looks like your radio has a bunch of trans turned backwards to the silk screen.
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148GTL-DX Very Weak AM receive
- Thread starter Dmans
- Start date
LC,
I have only removed 1 transistor in this unit. It was TR23-done today. I tested it with the Diode tester on my DMM and a cheap Chinese hfE tester and reinstalled it-the same backwards way to the silk screen it came out.
I don't know if the 80 year old gentleman that owns it ever had it working. He got it used and could never figure out what frequency he was on. It didn't receive in any mode when it came to me.
From my previous posts of the transistor readings (although the emitter and base were recorded backwards on all but TR8) I would have thought something would be apparent.
73's
David
Sonoma,
I never intended to start this kind of work and don't plan to continue it. I'm just trying to do somebody a favor.
I fiddle around with cheap junk of my own that I come across and if it doesn't get fixed, Oh well! It's my loss. I always seem to learn something in that process though.
73's
David
Do not mean to hi jack the thread.just curious as to what kind of audio tracer are you using Sonoma?
it is an old one. do not remember the brand right off hand. it is about 50 years old from what I remember. I have 2 of them and both work just fine.
I looked for the manual for them and they are Eico 147 and 147A. both do the job for me.
I looked for the manual for them and they are Eico 147 and 147A. both do the job for me.
Dmans,
not sure if you have noticed, but pages 42-45 of the service manual for this chassis are missing on the CBT site.
this is where the receiver alignment would be, so i am wondering if you aligned the receiver using that manual and stopped where it did or not?
specifically what happens when you tune L4 and L5, which are probably round metal cans with a larger slug in them and probably painted on top.
these are your AM only 455khz IF stage tuning cans and should be peaked in AM mode.
have you tried this?
if so, did they seem to peak or do nothing?
LC
not sure if you have noticed, but pages 42-45 of the service manual for this chassis are missing on the CBT site.
this is where the receiver alignment would be, so i am wondering if you aligned the receiver using that manual and stopped where it did or not?
specifically what happens when you tune L4 and L5, which are probably round metal cans with a larger slug in them and probably painted on top.
these are your AM only 455khz IF stage tuning cans and should be peaked in AM mode.
have you tried this?
if so, did they seem to peak or do nothing?
LC
LC,
They seemed to have a very sharp peak to them. Very little effect. I.e. less than 1/8 of a turn or so and ZERO noise/hiss/static etc.
Attached is the info I was using for tuning.
73's
David
Edit:
I used the info from Secret CB Vol 17 pages 55-58 to align.
They seemed to have a very sharp peak to them. Very little effect. I.e. less than 1/8 of a turn or so and ZERO noise/hiss/static etc.
Attached is the info I was using for tuning.
73's
David
Edit:
I used the info from Secret CB Vol 17 pages 55-58 to align.
here is a link to a page with the export service manuals.
see if you can find your chassis PB010 here.
http://www.zen96216.zen.co.uk/cb/uniden-esm.htm
LC
see if you can find your chassis PB010 here.
http://www.zen96216.zen.co.uk/cb/uniden-esm.htm
LC
LC,
I went through the alignment procedure as best I could (with my limited equipment) that you had linked to earlier. My "signal generator" is a Kenwood 440. I started transmitting an AM signal (27.185) at 5 watts into a dummy load and peaked the listed coils for best receive indication on the "S" meter. I then began reducing output power again going through the coils until I was unable to measure any output power of the 440. I also had my DMM on the speaker wires measuring the AC voltage. Both the "S" meter and AC voltage were peaking.
Since L4 is between TR9 and TR10, I believe I should concentrate my efforts in that area. I will measure again the transistor voltages of TR9 and TR10 as well as test the "specified" voltages at IC2 as it appears the output from these transistors goes to pin 1 of that IC. (Nomadradio had mentioned earlier about C19 and it was replaced in the initial recap of this unit and I had installed another new cap after Nomad's suggestion but to no avail)
Thanks to everyone for your help.
73's
David
P.S.
I did stay up until 1am this morning on this. Something about it I just can't let it go. I feel like it is going to be a simple solution and one of those "WTF moments"!!
I went through the alignment procedure as best I could (with my limited equipment) that you had linked to earlier. My "signal generator" is a Kenwood 440. I started transmitting an AM signal (27.185) at 5 watts into a dummy load and peaked the listed coils for best receive indication on the "S" meter. I then began reducing output power again going through the coils until I was unable to measure any output power of the 440. I also had my DMM on the speaker wires measuring the AC voltage. Both the "S" meter and AC voltage were peaking.
- L4 has very little affect on incoming signal.
Since L4 is between TR9 and TR10, I believe I should concentrate my efforts in that area. I will measure again the transistor voltages of TR9 and TR10 as well as test the "specified" voltages at IC2 as it appears the output from these transistors goes to pin 1 of that IC. (Nomadradio had mentioned earlier about C19 and it was replaced in the initial recap of this unit and I had installed another new cap after Nomad's suggestion but to no avail)
Thanks to everyone for your help.
73's
David
P.S.
I did stay up until 1am this morning on this. Something about it I just can't let it go. I feel like it is going to be a simple solution and one of those "WTF moments"!!
Do you have another radio that works well that you can use for comparison with receive sensitivity to the 148 DX?
If so get some meter readings at various power levels out of the Kenwood and see just how low you can go before the good working radio stops hearing the Kenwood signal. Make notes of those levels and then switch over to the 148 DX and see if you can still hear the Kenwood at the same low signal level as the well working radio. There is a chance that you are just not used to how quiet a 148 GTL receiver can be in am mode and sideband modes are always a bit louder with an empty Channel. Just something to check.
LC
If so get some meter readings at various power levels out of the Kenwood and see just how low you can go before the good working radio stops hearing the Kenwood signal. Make notes of those levels and then switch over to the 148 DX and see if you can still hear the Kenwood at the same low signal level as the well working radio. There is a chance that you are just not used to how quiet a 148 GTL receiver can be in am mode and sideband modes are always a bit louder with an empty Channel. Just something to check.
LC
We had a problem in the early 1980s with some CB radios built by Sanyo. They used the 2SC710 transistor, but the pinout was mirror-image from the data book. Emitter was on the right, not the left.
Figured it out, learned to check a new part and compare it to the orientation of the old one.
I have two versions of the 2SC1675 in stock. Same "mirror-image" difference in pinouts.
Just brings to mind the old carpenter's wisdom: "Measure once cut twice. Measure twice cut once".
73
Figured it out, learned to check a new part and compare it to the orientation of the old one.
I have two versions of the 2SC1675 in stock. Same "mirror-image" difference in pinouts.
Just brings to mind the old carpenter's wisdom: "Measure once cut twice. Measure twice cut once".
73
David-
Replace D26 and D27 (D11 & D12 on the 2950 are 1N60s) and check AM receive. If still bad, connect a jumper wire from the banded end (cathode) of D26 to ground. If receive is still low, check TR8, 9, and 10. if they check good, replace FL1 (FL1 in the 2950 is the same part as FL1 on the GTL-Dx). Hard to check FL1 w/o a scope, but they do fail and weak receive is the symptom.
- 399
Replace D26 and D27 (D11 & D12 on the 2950 are 1N60s) and check AM receive. If still bad, connect a jumper wire from the banded end (cathode) of D26 to ground. If receive is still low, check TR8, 9, and 10. if they check good, replace FL1 (FL1 in the 2950 is the same part as FL1 on the GTL-Dx). Hard to check FL1 w/o a scope, but they do fail and weak receive is the symptom.
- 399
unit_399,
I replaced D26 and D27 with 2-1N60's I "liberated" from a TRC-452 chassis. I believe that the diodes in the D11 and D12 position on my 2950 parts chassis (Board number EPT295013Z) had been previously replaced with "something different" from specifications. The TRC-452 was all factory stock.
I will try grounding the cathode of D26 tonight. If receives returns to normal what then?
I went through measuring transistors again and recorded the same as in the picture below. (with a notation as to the transistors used in the chassis at each position and the lead base of each). The service manual spec for voltages are to the right of the actual measurement.
Also checked voltages to IC1 and IC2 and recorded each. I know IC2 is dedicated to FM but was unsure if there could be a fault that would affect AM receive and to make sure it was "turning off" in AM receive mode.
I was a little unsure of the gain/hfE of these transistors-in particular TR9 and TR10 since L4 had little or no affect in receive tuning. Perhaps TR9 and TR10 should be removed for testing in my "Cheap Chinese Tester" or do the measured voltages reading tell me the transistors are working?
I will pull FL1 from the 2950 tonight. I did notice that the 2950 has 3 coils that closely resemble (metal can and blue core) L4 and L5 in the 148GTL-DX. (They are L3, L5 and L6 in the 2950 chassis) The part numbers for these are ECIFT12002 but gives little indication to me that they are the same part as the 148DX.
Enough of my rambling. I do appreciate everyone's help on this and will report my findings.
73's
David
I replaced D26 and D27 with 2-1N60's I "liberated" from a TRC-452 chassis. I believe that the diodes in the D11 and D12 position on my 2950 parts chassis (Board number EPT295013Z) had been previously replaced with "something different" from specifications. The TRC-452 was all factory stock.
I will try grounding the cathode of D26 tonight. If receives returns to normal what then?
I went through measuring transistors again and recorded the same as in the picture below. (with a notation as to the transistors used in the chassis at each position and the lead base of each). The service manual spec for voltages are to the right of the actual measurement.
Also checked voltages to IC1 and IC2 and recorded each. I know IC2 is dedicated to FM but was unsure if there could be a fault that would affect AM receive and to make sure it was "turning off" in AM receive mode.
I was a little unsure of the gain/hfE of these transistors-in particular TR9 and TR10 since L4 had little or no affect in receive tuning. Perhaps TR9 and TR10 should be removed for testing in my "Cheap Chinese Tester" or do the measured voltages reading tell me the transistors are working?
I will pull FL1 from the 2950 tonight. I did notice that the 2950 has 3 coils that closely resemble (metal can and blue core) L4 and L5 in the 148GTL-DX. (They are L3, L5 and L6 in the 2950 chassis) The part numbers for these are ECIFT12002 but gives little indication to me that they are the same part as the 148DX.
Enough of my rambling. I do appreciate everyone's help on this and will report my findings.
73's
David
The voltages you recorded for TR23 are correct for AM. The base voltage has the transistor turned on, and ground is being applied to the cathode of D26. If grounding the cathode of D26 with the clip lead brings the receive back then there is an open circuit between D26 and the collector of TR23. You might also want to check C76 for correct orientation, and that it is not shorted or leaky. Good luck & 73s.
- 399
- 399