UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Amateur and Military Radio

Notices

Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

Closed Thread
 
Thread Tools
Old 24th Jun 2020, 4:15 pm   #1
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Question PCMA001S No Rx or Tx issues...

Hi
I have a CB radio (Nato 2000) that is showing all sorts of weird and strange readings...

I've tested the most common failure points and thought I had at leats part of the problem figured out, but the issue(s) continue and it has me completely confused to be honest!

I did wonder if the VCO block was fubar, after replacing Q30 and Q36 I did reset the voltage at TP3 but it's gone again?

The main thing that isn't helping is someone's added some Relay/Capacitor Franken mod that I don't fully understand the reasoning behind?

I've Tested and Replaced...

D1 main board = Good
D1 CW board = Replaced
Q30 = Replaced (TIP120) Shorted between Collector and Emitter
Q36 Replaced (TIP120) Had a D880 fitted?

Just a quick note, although I can wield a soldering iron and follow instructions and How2's... I am a novice when it comes to electronics!
This is my first real go at trying to repair something like this!

A few pics...

Anyone have a better idea of whats causing the issue(s) ?

Would also appreciate an explanation of what the relay/capacitor franken thing is actually meant to be doing?

Thanks.
Attached Thumbnails
Click image for larger version

Name:	001.jpg
Views:	250
Size:	156.5 KB
ID:	209418   Click image for larger version

Name:	004.jpg
Views:	209
Size:	132.1 KB
ID:	209419   Click image for larger version

Name:	005.jpg
Views:	159
Size:	132.3 KB
ID:	209420   Click image for larger version

Name:	006.jpg
Views:	130
Size:	104.6 KB
ID:	209421  
VooDoo_Pete is offline  
Old 26th Jun 2020, 12:11 pm   #2
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Question Re: PCMA001S No Rx or Tx issues...

Ok,

Done some more checking of voltages and TP3 is a constant 5.71v...

Which points to a bad VCO block or even worse a bad PLL chip as far as I can figure out?

Anyone got any other ideas or things to check before I try and fix/source a replacement.
VooDoo_Pete is offline  
Old 27th Jun 2020, 12:58 pm   #3
Hans PE1KWH
Triode
 
Join Date: Jul 2016
Location: Hilversum, Netherlands
Posts: 33
Default Re: PCMA001S No Rx or Tx issues...

It's a little difficult to read your difficulties with it.
Strange readings is your first issue.
But what exactly do you mean by that ?

When working on pll's, VCO's and oscillators in general a frequency counter or 20 MHz oscilloscope is a very handy tool.
You have swapped components only based on the pll control signal value.
But a certain value tells you nothing about the oscillator is running or not or whether it's on the wrong frequency OR that the pll system is not running ok.

A pll needs a stable frequency as reference usually in that days based on a crystal oscillator. If that is not running or running at a different frequency the pll and vco are not able to output the requested frequency.
Hans PE1KWH is offline  
Old 27th Jun 2020, 1:22 pm   #4
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: PCMA001S No Rx or Tx issues...

Hans, sometimes people have to try whatever they have the means to try, rather than what might be the logical servicing approach.

Pete - the usual questions. You obviously have a meter. Do you also have a frequency meter? An oscilloscope?

I have not seen many PCMA001 PCBs, more familiar with the slightly older 121 and 125 chassis, but I see from some net images that the 001 uses the trademark 'green' Cybernet VCO block. These fail sufficiently frequently for one UK supplier to have produced a drop in substitute for them, scroll down the page until you get to 'VCO27', replacement VCO PCB. The PCB has 5 pins which are intended to drop directly into the holes vacated by a removed original block.

http://www.spectrumcomms.co.uk/CB_Kits.htm

I used one of those to replace the orange VCO block on a 125 chassis. They aren't completely ideal because the original block was potted to make it less vibration sensitive, whereas the replacement is not. However, they can make the difference between a set being usable, or otherwise a write-off.

As Heinz said, it would be better to adopt a logical approach rather than parts-change but if you have no choice but to continue with that approach then you could try one of those VCO PCBs. If it doesn't fix your fault you will still have a spare VCO which is a handy thing to have. Just email them to make sure it is also compatible with the PCMA001S first.

For the time being DO NOT adjust any of the adjustments in the unit if it was previously working with all the adjustments set as they are now.

The purpose of that add-on may have been to increase the tracking range of the VCO by switching more capacitance in at one end of the coverage. It presumably did work when it was added so leave it well alone for now.

Last edited by SiriusHardware; 27th Jun 2020 at 1:27 pm.
SiriusHardware is offline  
Old 27th Jun 2020, 1:29 pm   #5
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Post Re: PCMA001S No Rx or Tx issues...

Quote:
Originally Posted by Hans PE1KWH View Post
It's a little difficult to read your difficulties with it.
Strange readings is your first issue.
But what exactly do you mean by that ?
Q30 was showing 13.47v on both the collector and emitter, but when removed and retested showed as being good... This was removed again and showed a short between collector and emitter and was replaced. When replaced it showed good voltages but now is showing higher than expected voltages.

Q36 showed higher than expected voltages on base and emitter, this has been replaced but is still showing the same.

Quote:
When working on pll's, VCO's and oscillators in general a frequency counter or 20 MHz oscilloscope is a very handy tool.
I have a DMM with a frequency setting.

Quote:
You have swapped components only based on the pll control signal value.
But a certain value tells you nothing about the oscillator is running or not or whether it's on the wrong frequency OR that the pll system is not running ok.

A pll needs a stable frequency as reference usually in that days based on a crystal oscillator. If that is not running or running at a different frequency the pll and vco are not able to output the requested frequency.
The PLL is getting 10.23MHz reference at pin 3.

After replacing Q30 and Q36 I was able to reset the VCO Block to give 1.15vdc at TP3 with Band switch on D and Channel Selector on 40 as per the Service/Alignment Manual... but it has gone again and showing a constant 5.71v with minimal change when adjusting the VCO core?

So I am now a little out of my depth/experience and the reason for this thread requesting some help.
VooDoo_Pete is offline  
Old 27th Jun 2020, 1:33 pm   #6
Hans PE1KWH
Triode
 
Join Date: Jul 2016
Location: Hilversum, Netherlands
Posts: 33
Default Re: PCMA001S No Rx or Tx issues...

I know, but as Pete states he is a "beginner" ( no offence meant ) at repairing, those are the tools to look for and those can be obtained at reasonable prices these days.

Loops are the most difficult circuits to repair unless some measurements show in what part the failure is located. Reference oscillator, VCO or pll system.

There is also a good change it was "converted" to 10 meter with or without succes.....
Hans PE1KWH is offline  
Old 27th Jun 2020, 1:43 pm   #7
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Post Re: PCMA001S No Rx or Tx issues...

Quote:
Originally Posted by SiriusHardware View Post
Hans, sometimes people have to try whatever they have the means to try, rather than what might be the logical servicing approach.
I was following all the known/common faults that have been mentioned and documented by various people/sources on the internet.

Quote:
Pete - the usual questions. You obviously have a meter. Do you also have a frequency meter? An oscilloscope?
I have a DMM with frequnecy function... probably not the best... I also have a blackstar meteor 600 but need to source a BNC to Grabber/Hook clip cable of some description?

Quote:
I have not seen many PCMA001 PCBs, more familiar with the slightly older 121 and 125 chassis, but I see from some net images that the 001 uses the trademark 'green' Cybernet VCO block. These fail sufficiently frequently for one UK supplier to have produced a drop in substitute for them, scroll down the page until you get to 'VCO27', replacement VCO PCB. The PCB has 5 pins which are intended to drop directly into the holes vacated by a removed original block.

http://www.spectrumcomms.co.uk/CB_Kits.htm

I used one of those to replace the orange VCO block on a 125 chassis. They aren't completely ideal because the original block was potted to make it less vibration sensitive, whereas the replacement is not. However, they can make the difference between a set being usable, or otherwise a write-off.

As Heinz said, it would be better to adopt a logical approach rather than parts-change but if you have no choice but to continue with that approach then you could try one of those VCO PCBs. If it doesn't fix your fault you will still have a spare VCO which is a handy thing to have. Just email them to make sure it is also compatible with the PCMA001S first.

For the time being DO NOT adjust any of the adjustments in the unit if it was previously working with all the adjustments set as they are now.

The purpose of that add-on may have been to increase the tracking range of the VCO by switching more capacitance in at one end of the coverage. It presumably did work when it was added so leave it well alone for now.
Yes, next logical step (in my head anyway) was to change the VCO block as it appeared to me that the VCO was misbehaving?

I hopefully have another original one on the way to try, of course this could be faulty but worth a go before spending out on a aftermarket replacement from "spectrum" although most people seem to think they work ok.

I admit the spaghetti of wires in this cybernet multimode is rather confusing to me!?!
VooDoo_Pete is offline  
Old 27th Jun 2020, 1:47 pm   #8
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: PCMA001S No Rx or Tx issues...

Pete's posts are being delayed by new member moderation so Hans and I have both posted without seeing Pete's post #5. (But now I have seen it).

OK Pete, so that DMM seems to have an unusually good frequency meter feature, that will be useful. Do you know what the upper frequency limit of it is?
SiriusHardware is offline  
Old 27th Jun 2020, 1:52 pm   #9
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Question Re: PCMA001S No Rx or Tx issues...

Quote:
Originally Posted by SiriusHardware View Post
Pete's posts are being delayed by new member moderation so Hans and I have both posted without seeing Pete's post #5. (But now I have seen it).

OK Pete, so that DMM seems to have an unusually good frequency meter feature, that will be useful. Do you know what the upper frequency limit of it is?
Please see my post #7

I will check the limit on the DMM frequency range!

Last edited by VooDoo_Pete; 27th Jun 2020 at 2:00 pm.
VooDoo_Pete is offline  
Old 27th Jun 2020, 1:59 pm   #10
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: PCMA001S No Rx or Tx issues...

If you have another VCO on the way then we'll pause until you have had a chance to try that.

The Spectrum ones work perfectly OK and are not badly priced considering the parts cost, time it will take to make the PCB and hand-solder the components into it. I doubt they make much money from each one. But, a genuine replacement is always to be preferred if one can be found.
SiriusHardware is offline  
Old 27th Jun 2020, 2:00 pm   #11
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Default Re: PCMA001S No Rx or Tx issues...

Quote:
Originally Posted by SiriusHardware View Post
If you have another VCO on the way then we'll pause until you have had a chance to try that.

The Spectrum ones work perfectly OK and are not badly priced considering the parts cost, time it will take to make the PCB and hand-solder the components into it. I doubt they make much money from each one. But, a genuine replacement is always to be preferred if one can be found.
Frequency range on DMM isn't going to be must good past reading the 10.240MHz reference frequency... It really is supposed to be for reading Hz... like mains etc... I will need to source a BNC to grabber/hook clip cable for the blackstar meter!

Last edited by VooDoo_Pete; 27th Jun 2020 at 2:03 pm. Reason: Added info...
VooDoo_Pete is offline  
Old 27th Jun 2020, 2:11 pm   #12
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: PCMA001S No Rx or Tx issues...

The other thing is that a DMM won't have enough digits to show the frequency at the kind of resolution you will eventually need for this kind of work - ideally down to 10Hz or less, so 27.xxx.xxx (7 or 8 digits).

Therefore yes, try to get that frequency meter into a usable configuration before the VCO arrives.
SiriusHardware is offline  
Old 27th Jun 2020, 2:20 pm   #13
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Thumbs up Re: PCMA001S No Rx or Tx issues...

Quote:
Originally Posted by SiriusHardware View Post
The other thing is that a DMM won't have enough digits to show the frequency at the kind of resolution you will eventually need for this kind of work - ideally down to 10Hz or less, so 27.xxx.xxx (7 or 8 digits).

Therefore yes, try to get that frequency meter into a usable configuration before the VCO arrives.
I'm on it...

Been told replacement VCO was dropped in the post last night.
VooDoo_Pete is offline  
Old 1st Jul 2020, 4:18 pm   #14
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Post Re: PCMA001S No Rx or Tx issues...

Ok, Replacement VCO block received and fitted...

Set VCO to 1.15v on Band D Channel 40, recheck voltage is at least 4.25v on band A Channel 1. --- Yes!

So at the moment it appears a bad VCO and Q30 were the issues?

I need to get an oscilloscope next so I can go through a complete alignment to double check everything...

The relay/capacitor franken mod is bugging me as it isn't original.

The BNC to Hook clips cable turned up too and I also dug out an old DMM with broken positive lead and fitted some mini crocodile clips instead... which are very useful I have to say!
Attached Thumbnails
Click image for larger version

Name:	014.jpg
Views:	162
Size:	123.8 KB
ID:	210025   Click image for larger version

Name:	015.jpg
Views:	139
Size:	107.5 KB
ID:	210026   Click image for larger version

Name:	016.jpg
Views:	153
Size:	112.9 KB
ID:	210027   Click image for larger version

Name:	017.jpg
Views:	136
Size:	122.7 KB
ID:	210028   Click image for larger version

Name:	018.jpg
Views:	121
Size:	102.4 KB
ID:	210029  

VooDoo_Pete is offline  
Old 1st Jul 2020, 6:16 pm   #15
Hans PE1KWH
Triode
 
Join Date: Jul 2016
Location: Hilversum, Netherlands
Posts: 33
Default Re: PCMA001S No Rx or Tx issues...

Good show !
Nice to hear it's working again or at least appears so.

An oscilloscope and frequency counter are really nice tools to have when working on HF equipment.
Hans PE1KWH is offline  
Old 1st Jul 2020, 6:18 pm   #16
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: PCMA001S No Rx or Tx issues...

Glad your hunch re: VCO proved correct, but it would have been useful to have a spare one anyway because they do fail.

As to that mod, try all possible band selections and see if that relay is only activated when you switch to one particular band or certain bands. It's hard to imagine why anyone would feel the need to 'spread' one of these when they are already a five or six? band radio.
SiriusHardware is offline  
Old 1st Jul 2020, 6:46 pm   #17
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: PCMA001S No Rx or Tx issues...

Actually. having looked properly at you photos it's pretty clear that the green wire is just going to a handy ground where the VCO is and is nothing to actually do with the VCO. I take it the green and blue wires are the ones associated with the mod, so where does the blue wire go?
SiriusHardware is offline  
Old 1st Jul 2020, 7:51 pm   #18
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Thumbs up Re: PCMA001S No Rx or Tx issues...

Quote:
Originally Posted by Hans PE1KWH View Post
Good show !
Nice to hear it's working again or at least appears so.

An oscilloscope and frequency counter are really nice tools to have when working on HF equipment.
I'll use it over the next few days and see how it behaves...

Re: Oscilloscopes, I was going to get one of the Cheapish ones currently available... Hantek or similiar, but wondered if an older Tektronics TDS220 or similiar would be a better option?

Last edited by VooDoo_Pete; 1st Jul 2020 at 8:07 pm. Reason: Spelling...
VooDoo_Pete is offline  
Old 1st Jul 2020, 8:04 pm   #19
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Post Re: PCMA001S No Rx or Tx issues...

Quote:
Originally Posted by SiriusHardware View Post
Glad your hunch re: VCO proved correct, but it would have been useful to have a spare one anyway because they do fail.
May have got there unconventionally but yes, seems to be working at this moment... time will tell.

Quote:
As to that mod, try all possible band selections and see if that relay is only activated when you switch to one particular band or certain bands. It's hard to imagine why anyone would feel the need to 'spread' one of these when they are already a five or six? band radio.

Actually. having looked properly at you photos it's pretty clear that the green wire is just going to a handy ground where the VCO is and is nothing to actually do with the VCO. I take it the green and blue wires are the ones associated with the mod, so where does the blue wire go?
I don't understand why it's there either, as you say depending on the model these can have anything from L-Low to S-High (26.065 - 28.305)

The thin green wire is original as far as I can tell...
The thin Blue wire is used for the High/Mid/Low Power Switch...

The Yellow from the mod goes to Post 11 linked to Q30
The White from the mod goes to the Mode Switch

The thick Green Wire is not original...
Attached Thumbnails
Click image for larger version

Name:	014.jpg
Views:	186
Size:	124.4 KB
ID:	210048   Click image for larger version

Name:	0015.jpg
Views:	126
Size:	114.5 KB
ID:	210049   Click image for larger version

Name:	016.jpg
Views:	202
Size:	118.6 KB
ID:	210050   Click image for larger version

Name:	017.jpg
Views:	121
Size:	132.1 KB
ID:	210051   Click image for larger version

Name:	018.jpg
Views:	110
Size:	121.8 KB
ID:	210052  


Last edited by VooDoo_Pete; 1st Jul 2020 at 8:22 pm. Reason: Add Pictures...
VooDoo_Pete is offline  
Old 2nd Jul 2020, 1:32 pm   #20
VooDoo_Pete
Triode
 
Join Date: Jun 2020
Location: Medway Towns, Kent, UK.
Posts: 26
Post Re: PCMA001S No Rx or Tx issues...

Working reports on FM UK40 and Mids... Haven't tested anything else yet.

A little low on frequency on Mids so definately needs full alignment...

But seems to be working ok so far!

Picked up a 20.555MHz crystal for it so I can shift the bands up one... And possibly two as the 20.555 crystal is used for H-Highs and S-Highs apparently?

Also looking at doing afew other little tweaks like improving the FM Tx audio (not sure if the PCMA001S needs this tweak or not though) and the popping squelch.
VooDoo_Pete is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:33 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.