the PLL is running out of control action, and the control voltage is at the minimum, or at the maximum of its range. If it is easier, I would check the VCO control voltage first 73 John

23rd Mar 2017, 5:50 pm	#11
simonjp Tetrode Join Date: Sep 2014 Location: Lewes, East Sussex, UK. Posts: 55	Re: Kenwood R5000 gone weird on LSB Hi John Back from the salt mine, so able to continue on the r5000. the frequency was 34.9744 Mhz and I think it should be 34.3Mhz 73 simon

23rd Mar 2017, 10:43 pm	#12
John KC0G Hexode Join Date: Mar 2009 Location: Minneapolis, Minnesota, USA. Posts: 278	Re: Kenwood R5000 gone weird on LSB Hello Simon I also think that it should be 34.3MHz. I presume that PLL gives 33.7MHz on USB ? If so, the VCO can cover the range, and then what - bad data? Good luck and 73 John

23rd Mar 2017, 11:33 pm	#13
simonjp Tetrode Join Date: Sep 2014 Location: Lewes, East Sussex, UK. Posts: 55	Re: Kenwood R5000 gone weird on LSB Hi John. Yes, USB is fine... I've given up for tonight, I hate the service manual.. So many schematics cut in half and on different pages, makes it very difficult to follow the circuit. I have identified that it all "kicks off" from A0 and A1 of the 7800 microprocessor. I am trying to trace the cct from their, forwards to the pll.. Mainly cos I just cannot get my head around how the damn pll works with that "swallow" counter.. Bit out of my depth their, so I am hoping that I might find a broken wire whilst I am tracing the logic from the uP.. instead of banging my head against a wall with the PLL. I'll give it a few more days, thenif I cant find it I'll move the radio into the sales section and get shot at a bargain price, or scrap it... It seems that even the case, knobs etc fetch good money.